The Q-factor describes the width of the crank and should be as small as possible for biomechanical reasons. A Q-factor that is too large can even cause knee pain.
How to measure the Q-factor correctly
The easiest way to measure the Q-factor is with a folding rule: To do this, bring the crank into a horizontal position and place the folding rule on one side at the height of the pedal from above. To do this, insert the folding rule through the spokes of the rear wheel. Now turn the other crank arm backwards until the arm rests on the folding rule. The value can now be read off exactly.
The value is usually between 156 and 173 millimetres. Double cranks are generally narrower than triple variants. E-bikes and fat bikes are usually very wide.
Some examples of common Q-factor dimensions
SRAM XX = 156/166 mm; Shimano XTR 2014 = 163/168 mm; Shimano XT 2014 = 174 mm.
