Surely the rear mech takes up any chain slack and prevents chain loss.
It does, until you hit a bump. There are rear dérailleurs now with a clutch in the P-Pivot which prevents the flapping chain usually associated with bumps, but 105 isn't one of them.
@gbj_tester started
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It does, until you hit a bump. There are rear dérailleurs now with a clutch in the P-Pivot which prevents the flapping chain usually associated with bumps, but 105 isn't one of them.