Abstract:
A disc brake caliper for conversion of a motorcycle with a linked braking system to a trike integrates two or more separate sets of opposed braking cylinders and pads within a single housing. Braking cylinder sets are not connected to other braking cylinder sets within the housing. Each set of braking cylinders is connected to and actuated independently by a different master cylinder. At least two braking cylinder sets within a housing have different diameters, the diameters of each set being chosen to produce a desired amount of braking pressure in response to an expected amount of hydraulic pressure from a master cylinder actuating the set. Both the diameter of each braking cylinder set and ratio of diameters between different braking cylinder sets are chosen to produce the optimum rear wheel braking pressure allocation for a given braking control system and vehicle configuration with no changes to the master cylinders or the front wheel braking system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   None. 
   BACKGROUND AND SUMMARY 
   Motorcycle enthusiasts number in the hundreds of thousands. Many riders, especially those who enjoy long-distance touring, prefer the power and stability of large touring bikes. To gain additional stability and load-carrying capacity, a sizeable minority have opted to convert their two-wheeled motorcycles to three-wheeled vehicles, or “trikes.” 
   In such a conversion most of the systems of the motorcycle are typically retained except for the rear portions of the drive train, the rear suspension, and the rear brake system. However, since the handling characteristics of a three-wheeled vehicle are very different than those of a two-wheeled vehicle, some modifications are needed to allow safe and comfortable operation of the vehicle. 
   Safe and effective modifications to the brake system are especially critical. Motorcycles have traditionally employed a foot pedal to actuate the rear brake and a hand lever to actuate the front brake. In motorcycles with hydraulic braking systems, the foot pedal and the hand lever each actuate a different master cylinder. 
   Since a motorcycle tends to pitch forward when braking, placing more downward, friction-producing force on the front wheel, skilled operators usually apply more braking pressure to the front wheel than to the rear wheel. However, relatively unskilled motorcycle operators often instinctively rely too heavily on the rear brake to stop the motorcycle, resulting in an uncontrolled skid. To provide safe and effective braking regardless of operator misjudgment, some motorcycle manufacturers have equipped their products with braking systems that link the front and rear brakes with control systems that allocate the optimum amount of braking pressure to each wheel no matter which master cylinder is actuated. 
   Linked braking systems on motorcycles usually allocate more braking pressure to the front wheel. Unfortunately, that pressure allocation is usually not suitable for a trike. The trike, of course, has two wheels in the rear. Those rear wheels are usually larger than the rear wheel of a motorcycle, resulting in more road contact area and braking friction. Also, a trike often carries more weight in the rear in the form of passengers and luggage. Diverting extra braking pressure to the front wheel of a trike may result in ineffective and erratic braking and may in some cases destabilize the vehicle. 
   Some modification to the braking system of a trike conversion is clearly needed, but since modifications to the original motorcycle brake master cylinders and control systems are both cost-prohibitive and likely to raise complex engineering and safety issues, most modifications known in the art have relied on various ways of connecting, disconnecting, or redirecting the master cylinder outputs. 
   In one known modification the outputs from the front and rear master cylinders are directly connected. This modification provides no ability to optimize the front-to-rear braking pressure allocation and often produces an odd “feel” to the brake foot pedal, causing the pedal to “drop” and the trike to roll backward slightly once the vehicle has stopped and the braking pressure has eased. 
   In another known modification, one master cylinder is simply disconnected and remaining master cylinder (usually the rear) is used to drive the entire braking system. This modification allows more even pressure distribution, but greatly reduces available braking force and user control while still providing no effective means for optimizing braking pressure distribution. 
   Still another approach is to direct all hand lever brake pressure to the front brake and all foot pedal brake pressure to the rear brake. Although this approach preserves available braking pressure and operator control, it negates the safety features provided by linked control systems. 
   What is needed is a simple, safe, and inexpensive motorcycle brake system modification for motorcycle conversions that preserves the advantages of the motorcycle&#39;s original linked braking control systems, requires no changes to the original master cylinders or front braking systems, and provides a means for optimizing the front-to-rear allocation of braking pressure. 
   The present invention provides such a modification. A preferred embodiment of the present invention comprises a disc brake caliper that integrates two or more separate sets of opposed braking cylinders and pads within a single housing. Braking cylinder sets are not connected to other braking cylinder sets within the housing. Each set of braking cylinders is connected to and actuated independently by a different master cylinder. 
   The amount of braking pressure exerted by a braking cylinder set is proportional to diameter of the cylinders in the set. In a preferred embodiment of the present invention, at least two braking cylinder sets within a housing have different diameters, the diameters of each set being chosen to produce a desired amount of braking pressure in response to an expected amount of hydraulic pressure from the master cylinder actuating the set. Both the diameter of each braking cylinder set and ratio of diameters between different braking cylinder sets are chosen to produce the optimum rear wheel braking pressure allocation for a given braking control system and vehicle configuration, with no changes to the master cylinders or the front wheel braking system. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of a brake caliper and rotor. 
       FIG. 2  is an exploded view of the brake caliper of the present invention. 
       FIG. 3  shows a cross-section of an elevation view of an inner caliper half of the present invention. 
       FIG. 4  shows a cross-section of a plan view of an inner caliper half of the present invention. 
       FIG. 5  shows a cross-section of an elevation view of an outer caliper half of the present invention. 
       FIG. 6  shows a cross-section of a plan view of an outer caliper half of the present invention. 
       FIG. 7  shows a top view of the assembled disk brake caliper of the present invention. 
       FIG. 8  shows an end view of the assembled disk brake caliper of the present invention. 
       FIG. 9  shows an isometric view of a hydraulic fluid distribution block as used in a preferred embodiment of the present invention. 
       FIG. 10  shows a cross-section of an end view of the hydraulic fluid distribution block of  FIG. 9 . 
       FIG. 11  shows a simplified schematic of the braking system of a HONDA® Model GL1800 motorcycle as is known in the art. 
       FIG. 12  shows a simplified schematic of a preferred embodiment of the present invention as installed on a HONDA® Model GL1800 motorcycle converted to a three-wheeled vehicle. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a disk brake rotor and caliper. The rotor  110  is mounted on a rotating hub (not shown) that is mounted on an axle (not shown) that rotates within an upright (not shown). The hub, axle, and upright are known in the art and are not subjects of the present invention. The rotor  110  is a disk with an outer annular friction surface  112  facing away from the upright and with a substantially identical inner annular friction surface (not shown) facing toward the upright. A brake caliper  120  is mounted on the upright so that the rotor  110  may pass through a portion of the brake caliper  120  as the rotor  110  turns. 
     FIG. 2  shows an exploded view of a preferred embodiment of the brake caliper of the present invention. An outer caliper half  210  is fastened to an inner caliper half  220  by fasteners  221 ,  222 ,  225 ,  228 ,  229 , each fastener passing through a hole  238 ,  236 ,  233 ,  241 ,  243  (respectively) drilled through the inner caliper half to screw into corresponding threaded holes (not shown) in the outer caliper half  210 . 
   In a preferred embodiment, the fasteners  221 ,  222 ,  225 ,  228 ,  229  are socket head cap screws. Screws with different caps may be used, and a fine-threaded screw may be used if the threads in the outer caliper half screw holes are roll-formed. In a preferred embodiment, the assembled caliper halves attach to the upright (not shown) via brackets (not shown) with button-head cap screws (not shown) passing through holes in mounting ears  239 ,  240 . Other types of screws or bolts may be substituted. 
   A primary port  275  communicates with an inner primary cylinder  230  and an inner primary crossover port  242  through passages (not shown) within the inner caliper half  220 . The hydraulic ports and passages within the present invention are preferably 0.125 inch in diameter. Larger port and passage diameters increase the volume of hydraulic fluid within the system without increasing the maximum hydraulic pressure transmitted. Smaller port and passage diameters delay the transmission of hydraulic pressure and may be used in alternate embodiments to cause delays between the application of pressure to different brake pads. 
   Hydraulic pressure applied at the primary port  275  is contained by a fluid seal  260  and a wiper seal  261 , forcing an inner primary piston  263  against an inner primary brake pad  264 . The brake pad  264  is in turn forced against the inner annular friction surface of the rotor (not shown). 
   In a preferred embodiment, the fluid seal  260  has a square cross-section (not shown) and the wiper seal  261  has a cruciate, or “X” cross-section (not shown). Both have inside diameters corresponding to the outside diameter of the inner primary piston  263 . The wiper seal  261  is preferably a QUAD RING® manufactured by Minnesota Rubber of Minneapolis, Minn. The outer lip (not shown) of the wiper seal  261  excludes contaminants, while the inner lip (not shown) acts as both a secondary contaminant seal and a secondary fluid seal. 
   In a preferred embodiment, the inner primary piston  263  has an optimum outside diameter of 0.875 inch, allowing simultaneous activation of all primary pistons in the braking system while maintaining effective braking pressure. The outside diameter may range up to 1.125 inch without a significant reduction in the hydraulic force transmitted to the inner primary piston  263 . Diameters larger than 1.125 inch may increase system fluid volume enough to require compensating modifications to the rear brake master cylinder (not shown in  FIG. 2 ) and other components. The diameter may range as far below 0.875 inch as is desired, but with a proportionate loss in braking pressure. The inner primary cylinder  230  is sized to accommodate the inner primary piston  263  according to design criteria well known in the art. 
   When the outer caliper half  210  is fastened to the inner caliper half  220 , an outer primary crossover port (not shown) aligns with the inner primary crossover port  242 , and the interface between the ports is sealed by an O-ring  262 . The outer caliper half  210  contains an outer primary cylinder (not shown) that is the same diameter as and axially aligned with the inner primary cylinder  230 . 
   Hydraulic pressure applied at the primary port  275  is also transmitted from the inner primary crossover port  242  to the outer primary crossover port, then through passages (not shown) within the outer caliper half  210  to the outer primary cylinder. The hydraulic pressure is contained by a fluid seal  267  and a wiper seal  268 , forcing the outer primary piston  266  against an outer primary brake pad  265 . The outer primary brake pad  265  is in turn forced against the outer annular friction surface of the rotor (not shown), balancing the opposing pressure by the inner primary brake pad  264  to create braking friction. 
   The outer primary cylinder and corresponding seals  268 ,  267 , piston  266 , and brake pad  265  have dimensions essentially identical to those of the inner primary cylinder  230  and corresponding seals  260 ,  261 , piston  263 , and brake pad  264 , respectively. 
   The inner primary brake pad  264  and the outer primary brake pad  265  are prevented from moving radially with respect to the rotor by a primary pin  226  that passes through a pin hole  232  through the inner caliper half, a pin hole  272  in the inner primary brake pad  264 , a pin hole  271  in the outer primary brake pad  265 , and into an axially-aligned pin hole (not shown) that partially penetrates the outer caliper half  210 . The primary pin  226  is held in place by a retaining clip  227 , a straight portion of the retaining clip  227  passing through a hole  286  in the primary pin  226  to lock the primary pin  226  and the primary brake pads  264 ,  265  in place. The primary brake pads  264 ,  265  slide freely on the primary pin  226  in directions normal to the friction surfaces of the rotor. In a preferred embodiment, the retaining clip  227  is a hairpin cotter pin, although a hammerhead cotter pin, bow tie cotter pin, and other pins known in the art can be substituted. 
   The inner primary brake pad  264  rests within a slot  277  milled into the inner caliper half  220 . In a preferred embodiment, the slot  277  is between 0.005 inch and 0.010 inch wider than the inner primary brake pad  264 , allowing the brake pad to move freely at normal operating temperatures and preventing the brake pad from moving tangentially with respect to the rotor. Similarly, the outer primary brake pad  265  rests within a slot  279  milled into the outer caliper half  210 . This slot  279  is also between 0.005 inch and 0.010 inch wider than the outer primary brake pad  265  and prevents the pad from moving tangentially with respect to the rotor. An inner rotor slot  280  is milled into the lower portion of the inner caliper half  220  with a radius slightly larger than that of the rotor so as to accommodate the passage of the rotor. 
   The present invention additionally comprises an integral secondary braking mechanism. A secondary port  235  communicates with an inner secondary cylinder  231  and an inner secondary crossover port  237  through passages (not shown) within the inner caliper half  220 . Secondary passages do not communicate with primary passages, so the primary and secondary brake assemblies may operate independently. Hydraulic pressure applied at the secondary port  235  is contained by a fluid seal  250  and a wiper seal  251 , forcing an inner secondary piston  253  against an inner secondary brake pad  254 . The brake pad  254  is in turn forced against the inner annular friction surface of the rotor (not shown). 
   In a preferred embodiment, the secondary braking system components are essentially the same as the primary braking system components in all respects except diameter. The fluid seal  250  has a square cross-section (not shown) and the wiper seal  251  has a cruciate, or “X” cross-section (not shown). Both have inside diameters corresponding to the outside diameter of the inner secondary piston  253 . The wiper seal  251  is preferably a QUAD RING®. 
   The optimum diameter for the inner secondary piston  253  is 0.750 inch, although it may range up to 1.000 inch without requiring compensating modifications to the front wheel master cylinder (not shown in  FIG. 2 ) or other brake system parts to maintain optimum hydraulic fluid pressure. The diameter may range as far below 0.750 inch as desired, but with a proportionate loss of braking power. The inner secondary cylinder  231  is sized to accommodate the inner secondary piston  253  according to design criteria well known in the art. 
   When the outer caliper half  210  is fastened to the inner caliper half  220 , an outer secondary crossover port (not shown) aligns with the inner secondary crossover port  237 , and the interface between the ports is sealed by an O-ring  252 . The outer caliper half  210  contains an outer secondary cylinder (not shown) that is the same diameter as and axially aligned with the inner secondary cylinder  231 . 
   Hydraulic pressure applied at the secondary port  235  is transmitted from the inner secondary crossover port  237  to the outer secondary crossover port, then through passages (not shown) within the outer caliper half  210  to the outer secondary cylinder. The hydraulic pressure is contained by the fluid seal  258  and the wiper seal  257 , forcing the outer secondary piston  256  against an outer secondary brake pad  255 . The outer secondary brake pad  255  is in turn forced against the outer annular friction surface of the rotor (not shown), balancing the opposing pressure by the inner secondary brake pad  254  to create braking friction. 
   The outer secondary cylinder and corresponding seals  258 ,  257 , piston  256 , and brake pad  255  have dimensions essentially of identical to those of the inner secondary cylinder  231  and corresponding seals  250 ,  251 , piston  253 , and brake pad  254 , respectively. 
   Both the inner secondary brake pad  254  and the outer secondary brake pad  255  are prevented from moving radially with respect to the rotor by a secondary pin  224  that passes through a pin hole  234  through the inner caliper half, a pin hole  273  in the inner secondary brake pad  254 , a pin hole  274  in the outer secondary brake pad  255 , and into an axially-aligned pin hole (not shown) that partially penetrates the outer caliper half  210 . The secondary pin  224  is held in place by a retaining clip  223 , a straight portion of the retaining clip  223  passing through a hole  284  in the secondary pin  224  to lock the secondary pin  224  and the secondary brake pads  254 ,  255  in place. The secondary brake pads  254 ,  255  slide freely on the secondary pin  224  in directions normal to the friction surfaces of the rotor. The same retaining clips used for the primary pin  226  may be used for the secondary pin  224 . 
   The inner secondary brake pad  254  rests within a slot  276  milled into the inner caliper half  220 . The slot  276  is between 0.005 inch and 0.010 inch wider than the inner secondary brake pad  254  and prevents the pad from moving tangentially with respect to the rotor. Similarly, the outer secondary brake pad  255  rests within a slot  278  milled into the outer caliper half  210 . The slot  278  is between 0.005 inch and 0.010 inch wider than the outer secondary brake pad  255  and prevents the pad from moving tangentially with respect to the rotor. An outer rotor slot (not shown) is milled into the lower portion of the outer caliper half  210  to accommodate the passage of the rotor. The outer rotor slot has a radius slightly larger than that of the rotor and is positioned to align with the inner rotor slot  280 . 
     FIG. 3  shows a cross-section of an elevation view of the inner caliper half  220 . A primary bleeder screw (not shown) screws into a threaded primary bleed port  310  that communicates with the inner primary crossover port  242 . The primary bleed port  310  facilitates the removal of air and impurities from within the primary hydraulic system, as is known in the art. Hydraulic pressure within the inner primary cylinder  230  is transmitted through an inner primary passage  315  to the inner primary crossover port  242 . 
   Similarly, a secondary bleeder screw (not shown) screws into a threaded secondary bleed port  320  that communicates with the inner secondary crossover port  237 . The secondary bleed port  320  facilitates the removal of air and impurities from within the secondary hydraulic system, as is known in the art. Hydraulic pressure within the inner secondary cylinder  231  is transmitted through an inner secondary passage  325  to the inner secondary crossover port  237 . Both the primary and secondary bleeder screws are preferably 5/16-inch, 90-degree seat screws. Significantly smaller screws do not provide an adequate flow rate, and significantly larger screws are incompatible with compact caliper design. 
     FIG. 4  shows a cross-section of a plan view of the inner caliper half  220 . Hydraulic pressure applied at the primary port  275  is transmitted through a passage  410  to the inner primary cylinder  230 . Similarly, hydraulic pressure applied at the secondary port  235  is transmitted through a passage  420  to the inner secondary cylinder  231 . 
     FIG. 5  shows a cross-section of an elevation view of the outer caliper half  210 . Hydraulic pressure at the inner secondary cross port  237  (shown in  FIG. 3 ) is transmitted through the outer secondary crossover port  510  and the outer secondary passage  515  to the outer secondary cylinder  512 . Hydraulic pressure within the outer secondary cylinder  512  is contained by a fluid seal  258  and a wiper seal  257 , forcing the outer secondary piston  256  against an outer secondary brake pad  255  (shown in  FIG. 2 ). 
   Similarly, hydraulic pressure at the inner primary crossover port  242  (shown in  FIG. 3 ) is transmitted through the outer primary crossover port  520  and the outer primary passage  525  to the outer primary cylinder  522 . Hydraulic pressure within the outer primary cylinder  522  is contained by a fluid seal  268  and a wiper seal  267 , forcing the outer primary piston  266  against an outer primary brake pad  255  (shown in  FIG. 2 ). 
     FIG. 6  shows a cross-section of a plan view of the outer caliper half  210 .  FIG. 7  shows a top view of the assembled disk brake caliper. Two aligned slots  277 ,  279  form a rectangular opening  710  that allows easy access to a retaining clip  227 , primary pin  226 , and the primary brakes pads  264 ,  265 , disposed on either side of the rotor  110 . Similarly, two aligned slots  276 ,  278  form a rectangular opening  720  that allows easy access to a retaining clip  223 , secondary pin  224 , and the secondary brakes pads  254 ,  255 , disposed on either side of the rotor  110 . The rectangular openings  710 ,  720  facilitate inspection and replacement of brake pads. 
     FIG. 8  shows an end view of the assembled disk brake caliper. An outer rotor slot  810  is milled into the outer caliper half  210  with a radius to accommodate the rotor (not shown). Similarly, an inner rotor slot  280  is milled into the inner caliper half  220  with the same radius to accommodate the rotor. 
     FIG. 9  shows a hydraulic fluid distribution block  910  as used in a preferred embodiment of the present invention. The hydraulic fluid distribution block  910  is mounted on a vehicle by socket head cap screws or other known fasteners (not shown) passing through holes  940 ,  945  in the hydraulic fluid distribution block  910 . A hydraulic supply line (not shown) is attached to a first intake port  920 . A second hydraulic supply line (not shown) is attached to a second intake port  930 . 
     FIG. 10  shows a cross section of an end view of the hydraulic fluid distribution block  910 . Hydraulic pressure applied to the first intake port  920  is distributed to two output ports  925 ,  1010 . The port configuration shown in  FIG. 10  is duplicated for a second intake port  930  (shown in  FIG. 9 ), which distributes hydraulic pressure applied to the second intake port  930  to an output port  935  (shown in  FIG. 9 ) and a similar output port (not shown) on the opposite side of hydraulic fluid distribution block  910 . The output ports supplied by the first intake port  920  do not communicate with the output ports supplied by the second intake port  930 . The cylinder actuation pattern described above may vary somewhat between different makes and models of motorcycles, but the essential functions remain the same. 
   The present invention as described above provides a means for modifying a motorcycle braking system when the motorcycle is converted to a trike. To better understand how the conversion is effected and why it is necessary, it is useful to review the mechanism and operation of the braking system of a motorcycle prior to conversion. 
     FIG. 11  shows a simplified schematic of the braking system of a HONDA® Model GL1800 motorcycle as is known in the art. A front wheel  1102  and a rear wheel  1104  support a chassis  1100  and handlebars  1106  that rotate the front wheel  1102  to steer the vehicle. Since more braking force is usually applied to the front wheel  1102  than to the rear wheel  1104 , the vehicle is equipped with two front wheel rotors  1130 ,  1140  and brake calipers  1131 ,  1141  and a single rear wheel rotor  1150  and brake caliper  1151 . Each caliper has three pistons, each piston actuating a separate brake pad. 
   When an operator depresses the brake pedal (not shown) the foot brake master cylinder  1110  is actuated, increasing hydraulic pressure in connected hydraulic lines  1153 ,  1137 ,  1145 . One hydraulic line  1153  actuates the center piston  1154  of the rear brake caliper  1151 . A second hydraulic line  1145  actuates the two outer pistons  1142 ,  1146  of the left front brake caliper  1141 . A third hydraulic line  1137  transmits pressure to a delay valve  1112  that briefly delays transmission of pressure through a hydraulic line  1133  to the center piston  1134  of the right front brake caliper  1131 , allowing the operator to briefly direct more braking force to the rear wheel  1104  to make minor speed adjustments on low-traction surfaces. Once the delay period is exceeded, the right front brake caliper  1131  is partially engaged, providing additional braking torque to the front wheel  1102 . 
   When an operator compresses the hand brake lever (not shown), the hand brake master cylinder  1120  is actuated, transmitting pressure directly to two hydraulic lines  1135 ,  1143 . Pressure in one hydraulic line  1135  actuates the two outer pistons  1132 ,  1136  of front right brake caliper  1131 . Pressure in the other hydraulic line  1143  actuates the center piston  1144  of the left front brake caliper  1141 . 
   As the front left brake caliper  1141  is engaged, torque on the caliper moves the caliper with respect to a secondary master cylinder  1148 , actuating the secondary master cylinder  1148  and transmitting pressure to a proportional control valve  1114  via a line  1147 . The proportional control valve  1114  adjusts transmitted pressure according to braking conditions and transmits adjusted pressure through a line  1155  to actuate the two outer rear brake pistons  1152 ,  1156  of the rear brake caliper  1151 , thereby providing some rear braking action even when the hand brake lever alone is engaged. 
   As is readily apparent, the braking system just described is complex and carefully balanced to provide optimum braking for a two-wheeled vehicle. However, when the two-wheeled vehicle is converted to a three-wheeled vehicle, the balance of braking pressures provided to the rear wheels is no longer optimum. 
   Since a motorcycle tends to pitch forward when braking, placing more downward, friction-producing force on the front wheel, the optimum front-to-rear ratio of braking force for a motorcycle is typically about 60% front to 40% rear. To provide this ratio regardless of operator misjudgment, some motorcycle manufacturers have equipped their products with braking systems that link the front and rear brakes with control systems that automatically allocate braking pressure at this ratio no matter which master cylinder or combination of cylinders is actuated. 
   The trike, however, has two wheels in the rear, and each rear wheel is usually larger than the rear wheel of a motorcycle. The result is more road contact area and braking friction. Larger wheels allow the use of larger brake rotors. If each wheel is equipped with a brake, the resulting increase in hydraulic system volume may exceed the capacity of the actuating master cylinder, causing a drop in braking pressure. Also, a trike often carries more weight in the rear in the form of passengers and luggage. An unsuitable balance of braking pressure between the front wheel and rear wheels of a trike may result in ineffective and erratic braking and may in some cases destabilize the vehicle. An optimum front-to-rear braking pressure balance for a HONDA® Model GL1800 motorcycle converted to a trike is 50/50, but other ratios may be desirable for specific vehicle models, control systems, and configurations. 
   Some braking system modifications must clearly be made during a conversion, but cost and safety issues make it highly desirable that those modifications be simple and easy to implement. A variety of relatively crude modifications are known in the art but do not provide the ability to retain the advantages of the original linked braking system while optimizing the manner in which the rear wheel calipers respond to the output of each master cylinder. 
   The present invention provides such modifications.  FIG. 12  shows a simplified schematic of a preferred embodiment of the present invention as installed on a HONDA® Model GL1800 motorcycle converted to a three-wheeled vehicle. The three-wheeled chassis  1200  comprises the engine (not shown), front wheel  1102 , handle bars  1106 , and most of the original control systems and two-wheeled chassis  1100  except for the rear wheel, rear brakes, and rear suspension. In place of the rear components of the two-wheeled vehicle are mounted a modified chassis  1202  with a left rear wheel  1204 , a right rear wheel  1206 , and the modified rear braking system of the present invention. 
   During modification, the rear brake components of the two-wheeled vehicle are disconnected and the rear suspension components (not shown), rear wheel  1104  (shown in  FIG. 11 ), and rear brake components  1150 ,  1151 ,  1152 ,  1154 ,  1156  (shown in  FIG. 11 ) are removed. As shown in  FIG. 12 , these components are replaced by a modified chassis  1202 , a left rear wheel  1204 , a right rear wheel  1206 , a hydraulic fluid distribution block  910 , hydraulic lines  1252 ,  1256 ,  1262 ,  1266 , a left rear brake caliper  1250 , and a right rear brake caliper  1260 . 
   The hydraulic line  1153  from the foot brake master cylinder  1110  is connected to the first intake port  920  on the hydraulic fluid distribution block  910  to actuate the primary brake assemblies. Fluid pressure applied to the first intake port  920  is distributed to an output port  925 , which in a preferred embodiment transmits pressure to a residual pressure control valve  1274 . The residual pressure control valve  1274  is in turn connected through a hydraulic line  1262  to a right primary port  1264  (corresponding to the primary port  275  shown in  FIG. 7 ) in a right brake caliper  1260  (essentially identical to the brake caliper shown in  FIG. 7 ) mounted proximate to the right wheel  1206 . 
   The residual pressure control valve  1274  maintains a pressure of approximately 2 psi within the hydraulic line  1262  and the right brake caliper  1260 , essentially taking up “slack” between system components and thereby reducing the time required for the right brake caliper  1260  to respond to pressure applied by the foot brake master cylinder  1110 . 
   Fluid pressure applied to the first intake port  920  is also distributed to the output port  1010 , which in a preferred embodiment transmits pressure to a residual pressure control valve  1270 . The residual pressure control valve  1270  is in turn connected through a hydraulic line  1252  to a left primary port  1254  in a left brake caliper  1250  mounted proximate to the left wheel  1204 . The left brake caliper  1250  is essentially a mirror image of the right brake caliper  1260 , with an outer caliper section rotated 180 degrees to face the left wheel  1204 , but with the primary brake assembly still nearest the front of the vehicle. 
   The hydraulic line  1155  from the proportional control valve  1114  is connected to the second intake port  930  to actuate the secondary brake assemblies. Fluid pressure applied to the second intake port  930  is distributed to an output port  935 , which in a preferred embodiment transmits pressure to a residual pressure control valve  1276 . The residual pressure control valve  1276  is in turn connected through a hydraulic line  1266  to a right secondary port  1268  (corresponding to the secondary port  235  shown in  FIG. 7 ) in the right brake caliper  1260 . 
   Fluid pressure applied to the first intake port  930  is also distributed to an output port  1210 , which in a preferred embodiment transmits pressure to a residual pressure control valve  1272 . The residual pressure control valve  1272  is in turn connected through a hydraulic line  1256  to a left secondary port  1258  in a left brake caliper  1250 . Each residual pressure control valve  1270 ,  1272 ,  1274 ,  1276  has the same characteristics and performs the same function. 
   When an operator depresses the brake pedal (not shown) the foot brake master cylinder  1110  is actuated, increasing hydraulic pressure in connected hydraulic lines  1153 ,  1137 ,  1145 . One hydraulic line  1153  transmits pressure to primary ports  1254 ,  1264  in the rear brake calipers  1250 ,  1260 , actuating the rear primary brake assemblies, which, having larger pistons, create greater braking force than the single piston actuated in the two-wheeled vehicle. 
   A second hydraulic line  1145  actuates the two outer pistons  1142 ,  1146  of the left front brake caliper  1141 . A third hydraulic line  1137  transmits pressure to a delay valve  1112  that briefly delays transmission of pressure through a hydraulic line  1133  to the center piston  1134  of the right front brake caliper  1131 , allowing the operator to briefly direct more braking force to the rear wheel  1104  to make minor speed adjustments on low-traction surfaces. Once the delay period is exceeded, the right front brake caliper  1131  is partially engaged, providing additional braking torque to the front wheel  1102 . 
   When an operator compresses the hand brake lever (not shown), the hand brake master cylinder  1120  is actuated, transmitting pressure directly to two hydraulic lines  1135 ,  1143 . Pressure in one hydraulic line  1135  actuates the two outer pistons  1132 ,  1136  of front right brake caliper  1131 . Pressure in the other hydraulic line  1143  actuates the center piston  1144  of the left front brake caliper  1141 . 
   As the front left brake caliper  1141  is engaged, torque on the caliper moves the caliper with respect to a secondary master cylinder  1148 , actuating the secondary master cylinder  1148  and transmitting pressure to a proportional control valve  1114  via a line  1147 . The proportional control valve  1114  adjusts transmitted pressure according to braking conditions and transmits adjusted pressure through a line  1155  to the secondary ports  1258 ,  1268  in the rear brake calipers  1250 ,  1260 , actuating the rear secondary brake assemblies, providing some rear braking action even when the hand brake lever alone is engaged. 
   As described above and shown in  FIGS. 3 and 5 , the outer secondary cylinder  512  and the inner secondary cylinder  231  are of a smaller diameter than the outer primary cylinder  522  and inner primary cylinder  230 . Since a large hydraulic piston produces more force at a given hydraulic pressure than a small piston, the size difference produces a proportionate difference in pressures exerted by the primary and secondary braking systems. Combined with the ability to operate the primary and secondary braking systems independently, selection of primary and secondary cylinder diameters and of the ratio between these diameters therefore provides a means for selecting the ratio of front-to-rear braking pressures while retaining the safety features of a linked braking system. As long as the cylinder diameters chosen do not increase the hydraulic system volume beyond the output capacities of the master cylinders, the present invention facilitates the simple, effective, and safe conversion of a motorcycle to a trike with no changes to the master brake cylinders or front wheel braking system. 
   The preferred primary and secondary cylinder diameters described above are optimized for use with HONDA® Linear Braking Systems and Automatic Braking Systems as used on HONDA® Model GL1800 motorcycles for years 2001 through 2003. However, those skilled in the art can readily see that other cylinder diameters and ratios may be determined and used to optimize performance for other braking systems, and that the present invention is in no way limited to use with HONDA® motorcycles or even to three-wheeled vehicles. 
   The principles, embodiments, and modes of operation of the present invention have been set forth in the foregoing specification. The embodiments disclosed herein should be interpreted as illustrating the present invention and not as restricting it. For example, the present invention may integrate any desired number of independent braking cylinders into one caliper. Alternatively, more than one caliper may be used to brake each wheel, either on the same rotor or on different rotors, with each caliper that is braking a given wheel connected to a separate master cylinder output or combination of master cylinder outputs and with the ratios between wheel cylinder diameters chosen to provide an optimum brake pressure distribution. A caliper may contain pairs of opposing cylinders or may be free-floating with a single cylinder for each input line. 
   The foregoing disclosure is not intended to limit the range of equivalent structure available to a person of ordinary skill in the art in any way, but rather to expand the range of equivalent structures in ways not previously contemplated. Numerous variations and changes can be made to the foregoing illustrative embodiments without departing from the scope and spirit of the present invention.