Q&A Forks and the bottom bracket

Moving to carbon and BB ID


Q: I would like to upgrade my set of forks on my current racing bike. How easy is it to change them to carton fibre? Also, how do I tell whether my bottom bracket is English or Italian?
Ricky Benjamin, email


A: Swapping forks is simplicity itself. However, in order to preserve your steering geometry, it’s important to find a fork with the same height from dropout to crown race seat (ie, the shoulder on top of the fork crown that supports the steering bearing). It’s also a good idea to find a fork with the same or similar rake, which is typically about 45mm. You can measure this by aligning a straight edge with the centre line of the fork steerer tube and measuring from that line to the centre of the wheel spindle.
The other consideration is steering bearing size. If you are swapping from a steel fork, it will almost certainly have a 1in steerer tube, probably threaded. It is possible to find a carbon fork with threaded aluminium steerer, but now is a good time to go for a threadless system, which will require a new threadless headset and handlebar stem as well as the fork. The advantage lies in weight reduction and overall front-end stiffness.

Only Italian frames have an Italian bottom bracket shell thread, because the British system is better.This is because, as with the pedals, it has left- and right-hand threads to prevent it unscrewing thanks to thread precession.

But be careful; the right-hand bottom bracket cup has a left-hand thread, whereas a left-hand pedal has a left-hand thread. The Italian system uses two right-hand threads, which at 36mm outside diameter are larger than the 34.8mm (1.37in) British thread. Some Italian frames, including all Bianchis, use the British system. If possible, measure the outside diameter of the cup. The difference is small, however, and not easily discerned. You could try unscrewing the right-hand cup anticlockwise but, if you’re wrong it will get tighter. The best idea is to contact the manufacturer or importer of your bike and simply ask them.


Richard Hallet