My main worry about going 10 speed used to be chains. I break 9 speed chains and they are Shimano XT so it is just the power going in that breaks them on the Offroad uphills. But I would be loath to use ultegra 10 spd chains offroad.
Mountain Bikes are starting to see 10spd now and I noticed that the 10spd are now being done in XT- so Can't see a problem in the future.
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How long was I in the army? Five foot seven.
Spike Milligan