Tool
Motorcycle Gearing Calculator
Final drive is rear sprocket teeth divided by front sprocket teeth. Enter the pair you plan to fit. If you also enter the stock pair, the calculator reports the percent change in that ratio.
Final-drive ratio
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When to use this calculator
Use it when you already know the tooth counts for a countershaft or rear sprocket. The page does not store a catalog of Yamaha or Honda gearboxes. Those ratios belong on the speed-in-gear page, where you enter them yourself.
A higher final-drive ratio is shorter gearing. The engine turns more times for each turn of the rear wheel, so launch improves and highway RPM rises. A lower ratio is taller gearing.
The percent change is (new ratio − stock ratio) ÷ stock ratio. It is a change in reduction, not a promise about elapsed time in a quarter mile.
If you need MPH at a chosen RPM, open the speed-in-gear table and keep the same tooth counts.
Worked pairs
The ratio is 2.813 : 1. That pair is a common street final drive.
Dropping the front sprocket by one tooth raises the ratio by 6.67 percent. Would that extra reduction be worth the higher interstate RPM on your bike?
Two more teeth on the rear raises the ratio by 4.44 percent. The chain will also sit on a larger sprocket, so check the adjustment range before you order.
Technical questions
Why is the ratio rear divided by front?
The front sprocket drives the chain. The rear sprocket is larger on a street motorcycle, so the wheel turns more slowly than the countershaft. Rear ÷ front is that reduction. 45 ÷ 16 is 2.813.
Does a one-tooth front change equal a one-tooth rear change?
No. One tooth on a 16-tooth front is a larger fraction of the pair than one tooth on a 45-tooth rear. That is why 15/45 and 16/47 are not interchangeable even though both are “one tooth shorter” in casual speech.
What happens if I enter zero teeth?
The field shows an error. The calculator will not print Infinity or a blank ratio from a zero denominator.