Work out motorcycle chain sprocket ratio instantly with clear inputs, formula shown and shareable results.
Final drive ratio is rear teeth over front. Changing the front sprocket by one tooth alters the ratio by 6% or more, while one tooth on the rear changes it by about 2% — which is why front sprocket changes are the blunt instrument and rear changes the fine adjustment.
Final drive
ratio = rear teeth / front teeth; one front tooth is worth about three rear teeth
Rear for fine tuning, front for a big change. A smaller front sprocket also increases chain wear because of the tighter wrap angle.
Quicker acceleration and lower top speed, with higher cruising rpm and worse economy. Gearing up does the reverse.