Q. You often read in tests that a bike has a low or high bottom bracket, but what measurement does that refer to and what difference does it make?
Jeffery Andies, St Leonards on Sea
A. Bottom bracket height is the distance to the ground from the centre of the BB axle. The ideal bottom bracket height varies quite a lot, depending on bike purpose and how much travel it has. Anything near or below 13in on full suspension bikes definitely reduces pedal clearance on rocky or rutted terrain but adds stability at high speeds. In contrast, 14in or above bottom brackets mean you can pedal through more stuff (rocks, corners, etc.) but they tend to feel more wobbly and nervous at slow speeds.