Motorcycle sprocket calculator
Type the teeth on your front and rear sprockets now, and the ones you’re thinking of fitting. You see how much shorter or taller the gearing gets, and what that does to your revs.
6.7% shorter
Now 16/44 = 2.750 : 1. After the change 15/44 = 2.933 : 1. Shorter gearing: the engine turns faster for the same road speed, so the bike pulls harder in each gear and each gear tops out at a lower speed.
Plain arithmetic: final drive ratio = rear teeth ÷ front teeth. With the gearbox and tyres unchanged, the revs at any road speed change by the same proportion as that ratio.
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How to use it
Count the teeth on the front sprocket (the small one on the gearbox) and the rear one (the big one on the wheel). Type those in, then the pair you want to try. Add your revs at a speed you know, or your speed at some revs you know, and the tool shows what they become after the change. The link in your address bar keeps your numbers, so you can send them to whoever is doing the work.
How it is worked out
The final drive ratio is the rear teeth divided by the front teeth. A bigger number is shorter gearing: the engine turns more times for each turn of the back wheel.
| Set-up | Sum | Ratio |
|---|---|---|
| 16 front, 44 rear | 44 ÷ 16 | 2.750 : 1 |
| 15 front, 44 rear | 44 ÷ 15 | 2.933 : 1 |
| 16 front, 46 rear | 46 ÷ 16 | 2.875 : 1 |
Going from 16/44 to 15/44 makes the ratio 6.7% bigger. With the gearbox and tyres left alone, the engine then turns 6.7% faster at any road speed. So 5,000 rpm becomes about 5,333 rpm at the same speed. Turn that round and, at the same revs, the bike goes 6.25% slower in each gear.
One tooth at the front, or a few at the back?
As the table shows, one tooth off the front sprocket changes the ratio more than two teeth on the back. That is because the front sprocket is smaller, so each tooth is a bigger share of it. A different number of teeth can also need a different chain length, so ask whoever fits the parts before you order.
Written by Craig Fearn, Throttlefolio. Last updated .
Questions answered
How do I work out my motorcycle gear ratio?
Divide the rear sprocket’s teeth by the front sprocket’s teeth. 44 ÷ 16 is 2.75 : 1.
Does a smaller front sprocket mean more revs?
Yes. Fewer teeth at the front makes the ratio bigger, so the engine turns faster at the same road speed.
How much difference does one tooth make?
It depends on the sprocket. On a 16-tooth front, one tooth less makes the ratio 6.7% bigger.