Today I was out riding and decided to sprint a little ways, so I shifted up into the never-really-used 52x12 combination (the highest gear on my bike) and as soon as I opened it up, the chain jumped off the big ring. I've determined that it's not a derailleur issue, but could be a bad chain, overly flexible BB, or some other crankset issue. One other noteworthy thing is that it only jumps when I'm pedaling downward with my left foot, opposite the crank.
Any ideas what the problem could be, and more importantly, how to fix it? I'm tempted to just take it to the LBS tonight or tomorrow and let them deal with it.
Any ideas what the problem could be, and more importantly, how to fix it? I'm tempted to just take it to the LBS tonight or tomorrow and let them deal with it.