I snapped my rear mech off 160km into the Dirty Reiver 200 yesterday. Just riding along a gravel path, no sticks or big rocks involved. Here’s why I think it broke. Is there an alternative reason? I just want to be sure it doesn’t happen again.
Bike is set up with a Superstar 38T chainring, XT cassette, Deore 9 speed (non shaddow) rear mech and an XT chain. The chain is neither too short or too long; the long cage mech takes up all the slack w/o being overly tight in the big-big combination.
Hub is a Superstar Switch Ultra Rear Hub with a steel freehub body. I’ve noticed a few times that the freehub drags a little when freewheeling, i.e. it is still going round slightly with the wheel rotation. Just enough that I’ve noticed the chain sagging a little above the chainstay.
So it would appear that it stuck badly yesterday, pulled a lot of chain above the chainstay, shortening the amount of chain between the chainring and mech, hence snapping the gear hanger.
Does that sound about right?