Originally Posted by
steffie224
I was on flat, clean roadway. I wan't shifting, but had shifted to a very low gear minutes before due to a strong beach headwind.
Thanks so much for your input. I'm very curious as to how this happened so as not to let it happen so soon again. There was no quick fix, and had to have someone drive out to pick me up. I'd really hate to have this happen really far from home.
5:1 it was a mis-adjused low gear limit screw. This allowed the RD to move too far inboard and snag a spoke or put the chain over the top of the cassette causing similar results. Limit screws don't move by themselves, but if, for example the bike fell over bending the derailleur hanger inward slightly, that would be change the setting. It could go unnoticed for days, weeks or months because it would only become a problem when you shifted to the innermost sprocket.
It might also be the "B" screw setting which controls the angle of the RD to the frame. If the RD rides too high he jockey wheel could interact with a cassette sprocket, causing the RD to be kicked back with enough force to break it or the hanger. Again a problem that often doesn't show up except in the lower gears.
REI will do the repair, but if you're concerned about a re occurrence during your trip this August, you can prevent it by having he bike checked before starting, and doing a quick daily 1 minute check of brakes, RD, tires, wheel alignment, headset, and other basic adjustments. (the check takes less than a minute unless problems are discovered and need fixing) BTW- if you're doing a long out of town tour, buy and carry a spare derailleur hanger (if it's replaceable). These are easily replaced on the road, but there are so many different ones that you might not be able to buy the right one on the road.