Bike chain-cassette disaster
I did my race rehearsal today and had something happen to me that I haven't experienced in >10 years on the bike, but now happened 3 times in 2 days: When climbing in the small chainring and shifting down one gear to the lowest gear in my cassette, the chain over-shifted and became lodged betwen the casette and spokes. The tension on the chain led it to get lodged all the way down to the axle, and because the chainrings for the smallest rings aren't solid down to the axle, the chain became lodged underneath the chainring and was impossible to remove.
Given this has never happened to me before and I also had some shifting problems this weekend, I'm assuming it has something to do with my rear derailleur and it will be easily solved with a full tuneup and a close look by the bike mechanic. Has anyone experienced this before, and if so, what is the root cause? Thanks in advance for any help, I'm two weeks out from race day and a bit stressed about this.
Comments
Sounds like a limit-screw issue on the derailleur cage. The jockey pulleys need to line up perfectly with cassette sprockets. There are screws to adjust that ravel on both the high and low ends. The other cause might be a too-short/tight cable, from excessive adjustment, if you have been turning the barrel screws that "shorten" or "lengthen" the cable. A cable that's too loose will cause the opposite problem - the chain falls off the smallest cog when downshifted all the way.
Easily fixed.
I've been having similar issues, dropping the chain off the small chainring, and from the small cog in back. I went through the limit screw adjustments for both derailleurs and it doesn't look like that was the issue, at least in front. I actually had to move the low limit on the front derailleur in toward the frame as the chain was rubbing in the small-chainring/big-cog combination. The chain length looks pretty good; no sag in the small/small combination. Shifting is pretty clean. I have a 34/50 in front and 11-32 11-speed in back with long cage derailleur.
Any ideas what could be going on, and what I can do to avoid a drop in the IM next week? I've been dropping the chain about once every 6 hours of riding lately.
That said, if you can figure out how to intentionally throw your front chain ring, you can practice bringing it back up. You can "save" a front chain ring loss with some carful manipulation of the derailleur...basically just "shifting" it back onto the ring. If you haven't tried this before, once someone tells you, it's pretty amazing once you get the hang of it. Can't say I've ever experienced a loss in the back, so I don't have any tricks to offer.
U can buy one of these:
http://www.bicyclettesdehull.com/fr/product/genetic-anti-drop-attrape-chaine-brase-aluminium-noir
I've tried shifting the chain back on, but too often by the time I realize it has dropped it is jammed in tightly. For the IM this weekend I'll focus on lightening the load when shifting and watch the cross-chaining.