Garage tool

Chain length

The question after the gearing change: will my chain still fit?

Start from a bike's stock gearing

Pick a bike to fill in its stock sprockets and chain pitch.

Chain pitch

Links now (count them)

Now

Front teeth

Rear teeth

After the change

Front teeth

Rear teeth

Chain lengths

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Worked from the standard chain-length formula, from where the axle sits with the chain you have now. Check the adjusters have room for the move and set the slack to the figure your manual prints.

Rule of thumb

Two teeth on the rear, or about one on the front, is roughly one link of chain. The calculator does it exactly: it works out your axle-to-countershaft distance from the chain you have, then the length the new sprockets need, rounded up to an even number of links. Pick the gearing first in the gearing calculator.