Graham Snowden, Chesterfield
A: Shimano gears can rotate forward and backwards around their anchor bolt which makes it easier for them to just push out of the way without really thinking about it. SRAM mechs can't rotate forwards of the 'parallelogram (main body of the mech) horizontal' position, though, which means the cassette tends to get caught on them.
To whip the wheel in or out pull the mech back with your hand so that the parallelogram is vertical and the wheel will just slide past.
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