Welcome to our Ask a Mechanic column where our expert mechanic Daniel Slusser answers your bike maintenance questions. If you have a question for Daniel, please post it on our Facebook Wall or e-mail Daniel directly at firstname.lastname@example.org. Today’s column discusses how to avoid the costly mistake of shifting your rear derailleur into your spokes.
I was out on a road ride last week and when I got to the steepest part of the climb I went to shift into my lowest gear in back and the rear derailleur shifted right into the spokes. Now I need a new derailleur, a bunch of replacement spokes and a new derailleur hanger! This has happened to me before but I didn’t get this much damage. Why does this happen? Do I need a new mechanic? From: Jeremy
There are two possibilities that created this problem. The first is that the mechanic made a mistake. That is to say, the lower limit screw on the rear derailleur might not have been adjusted in far enough thereby allowing the rear derailleur to shift too far inboard, ending up in the spokes. I suspect that this is not what caused the problem, because if it was, it likely would have occurred shortly after having your bike serviced.
What probably happened is your bike took a tumble that bent your rear derailleur, derailleur hanger, or both. This usually happens when a bike accidentally tips over, or the rear derailleur gets bumped, or when a crash occurs. Such an impact to the rear derailleur will invariably bend the assembly inboard, closer to the spokes in the rear wheel. With everything moved closer to the spokes, the low limit screw either has to be readjusted or the derailleur hanger needs to be realigned or replaced otherwise the derailleur will shift into the spokes.
Anytime your rear derailleur takes an impact, stand behind the bike and look to make sure that the derailleur lines up vertically with the cogs in the cassette, or your next ride could end abruptly and you could be out a bit of cash.
Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.