Abstract:
The present disclosure generally relates to a spherical or curved skateboard wheel with a grind face that is interchangeable with ordinary, standardized skateboard wheels used in the marketplace. The wheel in some embodiments provides greater weight to the board and protects internal bearings by not resulting in preferential shock positions within each wheel. Further, the spherical wheels allow for higher speed, reduced friction with the road surface when desired, reduction of random bounces of the board during tricks, and increased maneuverability over dry, granular, or soft surfaces.

Description:
RELATED APPLICATION 
       [0001]    This application is a continuation-in-part of and claims the benefit of and priority from U.S. patent application Ser. No. 12/775,077, filed May 6, 2010, entitled SKATEBOARD WHEEL AND METHOD OF MANEUVERING THEREWITH, which application is expressly incorporated herein by reference. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure generally relates to a spherical skateboard wheel and method of maneuvering a skateboard therewith, and more specifically, to a new geometry of skateboard wheel capable of mounting on existing skateboard frames with an internal bearing set for greatly improving a wide range of properties of the skateboard and different methods of maneuvering therewith. 
       BACKGROUND 
       [0003]    In the early 1970s, plywood boards combined with quad-wheeled hardware allowed children to move around and perform tricks and stunts while riding on the wooden board. By the mid-1980s, Skateboards were mass produced in the United States to the pleasure of many adolescents. A boarder propels himself by pushing off on the ground with one foot while the other remains on the board. When the board moves down a slope, a boarder can simply stand with both feet and lean slightly more to one side of the board than the other to steer the board in the desired direction. 
         [0004]    Most skateboards are made with a deck, such as a board 28 to 33 inches long, made of wood, fiberglass, bamboo, resin, Kevlar, carbon fiber, aluminum, plastic or any other material with sufficient strength and rigidity to support both the hardware and the boarder.  FIG. 1  from the prior art illustrates one such typical skateboard. 
         [0005]    Decks are of variable sizes. For example, most are 7 to 10 inches in width or even wider for greater stability. They are designed for a boarder to use one foot at an angle on the board and be able to press with the heel to steer the board in a first direction, and alternatively, to press down with the toes to steer the board in the opposite direction. 
         [0006]    Decks can be painted or customized with artwork, and the underside of the deck can include a shock resistant or abrasion-resistant laminated material. Many of the tricks performed with a skateboard result in strong impacts and friction to the board in the area between two pairs of wheels for some level of stability. Grip tape or other type of nonslip surface treatment can be applied to the top of the board to help boarders perform different tricks. For example, if the board is bounced off the ground onto a stainless steel hand rail, the board slide downwards. The grip tape on the top of the deck provides stability for the boarder while the bottom side of the deck, often painted, allows the boarder to slide on rails or other surfaces and fixtures. 
         [0007]    While skateboards may appear to be simple devices, their competitive use is extremely complex and calls into play advanced notions of dynamics, impact resistance, static and dynamic friction, rotational inertia, and the like. The desire of skateboarders to customize every aspect of their skateboards is well known. Much like musical instruments, each board is somewhat unique and reacts differently to different solicitations. Over the decades, the practice of this sport has been influenced, much like surfing and motorcycling, by a strong instinct of freedom, independence, and individualism. For this reason, any aesthetic change, much like any functional change, is also highly desirable. 
         [0008]    As shown on  FIG. 1 , two sets of wheels are attached to the underside of the deck using a truck. Trucks are generally made of an aluminum alloy and include a grommet to provide the axis of the wheels with some degree of flexibility of movement. Most trucks and their grommets allow for a movement of the deck over the ground on which the skateboard can rotate left or right by as much as 38 to 50 degrees. Wheels are attached to an axle that runs through a hanger located inside the truck. 
         [0009]    Wheels of a skateboard are generally fixed to the axle using standardized wheels with ball bearings located inside the wheel and locked in place with a nut. Since one of the most vulnerable portions of the skateboard is the wheel and the bearing set, a boarder typically knows how to service and replace wheels and bearings. Skateboard wheels are generally made of a hard polyurethane and come in many sizes and shapes, though they are generally cylindrical as illustrated at  FIGS. 1 and 2 .  FIG. 2  shows how two bearing sets can be placed on each side of a central portion to hold the wheel in place. 
         [0010]    Larger wheels can have an external diameter of 54 to 85 mm in size. They roll faster and can more easily roll over cracks in pavements than smaller wheels. Smaller wheels of 48 to 54 mm in size are designed to keep the board closer to the ground and require less force to accelerate. Lower boards have a different center of gravity and thus handle differently. 
         [0011]    Normal wheels range from a hardness of Shore A 75 (very soft) to about A 101 (very hard). As the A scale stops at 100, any wheels labeled 101 A or higher are harder but use a different durometer scale. Some wheels are sold using a B or D hardness scale as those scales have a larger and more accurate range of hardness. Finally, bearings over the years have been standardized to a fixed size, namely, an outer diameter of 22 mm, a width of 7 mm, and a bore of 8 mm, which together is called the 608 standard industrial size. The bearings are generally made of steel, though silicon nitride and high-tech ceramic, can be used. As for the hardness of the wheels, the ABEC scale is used. These values range from ABEC1 to ABEC9. In most models of skateboards, the bolt is a 10-32 UNC bolt, usually an Allen or Phillips head, and has a matching nylon locknut.  FIGS. 1 and 2  show a typical skateboard from the prior art with cylindrical wheels. 
         [0012]    Other types of wheels have been developed over the years with different shapes. For example, the prior art of  FIGS. 3 and 4  show the wheel is round and ball shaped. The balls are attached through their center axis and require a different style of attachment. What is required is a simplified system for using a ball-shaped wheel on a skateboard that does not require specific adaptation and results in completely novel maneuvering dynamics for the skateboarder. 
         [0013]    What is further required is a skateboard wheel providing the advantages of a curved outer surface but may not have the outer surface of a true sphere. A wheel is also required that provides the structure to enable a skateboard rider to perform substantially all of the stunts and tricks that can be performed on a traditional wheel while providing the improvements as previously discussed. 
       SUMMARY 
       [0014]    The present disclosure generally relates to a spherical or curved skateboard wheel that is interchangeable with ordinary, standardized skateboard wheels used in the marketplace. The wheel in some embodiments provides greater weight to the board and protects the internal bearings by avoiding preferential shock positions within each wheel. Further, the spherical wheels allow for a higher rate of speed, reduced friction when steering the board, reduction of random bounces of the board during tricks, and increased maneuverability over dry, granular, or soft surfaces. 
         [0015]    The curved skateboard wheel may also include a grind face that enables the rider to more easily perform tricks and stunts that otherwise would be more difficult if the entire outer surface of the wheel is curved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Certain embodiments are shown in the drawings. However, it is understood that the present disclosure is not limited to the arrangements and instrumentality shown in the attached drawings. 
           [0017]      FIG. 1  is a perspective illustration of a skateboard from the prior art. 
           [0018]      FIG. 2  is cut view of a skateboard axle and wheel according to an embodiment from the prior art. 
           [0019]      FIG. 3  is a side view of a skateboard from the prior art equipped with spherical wheels with external connections according to an embodiment from the prior art. 
           [0020]      FIG. 4  is a rear view of the skateboard of  FIG. 3  from the prior art. 
           [0021]      FIG. 5  is a perspective view of a new spherical skateboard wheel according to an embodiment of the present disclosure. 
           [0022]      FIG. 6A  is a side view of the wheel of  FIG. 5 . 
           [0023]      FIG. 6B  is a plan view of the wheel of  FIG. 5  taken along cut line  6 B- 6 B as illustrated on  FIG. 6A . 
           [0024]      FIG. 7  is a perspective illustration of a skateboard equipped with four wheels as illustrated in  FIG. 5  according to an embodiment of the present disclosure. 
           [0025]      FIG. 8  is a diagram illustrating the comparative contact traces of a skateboard with cylindrical wheels from the prior art and the skateboard with spherical wheels shown at  FIG. 7 . 
           [0026]      FIG. 9  is a diagram illustrating the movement of wheels on a skateboard as a user pushes on a portion of the deck to steer the board. 
           [0027]      FIG. 10  illustrates the relative trace movement over the ground associated with steering a skateboard from the prior art. 
           [0028]      FIG. 11  illustrates the relative trace movement over the ground associated with steering the skateboard as shown at  FIG. 7 . 
           [0029]      FIG. 12  is a momentum diagram of the different forces on the wheels of a skateboard from the prior art. 
           [0030]      FIG. 13  is a momentum diagram of the different forces on the wheels of a skateboard as shown at  FIG. 7 . 
           [0031]      FIG. 14  is a diagram illustrating the steps of a method for upgrading a skateboard. 
           [0032]      FIG. 15  is a perspective view of a new ellipsoidal skateboard wheel with grind face according to an embodiment of the present disclosure. 
           [0033]      FIG. 16A  is a side view of the wheel of  FIG. 15   
           [0034]      FIG. 16B  is a plan view of the wheel of  FIG. 15  taken along cut line  16 B- 16 B as illustrated on  FIG. 16A   
           [0035]      FIG. 17  is a diagram illustrating an ellipsoid. 
           [0036]      FIG. 18  is a diagram illustrating the steps of a method for upgrading a skateboard. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    For the purposes of promoting and understanding the principles disclosed herein, reference is now made to the preferred embodiments illustrated in the drawings, and specific language is used to describe the same. It is nevertheless understood that no limitation of the scope of the invention is hereby intended. Such alterations and further modifications in the illustrated devices and such further applications of the principles disclosed and illustrated herein are contemplated as would normally occur to one skilled in the art to which this disclosure relates. 
         [0038]    The current disclosure relates to a new type of wheel  1  for a skateboard  100  having several unique properties alone or when used in combination with a board already equipped with ordinary wheels as shown at  FIG. 1 . To illustrate the differences associated with mounting wheel  1  as illustrated on  FIG. 5  on a skateboard  100  as shown in  FIG. 7 , an understanding of some skateboard dynamics are needed. 
         [0039]    A spherical wheel  1  as shown in  FIG. 5  is compact and is also one of the most structurally sound shape. Rounded balls are difficult to damage and chip. As a consequence, to withstand the same level of strain and shear forces as conventional skateboard wheels, spherical wheel  1  can be made with material having lower resistance to impact and wear. Further, spherical wheels  1  has a greater capacity to bounce under impact as a greater level of energy placed on the body transits through its center of gravity as the normal perpendicular direction at any area on the surface of a rounded body is the center of the rounded body. 
         [0040]    Skateboards as known in the art have cylindrical wheels as shown in  FIG. 2 , or smaller wheels of somewhat different shape. For example, in-line skates have narrow, cylindrical wheels with curved edge surfaces. The cylindrical wheels shown in  FIG. 8  have an width (H) and contact the ground over a wide track as shown in  FIG. 8 . Obvious advantages of the use of this style of wheels is the inherent stability of the skateboard, as a great effort is needed to flip the skateboard. Further, the wheels are not exceptionally fast as they have high surface contact with the ground and face high frictional resistance. As a consequence, the maximum speed of a board is limited by the size and diameter of the wheels. A slower wheel profile may be preferable for children. 
         [0041]    Outdoor surfaces have asperities such as cracks in sidewalk cement, a rugged surface finish on asphalt streets, and obstacles such as rocks, pebbles, and metal drains openings. As more surface areas is traversed by wide wheels, a higher number of asperities must be rolled over. This is shown in  FIG. 8  where the trace left by rounded wheels (h) is compared with the larger trace of larger cylindrical wheels (H). 
         [0042]    On both a microscopic and macroscopic level, ground asperities result in a dynamic friction (μ d ) that in turn results in a frictional force (F d =μ d *S) that opposes the movement of the board. In this equation, S is the contact surface area such as S=(∂v/∂t)*H and where v is the velocity of the board on flat ground. Movement of the board is generated by a push and ultimately a downward component of the weight of the skateboarder if the board is on a negative incline. Forces that oppose movement include friction inside each wheel and the dynamic friction force F d .  FIG. 8  illustrates how a wheel with a narrower trace, such as a spherical wheel, contacts the ground over a smaller width (h) and therefore encounters a lower frictional force at the same speed. 
         [0043]    The wheels  1  do not always travel in a single direction. A skateboarder often directs the skateboard by placing the weight (W) as shown at  FIG. 9  downwards on a portion of the board to create different effects. When the weight is placed on an external area the two sets of wheels rotate inwards by an angle θ and thus the board also steers or rotates with the same approximate angle. The rotation of the wheels on the pavement is illustrated by two small arrows  110 ,  111 .  FIGS. 10 and 11  show how the contact area below a single wheel is instantly slid over the ground from a first position  121 ,  131  to a second position  122 ,  132 . As a result of this translation and rotation, additional dynamic and static frictional forces are created on the board resulting from the torsion of the surface below the wheel in addition to the width (H v. h). The greater the surface area of contact, the greater the force W is needed on the board to steer and initiate the rotation. 
         [0044]    For example, if the width is reduced from H to h, where the contact area of a spherical surface is reduced to the smallest required size, the board will require less pressure from the rider to rotate the wheels. Thus, the board will be more reactive and will require less force to move and maneuver. Further, as less energy is used to overcome friction, the maximum speed of the board is increased. Alternatively, it is often the practice of skateboarders to zig-zag down a hill to demonstrate facility and/or to slow down the board, the spherical wheels  1  will also change this behavior. 
         [0045]      FIGS. 12 and 13  are momentum diagrams of a skateboard equipped with cylindrical and spherical wheels, respectively. These diagrams show how different momentum forces are created in a board. As a skateboarder pushes downwards on the board F 1  to initiate a wheel rotation, with an assumed fixed width deck, a momentum M 1  is created that is equal to M 1 =L 1 *F 1 . For the purpose of the example, the same force F 1  and the same resulting momentum M 1  is create into both boards shown in  FIGS. 12 and 13 . The truck transfers the momentum M 1  to the point of contact where a reaction is created on the ground (R 1  or R 2 ). Based on the distance where the reaction force is produced (L 2  v. L 3 ) the reaction will differ. Since R 1 *L 2 =M 1 =R 2 *L 3 , and L 2  and L 3  are fixed values, we find that L 3 =L 2 −½W, resulting in the following equation: 
         [0000]    
       
         
           
             
               
                 R 
                 1 
               
               
                 R 
                 2 
               
             
             = 
             
               
                 
                   L 
                   3 
                 
                 
                   L 
                   2 
                 
               
               = 
               
                 
                   
                     
                       L 
                       2 
                     
                     - 
                     
                       W 
                       2 
                     
                   
                   
                     L 
                     2 
                   
                 
                 = 
                 
                   W 
                   
                     2 
                     * 
                     
                       L 
                       2 
                     
                   
                 
               
             
           
         
       
     
         [0046]    At the same point of attachment, unlike the devices from the prior art shown in  FIGS. 3 and 4 , the reaction force R 2  is always greater than the reaction R 1 , and as shown in  FIG. 7 , the point of reaction R 2  can be calibrated to fall closer to the internal axis of the board to improve the dynamics of the board. For a spherical wheel  1 , unlike other wheels types, the reaction R 2  is always perpendicular to the surface of the body and therefore is directed to the center of the wheel  1 , in this case the point of attachment on the axle. The force is accordingly centered between the bearing sets located inside the wheel  1  to help protect the wheel material. 
         [0047]    In the illustration shown at  FIG. 12 , the force R 1  is perpendicular to the external edge of the wheel until the wheels on the other side lift from the ground. R 1  may result in greater local chipping of the wheel  1  creating strain concentrations and shear forces in the bearing often offset from the force. In the spherical wheel  1 , no shear force or strain concentration is created in the bearing sets located in bearing grooves  41 ,  42  each side of the locking lip  40 . In the prior art shown in  FIGS. 3 and 4 , the force R 2  is not located at the connection point or inside of bearing set. 
         [0048]    Further advantages of a spherical wheel  1  include an easier surface to clean, a stronger wheel structure because spheres are inherently stronger than cylinders, and a wheel capable of offering its full support even if the board is lifted on its side and is being manipulated partly off the ground. In conventional wheels or even in the wheel system shown in  FIGS. 3 and 4 , the ground simply cannot be ridden with the board at 45 degrees as the reaction force from the ground is unstable as it is on an edge of the wheel. 
         [0049]    In one contemplated embodiment, the central opening  20  is 14 mm long and has an internal radius of 15 mm. Lateral bearing openings  21  for the bearing sets are also 7 mm thick and have an external diameter of 22 mm. A small, conical opening  22  is made to guide insertion of the bearing where the external opening is a maximum of 25.4 mm. In one embodiment, the sphere has an outer diameter  23  of 54 mm. 
         [0050]    The material used in one embodiment is polyurethane without regrind having a durometer value of 87 A, 95 A, 99 A or 100 A. The external finish on the external surfaces is SP1 grade 1 and in the internal surfaces SP1 grade 2. One other known advantages of using a spherical wheel  1  in conjunction with a skateboard having a deck with two trucks, each with grommets and axles having principal axis perpendicular to the body of the deck, is that any asperity or irregularity of the external surface of the wheel, such as, for example, molding asperities, will be shaved or worn off as the wheel  1  is used. In another embodiment, the regularly shaped external wheel surface allows for the creation of an external contact area either as part of the wheel  1  or attached to the external surface of the wheel having a curved ring shape. 
         [0051]    Further, the use of a spherical wheel  1  allows the board to move over an area with particles, dirt, gravel, or other material and displace laterally the material much like a ship advances through water, allowing for better penetration of the board over these mediums. 
         [0052]    Different methods of manufacturing the wheel  1  are contemplated. The wheel  1  can be injected into a mold having the internal configuration as shown in  FIG. 6B . Creation of the wheel  1  machined from a sphere is also contemplated. In any order, a cylindrical perforation  20  of the minimum diameter can be made from one side of the rounded sphere to the opposing side. The perforation resulting in areas where the sphere can be placed flat on a surface during machining steps. A second larger perforation can be made either at a light angle  22  or directly at the external diameter  21  of bearings on either side of the central perforation  20 , and finally, a third perforation is made to complete the structure by either doing the light angle  22  or the seating area  41 ,  42  for the bearings having a fixed external diameter. 
         [0053]    What is described and also shown in  FIG. 14  is a method  200  for upgrading a skateboard  100 , the method comprising the steps of removing  201  a nut holding at least one cylindrical wheel  1  from an axle of a truck connected to a deck of a skateboard, placing  202  and securing a bearing set in a bearing groove inside of an inner opening  20  of a first wheel with a spherical external surface  51 , where the inner opening  20  includes an inner locking lip  40  adjacent to the bearing set inserted in the bearing groove  41  and a guide angle  22  for guiding the bearing set to the bearing groove  41 , and sliding  203  the first wheel equipped with the bearing set over the axle. Further steps include locking  204  in place the first wheel using a locking nut mounted on the axle to secure the locking lip  40  and the bearing set to the axle to allow the first wheel to rotate around the axle. 
         [0054]    In another embodiment, what is contemplated is the step of placing  207  and securing at least a second bearing set in the bearing groove  42  inside of the inner opening  20  of a second wheel of identical configuration as the first wheel, sliding  203  the second wheel equipped with the bearing set over the axle of the truck, and locking  204  in place the second wheel using a second locking nut mounted on the axle to secure the locking lip and the bearing set of the second wheel to the axle to allow the second wheel to rotate around the axle. The selection step of wheels is shown in  FIG. 14  as  206 . 
         [0055]    What is also contemplated is a method for altering the center of gravity and changing the maneuverability of a skateboard  1 , the method comprising the step of replacing a set of at least two cylindrical shaped wheels as shown in  FIG. 1  or  2  with spherical wheels as shown in  FIG. 7  adapted for mounting on an axle of the at least two cylindrical wheels. The method includes a configuration as shown in  FIGS. 12 and 13  where the spherical wheels are of a diameter  23  of approximately the length of the cylindrical wheels W and where the spherical wheels  1  include an outer surface  51  having a spherical shape with a rounded contact area for rolling as shown in  FIG. 8  and an inner surface with two bearing grooves  41 ,  42  adjacent to a central locking lip  40  inside an inner opening  20  and where the two bearing grooves  41 ,  42  used inside the cylindrical wheels as shown in  FIG. 2  are placed inside the two bearing grooves  41 ,  42  of the spherical wheels  1  as shown in  FIG. 5 . 
         [0056]    Finally, in yet another embodiment,  FIG. 7  shows is a skateboard  100  comprising a flat deck  61 , at least a truck  62  connected to the flat deck  61  including an axle  63  with opposite ends  64 ,  65  and a grommet  66  between the opposite ends of the axle  64 ,  65 , and at least two wheels  67 ,  68 , each wheel located at one of the opposite ends of the axle  64 ,  65 , each wheel  67 ,  68  pivotally connected to roll along an axis of the axle  63  using a bearing set and a nut, and where each of the at least two wheels  67 ,  68  has a spherical outer surface  51 . 
         [0057]      FIG. 7  also shows that the skateboard  100  includes two trucks  62 ,  72 , each connected to the flat deck  61 , where each truck  62 ,  72  includes an axle  63 ,  73  as shown with opposite ends  64 ,  65 , and  74 ,  75  and a grommet  66 ,  76  between the opposite ends of each axle. 
         [0058]    In another embodiment, the spherical wheels  501  also include a grind face as shown in  FIG. 15 . The grind face  530  is a planar surface generally perpendicular to the center axis of the axle of the truck when the wheel is mounted on a skateboard. The grind face  530  is symmetrical on both sides of wheel  501  on the axis of the mounting holes of wheel  501 . The grind face  530  truncates the curved shape of the outer surface of the wheel as previously described and results in a wheel with a width smaller than that of a sphere. In one embodiment the outer surface is truncated such that the overall width of the wheel measures between 34 mm and 37 mm. The grind face  530  gives the wheel a surface that enables the rider to perform stunts and tricks that require such a surface. A grind surface at an angle other than perpendicular to the center axis of the truck could be used. As such, any generally flat surface on the ends of a curved outer surface skateboard wheel that provides the characteristics as described is contemplated. 
         [0059]    In a contemplated embodiment with the grind face  530 , the wheel  501  has a central opening  520  and is 10 mm long and has an internal diameter of 15 mm. The wheel  501  also has counterbores that serves as lateral bearing openings  521  for the bearing sets. The lateral bearing openings  521  are 9 mm thick and have an external diameter of 22 mm. A shallow, concave opening  522  is made to help guide insertion of the bearing and to help reduce the mass of overall wheel  501 . The concave opening is sized such that the ring-shaped planar surface of grind face  530  has a width  532  of approximately 5 mm. 
         [0060]    In another contemplated embodiment, the wheel is not spherical but is ellipsoidal in shape. As such, the outer surface of the wheel is rounded but is also elongated in the direction along the axis of the truck of the skateboard. As is known to one of ordinary skill in the art, an ellipsoid is a three-dimensional shape with curved outer surfaces that can be defined by three radii each measured along one of the three axes of a Cartesian coordinate system. The three radii that can define an ellipsoid are shown in  FIG. 17  and are labeled r 1 , r 2 , and r 3 . The radii, r 1 , r 2 , and r 3 , can also be described as an axial radius, a width radius, and a height radius, respectively. In the special case in which r 1 , r 2 , and r 3  are equal, the ellipsoid is a sphere. In the case where r 1  is larger than, r 2 , and r 3 , an elongated curved surface is defined. 
         [0061]    In one contemplated embodiment, r 1 , r 2 , and r 3  are equal and the outer surface of wheel  501  is a that of a sphere. The radii that define the outer surface of the wheel of this embodiment measure in the range of 26 mm to 30 mm, however, other radii can be used that provide the characteristics of this disclosure. In another embodiment, r 2  is equal to r 3  but r 1  is larger. In this type of embodiment, for example, r 1  and r 2  can both measure 30 mm but r 1  measures 60 mm. In this type of embodiment, a cross-section of the wheel is a circle in a plane perpendicular to the center axis of the mounting axle of the truck and the cross-section is elliptical in a direction along the center axis truck axle. While the term ellipsoid is used in this disclosure, any curved surface with the characteristics described herein or with an outer curved rolling surface is contemplated. 
         [0062]    In an embodiment with an ellipsoidal wheel, the wheel may also contain a grind face as previously described. The grind face truncates the ellipsoidal outer surface and results in a generally flat surface providing the characteristics as preciously described. 
         [0063]    What is described and also shown in  FIG. 18  is a method  600  for upgrading a skateboard  100 , the method comprising the steps of removing  601  a nut holding at least one cylindrical wheel  501  from an axle of a truck connected to a deck of a skateboard, placing  602  and securing a bearing set in a bearing groove inside of an inner opening  520  of a first wheel with an ellipsoidal external surface  551 , where the inner opening  520  includes an inner locking lip  540  adjacent to the bearing set inserted in the bearing groove  541  and a concave surface  522  for guiding the bearing set to the bearing groove  541 , and sliding  603  the first wheel equipped with the bearing set over the axle. Further steps include locking  604  in place the first wheel using a locking nut mounted on the axle to secure the locking lip  540  and the bearing set to the axle to allow the first wheel to rotate around the axle. 
         [0064]    In another embodiment, what is contemplated is the step of placing  607  and securing at least a second bearing set in the bearing groove  542  inside of the inner opening  520  of a second wheel of identical configuration as the first wheel, sliding  603  the second wheel equipped with the bearing set over the axle of the truck, and locking  604  in place the second wheel using a second locking nut mounted on the axle to secure the locking lip and the bearing set of the second wheel to the axle to allow the second wheel to rotate around the axle. The selection step of wheels is shown in  FIG. 18  as  606 . 
         [0065]    What is also contemplated is a method for altering the center of gravity and changing the maneuverability of a skateboard, the method comprising the step of replacing a set of at least two cylindrical shaped wheels as shown in  FIG. 1  or  2  with ellipsoidal wheels with a grind face  530  as shown in  FIG. 15  adapted for mounting on an axle of the at least two cylindrical wheels. The method includes a configuration where the ellipsoidal wheels with grind face include an outer surface  551  having an ellipsoidal shape with a rounded contact area for rolling and an inner surface with two bearing grooves  541 ,  542  adjacent to a central locking lip  540  inside an inner opening  520  and where the two bearings used inside the cylindrical wheels as shown in  FIG. 2  are placed inside the two bearing grooves  541 ,  542  of the ellipsoidal wheels  501  as shown in  FIG. 15 . 
         [0066]    It is understood that the preceding detailed description of some examples and embodiments of the present invention may allow numerous changes to the disclosed embodiments in accordance with the disclosure made herein without departing from the spirit or scope of the invention. As one of ordinary skill in the art understands, references have been made to specific figures and characteristics of the invention, however, the teachings of the disclosure are transferable between the various examples and embodiments described and have not been made to limit the scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention but to provide sufficient disclosure to one of ordinary skill in the art to practice the invention without undue burden.