Off-road motorcycles typically have chain-and-sprocket drives from the transmission output shaft to the rear wheel. Some road bikes use enclosed transmission shafts and gear drives instead of a chain and sprockets. The advantage of chain drives is light weight, but exposure to the dust and mud of off-road riding reduces their reliability. Enclosed shaft drives are protected from the elements. Design a lightweight shaft-drive system for the off-road motorcycle of Figures P9-1 and P9-2. Assume an engine of 60 HP at 9 000 rpm. Low gear in the transmission has a ratio of 1:4, and the final drive ratio from transmission output shaft to rear wheel should be approximately 1:3.5. At least one universal joint will be needed in the driveshaft to accommodate the suspension motion. Some combination of spur (or helical) and bevel gears will be needed. Suitable bearings, housings, and seals should be specified. It will be of value to inspect a similar motorcycle shaft-drive system to obtain additional information on its general design.

2295 shock Time 0.00 sec Force of Rear Axle frame IFI (lb) 3072.00 Position of Cycle Frame 28. 22 in 18.54 in 1 2048.00 Velocity of Front Axle IVI (mph) 32.00 1024.00 24.00 0.4 cm t (sech 2 Www www2.00 Force at Swing Arm Pivot 0.00 FI (b) 1024.00 8.00 17 68.00 12.00 6.40 0.40 (sec) 20 Velocity of Shock Strut Arm vy (mph) 16.00 512.00 AL wheel 256.00 0.00 9.40 Wit (soc wurde 10.40 t (sec) 11.20 FIGURE P9-1 Geometry of an Off-Road Motorcycle Rear-Wheel Suspension System FIGURE P9-2 Simulation of Forces Generated by a Motorcycle Jumping and Landing on Its Rear Wheel 2295 shock Time 0.00 sec Force of Rear Axle frame IFI (lb) 3072.00 Position of Cycle Frame 28. 22 in 18.54 in 1 2048.00 Velocity of Front Axle IVI (mph) 32.00 1024.00 24.00 0.4 cm t (sech 2 Www www2.00 Force at Swing Arm Pivot 0.00 FI (b) 1024.00 8.00 17 68.00 12.00 6.40 0.40 (sec) 20 Velocity of Shock Strut Arm vy (mph) 16.00 512.00 AL wheel 256.00 0.00 9.40 Wit (soc wurde 10.40 t (sec) 11.20 FIGURE P9-1 Geometry of an Off-Road Motorcycle Rear-Wheel Suspension System FIGURE P9-2 Simulation of Forces Generated by a Motorcycle Jumping and Landing on Its Rear Wheel