How to Find Motorcycle Gear Ratios

Motorcycle transmissions are constant-mesh transmissions. The gear clusters are mounted on parallel shafts in the transmission housing. The shifter mechanism slides these clusters along the shafts, and determines the gear ratio being used at the time. Power flows into the transmission at the drive shaft. The drive shaft gear clusters are either splined or dogged to the mainshaft. The mainshaft gears engage into the countershaft gear clusters and transmits power to the countershaft. The countershaft delivers power at the current gear ratio to the drive sprocket/pulley, which in turn rotates the rear wheel.

Things You'll Need

• Mechanic's tools
• Catch pan

Instructions

1. Shift the transmission into first gear. Remove the shift rod from the top of the shift mechanism. Remove the shift mechanism mounting bolts from the shifter housing and lift the mechanism off of the transmission. Remove the transmission drain plug and fully drain the transmission fluid into the catch pan.

2. Loosen the rear axle and loosen the axle adjusters to slacken the drive chain/belt. Slip the chain/belt off of the transmission drive sprocket/pulley. Remove the transmission drive sprocket/pulley from the transmission output shaft.

3. Unbolt the transmission shaft plate on the side of the transmission. Carefully slide the shafts and gears free of the transmission case. Note the gears on the mainshaft and countershaft that are currently engaged. Count the teeth on the driven gear on the countershaft. Count the teeth on the drive gear on the mainshaft. Divide the driven number by the drive number. This is your first gear ratio.

4. Shift the shifter mechanism through neutral into second gear. Move the shifter forks on the gear clusters to mimic the shifter motion. Identify the gears that are now engaged. Count the teeth on them and divide the driven number by the drive number. This is your second gear ratio. Repeat this process for the remaining gears.

Tips & Warnings

• Direct-drive transmissions, such as Harley-Davidsons, will be a 1:1 ratio in top gear. Overdrive transmissions could have a top-gear drive ratio where the transmission puts out a ratio greater than 1:1 (such as 1:1.2 or greater). This is more common on high-performance bikes and/or touring models where sustained high speeds are anticipated. Overdrive transmissions will give slightly better fuel economy at highway speeds in top gear.