Technical information

What chain size and length do I need?

All current Brompton bicycles are built with 3/32” width chains.

The chain must have the correct number of links and this will depend on the combination of chainring and sprocket/s as set out below.


ONE rear sprocket

TWO rear sprockets


12T or 13T


16T/12T, 16T/13T or 15T/13T



12T or 13T


16T/12T, 16T/13T or 15T/13T









12T, 13T, 14T


16T/12T, 16T/13T or 15T/13T








Generally, all 2 speed bikes are fitted with a 54T chainwheel, 6 and 3 speed bikes are fitted with a 50T chainwheel and B75 bikes are fitted with a 44T. You can check this on the chainwheel itself which has a number printed on it. 

Chains for each of the different gearing options are available as spare parts from authorised dealers. The 3/32” width chains come with a tool-free connecting link. As with our other spares and accessories, these are not sold directly from our factory but are available from authorised Brompton dealers either directly from their stock, or by asking them to order the parts.

When fitting a new chain the sprockets must be replaced at the same time.

Some earlier Bromptons will have been built with 1/8” chains and sprockets. The combinations of chain wheel and sprocket required are the same as in the table above, but the 1/8” chain must, of course, be used in combination with 1/8” sprockets only. The tool-free connecting link cannot be used with a 1/8” width chain. 

Some spares can be ordered online in some countries or through an authorised Brompton retailer.

Click on dealer locator to find your nearest one.

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