The sound of the chain slapping around when riding over rough ground isn’t one of our mountain biking highlights, nor is it to helpful when such action leads to the chain falling of the chainset.

To get round this issue Shimano has added a nifty new feature to its latest XTR rear mech (RD-M985). A clutch ‘stabiliser’ system, basically a switch at the pulley cage which increases the spring tension, is intended to only allow small movements for chain growth but drastically cuts down the range of movement when you’re rattling down a steep and rough descent.

It can be switched off for removal of the rear wheel. It’s expect to be available in June 2011, and will cost £169.99. and