Guide

How final drive changes acceleration and cruising RPM

Final drive on a chain motorcycle is rear sprocket teeth divided by front sprocket teeth. That number sits in the overall reduction together with the primary ratio and the gearbox ratio for the gear you are in.

When final drive rises, the engine turns more times for each turn of the rear wheel. At a standing start, that extra reduction is what riders mean by shorter gearing: the same clutch work produces a stronger pull. At a steady 70 MPH, the same extra reduction is extra RPM. The Motorcycle Gearing Calculator reports the percent change in the ratio. The speed-in-gear table shows the MPH cost at one RPM. The RPM calculator shows the cruise-RPM cost at one road speed.

Shorter versus taller in the numbers

16/45 is 2.813 : 1. 15/45 is 3.000 : 1, which is 6.67 percent shorter. 16/47 is 2.938 : 1, which is 4.44 percent shorter than 16/45. A one-tooth front change is the larger move on a typical street countershaft.

The gearbox does not change when you swap sprockets. First gear is still first gear. What changes is the final multiplier after the transmission. That is why a sprocket change moves every row of the speed table by the same percent.

What a sprocket pair cannot do

It cannot add power. It cannot fix a clutch that is already fading. It cannot tell you whether the chain will still fit the swingarm after a large rear-sprocket increase. Those are shop checks. The calculators stay with ratio, speed, and RPM.

If you want the percent first, use the Motorcycle Gearing Calculator or the Sprocket Calculator. If you want the table, open speed in gear.