snow and autoshifting

Since 2001, over 90,000 cyclist's have joined Cycling Forums to discuss topics from general cycling to equipment, training, racing and travel or vacation destinations (especially in europe during the tour de france). We also feature an great deals in our online store, 100's of articles, classifieds and product reviews.

I was noticing while riding my bike through snow that my derailer tended to continuously shift gears as I rode my bike through the snow. The cable run beneth the bottom bracket got caked with snow. Could this be the problem?

Could this be the problem?
Well, an autoshift put me in a cast and off the bike for nearly 3 months, so ya, it could be a problem. It's the slight flexing in the frame when the shifter cable isn't moving freely that causes it. Normally you'd lube the part where the cable goes around the BB, but in your case you'd have to not let the cable get covered with snow. How you would do that, I do not know, but I'm thinking fenders (however the fenders might collect snow and not allow the wheels to turn).

Well, an autoshift put me in a cast and off the bike for nearly 3 months, so ya, it could be a problem. It's the slight flexing in the frame when the shifter cable isn't moving freely that causes it. Normally you'd lube the part where the cable goes around the BB, but in your case you'd have to not let the cable get covered with snow. How you would do that, I do not know, but I'm thinking fenders (however the fenders might collect snow and not allow the wheels to turn).Well I notice that most of the mountain bikes route the shifting cables accross the top tube, with the front one going down the seat tube, and the rear one continuing allong the seat stay. How hard would it be to reroute the cable in this manner? Is this the likely cause of this problem.

And putting you in a cast? That sounds a bit extreme. The sudden snap that I kept feeling in my peddles wasn't very nice, but I didn't think it was dangerous.

It could probably be re-routed using zip ties (or something else serving the same purpose) to hold the cable to the frame, and using a casing on the cable for the whole length, whoever you would have to disconect the cable from the deraikler, meaning you would have to re-adjust it, which would probably be the most difficult part.

And yeah, I was sprinting when it shifted on me, my foot slipped out of the strapless toe clips I was using, I tried to pull my foot back on to the pedal, ended up going down anyway, arms still on the drops... In traffic this could have turned out a lot worse...

I was noticing while riding my bike through snow that my derailer tended to continuously shift gears as I rode my bike through the snow. The cable run beneth the bottom bracket got caked with snow. Could this be the problem?
If it doesn't happen when the cables are clean, then I think you may have cornered it. All sorts of screwy things happen to brakes, derailleurs, chains, wheels, fenders, and controls when they become caked with ice and mud.