Clutch and Driveline Considerations: When installing any performance engine you should consider upgrading your clutch and inspecting or replacing your Primary Chain and adjuster. Increased power levels and aggressive riding styles can cause stock or worn components to fail or work poorly and they may need to be upgraded.
Gearing Considerations:When installing a performance engine selecting the proper gearing is very important in achieving the performance levels you desire. In many cases engines with less power that are geared properly can outperform more powerful engines that are geared poorly for particular applications. Another important factor is gross vehicle weight Motorcycles that are heavy should not be geared with highway gears and a Six Speed unless the engine used is very, very powerful. On these types of bikes a 3.2-3.37 ratio will give much better acceleration. On most late model motorcycles the factory gearing is a good choice for all around riding. In lighter bikes we recommend a 2.92 to 3.15 overall ratio for highway riding. On heavier bikes used for highway riding or lighter bikes wanting quick acceleration for around town riding use 3.23 to 3.37 overall ratio. The following rpm/mph figures are based on a rear tire diameter of 26″ or 12.5″ from the ground to the center of your axle Changing tire diameter 1″ = approx. 2.6 mph.
Some common gear ratios are:
Stock 1995 FLH® models 36t clutch basket divided by 25t engine sprocket = 1.44 1.44 x 2.19 = 3.15 overall
70t rear pulley divided by 32t transmission pulley = 2.19 3000 rpm @ 74mph
Stock 1995 Softails® 36t clutch basket divided by 25t engine sprocket = 1.44 1.44 x 2.03 = 2.92 overall
65t rear pulley divided by 32t transmission pulley = 2.03 3000 rpm @ 79mph
Stock 1991 all models 37t clutch basket divided by 24t engine sprocket = 1.54 1.54 x 2.19 = 3.37 overall
70t rear pulley divided by 32t transmission pulley = 2.19 3000 rpm @ 69mph
Ultima® belt drives 71t clutch basket divided by 45t engine pulley = 1.6 1.6 x 2 = 3.20 overall
with chain rear 48t rear sprocket divided by 24t transmission sprocket = 2 3000 rpm@ 73mph