Patent Publication Number: US-11661124-B2

Title: Tracked vehicle with adjustable track spacing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/076,537, filed on Aug. 8, 2018, and issued as U.S. Pat. No. 11,173,971 on Nov. 16, 2021, which is a national stage patent application of International Patent Application No. PCT/US2017/016980 filed on Feb. 8, 2017, which claims priority from U.S. Provisional Patent Applications 62/292,856, 62/328,965 and 62/348,369 respectively filed on Feb. 8, 2016, Apr. 28, 2016 and Jun. 10, 2016. The contents of the aforementioned applications are incorporated by reference herein. 
    
    
     FIELD 
     The invention relates generally to off-road vehicles comprising track systems (e.g., agricultural vehicles such as tractors, harvesters, combines, etc.). 
     BACKGROUND 
     Agricultural vehicles (e.g., tractors, harvesters, combines, etc.) sometimes comprise track systems (instead of wheels with tires) to enhance their traction and floatation in agricultural fields, which may be soft, slippery, and/or uneven (e.g., soil, mud, etc.). 
     The agricultural fields on which agricultural vehicles are designed to travel may have different field configurations, such as different configurations of row crops. For example, some agricultural fields may have a “narrow” configuration of row crops (i.e., row crops that are relatively close to one another), while other agricultural fields may have a “wide” configuration of row crops (i.e., row crops that are relatively distant from one another). This may be problematic for an agricultural vehicle since a spacing between laterally-adjacent track systems of the agricultural vehicle may have to vary in order to accommodate such different row crop configurations. 
     Other off-road vehicles, such as construction vehicles (e.g., loaders, bulldozers, excavators, etc.), forestry vehicles (e.g., feller-bunchers, tree chippers, knuckleboom loaders, etc.) and other industrial vehicles, may be affected by similar considerations in some cases. 
     For these and other reasons, there is a need to improve vehicles comprising track systems. 
     SUMMARY 
     According to various aspects of the invention, there are provided track systems for traction of a vehicle in which a spacing of laterally-adjacent ones of the track systems in a widthwise direction of the vehicle is adjustable. This may facilitate use of the vehicle in different conditions (e.g., in different field configurations, such as in different configurations of row crops, where the vehicle is an agricultural vehicle). For instance, the spacing of the laterally-adjacent ones of the track systems may be adjustable while the laterally-adjacent ones of the track systems are connected to a powertrain of the vehicle and/or without requiring use of additional parts (e.g. spacers). 
     For example, according to an aspect of the invention, there is provided a track system of a plurality of track systems for traction of a vehicle. The vehicle comprises a frame and a powertrain. The track system is mountable on a first side of the vehicle. A laterally-adjacent one of the track systems is mountable on a second side of the vehicle. The track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, a plurality of idler wheels for guiding the track, and a frame supporting the idler wheels. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system. The plurality of idler wheels also includes a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. The drive wheel is unsupported by the frame of the track system and is supportable entirely by the axle of the vehicle. A spacing of the track system and the laterally-adjacent one of the track systems in a widthwise direction of the vehicle is adjustable. 
     According to another aspect of the invention, there is provided a vehicle comprising a frame, a powertrain, and a plurality of track systems for traction of the vehicle. A first one of the track systems is mounted on a first side of the vehicle and a second one of the track systems is mounted on a second side of the vehicle. Each track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, a plurality of idler wheels for guiding the track and a frame supporting the idler wheels. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system. The plurality of idler wheels also includes a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. The drive wheel is unsupported by the frame of the track system and is supported entirely by the axle of the vehicle. A spacing of the first one of the track systems and the second one of the track systems in a widthwise direction of the vehicle is adjustable. 
     According to another aspect of the invention, there is provided a track system of a plurality of track systems for traction of a vehicle. The vehicle comprises a frame and a powertrain. The track system is mountable on a first side of the vehicle. A laterally-adjacent one of the track systems is mountable on a second side of the vehicle. The track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, a plurality of idler wheels for guiding the track, and a frame supporting the idler wheels. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system. The plurality of idler wheels also includes a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. The drive wheel is supportable by a transmission mountable between the drive wheel and the axle of the vehicle. The transmission comprises planetary gearing. A spacing of the track system and the laterally-adjacent one of the track systems in a widthwise direction of the vehicle is adjustable. The transmission remains fixed in the widthwise direction of the vehicle while the spacing of the track system and the laterally-adjacent one of the track systems in the widthwise direction of the vehicle is adjusted. 
     According to another aspect of the invention, there is provided a vehicle. The vehicle comprises a frame, a powertrain, and a plurality of track systems for traction of the vehicle. A first one of the track systems is mounted on a first side of the vehicle and a second one of the track systems is mounted on a second side of the vehicle. Each track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, a plurality of idler wheels for guiding the track, and a frame supporting the idler wheels. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system. The plurality of idler wheels also includes a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. The drive wheel is supportable by a transmission mountable between the drive wheel and the axle of the vehicle. The transmission comprises planetary gearing. A spacing of the first one of the track systems and the second one of the track systems in a widthwise direction of the vehicle is adjustable. The transmission remains fixed in the widthwise direction of the vehicle while the spacing of the first one of the track systems and the second one of the track systems in the widthwise direction of the vehicle is adjusted. 
     According to another aspect of the invention, there is provided a track system of a plurality of track systems for traction of a vehicle. The vehicle comprises a frame and a powertrain. The track system is mountable on a first side of the vehicle. A laterally-adjacent one of the track systems is mountable on a second side of the vehicle. The track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, a plurality of idler wheels for guiding the track, and a frame supporting the idler wheels. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system. The plurality of idler wheels also includes a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. The drive wheel is supportable by a transmission mountable between the drive wheel and the axle of the vehicle. A spacing of the track system and the laterally-adjacent one of the track systems in a widthwise direction of the vehicle is adjustable. The transmission remains fixed in the widthwise direction of the vehicle while the spacing of the track system and the laterally-adjacent one of the track systems in the widthwise direction of the vehicle is adjusted. 
     According to another aspect of the invention, there is provided a vehicle. The vehicle comprises a frame, a powertrain, and a plurality of track systems for traction of the vehicle. A first one of the track systems is mounted on a first side of the vehicle and a second one of the track systems is mounted on a second side of the vehicle. Each track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, a plurality of idler wheels for guiding the track, and a frame supporting the idler wheels. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system. The plurality of idler wheels also includes a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. The drive wheel is supportable by a transmission mountable between the drive wheel and the axle of the vehicle. A spacing of the first one of the track systems and the second one of the track systems in a widthwise direction of the vehicle is adjustable. The transmission remains fixed in the widthwise direction of the vehicle while the spacing of the first one of the track systems and the second one of the track systems in the widthwise direction of the vehicle is adjusted. 
     According to another aspect of the invention, there is provided a track system of a plurality of track systems for traction of a vehicle. The vehicle comprises a frame and a powertrain. The track system is mountable on a first side of the vehicle. A laterally-adjacent one of the track systems is mountable on a second side of the vehicle. The track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, a plurality of idler wheels for guiding the track, and a frame supporting the idler wheels. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system. The plurality of idler wheels also includes a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. The track-engaging assembly also comprises a wheel carrier carrying respective ones of the roller wheels and configured to allow the respective ones of the roller wheels to rotate relative to the frame of the track system about an axis transversal to axes of rotation of the respective ones of the roller wheels. A spacing of the track system and the laterally-adjacent one of the track systems in a widthwise direction of the vehicle is adjustable. 
     According to another aspect of the invention, there is provided a vehicle. The vehicle comprises a frame, a powertrain, and a plurality of track systems for traction of the vehicle. A first one of the track systems is mounted on a first side of the vehicle and a second one of the track systems is mounted on a second side of the vehicle. Each track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, a plurality of idler wheels for guiding the track, and a frame supporting the idler wheels. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system. The plurality of idler wheels also includes a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. The track-engaging assembly also comprises a wheel carrier carrying respective ones of the roller wheels and configured to allow the respective ones of the roller wheels to rotate relative to the frame of the track system about an axis transversal to axes of rotation of the respective ones of the roller wheels. A spacing of the first one of the track systems and the second one of the track systems in a widthwise direction of the vehicle is adjustable. 
     According to another aspect of the invention, there is provided a track system of a plurality of track systems for traction of a vehicle. The vehicle comprises a frame and a powertrain. The track system is mountable on a first side of the vehicle. A laterally-adjacent one of the track systems is mountable on a second side of the vehicle. The track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, a plurality of idler wheels for guiding the track, and a frame supporting the idler wheels. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system. The plurality of idler wheels also includes a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. A given one of the roller wheels is rotatable relative to the frame of the track system about an axis transversal to an axis of rotation of the given one of the roller wheels. A spacing of the track system and the laterally-adjacent one of the track systems in a widthwise direction of the vehicle is adjustable. 
     According to another aspect of the invention, there is provided a vehicle. The vehicle comprises a frame, a powertrain, and a plurality of track systems for traction of the vehicle. A first one of the track systems is mounted on a first side of the vehicle and a second one of the track systems is mounted on a second side of the vehicle. Each track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, a plurality of idler wheels for guiding the track, and a frame supporting the idler wheels. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system. The plurality of idler wheels also includes a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. A given one of the roller wheels is rotatable relative to the frame of the track system about an axis transversal to an axis of rotation of the given one of the roller wheels. A spacing of the first one of the track systems and the second one of the track systems in a widthwise direction of the vehicle is adjustable. 
     According to another aspect of the invention, there is provided a track system of a plurality of track systems for traction of a vehicle. The vehicle comprises a frame and a powertrain. The track system is mountable on a first side of the vehicle. A laterally-adjacent one of the track systems is mountable on a second side of the vehicle. The track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates and a plurality of idler wheels for guiding the track. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system, and a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. The track-engaging assembly also comprises a frame supporting the idler wheels. The track system also comprises a movable joint allowing the frame of the track system to move relative to the frame of the vehicle when travelling on an uneven terrain. The movable joint is located inboard of the drive wheel. A spacing of the track system and the laterally-adjacent one of the track system in a widthwise direction of the vehicle is adjustable. 
     According to another aspect of the invention, there is provided a vehicle. The vehicle comprises a frame, a powertrain, and a plurality of track systems for traction of the vehicle. A first one of the track systems is mounted on a first side of the vehicle and a second one of the track systems is mounted on a second side of the vehicle. Each track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, a plurality of idler wheels for guiding the track, and a frame supporting the idler wheels. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system. The plurality of idler wheels also includes a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. The track system also comprises a movable joint allowing the frame of the track system to move relative to the frame of the vehicle when travelling on an uneven terrain. The movable joint is located inboard of the drive wheel. A spacing of the first one of the track systems and the second one of the track systems in a widthwise direction of the vehicle is adjustable. 
     According to another aspect of the invention, there is provided a track system of a plurality of track systems for traction of a vehicle. The vehicle comprises a frame and a powertrain. The track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, and a plurality of idler wheels for guiding the track. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system, and a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. The track-engaging assembly also comprises a frame supporting the idler wheels. The track system comprises a movable joint allowing the frame of the track system to move relative to the frame of the vehicle when travelling on an uneven ground area. The movable joint is located inboard of the drive wheel. 
     According to another aspect of the invention, there is provided a vehicle. The vehicle comprises a frame, a powertrain, and a plurality of track systems for traction of the vehicle. A first one of the track systems is mounted on a first side of the vehicle and a second one of the track systems is mounted on a second side of the vehicle. Each track system comprises a track and a track-engaging assembly for driving and guiding the track around the track-engaging assembly. The track-engaging assembly comprises a drive wheel for driving the track when an axle of the vehicle rotates, a plurality of idler wheels for guiding the track, and a frame supporting the idler wheels. The plurality of idler wheels includes a leading idler wheel and a trailing idler wheel spaced apart in a longitudinal direction of the track system. The plurality of idler wheels also includes a plurality of roller wheels between the leading idler wheel and the trailing idler wheel in the longitudinal direction of the track system. The track system also comprises a movable joint allowing the frame of the track system to move relative to the frame of the vehicle when travelling on an uneven terrain. The movable joint is located inboard of the drive wheel. 
     These and other aspects of the invention will now become apparent to those of ordinary skill in the art upon review of the following description of embodiments of the invention in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A detailed description of embodiments of the invention is provided below, by way of example only, with reference to the accompanying drawings, in which: 
         FIG.  1    shows an example of an agricultural vehicle comprising track systems in accordance with an embodiment of the invention; 
         FIG.  2    shows a perspective view of a powertrain of the agricultural vehicle as connected to respective ones of the track systems, whereby a spacing of laterally-adjacent ones of the track systems is in a narrow tread setting; 
         FIG.  3    shows a perspective view of the powertrain of the agricultural vehicle as connected to respective ones of the track systems, whereby the spacing of laterally-adjacent one of the track systems is in a wide tread setting; 
         FIG.  4    shows a perspective view of a front one of the track systems; 
         FIG.  5    shows a perspective view of a rear one of the track systems; 
         FIG.  6    shows another perspective view of the track system of  FIG.  5   ; 
         FIG.  7    shows a side view of the track system of  FIG.  5   ; 
         FIG.  8    shows a plan view of a track of the front or rear track system; 
         FIG.  9    shows a side elevational view of the track; 
         FIG.  10    shows a plan view of an inner side of the track; 
         FIG.  11    shows a cross-sectional view of the track; 
         FIG.  12    shows a perspective view of a traction projection of the track; 
         FIGS.  13  and  14    show perspective views of a rear final drive unit of the powertrain of the agricultural vehicle; 
         FIG.  15    shows part of a transmission of the rear final drive unit of  FIGS.  13  and  14   ; 
         FIG.  16    shows a drive wheel of a track-engaging assembly of the track system; 
         FIGS.  17  and  18    show a perspective view and a side view of a front final drive unit of the powertrain of the agricultural vehicle; 
         FIG.  19    shows mid-rollers of the track-engaging assembly engaging the inner side the track; 
         FIGS.  20  and  21    show perspective views of a mid-roller of the track-engaging assembly; 
         FIGS.  22  and  23    show a front view and a side view of the mid-roller; 
         FIG.  24    shows the mid-roller wheel mounted on an axle via a hub; 
         FIG.  25    shows a partial cross-sectional side view of a lower portion of the track system, including a bogie carrying the mid-rollers; 
         FIG.  26    shows a top view of the lower portion of the track system with two idler wheels being omitted; 
         FIGS.  27  and  28    show front and rear perspective views of an upper portion of a frame of the track-engaging assembly of the track system; 
         FIG.  29    shows a partial cross-sectional view of a retaining mechanism of the track system; 
         FIG.  30    shows a cross-sectional view of the front track system as it is engaged by the front final drive unit; 
         FIGS.  31  and  32    shows rear perspective views of the front track system in the narrow tread setting and in the wide tread setting, respectively; 
         FIG.  33    shows the track systems according to another embodiment; 
         FIG.  34    shows the track systems of  FIG.  33    mounted onto the agricultural vehicle as front ones of the track systems are steered; 
         FIG.  35    shows a perspective view of a front one of the track systems of  FIG.  33   ; 
         FIG.  36    shows a perspective view of a track-engaging assembly of the front one of the track systems of  FIG.  35   ; 
         FIG.  37    shows a perspective view of a transmission and support arms connected to the track system of  FIG.  35   ; 
         FIG.  38    shows gearing and a housing of the transmission of  FIG.  37   ; 
         FIG.  39    shows a drive wheel of the track system of  FIG.  35    coupled to the housing of the transmission; 
         FIGS.  40  to  42    show cross-sectional views of the track system of  FIG.  35    when adjusted at different positions relative to the transmission; 
         FIG.  43    shows an example of a retaining mechanism of an upper member of a frame of the track system of  FIG.  35   ; 
         FIG.  44    shows another example of the retaining mechanism of  FIG.  43   ; 
         FIG.  45    shows a side elevation view of the track system of  FIG.  35   ; 
         FIG.  46    shows a perspective view of the upper member of the frame of the track system of  FIG.  35   ; 
         FIGS.  47 A and  47 B  show cross-sectional views of the track system of  FIG.  35    when the upper member of the frame is mounted on an outboard side and on an inboard side of the drive wheel, respectively; 
         FIG.  48    shows a perspective view of a rear one of the track systems of  FIG.  33   ; 
         FIGS.  49  and  50    show front and rear perspective views of a track-engaging assembly of the track system of  FIG.  48   ; 
         FIG.  51    shows a cross-sectional view of the track-engaging assembly of  FIG.  49   ; 
         FIGS.  52  and  53    show cross-sectional views of the track-engaging assembly of  FIG.  49    when adjusted at different positions relative to the final drive unit of the powertrain of the agricultural vehicle; 
         FIGS.  54  and  55    shows the track systems of  FIG.  33    in the wide tread setting and the narrow tread setting, respectively; 
         FIG.  56    shows an example of an embodiment of a lateral load distribution mechanism of the bogie of  FIG.  25    in which the bogie has a roll motion capability to cause the mid-rollers to engage the track evenly in a widthwise direction of the track; 
         FIG.  57    shows the bogie of  FIG.  56    including upper and lower structures of the bogie; 
         FIG.  58    shows a cross-sectional view of the bogie taken along line  58 - 58  as shown in  FIG.  57   ; 
         FIG.  59    shows the track system of  FIG.  56    implementing the lateral load distribution mechanism for evenly distributing a load along a widthwise direction of the track while the agricultural vehicle is travelling on a crowned road; 
         FIG.  60    shows an example of an embodiment in which the final drive unit is provided with a reinforcing support between a body of the final drive unit and the track system; 
         FIG.  61    shows a front view of the reinforcing support of  FIG.  60   ; 
         FIGS.  62  and  63    show a front and a rear view of an example of another embodiment of a rear track system; 
         FIGS.  64  and  65    show front and rear perspective views of a track-engaging system of the track system of  FIG.  62   , with idler wheels thereof removed to more clearly show the components of the track-engaging system; 
         FIGS.  66  and  67    show front and rear perspective views of a frame of the track system of  FIG.  62   ; 
         FIGS.  68  and  69    show front and rear perspective views of an inboard pivot of the track system of  FIG.  62   ; 
         FIG.  70    shows a bottom perspective view of an embodiment of a final drive unit used in connection with the track system of  FIG.  62   ; 
         FIG.  71    shows a side view of the track-engaging system of  FIG.  64    when the spacing of laterally-adjacent track systems is in a narrow tread setting; 
         FIG.  72    shows a top view of the track system of  FIG.  62    when the spacing between the laterally-adjacent track systems is in a narrow tread setting; 
         FIG.  73    shows a cross-sectional view of the track-engaging system of  FIG.  71   ; 
         FIG.  74    shows a side view of the track-engaging system of  FIG.  64    when the spacing of the laterally-adjacent track systems is in a wide tread setting; 
         FIG.  75    shows a top view of the track system of  FIG.  62    when the spacing of the laterally-adjacent track systems is in a wide tread setting; 
         FIG.  76    shows a front view of a front track system in accordance with the embodiment of  FIG.  62   ; and 
         FIG.  77    shows a perspective view of a frame of the front track system of  FIG.  76   . 
     
    
    
     It is to be expressly understood that the description and drawings are only for the purpose of illustrating certain embodiments of the invention and are an aid for understanding. They are not intended to be a definition of the limits of the invention. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG.  1    shows an example of an agricultural vehicle  10  in accordance with an embodiment of the invention. In this embodiment, the agricultural vehicle  10  is a tractor. In other embodiments, the agricultural vehicle  10  may be a combine harvester, another type of harvester, or any other type of agricultural vehicle. 
     The agricultural vehicle  10  comprises a frame  12 , a powertrain  15 , a steering system  17 , a plurality of track systems  16   1 - 16   4  (which can be referred to as “undercarriages”), and an operator cabin  20  that enable an operator to move the agricultural vehicle  10  on the ground. The vehicle  10  can travel in an agricultural field to perform agricultural work using a work implement  18 . The vehicle  10  can also be “roading”, i.e., travelling on a road (i.e., a paved road having a hard surface of asphalt, concrete, gravel, or other pavement), such as between agricultural fields. The agricultural vehicle  10  has a front  107  and a rear  109  that define a longitudinal direction of the vehicle  10 , left and right sides  111   1 ,  111   2  that define a widthwise direction of the vehicle  10 , and a height direction that is perpendicular to its longitudinal direction and its widthwise direction. 
     As will be further discussed later, in this embodiment, a spacing S of laterally-adjacent ones of the track systems  16   1 - 16   4  of the agricultural vehicle  10  in the widthwise direction of the vehicle  10 , such as the spacing S of the track systems  16   1 ,  16   2  in the front  107  of the agricultural vehicle  10  and/or the spacing S of the track systems  16   3 ,  16   4  in the rear  109  of the vehicle  10 , is adjustable so as to facilitate use of the agricultural vehicle  10  in different field configurations, such as in different configurations of row crops (e.g., different “tread settings” for different field configurations). Notably, in this embodiment, as shown in  FIGS.  2  and  3   , the spacing S of the laterally-adjacent ones of the track systems  16   1 - 16   4  of the agricultural vehicle  10  is adjustable while the laterally-adjacent ones of the track systems  16   1 - 16   4  of the agricultural vehicle  10  are connected to the powertrain  15  and/or without requiring use of additional parts (e.g. spacers). 
     The powertrain  15  is configured for generating motive power and transmitting motive power to the track systems  16   1 - 16   4  to propel the agricultural vehicle  10  on the ground. To that end, the powertrain  15  comprises a prime mover  14 , which is a source of motive power that comprises one or more motors. For example, in this embodiment, the prime mover  14  comprises an internal combustion engine. In other embodiments, the prime mover  14  may comprise another type of motor (e.g., an electric motor) or a combination of different types of motor (e.g., an internal combustion engine and an electric motor). 
     The prime mover  14  is in a driving relationship with the track systems  16   1 - 16   4 . That is, the powertrain  15  transmits motive power generated by the prime mover  14  to one or more of the track systems  16   1 - 16   4  in order to drive (i.e., impart motion to) these one or more of the track systems  16   1 - 16   4 . The powertrain  15  may transmit power from the prime mover  14  to the track systems  16   1 - 16   4  in any suitable way. In this embodiment, the powertrain  15  comprises a front differential  27 , a rear differential  29 , and final drive units  35   1 - 35   4  including final drive axles  56   1 - 56   4  between the prime mover  14  and the track systems  16   1 - 16   4  for transmitting motive power from the prime mover  14  to the track systems  16   1 - 16   4 . An automatic transmission (e.g., a continuously variable transmission (CVT)) or any other suitable type of transmission may be used. 
     The work implement  18  is used to perform agricultural work. For example, in some embodiments, the work implement  18  may be a combine head, a cutter, a scraper pan, a tool bar, a planter, or any other type of agricultural work implement. 
     The operator cabin  20  is where the operator sits and controls the agricultural vehicle  10 . More particularly, the operator cabin  20  comprises a user interlace  70  including a set of controls that allow the operator to steer the agricultural vehicle  10  on the ground and operate the work implement  18 . For example, in this embodiment, the user interlace  70  comprises an accelerator, a brake control, and a steering device that are operable by the operator to control motion of the agricultural vehicle  10  on the ground and operation of the work implement  18 . The user interlace  70  also comprises an instrument panel (e.g., a dashboard) which provides indicators (e.g., a speedometer indicator, a tachometer indicator, etc.) to convey information to the operator. 
     The track systems  16   1 - 16   4  engage the ground to propel the agricultural vehicle  10 . Respective ones of the track systems  16   1 - 16   4  are located on the left and right sides  111   1 ,  111   2  of the vehicle  10 . With additional reference to  FIGS.  4  and  5   , which depict the front track system  16   1  and the rear track system  16   3  respectively, each track system  16   i  comprises a track-engaging assembly  21  and a track  22  disposed around the track-engaging assembly  21 . In this embodiment, the track-engaging assembly  21  comprises a plurality of wheels which, in this example, includes a drive wheel  24  and a plurality of idler wheels that includes front (i.e., leading) idler wheels  23   1 ,  23   2 , rear (i.e., trailing) idler wheels  26   1 ,  26   2 , and roller wheels  28   1 - 28   R  (i.e., the roller wheels  28   1 - 28   4  in the case of the track systems  16   1 ,  16   2  and the roller wheels  28   1 - 28   6  in the case of the rear track systems  16   3 ,  16   4 ). The track system  16   i  also comprises a frame  13  which supports various components of the track system  16   i , including the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   R . The track system  16   i  has a longitudinal direction and a first longitudinal end  57  and a second longitudinal end  59  that define a length L T  of the track system  16   i  along a longitudinal axis  61  that defines the longitudinal direction of the track system  16   i . The track system  16   i  has a widthwise direction and a width that is defined by a width W of the track  22 . The track system  16   i  also has a height direction that is normal to its longitudinal direction and its widthwise direction. 
     Each of the front ones of the track systems  16   1 - 16   4  is steerable by the steering system  17  of the agricultural vehicle  10  in response to input of the user at the steering device to change an orientation of that track system relative to the frame  12  of the agricultural vehicle  10  in order to steer the agricultural vehicle  10  on the ground. To that end, each of the front ones of the track systems  16   1 - 16   4  is pivotable about a steering axis  25  of the agricultural vehicle  10 . An orientation of the longitudinal axis  61  of each of the front ones of the track systems  16   1 - 16   4  is thus changeable relative to a longitudinal axis  97  of the agricultural vehicle  10 . 
     The track  22  engages the ground to provide traction to the agricultural vehicle  10 . A length of the track  22  allows the track  22  to be mounted around the track-engaging assembly  21 . In view of its closed configuration without ends that allows it to be disposed and moved around the track-engaging assembly  21 , the track  22  can be referred to as an “endless” track. With additional reference to  FIGS.  8  to  11   , the track  22  comprises an inner side  45 , a ground-engaging outer side  47 , and lateral edges  49   1 ,  49   2 . The inner side  45  faces the wheels  23   1 ,  23   2 ,  24 ,  26   1 ,  26   2 ,  28   1 - 28   R , while the ground-engaging outer side  47  engages the ground. A top run  65  of the track  22  extends between the longitudinal ends  57 ,  59  of the track system  16   i  and over the wheels  23   1 ,  23   2 ,  24 ,  26   1 ,  26   2 ,  28   1 - 28   R , while a bottom run  66  of the track  22  extends between the longitudinal ends  57 ,  59  of the track system  16   i  and under the wheels  23   1 ,  23   2 ,  24 ,  26   1 ,  26   2 ,  28   1 - 28   R . The bottom run  66  of the track  22  defines an area of contact  63  of the track  22  with the ground which generates traction and bears a majority of a load on the track system  16   i , and which will be referred to as a “contact patch” of the track  22  with the ground. The track  22  has a longitudinal axis  19  which defines a longitudinal direction of the track  22  (i.e., a direction generally parallel to its longitudinal axis) and transversal directions of the track  22  (i.e., directions transverse to its longitudinal axis), including a widthwise direction of the track  22  (i.e., a lateral direction generally perpendicular to its longitudinal axis). The track  22  has a thickness direction normal to its longitudinal and widthwise directions. 
     In this embodiment, the track  22  is relatively narrow. For instance, this may be helpful to allow the track  22  to fit between rows of crops such as to leave the crops undisturbed when the agricultural vehicle  10  traverses an agricultural field. In turn, this may allow the agricultural field to have a greater crop density. For instance, in some embodiments, a ratio of a width W v  of the agricultural vehicle  10  (measured between laterally-outwardmost ones of the track systems  16   1 - 16   4 ) over the width W of the track  22  may be at least 5, in some cases at least 7, in some cases at least 10, in some cases at least 12, and in some cases even more. For example, in some embodiments, the width W of the track  22  may be no more than 30 inches, in some cases no more than 25 inches, in some cases no more than 20 inches, in some cases no more than 18 inches, in some cases no more than 16 inches, and in some cases even less (e.g., 14.5 inches). The width W of the track  22  may have any other suitable value in other embodiments. 
     The track  22  is elastomeric, i.e., comprises elastomeric material, to be flexible around the track-engaging assembly  21 . The elastomeric material of the track  22  can include any polymeric material with suitable elasticity. In this embodiment, the elastomeric material of the track  22  includes rubber. Various rubber compounds may be used and, in some cases, different rubber compounds may be present in different areas of the track  22 . In other embodiments, the elastomeric material of the track  22  may include another elastomer in addition to or instead of rubber (e.g., polyurethane elastomer). 
     More particularly, the track  22  comprises an endless body  36  underlying its inner side  45  and ground-engaging outer side  47 . In view of its underlying nature, the body  36  will be referred to as a “carcass”. The carcass  36  is elastomeric in that it comprises elastomeric material  38  which allows the carcass  36  to elastically change in shape and thus the track  22  to flex as it is in motion around the track-engaging assembly  21 . 
     In this embodiment, the carcass  36  comprises a plurality of reinforcements embedded in its elastomeric material  38 . These reinforcements can take on various forms. 
     For example, in this embodiment, the carcass  36  comprises a layer of reinforcing cables  37   1 - 37   M  that are adjacent to one another and extend generally in the longitudinal direction of the track  22  to enhance strength in tension of the track  22  along its longitudinal direction. In this case, each of the reinforcing cables  37   1 - 37   M  is a cord including a plurality of strands (e.g., textile fibers or metallic wires). In other cases, each of the reinforcing cables  37   1 - 37   M  may be another type of cable and may be made of any material suitably flexible along the cable&#39;s longitudinal axis (e.g., fibers or wires of metal, plastic or composite material). 
     As another example, in this embodiment, the carcass  36  comprises a layer of reinforcing fabric  43 . The reinforcing fabric  43  comprises thin pliable material made usually by weaving, felting, knitting, interlacing, or otherwise crossing natural or synthetic elongated fabric elements, such as fibers, filaments, strands and/or others, such that some elongated fabric elements extend transversally to the longitudinal direction of the track  22  to have a reinforcing effect in a transversal direction of the track  22 . For instance, the reinforcing fabric  43  may comprise a ply of reinforcing woven fibers (e.g., nylon fibers or other synthetic fibers). 
     The carcass  36  may be molded into shape in a molding process during which the rubber  38  is cured. For example, in this embodiment, a mold may be used to consolidate layers of rubber providing the rubber  38  of the carcass  36 , the reinforcing cables  37   1 - 37   M  and the layer of reinforcing fabric  43 . 
     The inner side  45  of the endless track  22  comprises an inner surface  55  of the carcass  36  and a plurality of wheel-contacting projections  48   1 - 48   N  that project from the inner surface  55  and are positioned to contact at least some of the wheels  23   1 ,  23   2 ,  24 ,  26   1 ,  26   2 ,  28   1 - 28   R  to do at least one of driving (i.e., imparting motion to) the track  22  and guiding the track  22 . The wheel-contacting projections  48   1 - 48   N  can be referred to as “wheel-contacting lugs”. Furthermore, since each of them is used to do at least one of driving the track  22  and guiding the track  22 , the wheel-contacting lugs  48   1 - 48   N  can be referred to as “drive/guide projections” or “drive/guide lugs”. In some examples of implementation, a drive/guide lug  48   i  may interact with the drive wheel  24  to drive the track  22 , in which case the drive/guide lug  48   i  is a drive lug. In other examples of implementation, a drive/guide lug  48   i  may interact with the front and rear idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2  and/or the roller wheels  28   1 - 28   R  to guide the track  22  to maintain proper track alignment and prevent de-tracking without being used to drive the track  22 , in which case the drive/guide lug  48   i  is a guide lug. In yet other examples of implementation, a drive/guide lug  48   i  may both (i) interact with the drive wheel  24  to drive the track and (ii) interact with the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2  and/or the roller wheels  28   1 - 28   R  to guide the track  22  to maintain proper track alignment and prevent de-tracking, in which case the drive/guide lug  48   i  is both a drive lug and a guide lug. 
     In this embodiment, the drive/guide lugs  48   1 - 48   N  interact with the drive wheel  24  in order to cause the track  22  to be driven, and also interact with the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2  and the roller wheels  28   1 - 28   R  in order to guide the track  22  as it is driven by the drive wheel  24  to maintain proper track alignment and prevent de-tracking. The drive/guide lugs  48   1 - 48   N  are thus used to both drive the track  22  and guide the track  22  in this embodiment. 
     In this example of implementation, the drive/guide lugs  48   1 - 48   N  are arranged in a single row disposed longitudinally along the inner side  45  of the track  22 . The drive/guide lugs  48   1 - 48   N  may be arranged in other manners in other examples of implementation (e.g., in a plurality of rows that are spaced apart along the widthwise direction of the track  22 ). 
     In this embodiment, each drive/guide lug  48   i  is an elastomeric drive/guide lug in that it comprises elastomeric material  67 . The elastomeric material  67  can be any polymeric material with suitable elasticity. More particularly, in this embodiment, the elastomeric material  67  includes rubber. Various rubber compounds may be used and, in some cases, different rubber compounds may be present in different areas of the drive/guide lug  48   i . In other embodiments, the elastomeric material  67  may include another elastomer in addition to or instead of rubber (e.g., polyurethane elastomer). The drive/guide lugs  48   1 - 48   N  may be provided on the inner side  45  in various ways. For example, in this embodiment, the drive/guide lugs  48   1 - 48   N  are provided on the inner side  45  by being molded with the carcass  36 . 
     The ground-engaging outer side  47  comprises a ground-engaging outer surface  31  of the carcass  36  and a tread pattern  40  to enhance traction on the ground. The tread pattern  40  comprises a plurality of traction projections  58   1 - 58   T  projecting from the ground-engaging outer surface  31 , spaced apart in the longitudinal direction of the endless track  22  and engaging the ground to enhance traction. The traction projections  58   1 - 58   T  may be referred to as “tread projections” or “traction lugs”. 
     The traction lugs  58   1 - 58   T  may have any suitable shape. In this embodiment, each of the traction lugs  58   1 - 58   T  has an elongated shape and is angled, i.e., defines an oblique angle θ (i.e., an angle that is not a right angle or a multiple of a right angle), relative to the longitudinal direction of the track  22 . The traction lugs  58   1 - 58   T  may have various other shapes in other examples (e.g., curved shapes, shapes with straight parts and curved parts, etc.). 
     As shown in  FIG.  12   , each traction lug  58   i  has a periphery  69  which includes a front surface  80   1 , a rear surface  80   2 , two lateral surfaces  81   1 ,  81   2 , and a top surface  86 . The front surface  80   1  and the rear surface  80   2  are opposed to one another in the longitudinal direction of the track  22 . The two lateral faces  81   1 ,  81   2  are opposed to one another in the widthwise direction of the track  22 . In this embodiment, the front surface  80   1 , the rear surface  80   2 , and the lateral surfaces  81   1 ,  81   2  are substantially straight. The periphery  69  of the traction lug  58   i  may have any other shape in other embodiments (e.g., the front surface  80   1 , the rear surface  80   2 , and/or the lateral surfaces  81   1 ,  81   2  may be curved). The traction lug  58   i  has a front-to-rear dimension L L  in the longitudinal direction of the track  22 , a side-to-side dimension L W  in the widthwise direction of the track  22 , and a height H in the thickness direction of the track  22 . 
     In this embodiment, each traction lug  58   i  is an elastomeric traction lug in that it comprises elastomeric material  41 . The elastomeric material  41  can be any polymeric material with suitable elasticity. More particularly, in this embodiment, the elastomeric material  41  includes rubber. Various rubber compounds may be used and, in some cases, different rubber compounds may be present in different areas of the traction lug  58   i . In other embodiments, the elastomeric material  41  may include another elastomer in addition to or instead of rubber (e.g., polyurethane elastomer). 
     The traction lugs  58   1 - 58   T  may be provided on the ground-engaging outer side  47  in various ways. For example, in this embodiment, the traction lugs  58   1 - 58   T  are provided on the ground-engaging outer side  47  by being molded with the carcass  36 . 
     The track  22  may be constructed in various other manners in other embodiments. For example, in some embodiments, the track  22  may have recesses or holes that interact with the drive wheel  24  in order to cause the track  22  to be driven (e.g., in which case the drive/guide lugs  48   1 - 48   N  may be used only to guide the track  22  without being used to drive the track  22 , i.e., they may be “guide lugs” only), and/or the ground-engaging outer side  47  of the track  22  may comprise various patterns of traction lugs. 
     The drive wheel  24  is rotatable by power derived from the prime mover  14  to drive the track  22 . That is, power generated by the prime mover  14  and delivered over the powertrain  15  of the agricultural vehicle  10  can rotate a final drive axle  56   i  of a final drive unit  35   i , which causes rotation of the drive wheel  24 , which in turn imparts motion to the track  22 . 
     In this embodiment, as shown in  FIGS.  13  to  15   , the final drive unit  35   i  comprises an input  63  connectable to a given one of the front and rear differentials  27 ,  29  of the agricultural vehicle  10 , an output  71  constituting the final drive axle  56   i , and a transmission  72  between its input  63  and its output  71 . 
     In this embodiment, the transmission  72  of the final drive unit  35   i  comprises a first portion  77  associated with the input  63  of the final drive unit  35   i  and a second portion  79  associated with the output  71  the final drive unit  35   i . The first portion  77  of the transmission  72  has an axis  83  defined by the front or rear differential  27 ,  29 , while the second portion  79  of the transmission  72  has an axis  84  coaxial with an axis of rotation  78  of the final drive axle  56   i  which in this example is coaxial with an axis of rotation  90  of the drive wheel  24 . In this case, the axis  84  of the second portion  79  of the transmission  72  is spaced apart from the axis  83  of the first portion  77  of the transmission  72  in the height direction of the track system  16   i . Thus, in this case, the axis of rotation  90  of the drive wheel  24  is spaced apart from an axis of rotation of the front or rear differential  27 ,  29  in the height direction of the track system  16   i . In other cases, the axis of rotation  90  of the drive wheel  24  may be aligned with the axis of rotation of the front or rear differential  27 ,  29  in the longitudinal direction of the track system  16   i  and/or in the height direction of the track system  16   i . 
     In this embodiment, as shown in  FIG.  15   , the first portion  77  of the transmission  72  comprises an input shaft  91  connectable to the front or rear differential  27 ,  29  and leading to an input transmission wheel  92  and the second portion  79  of the transmission  72  comprises an output transmission wheel  93  leading to the final drive axle  56   i  that drives the drive wheel  24 . In this example, the transmission wheels  92 ,  93  are interconnected by an intermediate transmission member  96 . More particularly, in this embodiment, the transmission  72  comprises a gearbox, the first transmission wheel  92  is an input gear, the second transmission wheel  93  is an output gear, and the intermediate transmission member  96  comprises an idler gear. 
     In the embodiment depicted in  FIG.  15   , the transmission  72  comprises a multiplier gear set such that a rotational speed of the output gear  93  is greater than that of the input gear  92 . However, in other embodiments, the transmission  72  may comprise a reduction gear such that the rotational speed of the output gear  93  is less than that of the input gear  92  (e.g., by varying a size of respective ones of the input and output gears  92 ,  93 ). 
     With additional reference to  FIG.  16   , in this embodiment, the drive wheel  24  comprises a drive sprocket comprising a plurality of drive members  52   1 - 52   B  spaced apart along a circular path to engage the drive/guide lugs  48   1 - 48   N  of the track  22  in order to drive the track  22 . The drive wheel  24  and the track  22  thus implement a “positive drive” arrangement. More particularly, in this embodiment, the drive wheel  24  comprises two side discs  50   1 ,  50   2  which are co-centric and turn about a common axle  51  and between which the drive members  52   1 - 52   B  extend near respective peripheries of the side discs  50   1 ,  50   2 . In this example, the drive members  52   1 - 52   B  are thus drive bars that extend between the side discs  50   1 ,  50   2 . The drive wheel  24  and the track  22  have respective dimensions allowing interlocking of the drive bars  52   1 - 52   B  of the drive wheel  24  and the drive/guide lugs  48   1 - 48   N  of the track  22 . Adjacent ones of the drive bars  52   1 - 52   B  define an interior space  53  between them to receive one of the drive/guide lugs  48   1 - 48   N . Adjacent ones of the drive/guide lugs  48   1 - 48   N  define an inter-lug space  39  between them to receive one of the drive bars  52   1 - 52   B . The drive/guide lugs  48   1 - 48   N  and the drive bars  52   1 - 52   B  have a regular spacing that allows interlocking of the drive/guide lugs  48   1 - 48   N  and the drive bars  52   1 - 52   B  over a certain length of the drive wheel&#39;s circumference. Moreover, in this embodiment, the drive wheel  24  comprises a hub  115  for affixing the drive wheel  24  to the frame  13  of the track system  16   i . 
     The drive wheel  24  may be configured in various other ways in other embodiments. For example, in other embodiments, the drive wheel  24  may not have any side discs such as the side discs  50   1 ,  50   2 . As another example, in other embodiments, instead of being drive bars, the drive members  52   1 - 52   B  may be drive teeth that are distributed circumferentially along the drive wheel  24  or any other type of drive members. As another example, in embodiments where the track  22  comprises recesses or holes, the drive wheel  24  may have teeth that enter these recesses or holes in order to drive the track  22 . As yet another example, in some embodiments, the drive wheel  24  may frictionally engage the inner side  45  of the track  22  in order to frictionally drive the track  22  (i.e., the drive wheel  24  and the track  22  may implement a “friction drive” arrangement). 
     As described above, in this embodiment, the final drive axle  56   i  of each final drive unit  35   i  is offset in the height direction of the track system  16   i . This may allow an increased angle of wrap of the track  22  about the drive wheel  24 . 
     As shown in  FIG.  17   , the final drive units  35   1 ,  35   2  associated with the front track systems  16   1 ,  16   2  are similar to the final drive units  35   3 ,  35   4  associated with the rear track systems  16   3 ,  16   4 . However, each of the final drive units  35   1 ,  35   2  associated with the front track systems  16   1 ,  16   2  additionally comprises a steering knuckle  94  for steering a respective front track system  16   i . For instance, the steering knuckle  94  may be integrated with (i.e., integrally made with or fastened to another part of) the final drive unit  35   i . 
     The idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   R  are not driven by power supplied by the prime mover  14 , but are rather used to do at least one of supporting part of the weight of the agricultural vehicle  10  on the ground via the track  22 , guiding the track  22  as it is driven by the drive wheel  24 , and tensioning the track  22 . More particularly, in this embodiment, the front and rear idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2  maintain the track  22  in tension and help to support part of the weight of the agricultural vehicle  10  on the ground via the track  22 . As shown in  FIG.  18   , the roller wheels  28   1 - 28   R  roll on a rolling path  33  of the inner side  45  of the track  22  along the bottom run  66  of the track  22  to apply the bottom run  66  on the ground. In this case, as they are located between frontmost and rearmost ones of the wheels of the track system  16   i , the roller wheels  28   1 - 28   R  can be referred to as “mid-rollers”. 
     With additional reference to  FIGS.  19  to  23   , each mid-roller  28   i  comprises a hub portion  73 , a rim portion  74 , and a radially-extending portion  34  between the hub portion  73  and the rim portion  74 . The hub portion  73  is an inner portion of the mid-roller  28   i  which is associated with a hub  75  receiving an axle  76  for the mid-roller  28   i . The rim portion  74  is an outer portion of the mid-roller  28   i  which contacts the inner side  45  of the endless track  22 . The radially-extending portion  34  is an intermediate portion of the mid-roller  28   i  which extends radially between the hub portion  73  and the rim portion  74 . 
     The mid-roller  28   i  comprises a pair of lateral sides  30   1 ,  30   2  opposite one another and a peripheral side  32  between the lateral sides  30   1 ,  30   2 . The peripheral side  32  rolls on the inner side  45  of the track  22  to apply the bottom run  66  of track  22  on the ground. More particularly, in this embodiment, the mid-roller  28   i  rolls on the rolling path  33  which is delimited by some of the drive/guide lugs  48   1 - 48   N  such that, as the mid-roller  28   i  rolls, these drive/guide lugs pass next to the mid-roller  28   i . 
     In this embodiment, the mid-roller  28   i  may engage a significant extent of the width W of the track  22 . For example, in some embodiments, a ratio of a width R w  of the mid-roller  28   i  over the width W of the track  22  may be at least 0.2, in some cases at least 0.3, in some cases at least 0.4, and in some cases even more. 
     In addition, in this embodiment, as shown in  FIGS.  24  and  25   , the track system  16   i  comprises a wheel carrier  85  carrying the mid-rollers  28   1 - 28   R  and configured to allow movement of the mid-rollers  28   1 - 28   R  relative to the frame  13  of the track system  16   i . The wheel carrier  85 , which may be referred to as a “bogie”, comprises a wheel-carrying structure  89  to which are mounted the mid-rollers  28   1 - 28   R . 
     More particularly, in this embodiment, the bogie  85  is pivotable relative to the frame  13  of the track system  16   i  about a pivot  87  defining an axis of rotation  88  that is transversal, in this case perpendicular, to the longitudinal axis  61  of the track system  16   i . The bogie  85  thus imparts the mid-rollers  28   1 - 28   R  with a pivoting motion capability which may be referred to as a “pitch” motion. 
     Also, in this embodiment, with additional reference to  FIGS.  30  and  56  to  58   , the bogie  85  comprises a lateral load distribution mechanism  150  configured to increase a lateral extent C of the contact patch  63  of the track  22  on a ground surface GS. This may be particularly useful when the ground surface GS is sloped or uneven (e.g., uneven terrain in an agricultural field or a sloped road), such as shown in  FIG.  56    for example. 
     In this embodiment, the lateral load distribution mechanism  150  is configured to apply the mid-rollers  28   1 - 28   R  onto the bottom run  66  of the track  22  such as to increase the lateral extent C of the contact patch  63  of the track  22 . For example, in some embodiments, the lateral load distribution mechanism  150  may be configured to apply laterally-adjacent ones of the mid-rollers  28   1 - 28   R  onto the bottom run  66  of the track  22  to increase the lateral extent C of the contact patch  63  of the track  22 . The laterally-adjacent ones of the mid-rollers  28   1 - 28   R  are respective ones of these wheels that are generally aligned with respect to one another or otherwise closest to one another in the longitudinal direction of the track system  16   i  (e.g., the mid-rollers  28   1 ,  28   2 , and/or the mid-rollers  28   3 ,  28   4 , and/or the mid-rollers  28   5 ,  28   6 ). 
     The lateral load distribution mechanism  150  may be configured such that bottom track-contacting areas  146  of laterally-adjacent ones of the mid-rollers  28   1 - 28   R  are vertically movable relative to one another (i.e., movable relative to one another in the height direction of the track system  16   i ). The bottom track-contacting area  146  of a given one of the mid-rollers  28   1 - 28   R  is that area of the given one of the mid-rollers  28   1 - 28   R  which contacts the bottom run  66  of the track  22 . 
     In some embodiments, the lateral load distribution mechanism  150  may allow a “roll” motion of respective ones of the mid-rollers  28   1 - 28   R . That is, the lateral load distribution mechanism  150  may be configured to allow a motion of respective ones of the mid-rollers  28   1 - 28   R  relative to the frame  12  of the agricultural vehicle  10  that includes a rotation about a roll axis  164  which is transverse to their axes of rotation. In this case, the roll axis  164  is generally parallel to the longitudinal axis  61  of the track system  16   i . 
     For example, in some embodiments, the roll motion enabled by the lateral load distribution mechanism  150  may be implemented by the bogie  85 . More specifically, the bogie  85  may be movable relative to the frame  12  of the vehicle  10  to cause the mid-rollers  28   1 - 28   R  to rotate about the roll axis  164  as they engage the bottom run  66  of the track  22 . 
     More particularly, in some embodiments, as shown in  FIG.  56   , the bogie  85  is configured to define the roll motion and the pitch motion of respective ones of the mid-rollers  28   1 - 28   R . That is, the bogie  85  can define a rotation about the roll axis  164  parallel to the longitudinal axis  61  of the track system  16   i  and about the pitch axis  88  parallel to the widthwise direction of the track system  16   i . 
     As shown in  FIGS.  57  and  58   , in this embodiment, the bogie  85  comprises an upper structure  152  and a lower structure  154  connected to the upper structure  154 . The lower structure  154  is configured to provide the bogie  85  with its roll motion capability. The lower structure  154  comprises a pair of axle-retaining members  1561 ,  1562  spaced apart in the longitudinal direction of the track system  16   i , and a roll motion mechanism  158  connecting the axle-retaining members  156   1 ,  156   2  to one another. The axle-retaining members  156   1 ,  156   2  are configured to receive the axles  76  of the mid-rollers  28   1 - 28   4  (e.g., via a hole traversing each axle-retaining member  156   i ). Each axle  76  receives two laterally adjacent mid-rollers  28   i ,  28   j  thereon. 
     The roll motion mechanism  158  comprises a shaft  160  and an outer tube  162  receiving the shaft  160  therein. The shaft  160  extends in the longitudinal direction of the track system  16   i  and is connectable to the axle-retaining members  156   1 ,  156   2 . For example, the shaft  160  may be connected to the axle-retaining members  156   1 ,  156   2  via an interference fit. In other embodiments, the shaft  160  may be connected to the axle-retaining members  156   1 ,  156   2  in any other suitable way (e.g., via welding, fasteners, etc.). The outer tube  162  is mounted to the shaft  160  and extends between the axle-retaining members  156   1 ,  156   2 . The shaft  160  is rotatable within the outer tube  162  about an axis of rotation of the outer tube  162  which corresponds to the roll axis  164 . In this embodiment, the shaft  160  rotates within the outer tube  162  via a bearing  166  (e.g., a roller bearing) disposed between a peripheral surface of the shaft  160  and an inner surface of the outer tube  162 . The shaft  160  may rotate within the outer tube  162  via any other suitable mechanism in other embodiments. 
     The upper structure  152  of the bogie  85  is configured to provide the bogie  85  with its pitch motion capability. More particularly, the upper structure  152  comprises the pivot  87 . The upper structure  152  comprises a body  168  affixed to the lower structure  154  (e.g., via welding). The body  168  comprises a shaft-receiving aperture  170  for receiving therein a shaft  172 . The shaft  172  is rotatable within the shaft-receiving aperture  170  about an axis of rotation that corresponds to the pitch axis  88  defined by the pivot  87 . For example, the shaft-receiving aperture  170  may comprise a bearing  176  (e.g., a roller bearing) for enabling rotation of the shaft  172  within the shaft-receiving aperture  170 . As shown in  FIG.  58   , the shaft  172  is connected at its longitudinal end portions to the frame  13  of the track system  16   i  which supports the bogie  85 . 
     Thus, in this embodiment, the lateral load distribution mechanism  150  allows the bogie  85  to define the roll motion and the pitch motion about the roll and pitch axes  164 ,  88  respectively. Therefore, the bogie  85  allows the mid-rollers  28   1 - 28   4  to pivot about the roll axis  164  causing the mid-rollers  28   1 - 28   4  to apply the bottom run  66  of the track  22  more evenly on the ground surface GS. 
     The roll motion of respective ones of the mid-rollers  28   1 - 28   4  may be implemented by the lateral load distribution mechanism  150  in any other suitable way in other embodiments. 
     The mid-rollers  28   1 - 28   4  may not be mounted to a bogie in other embodiments. For example, the mid-rollers  28   1 - 28   R  may be mounted directly to the frame  13  of the track system  16   i  without any intervening bogie in other embodiments. 
     In this example of implementation, as shown in  FIG.  25   , the track system  16   i  may comprise a tensioner  95  for tensioning the track  22 . For instance, in this embodiment, the tensioner  95  comprises an actuator mounted at one end to the frame  13  of the track system  16   i  and at another end to a hub of the front idler wheels  23   1 ,  23   2 . This allows the tensioning mechanism  95  to modify a distance between the front idler wheels  23   1 ,  23   2  and the rear idler wheels  26   1 ,  26   2  in the longitudinal direction of the track system  16   i . 
     With reference to  FIGS.  2 ,  3  and  27  to  32   , in this embodiment, the agricultural vehicle  10  comprises a lateral track spacing adjustment mechanism  100  configured to adjust the spacing S of laterally-adjacent ones of the track  16   1 - 16   4  in the widthwise direction of the agricultural vehicle  10 . The lateral track spacing adjustment mechanism  100  thus allows the spacing S of the track systems  16   1 ,  16   2  and/or the spacing S of the track systems  16   3 ,  16   4  to be adjusted in order to facilitate use of the agricultural vehicle  10  in different field configurations, such as in different configurations of row crops (e.g., different “tread settings” for different field configurations). Notably, in this embodiment, the spacing S of the laterally-adjacent ones of the track systems  16   1 - 16   4  of the agricultural vehicle  10  is adjustable while the laterally-adjacent ones of the track systems  16   1 - 16   4  of the agricultural vehicle  10  are connected to the powertrain  15  and/or without requiring use of additional parts (e.g. spacers). 
     For purposes of this example, the lateral track spacing adjustment mechanism  100  will be discussed in relation to the spacing S of the track systems  16   1 ,  16   2 , although a similar discussion applies to the spacing S of the track systems  16   3 ,  16   4 . 
     The lateral track spacing adjustment mechanism  100  allows the spacing S of the track systems  16   1 ,  16   2  to be increased, i.e., by moving one or both of the track systems  16   1 ,  16   2  away from a center  117  of the vehicle  10  in the widthwise direction of the vehicle  10  such that the track systems  16   1 ,  16   2  are moved away from one another, and decreased, i.e., by moving one or both of the track systems  16   1 ,  16   2  towards the center  117  of the vehicle  10  in the widthwise direction of the vehicle  10  such that the track systems  16   1 ,  16   2  are moved towards one another. 
     In this embodiment, the lateral track spacing adjustment mechanism  100  comprises a portion  102  of each of the final drive units  35   1 ,  35   2 . Notably, in this embodiment, the lateral track spacing adjustment mechanism  100  is configured such that the spacing S of the track systems  16   1 ,  16   2  is adjustable while the final drive units  35   1 ,  35   2  remain fixed. That is, the final drive units  35   1 ,  35   2  do not have to be moved in order to adjust the spacing S of the track systems  16   1 ,  16   2 . Rather, the track systems  16   1 ,  16   2  are movable relative to the final drive units  35   1 ,  35   2  in the widthwise direction of the vehicle  10 . 
     More particularly, in this embodiment, the portion  102  of each final drive unit  35   i  that implements the lateral track spacing adjustment mechanism  100  comprises the final drive axle  56   i  and a support  104  for engaging the frame  13  of the track system  16   i . 
     In this embodiment, the support  104  comprises a plurality of support arms  106   1 ,  106   2  that protrude from a body  99  of the final drive unit  35   i  towards the track system  16   i . In this case, the body  99  of the final drive unit  35   i  comprises gearing of the transmission  72 . Each support arm  106   i  of the support  104  has a length L s  that is significant. For example, the length L s  of the support arm  106   i  may be greater than the width W of the track  22 . For example, in some cases, a ratio L s /W of the length L s  of the support arm  106   i  over the width W of the track  22  may be at least 1.1, in some cases at least 1.2, in some cases at least 1.3, in some cases at least 1.4, in some cases at least 1.5, and in some cases even more (e.g., 1.6, 1.7, 2, etc.). 
     The drive axle  56   i  of the final drive unit  35   i  has a length LD that is also significant. For example, the length LD of the drive axle  56   i  may be greater than the width W of the track  22 . For example, in some cases, a ratio of the length of the drive axle  56   i  over the width W of the track  22  may be at least 1.1, in some cases at least 1.2, in some cases at least 1.3, in some cases at least 1.4, in some cases at least 1.5, and in some cases even more (e.g., 1.6, 1.7, 2, etc.). 
     In this embodiment, the frame  13  of the track system  16   i  comprises an upper frame member  110  constituting a nonrotatable support  125  configured to receive the support arms  106   1 ,  106   2  of the support  104 . To that end, in this embodiment, the nonrotatable support  125  comprises a plurality of openings  1081 ,  1082  that are configured for receiving the support arms  106   1 ,  106   2 . In this embodiment, each support arm  106   i  is generally cylindrical and, accordingly, each opening  108   i  is also generally cylindrical. In this embodiment, the nonrotatable support  125  also comprises an opening  112  that is disposed centrally relative to the openings  108   1 ,  108   2  in the longitudinal direction of the track system  16   i . The opening  112  is configured for receiving therein the final drive axle  56   i  of the final drive unit  35   i . This will be described in more detail further below. The upper frame member  110  of the frame  13  may also comprise a connector  113  for connecting the upper frame member  110  of the frame  13  to a lower frame member  114  of the frame  13  which supports the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   R  as depicted in  FIG.  25   . In this example, the connector  113  comprises a pivot about which the lower frame member  114  may pivot relative to the upper frame member  110 . 
     The support arms  106   1 ,  106   2  and the drive axle  56   i  of the final drive unit  35   i  allow movement of the track system  16   i  relative to the final drive unit  35   i  in the widthwise direction of the vehicle  10 . 
     In this embodiment, the frame  13  is configured such that a tension of the track  22  is distributed more evenly throughout the frame  13 . For instance, in this embodiment, the shape of the upper frame member  110  of the frame  13 , which extends frontwardly and rearwardly of the drive wheel  24 , may allow distribution of the tension of the track  22  towards a front and a rear portion of the upper frame member  110  of the frame  13  in order to minimize stress at the final drive axle  56   i . 
     As shown in  FIGS.  29  and  30   , in this example, the hub  115  of the drive wheel  24  is received in the opening  112  of the upper frame member  110  of the frame  13  and is rotatable relative to the upper frame member  110  of the frame  13 . For example, to that end, a bearing  116  may be disposed in the opening  112 , between the hub  115  and the upper member  110  of the frame  113 . A sealing member may also be disposed between the hub  115  and the upper member  110  of the frame  13  to seal the bearing  116  from exterior contaminants. 
     In this embodiment, the track system  16   i  comprises a retaining mechanism  118  for selectively securing the track system  16   i  to the final drive unit  35   i . More specifically, in this embodiment, the retaining mechanism  118  comprises a retaining member  120  that is configured to receive and selectively retain the final drive axle  56   i  of the final drive unit  35   i . In particular, the retaining member  120  may be adjusted to prevent relative movement between the final drive axle  56   i  and the retaining member  120 . In this example of implementation, the retaining member  120  comprises a taper lock bushing  122 . Tightening of fasteners  124  of the taper lock bushing  122  causes an opening of the taper lock bushing  122 , which is configured to receive the final drive axle  56   i , to shrink. This prevents movement of the final drive axle  56   i  relative to the taper lock bushing  122 . Conversely, loosening of the fasteners  124  of the taper lock bushing  122  causes the opening of the taper lock bushing  122  to expand and therefore allow relative movement of the final drive axle  56   i  relative to the taper lock bushing  122 . The retaining mechanism  118  may comprise other retaining members  135  similar to the retaining member  120  in order to receive and selectively retain the supports arms  106   1 ,  106   2  of the support  104 . 
     Due to the nature of its retaining members  120 , in this embodiment, the retaining mechanism  118  of the track system  16   i  can provide a continuous range of adjustment positions of the track system  16   i  relative to the final drive unit  35   i . In turn, this may allow the spacing S of the track systems  16   1 ,  16   2  and/or the spacing S of the track systems  16   3 ,  16   4  to have any value within a range of its minimal and maximal values. In other words, the spacing S may have any of an infinite number of values within a given range. 
     In order to adjust the spacing S of the track systems  16   1 ,  16   2  and/or the spacing S of the track systems  16   3 ,  16   4 , a user (e.g., the operator of the vehicle  10 ) loosens the retaining members  120  of the retaining mechanism  116  of a selected track system  16   i  and displaces the track system  16   i  relative to the corresponding final drive unit  35   i . The operator then tightens the retaining members  120  of the retaining mechanism  116  to secure the track system  16   i  to the final drive unit  35   i  at a selected distance therefrom. The user then repeats the same process on a laterally opposite track system  16   j  to obtain the desired spacing S between the track systems  16   i ,  16   j . 
     This allows the user to adjust the spacing S of the track systems  16   1 ,  16   2  and/or the spacing S of the track systems  16   3 ,  16   4  to have a “narrow” tread setting, as shown in  FIG.  31   . In the narrow tread setting, the body  99  of the final drive units  35   1 ,  35   2  and/or the final drive units  35   3 ,  35   4  are relatively close to their corresponding track systems  16   1 ,  16   2  and/or  16   3 ,  16   4 . Moreover, in the narrow tread setting, the final drive axle  56   i  and the support arms  106   1 ,  106   2  of a respective final drive unit  35   i  extend beyond the track  22  of the respective track system  16   i  in the widthwise direction of the track system  16   i . That is, the final drive axle  56   i  and the support arms  106   1 ,  106   2  of a respective final drive unit  35   i  overlap an entirety of the width W of the track  22  and extend outwardly beyond a laterally-outward edge  119  of the track  22  (i.e., a lateral edge of the track  22  facing away from the center  117  of the vehicle  10 ). 
     Alternatively, the user may adjust the spacing S of the track systems  16   1 ,  16   2  and/or the spacing S of the track systems  16   3 ,  16   4  to have a “wide” tread setting, as shown in  FIG.  32   . In the wide tread setting, the body  99  of the final drive units  35   1 ,  35   2  and/or the final drive units  35   3 ,  35   4  are relatively distant to their corresponding track systems  16   1 ,  16   2  and/or  16   3 ,  16   4 . Moreover, in the wide tread setting, the final drive axle  56   i  and the support arms  106   1 ,  106   2  of a respective final drive unit  35   i  do not extend beyond the track  22  of the respective track system  16   i  in the widthwise direction of the track system  16   i . That is, the final drive axle  56   i  and the support arms  106   1 ,  106   2  of a respective final drive unit  35   i  do not extend outwardly of the laterally-outward edge  119  of the track  22 . 
     The agricultural vehicle  10 , including the track systems  16   1 - 16   4 , may be implemented in various other ways in other embodiments. 
     For instance,  FIGS.  33  and  34    show an example of another embodiment of the track systems  16   1 - 16   4 . In this embodiment, the front ones of the track systems  16   1 - 16   4  are implemented differently from the rear ones of the track systems  16   1 - 16   4 , but each of the track systems  16   1 - 16   4  includes features as discussed above, including the lateral load distribution mechanism  150 , the lateral track spacing adjustment mechanism  100 , etc. 
     As shown in  FIG.  34   , the front track systems  16   1 ,  16   2  are steerable to change their orientation relative to the frame  12  of the vehicle  10  in order to steer the vehicle  10  on the ground. The front track system  16   1  will be described, with an understanding that the front track system  16   2  is similarly arranged. 
     In this embodiment, the drive wheel  24  of the track system  16   1  is entirely supported by the final drive axle  56   i  and is unsupported by the frame  13  of the track system  16   1 . All loading exerted by the drive wheel  24 , including its weight, is transmitted through the final drive axle  56   i , and thus is not transmitted through the frame  13  of the track system  16   1 . The tension of the track  22  is taken up by the drive wheel  24 . The drive wheel  24  may thus be seen as a “floating” drive wheel in that it is unconnected to and isolated from the frame  13  of the track system  16   1 . To that end, in this embodiment, the drive wheel  24  is only (i.e., exclusively) supported by a rotatable support  202  that is rotatable by the final drive axle  56   i . This is in contrast to the embodiment considered above in respect of  FIGS.  4  to  7  and  27  to  32    in which the drive wheel  24  is supported by the nonrotatable support  125 , namely the upper frame member  110 , which transmits loading exerted by the drive wheel  24 , including its weight, through the frame  13  of the track system  16   1  and in which the tension of the track  22  is partly taken up by the upper frame member  110 . 
     More particularly, in this embodiment, with additional reference to  FIGS.  37  and  38   , the final drive unit  35   1  associated with the track system  16   1  comprises a transmission  204  including an input  206  connected to the final drive axle  56   i  and an output  208  which constitutes the rotatable support  202 . In this example, the transmission  204  comprises gearing  210  and a housing  212  that houses the gearing  210 . More specifically, in this case, the gearing  210  is planetary gearing including a sun gear  214 , a plurality of planet gears  216   1 - 216   P  and a ring gear  218 . The sun gear  214  is coupled to the final drive axle  56   i  in any suitable manner (e.g., via a key, a press-fit, a taper lock bushing, etc.) such as to cause the final drive axle  56   i  to drive the sun gear  214 . The planet gears  216   1 - 216   P  are driven by the sun gear  214  and in turn drive the ring gear  218 . The ring gear  218  is comprised by the housing  212  of the transmission  204  such that the planet gears  216   1 - 216   P  drive the housing  212 . 
     The drive wheel  24  is mounted to the housing  212  so as to rotate with the housing  212 . In this example of implementation, as shown in  FIG.  39   , the drive wheel  24  is mounted to the housing  212  via a connector  220  which is fastened to the housing  212  and to the drive wheel  24 . In particular, in this example of implementation, the connector  220  is a generally circular member comprising a first flanged portion  222  and a second flanged portion  224 . The first flanged portion  222  is fastened to the drive wheel  24  while the second flanged portion  224  is fastened to the drive wheel  24 . The connector  220  is detachably fastened to the housing  212 . That is, fastening of the connector  220  to the housing  212  is non-permanent (i.e., the connector  220  can also be unfastened from the housing  212 ). For example, the second flanged portion  224  of the connector  220  may be fastened to the housing  212  via fasteners  225  (e.g., bolts and/or nuts). To that end, in this example of implementation, as shown in  FIG.  37   , the housing  212  comprises a plurality of mounts  226   1 - 226   P  (e.g., threaded holes) for receiving respective ones of the fasteners  225 . 
     The connector  220  may be an integral part of the drive wheel  24  in some embodiments. That is, the connector  220  may be an extension of the drive wheel  24  such that the drive wheel  24  is fastened directly to the housing  212  of the transmission  204 . 
     In this embodiment, the lateral track spacing adjustment mechanism  100  of the track system  16   1  is configured such that the drive wheel  24 , the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   4 , the frame  13 , and the track  22  are movable relative to the transmission  204 , the final drive axle  56   i , and the support arms  106   1 ,  106   2  of the final drive unit  35   i  in the widthwise direction of the track system  16   1 . More particularly, in this embodiment, the drive wheel  24  is movable relative to the transmission  204  and the final drive axle  56   i  by sliding relative to the housing  212  of the transmission  204  in the widthwise direction of the track system  16   1 . 
     For instance, in this example, the drive wheel  24  is mounted onto the housing  212  by its hub  115  which defines an opening for receiving the housing  212 . The mounts  226   1 - 226   P  of the housing  212  are distributed along a length of the housing  212  (i.e., in the widthwise direction of the track system  16   i ) such as to form subsets of the mounts  226   1 - 226   P  which are aligned with one another along the length of the housing  212 . The drive wheel  24  is slidable relative to the housing  212  of the transmission  204  in the widthwise direction of the track system  16   1  such as to align the connector  220  with a given subset of the mounts  226   1 - 226   P . The drive wheel  24  is then fastened to the housing  212  via the connector  220  to the given subset of the mounts  226   1 - 226   P  which imparts a fixed position to the drive wheel  24  relative to the transmission  204 , the final drive axle  56   i  and the support arms  106   1 ,  106   2  of the final drive unit  35   i  in the widthwise direction of the track system  16   1 . If a different position of the drive wheel  24  is desired relative to the transmission  204 , the final drive axle  56   i  and the support arms  106   1 ,  106   2 , the drive wheel  24  is unfastened from the housing  212 , the connector  220  is aligned with a different subset of the mounts  226   1 - 226   P  and the drive wheel  24  is fastened to the different subset of the mounts  226   1 - 226   P . This allows the operator to adjust the spacing S of the track systems  16   1 ,  16   2  as shown in  FIGS.  40  to  42   . For example, the spacing S of the track systems  16   1 ,  16   2  can be adjusted to have the narrow tread setting (shown in  FIG.  40   ), the wide tread setting (shown in  FIG.  42   ), or a setting in between the narrow and wide tread settings (shown in  FIG.  41   ). In this embodiment, in the narrow tread setting, the supports arms  106   1 ,  106   2  of the final drive unit  35   i  extend beyond the track  22  in the widthwise direction of the track system  16   1 . 
     In this embodiment, the drive wheel  24  is thus not connected to the frame  13  of the track system  16   1 . Rather, the drive wheel  24  is movable independently from the frame  13  of the track system  16   1  when installing the track system  16   1  onto the vehicle  10 . For instance, when installing the track system  16   1  onto the vehicle  10 , the drive wheel  24  may be placed on the final drive unit  35   i  first and secured thereto at a desired tread setting, and then the frame  13 , to which the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   4  are mounted, may be placed on the final drive unit  35   i , notably in engagement with the support arms  106   1 ,  106   2 , and secured thereto. 
     Moreover, in this embodiment, the frame  13  of the track system  16   i  comprises an upper frame member  230  for receiving the support arms  106   1 ,  106   2 . In this embodiment, the upper frame member  230  is disposed on an outboard side of the track system  16   i  (i.e., on a side of the drive wheel  24  away from the center  117  of the vehicle  10 ) and comprises a pivot  234  about which the lower frame member  114  of the frame  13  may pivot relative to the upper frame member  230 . The upper frame member  230  comprises a retaining mechanism  232  for retaining the support arms  106   1 ,  106   2 . 
     The retaining mechanism  232  may be implemented in various ways. In this embodiment, as shown in  FIG.  43   , the retaining mechanism  232  comprises a bushing  235  for receiving and retaining a respective one of the support arms  106   1 ,  106   2  therein. More specifically, the bushing  235  is a taper lock bushing comprising a central opening  236  in which the support arm  106   i  is received and a plurality of adjustment openings  238   1 - 238   N  on a periphery of the taper lock bushing  235  for receiving respective fasteners  240 . As the fasteners  240  are engaged further into the adjustment openings  238   1 - 238   N , the central opening  236  tightens around the support arm  106   i . The retaining mechanism  232  comprises a taper lock bushing  235  for each of the support arms  106   1 ,  106   2 . 
     The retaining member  135  described above with respect to the embodiment of  FIGS.  4  to  7  and  27  to  32    may be configured in a similar manner to the retaining mechanism  232 . The retaining mechanism  232  (or the retaining member  135 ) may retain the support arms  106   1 ,  106   2  in other ways in other embodiments. 
     For instance, in another embodiment, as shown in  FIG.  44   , the retaining mechanism  232  comprises one or more set screws  242  that engage a respective one of the support arms  106   1 ,  106   2 . In particular, in such embodiments, the retaining mechanism  232  comprises an opening  244  in which a support arm  106   i  is received and a set screw opening  246  generally transversal to the opening  244 . The set screw opening  246  is configured to receive the set screw  242  and is therefore threaded accordingly. In this example of implementation, the support arm  106   i  may have a flat  248  machined or otherwise formed onto its periphery to securely engage the set screw  242 . It is noted that more set screws may be used (e.g., two or more set screws). 
     In this embodiment, as shown in  FIG.  45   , a pivot axis  233  of the pivot  234  of the upper frame member  230  of the track system  16   1  is located at or close to a “neutral” position NP of the track system  16   1  which lies at an intersection of a resultant tension force F T,R  from the track  22  at the rear idler wheels  26   1 ,  26   2  and a resultant tension force F T,F  from the track  22  at the front idler wheels  23   1 ,  23   2  when the track system  16   1  is at rest (i.e., immobile). In this example, this neutral position NP is also intersected by a vertical load W T  from the vehicle  10  applied by the final drive axle  56   i . This may help to minimize generation of moments which tend to occur if and when the resultant tension forces F T,F , F T,R  and the load W T  are not oriented to intersect the pivot  234  of the upper member  230 . In that sense, the neutral position NP can be viewed as a “moment-neutralizing” position of the track system  16   1 . Each of the resultant tension forces F T,F , F T,R  is the sum of tension force components FT (not shown at the rear idler wheels  26   1 ,  26   2 ) exerted by the track  22  on respective ones of the front and rear idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 . A line passing through the neutral position NP and the axis of rotation of the front idler wheels  23   1 ,  23   2  bisects an angle of wrap a of the track  22  on the front idler wheels  23   1 ,  23   2 , and a line passing through the neutral position NP and the axis of rotation of the rear idler wheels  26   1 ,  26   2  bisects an angle of wrap of the track  22  on the rear idler wheels  26   1 ,  26   2 . 
     More particularly, in this embodiment, the pivot axis  233  of the pivot  234  of the upper frame member  230  of the track system  16   1  is located within a relatively small zone Z centered at the neutral position NP of the track system  16   1 . For instance, in some embodiments, a ratio R PN /H of a radius R PN  of the relatively small zone Z centered at the neutral position NP of the track system  16   1  in which the pivot  234  is located over the height H of the track system  16   i  may be no more than 20%, in some cases no more than 15%, in some cases no more than 10%, in some cases no more than 5%, and in some cases even less. 
     In this example of implementation, the pivot axis  233  of the pivot  234  of the upper frame member  230  of the track system  16   1  is located at the neutral position NP of the track system  16   1 , i.e., the ratio R PN /H of the radius R PN  of the relatively small zone Z centered at the neutral position NP of the track system  16   1  in which the pivot  234  is located over the height H of the track system  16   i  is 0. 
     This neutral position of the pivot  234  at which the upper member  230  is pivotable relative to the lower member  114  may help minimize a tendency of having moments induced when the track system  16   1  is propelled by the final drive unit  35   i . Notably, when the track system  16   1  is in motion (i.e., the track  22  is driven by the drive wheel  24 ), the traction exerted by the track  22  on the ground may result in a traction force component being complimentary to a given one of the resultant tension forces F T,R , F T,F . This will result in a sum of the given one of the resultant tension forces F T,R , F T,F  and the traction force component not being oriented to intersect the pivot  234  which in turn will cause a moment to be induced about the pivot  234 . However, because the pivot  234  is at the neutral position NP, the moment that is induced may be minimal compared to a scenario where the pivot  234  would not be at the neutral position NP. This may be particularly important when the vehicle  10  is used to pull a heavy load (e.g., a work implement) from its drawbar (not shown). 
     In this embodiment, as shown in  FIGS.  36  and  46   , the frame member  230  that is mounted to the support arms  106   1 ,  106   2  is shaped to clear the transmission  204 . More particularly, in this embodiment, the frame member  230  is contoured to extend from the support arm  106   1  to the support arm  106   2  without interfering with the transmission  204 . In this example, the frame member  230  includes a recess  250  that forms a depression to receive the transmission  204 . More specifically, the frame member  230  comprises a pair of angled portions  2521 ,  2522  that form the recess  250  therebetween. The angled portions  2521 ,  2522  are oriented such as to define an obtuse angle therebetween and thus impart a V-shape to the frame member  230 . Moreover, the frame member  230  comprises an opening  254  extending from a bottom surface of the frame member  230  (not shown) to a top surface  256  of the frame member  230 . The opening  254  is configured to receive at least part of the lower member  114  of the frame  13 . 
     In other words, the frame member  230  is designed geometrically such that an imaginary straight line run from centre to centre of the support arms  106   1 ,  106   2  would intersect the housing  212  of the transmission  204  to which the drive wheel  24  of the track system  16   i  is mounted. The proposed arrangement, allows sliding the frame member  230  relative to the housing  212  of the transmission  204  without creating an interference at any one of the adjustment positions. During the adjustment process, the transmission  204  stays fixed relative to the frame  12  of the vehicle  10 . It is noted that the length of the housing  212  of the transmission  204  determines the adjustment range of the track system  16   i . 
     In this embodiment, the frame member  230  may be reversible to be mountable inboard or outboard relative to the drive wheel  24 . More specifically, as shown in  FIGS.  47 A and  47 B , the frame member  230  can be mounted on an outboard side  258  of the drive wheel  24  (i.e., a side of the drive wheel  24  furthest from its associated final drive unit  35   i ) or on an inboard side  260  of the drive wheel  24  (i.e., a side of the drive wheel  24  closest to its associated final drive unit  35   i ). This may allow a greater difference between the spacing S of the track systems  16   1 ,  16   2  in the narrow tread setting and in the wide tread setting as the drive wheel  24  can be mounted closer to or further from the final drive unit  35   i  than if the frame member  230  were not reversible. 
     Optionally, in some embodiments, as shown in  FIGS.  60  and  61   , the final drive unit  35   i  may be provided with a reinforcing support  402  configured to reinforce the final drive unit  35   i , notably its final drive axle  56   i , from loads exerted by the drive wheel  24  of the track system  16   1 . The reinforcing support  402  is independent from the track system  16   1 , i.e., is not part of the track system  16   1 , and is disposed between the body  99  of the final drive unit  35   i  and the drive wheel  24 . In this embodiment, the reinforcing support  402  has a generally triangular shape and comprises a body  404  and a plurality of openings  406   1 - 406   N  for receiving respective ones of the final drive axle  56   i  and the support arms  106   1 ,  106   2 . The reinforcing support  402  comprises a retaining mechanism  408  at each opening  406   1  of the reinforcing support  402  for retaining a respective one of the final drive axle  56   i  and the support arms  106   1 ,  106   2 . The retaining mechanism  408  may be similar to the retaining mechanism  232  described above. For example, the retaining mechanism  408  may comprises a taper lock bushing, one or more set screws, or any other suitable retaining mechanism. The reinforcing support  402  may thus be mounted on the final drive unit  35   i  prior to installing the track system  16   1  on the final drive unit  35   i . The reinforcing support  402  may help minimize bending loads applied on the final drive axle  56   i  by the drive wheel  24  when it is unsupported by the frame  13  of the track system  16   1 . 
     The rear track systems  16   1 ,  16   2  are not steerable but rather their orientation relative to the frame  12  of the vehicle  10  is fixed. The rear track system  16   3  will be described, with an understanding that the rear track system  16   4  is similarly arranged. 
     In this embodiment, with reference to  FIGS.  48  and  49   , the drive wheel  24  of the track system  16   3  is entirely by the final drive axle  56   i  and is unsupported by the frame  13  of the track system  16   3 . All loading exerted by the drive wheel  24 , including its weight, is transmitted through the final drive axle  56   i , and thus is not transmitted through the frame  13  of the track system  16   3 . The tension of the track  22  is taken up by the drive wheel  24 . The drive wheel  24  may thus be seen as a “floating” drive wheel in that it is unconnected to and isolated from the frame  13  of the track system  16   3 . To that end, in this embodiment, the drive wheel  24  is only (i.e., exclusively) supported by a rotatable support  302  that is rotatable by the final drive axle  56   i . This is in contrast to the embodiment considered above in respect of  FIGS.  4  to  7  and  27  to  32    in which the drive wheel  24  is supported by the nonrotatable support  125 , namely the upper member  110 , which transmits loading exerted by the drive wheel  24 , including its weight, through the frame  13  of the track system  16   3  and in which the tension of the track  22  is partly taken up by the upper member  110 . 
     More particularly, in this embodiment, the track system  16   3  comprises a coupling  304  that couples the drive wheel  24  to the final drive axle  56   i  so that the drive wheel  24  rotates with the final drive axle  56   i , and the rotatable support  302  is constituted by the coupling  304 . In this example, the coupling  304  comprises a bushing  306 . For instance, in this case, the bushing  306  is a taper lock bushing similar to the taper lock bushing  122  described above. The drive wheel  24  is mounted to the final drive axle  56   i  via the bushing  306  such as to rotate with the bushing  306 . More specifically, in this embodiment, tightening of fasteners of the taper lock bushing  306  causes an opening of the taper lock bushing  306 , which is configured to receive the final drive axle  56   i , to shrink. This prevents movement of the final drive axle  56   i  relative to the taper lock bushing  306 . Conversely, loosening of the fasteners of the taper lock bushing  306  causes the opening of the taper lock bushing  306  to expand and therefore allow relative movement of the final drive axle  56   i  relative to the taper lock bushing  306 . 
     In this embodiment, the lateral track spacing adjustment mechanism  100  of the track system  16   3  is configured such that the drive wheel  24 , the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   6 , the frame  13 , and the track  22  are movable relative to the final drive axle  56   i  and the support arms  106   1 ,  106   2  of the final drive unit  35   i  in the widthwise direction of the track system  16   3 . More particularly, in this embodiment, the drive wheel  24  is movable relative to the final drive axle  56   i  by sliding relative to the final drive axle  56   i  in the widthwise direction of the track system  16   3 . 
     For instance, in this example, the drive wheel  24  is mounted onto the final drive axle  56   i  via the bushing  306 . Prior to adjusting the fasteners of the bushing  306 , the drive wheel  24  is slidable along the length of the final drive axle  56   i  in the widthwise direction of the track system  163 . Once the drive wheel  24  is set at a desired position relative to the final drive axle  56   i  and the support arms  106   1 ,  106   2 , the drive wheel  24  is secured to the final drive axle  56   i  by securing the fasteners of the bushing  306  which then retains the final drive axle  56   i . If a different position of the drive wheel  24  is desired relative to the final drive axle  56   i  and the support arms  106   1 ,  106   2 , the fasteners of the bushing  306  are unfastened such as to loosen the hold of the bushing  306  onto the final drive axle  56   i , and the drive wheel  24  is secured to the final drive axle  56   i  at the different position. This allows the operator to adjust the spacing S of the track systems  16   3 ,  16   4  as shown in  FIGS.  52  and  53   . For example, the spacing S of the track systems  16   3 ,  16   4  can be adjusted to have the narrow tread setting (shown in  FIG.  52   ), the wide tread setting (shown in  FIG.  53   ), or a setting in between the narrow and wide tread settings. In this embodiment, in the narrow tread setting, the support arms  106   1 ,  106   2  of the final drive unit  35   i  extend beyond the track  22  in the widthwise direction of the track system  16   3 . 
     In this embodiment, the drive wheel  24  is not connected to the frame  13  of the track system  16   3 . Rather, the drive wheel  24  is movable independently from the frame  13  of the track system  16   3  when installing the track system  16   3  onto the vehicle  10 . For instance, when installing the track system  16   3  onto the vehicle  10 , the drive wheel  24  may be placed on the final drive unit  35   i  first and secured thereto at a desired tread setting, and then the frame  13 , to which the idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2 ,  28   1 - 28   6  are mounted, may be placed on the final drive unit  35   i , notably in engagement with the support arms  106   1 ,  106   2 , and secured thereto. 
     Moreover, in this embodiment, the frame  13  of the track system  16   i  comprises an upper frame member  330  for receiving the support arms  106   1 ,  106   2 . In this embodiment, the upper frame member  330  is disposed on an outboard side of the track system  16   i  (i.e., on a side of the drive wheel  24  away from the center  117  of the vehicle  10 ) and comprises a pivot  334  about which the lower frame member  114  of the frame  13  may pivot relative to the upper frame member  330 . The upper frame member  330  comprises a retaining mechanism  332  for retaining the support arms  106   1 ,  106   2 . The retaining mechanism  332  may be implemented similarly to the retaining mechanism  232  described above. 
     Similarly to the track system  16   1  described above in respect of  FIG.  45   , in this embodiment, the pivot  334  of the upper frame member  330  of the track system  16   3  is located at or close to the neutral position NP of the track system  16   1  which lies at an intersection of the resultant tension force F T,R  from the track  22  at the rear idler wheels  26   1 ,  26   2  and the resultant tension force F T,F  from the track  22  at the front idler wheels  23   1 ,  23   2  when the track system  16   3  is at rest (i.e., immobile). In this example, this neutral position NP is also intersected by a vertical load W T  from the vehicle  10  applied by the final drive axle  56   i . This may help minimize generation of moments which tend to occur when the resultant tension forces F T,F , F T,R  and the load W T  are not oriented to intersect the pivot  334  of the upper member  330 . A line passing through the neutral position NP and the axis of rotation of the front idler wheels  23   1 ,  23   2  bisects the angle of wrap a of the track  22  on the front idler wheels  23   1 ,  23   2 , and a line passing through the neutral position NP and the axis of rotation of the rear idler wheels  26   1 ,  26   2  bisects the angle of wrap of the track  22  on the rear idler wheels  26   1 ,  26   2 . 
     More particularly, in this embodiment, the pivot  334  of the upper frame member  330  of the track system  16   3  is located within the relatively small zone Z centered at the neutral position NP of the track system  16   3 . For instance, in some embodiments, a ratio R PN /H of the radius R PN  of the relatively small zone Z centered at the neutral position NP of the track system  16   3  in which the pivot  334  is located over the height H of the track system  16   3  may be no more than 20%, in some cases no more than 15%, in some cases no more than 10%, in some cases no more than 5%, and in some cases even less. 
     In this example of implementation, the pivot  334  of the upper frame member  330  of the track system  16   1  is located at the neutral position NP of the track system  16   3 , i.e., the ratio R PN /H of the radius R PN  of the relatively small zone Z centered at the neutral position NP of the track system  16   1  in which the pivot  234  is located over the height H of the track system  16   i  is 0. 
     This neutral position of the pivot  334  at which the upper member  330  is pivotable relative to the lower member  114  may help minimize a tendency of having moments induced when the track system  16   3  is propelled by the final drive unit  35   i . Notably, when the track system  16   1  is in motion (i.e., the track  22  is driven by the drive wheel  24 ), the traction exerted by the track  22  on the ground may result in a traction force component that is complimentary to a given one of the resultant tension forces F T,R , F T,F . This will result in a sum of the given one of the resultant tension forces F T,R , F T,F  and the traction force component not being oriented to intersect the pivot  334  which in turn will cause a moment to be induced about the pivot  334 . However, because the pivot  334  is at the neutral position NP, the moment that is induced may be minimal compared to a scenario where the pivot  334  would not be at the neutral position NP. This may be particularly important when the vehicle  10  is used to pull a heavy load (e.g., a work implement) from its drawbar (not shown). 
     In this embodiment, the frame member  330  may be reversible to be mountable inboard or outboard relative to the drive wheel  24 . More specifically, the frame member  330  can be mounted on the outboard side  258  of the drive wheel  24  or on the inboard side  260  of the drive wheel  24 . This may allow a greater difference between the spacing S of the track systems  16   3 ,  16   4  in the narrow tread setting and in the wide tread setting as the drive wheel  24  can be mounted closer to or further from the final drive unit  35   i  than if the frame member  330  were not reversible. 
     As described above, optionally, the final drive unit  35   i  may be provided with the reinforcing support  402  that can be disposed between the body  99  of the final drive unit  35   i  and the drive wheel  24  of the track system  16   3 . 
     Thus, in this embodiment, as shown in  FIGS.  54  and  55    the lateral track spacing adjustment mechanism  100  of a respective one of the track systems  16   1 - 16   4  allows the spacing S between the track systems  16   1 ,  16   2  and the track systems  16   3 ,  16   4  to be adjusted from the narrow tread setting to the wide tread setting as desired. 
     For instance,  FIGS.  62  to  75    show an example of another embodiment of the track systems  16   1 - 16   4 . In this embodiment, the front ones of the track systems  16   1 - 16   4  are implemented differently from the rear ones of the track systems  16   1 - 16   4 , but each of the track systems  16   1 - 16   4  includes features as discussed above, including the lateral load distribution mechanism  150 , the lateral track spacing adjustment mechanism  100 , etc. 
     The rear track system  16   3  will be described, with an understanding that the rear track system  16   4  is similarly arranged. 
     In this embodiment, the track system  16   3  comprises a movable joint  410  that is located inboard of the drive wheel  24  and allows the frame  13  of the track system  16   3  to move relative to the frame  12  of the vehicle  10  when travelling on an uneven terrain. The movable joint  410  is located inboard of the drive wheel  24  in that it is located between the drive wheel  24  and the center  117  of the vehicle  10  in the widthwise direction of the vehicle  10 . This may help to allow better (e.g., narrower) adjustments of the spacing S of the track systems  16   3 ,  16   4 . 
     More particularly, in this embodiment, the movable joint  410  comprises a pivot  412  allowing the frame  13  of the track system  16   3  to pivot relative to the frame  12  of the vehicle  10  when travelling on the uneven terrain. The frame  13  of the track system  16   3  may thus pivot relative to the frame  12  of the vehicle  10  about a pivot axis  414  of the pivot  412  to accommodate the uneven terrain. 
     In this embodiment, the pivot  412  comprises an axle  420  and a support  421  carrying the axle  420 . The support  421  comprises a first body portion  416  and a second body portion  418  that is rotatable relative to the first body portion  416 . The first and second body portions  416 ,  418  of the support  421  are mounted to the axle  420  via respective openings configured for receiving the axle  420 . In this example of implementation, the first body portion  416  is fixedly mounted to the axle  420  such that the first body portion  416  is not rotatable relative to the axle  420 . This may be achieved by mounting the first body portion  416  onto the axle  420  via a press-fit or in any other suitable way. Contrary to the first body portion  416 , the second body portion  418  is rotatably mounted to the axle  420  such that the second body portion  418  is rotatable relative to the axle  420 . This may be achieved by disposing a bearing between the second body portion  418  and the axle  420 . It is noted that a similar result may be obtained if the first body portion  416  is rotatably mounted to the axle  420  while the second body portion  418  is fixedly mounted to the axle  420 . 
     The pivot  412  is configured to be associated with the final drive unit  35   3  of the powertrain  15 . Notably, the pivot  412  is configured to be attached to the final drive unit  35   3  such that the support  421  of the pivot  412  is mounted to the final drive unit  35   3 . In this example of implementation, the pivot  412  configured to be located beneath the final drive unit  35   3  such as by being fastened to the final drive unit  35   3  by a plurality of fasteners  422   1 - 422   F  between the pivot  412  and a housing  415  of the transmission  72 . The fasteners  422   1 - 422   F  engage openings  424   1 - 424   A  of the first body portion  416  of the support  421  and respective openings (not shown) of the housing  415  of the transmission  72 . The housing  415  of the transmission  72  may comprise a mounting member  425  at an underside of the final drive unit  35   3  for mounting the support  421  thereto. 
     In this embodiment, the frame  13  of the track system comprises a lower frame member  428  and an upper frame member  430 . As will be discussed in more detail below, the lower frame member  428  is pivotally connected to the upper frame member  430 . The lower frame member  428  carries the front and rear idler wheels  23   1 ,  23   2 ,  26   1 ,  26   2  and the mid-rollers  28   1 - 28   R  and thus may be referred to as a “wheel-carrying member”. The frame  13  further comprises an adjustment member  426  for adjusting the spacing S of the track system  16   3  and the track system  16   4  (i.e., the laterally-adjacent one of the track systems  16   1 - 16   4 ) in the widthwise direction of the vehicle  10 , as will be discussed in more detail below. In this embodiment, the adjustment member  426  is connected (e.g., fastened) to the wheel-carrying member  428 . In other embodiments, the adjustment member  426  may be integrally made with the wheel-carrying member  428 . 
     The pivot  412  is configured to be attached to the frame  13  of the track system  16   3 . For instance, as shown in  FIGS.  71  to  75   , the pivot  412  is connectable to the frame  13  of the track system  16   3  at a plurality of different positions P 1 -P N  spaced in the widthwise direction of the vehicle  10  to adjust the spacing S of the track system  16   3  and the track system  16   4  (i.e., the laterally-adjacent one of the track systems  16   1 - 16   4 ) in the widthwise direction of the vehicle  10 . More specifically, the pivot  412  is connectable to the adjustment member  426  at the different positions P 1 -P N  such as to adjust the spacing S of the track system  16   3  and the track system  16   4 . For example, the spacing S of the track systems  16   3 ,  16   4  may be adjusted to have the narrow tread setting (shown in  FIGS.  71  to  73   ), the wide tread setting (shown in  FIGS.  74  and  75   ), or a setting in between the narrow and wide tread settings. In this embodiment, in the narrow tread setting, the support arms  106   1 ,  106   2  of the final drive unit  35   3  extend beyond the track  22  in the widthwise direction of the track system  16   3 . 
     To that end, as shown in  FIGS.  66  and  67   , the adjustment member  426  comprises a lateral extension  432  projecting from the wheel-carrying member  428  in the widthwise direction of the track system  16   3  and to which the pivot  412  is connectable. More particularly, the second body portion  418  of the support  421  of the pivot  412  is connectable to the lateral extension  432  via a plurality of fasteners  442   1 - 442   F  which engage a plurality of openings  444   1 - 444   N  of the second body portion  418  and a plurality of openings  436   1 - 436   N  disposed at an upper side  434  of the lateral extension  432 . That is, the fasteners  442   1 - 442   F  engage the second body portion  418  and the lateral extension  432  of the adjustment member  426  such as to fasten the pivot  412  to the adjustment member  426 . In this embodiment, the openings  444   1 - 444   N  of the second body portion  418  are threaded for securely engaging the fasteners  442   1 - 442   F . In other embodiments, the openings  444   1 - 444   N  may be through holes and the fasteners  442   1 - 442   F  may instead be secured by nuts. 
     In this embodiment, the upper frame member  430  is disposed on an outboard side of the track system  16   3  (i.e., on a side of the drive wheel  24  away from the center  117  of the vehicle  10 ) and comprises a pivot  438  defining a pivot axis  440  about which the wheel-carrying member  428  of the frame  13  may pivot relative to the upper frame member  430 . According to one example, the pivot  438  may be implemented by a bearing disposed at a connection between the upper frame member  430  and the wheel-carrying member  428  of the frame  13 . 
     Thus, in this embodiment, the pivot  412  may be referred to as an “inboard” pivot since it is disposed on the inboard side  260  of the drive wheel  24  while the pivot  438  may be referred to as an “outboard” pivot since it is disposed on the outboard side  258  of the drive wheel  24 . Moreover, in this embodiment, as shown in  FIG.  73   , the pivot axis  414  of the inboard pivot  412  is coaxial with the pivot axis  440  of the outboard pivot  438 . 
     Furthermore, in this embodiment, as shown in  FIG.  63   , the pivot axis  414  of the inboard pivot  412  is located at or close to the neutral position NP of the track system  16   3 . For instance, in some cases, a ratio of a distance between the pivot axis  414  of the inboard pivot  412  and the neutral position NP of the track system  16   3  over the height H of the track system  16   3  may be no more than 20%, in some cases no more than 15%, in some cases no more than 10%, in some cases no more than 5%, and in some cases even less. 
     In this example of implementation, the pivot axis  414  of the inboard pivot  412  of the track system  16   3  is located at the neutral position NP of the track system  16   3 , i.e., the ratio of the distance between the pivot axis  414  of the inboard pivot  412  and the neutral position NP of the track system  16   3  over the height H of the track system  16   3  is 0. 
     As described above with respect to  FIG.  45   , the neutral position NP of the track system  16   3  lies at an intersection of the resultant tension force F T,R  from the track  22  at the rear idler wheels  26   1 ,  26   2  and a resultant tension force F T,F  from the track  22  at the front idler wheels  23   1 ,  23   2  when the track system  16   3  is at rest (i.e., immobile). In this example, this neutral position NP is also intersected by a vertical load W T  from the vehicle  10  applied by the final drive axle  56   i . 
     Furthermore, in this embodiment, as shown in  FIG.  70   , each support arm  106   i  of the final drive unit  35   3  comprises a plurality of openings  4461 - 446 N for attaching the support arm  106   i  to the frame  13  of the track system  16   3  via a plurality of fasteners  448   1 - 448   F . More particularly, the upper frame member  430  of the frame  13  of the track system  16   3  is fastenable to the support arm  106   i , beneath the support arm  106   i , such that the upper frame member  430  and the support arm  106   i  are fixed relative to one another when the track system  16   3  moves on uneven terrain. To that end, the upper frame member  430  comprises a plurality of openings (not shown) for receiving the fasteners  448   1 - 448   F  which fasten the upper frame member  430  to the support arms  106   1 ,  106   2 . In other words, in this embodiment, the supports arms  106   1 ,  106   2  of the final drive unit  35   3  are fastenable to the upper frame member  430  of the frame  13  of the track system  16   3 . In this embodiment, the openings  446   1 - 446   N  of the support arm  106   i  are disposed on a flat surface of the support arm  106   i . More specifically, in this example of implementation, the support arms  106   1 ,  106   2  of the final drive unit  35   3  are generally triangular and extend in the widthwise direction of the vehicle  10 . The openings  446   1 - 446   N  are disposed on a bottom-facing surface of the triangular support arm  106   i . 
     As will be understood, each set of openings  446   1 - 446   N  of the support arms  106   1 ,  106   2  is associated with a different position of the pivot  412 . That is, in order to adjust a position of the pivot  412  (i.e., to displace the pivot  412  to occupy a position P x ), the support  421  of the pivot  412  is secured to a different set of the openings  436   1 - 436   N  of the adjustment member  426  and the upper frame member  430  is secured to a corresponding set of the openings  446   1 - 446   N  of the support arms  106   1 ,  106   2 . As such, in this embodiment, the movable joint  410  and its pivot  412 , as well as the support arms  106   1 ,  106   2  are part of the lateral track spacing adjustment mechanism  100 . 
     In this embodiment, the drive wheel  24  of the track system  16   3  is entirely supported by the final drive axle  56   i  and is unsupported by the frame  13  of the track system  16   3 . All loading exerted by the drive wheel  24 , including its weight, is transmitted through the final drive axle  56   i , and thus is not transmitted through the frame  13  of the track system  16   3 . The tension of the track  22  is taken up by the drive wheel  24 . The drive wheel  24  may thus be seen as a “floating” drive wheel in that it is unconnected to and isolated from the frame  13  of the track system  16   3 . To that end, in this embodiment, the drive wheel  24  is only (i.e., exclusively) supported by the final drive axle  56   i . This is in contrast to the embodiment considered above in respect of  FIGS.  4  to  7  and  27  to  32    in which the drive wheel  24  is supported by the nonrotatable support  125 , namely the upper frame member  110 , which transmits loading exerted by the drive wheel  24 , including its weight, through the frame  13  of the track system  16   3  and in which the tension of the track  22  is partly taken up by the upper frame member  110 . 
     The front track systems  16   1 ,  16   2  are steerable to change their orientation relative to the frame  12  of the vehicle  10  in order to steer the vehicle  10  on the ground. As shown in  FIGS.  76  and  77   , each of the front track systems  16   1 ,  16   2  may be configured in a manner similar to that described with respect to  FIGS.  62  to  75    for adjusting the spacing S of the front track systems  16   1 ,  16   2  in the widthwise direction of the vehicle  10 . In this embodiment, as discussed above in relation to  FIGS.  33  to  47 B , the drive wheel  24  of each of the track systems  16   1 ,  16   2  is entirely supported by the final drive axle  56   i  and is unsupported by the frame  13  of the track system  16   i . All loading exerted by the drive wheel  24 , including its weight, is transmitted through the final drive axle  56   i , and thus is not transmitted through the frame  13  of the track system  16   i . Thus, in this embodiment, the drive wheel  24  is only (i.e., exclusively) supported by a rotatable support (such as the rotatable support  202 ) that is rotatable by the final drive axle  56   i . More particularly, the drive wheel  24  is mounted to a housing of the transmission such as to rotate with the housing (such as the housing  212  of transmission  204 ) as depicted in  FIG.  39   . 
     While the track systems  16   1 - 16   4  including their lateral track spacing adjustment mechanism  100  is useful in agricultural fields, in this embodiment, the track systems  16   1 - 16   4  can also perform well on roads since their lateral load distribution mechanism  150  may be useful when the lateral track spacing adjustment mechanism  100  is used for a wide track spacing. 
     The capability of the track systems  16   1 - 16   4  to better perform on roads may be particularly useful in situations in which the road&#39;s surface GS has a cross slope for leading water away from the road (i.e., to avoid water accumulation on the road), as shown in  FIG.  59   . In this case, the cross slope of the road&#39;s surface GS is such that the road has a crown, i.e., a highest point, at a center of the road in its widthwise direction and slopes downwardly on either side of the crown. For instance, in some cases an angle α defined between a horizontal axis and road&#39;s surface GS on either side of the crown may be at least 1°, in some cases at least 2°, in some cases at least 4°, and in some cases even higher (e.g., at least 6° or 8°). The angle α may have any other value in other cases. In view of its crown, the road may sometimes be referred to as a “crowned road”. 
     In this embodiment, each track system  16   i  may be configured to accommodate a shape of the road, including its crown in this example, so as to better distribute loading on its track  22  than a conventional track system. More specifically, the lateral load distribution mechanism  150  of the track system  16   i  allows better distribution of the loading on its track  22 . This may be of particular use when the spacing S between the laterally-adjacent track systems  16   i ,  16   j  is set to its wide tread setting via their respective lateral track spacing adjustment mechanisms  100  as shown in  FIG.  54    for example. Notably, when the spacing S is set to its wide tread setting, the lateral load distribution mechanism  150  may be particularly useful to reduce wear of the track  22  and/or other components of the track systems  16   1 - 16   4 . For example, in a scenario where the track systems  16   1 - 16   4  are compensating for the shape of the road (e.g., a crowned road) via their load distribution mechanisms  150 , as shown in  FIG.  59   , and that the spacing S between the laterally-adjacent track systems  16   i ,  16   j  is significant due to an adjustment made via the lateral track spacing adjustment mechanisms  100  of the track systems  16   i ,  16   j , a greater adjustment in the roll axis may be desired from the load distribution mechanism  150  in order to adequately compensate for the shape of the road. In essence, the greater the spacing S between the laterally-adjacent track systems  16   i ,  16   j , the greater the range of motion that will be desired from the load distribution mechanism  150  in order to adequately compensate for the shape of the road and thus distribute the load more evenly on the track systems  16   i ,  16   j . 
     Although the track systems  16   1 - 16   4  have been described as being mounted on the final drive unit  35   i , in other cases the drive wheel  24  may be mounted directly to a drive shaft of the vehicle  10  (i.e., without a transmission between the drive shaft and the drive wheel  24 ). This may be particularly the case for the rear track systems  16   3 ,  16   4  which are not steerable. 
     In some examples of implementation, any feature of any embodiment described herein may be used in combination with any feature of any other embodiment described herein. 
     Certain additional elements that may be needed for operation of some embodiments have not been described or illustrated as they are assumed to be within the purview of those of ordinary skill in the art. Moreover, certain embodiments may be free of, may lack and/or may function without any element that is not specifically disclosed herein. 
     Although various embodiments and examples have been presented, this was for the purpose of describing, but not limiting, the invention. Various modifications and enhancements will become apparent to those of ordinary skill in the art and are within the scope of the invention, which is defined by the appended claims.