Thursday, January 5, 2012

Bike fail

Some bikes come with an optional part called a spoke protector. A spoke protector is shaped like a disc and, on modern bikes, is usually made out of plastic. It fits on the rear wheel between the right-side spokes and the cassette, and it prevents the chain from jumping off the largest sprocket and getting caught in the spokes, which can cause a lot of expensive damage to the wheel and drive chain.

Spoke protectors are optional because the chain should never jump off the cassette. Bicycle derailleurs have a pair of screws, called the min and max screws or limit-stop screws, that forcibly prevent the derailleur from shifting too far left or right. On a well tuned bike, one where the limit-stop screws are set correctly, the rear derailleur can't shift far enough to the left to cause the chain to jump.

However, this morning I learned that my sporty, carbon fiber bike isn't a well tuned bike. I also relearned how finicky sports bikes are compared to, say, touring bikes. While I'm unsure whether my touring bike, which I've been using for heavy commuting for the last month, is well tuned, it has a spoke protector. That's because commuting or touring without such a cheap safeguard part is stupid, in the same way that removing the seat belts from a cargo van for performance reasons is stupid.

But for regular road bikes, which are rightly considered toys by most Americans, a spoke protector is yet another part that adds unnecessary grams—and in the worst place, the wheel. Also, spoke protectors make bicycles look less sporty. So most sports bikes don't have them.

The problem, as I've discovered the hard way, is that one doesn't know for sure whether a bike's chain can jump until after it has done so. I've ridden my bike for two years and several thousand miles, and this morning, for the first time ever, the chain jumped. It happened while I accelerated with a medium effort from a quiet intersection. I didn't know what happened at first, only that something had slid undone or had broken. For the few seconds until I came to a halt, I heard awful grinding and popping sounds.

I don't yet know what the total damage is because, as of writing this, I haven't been able to pry the chain from the wheel. I can see that a lot of the chain was ground away where it wedged itself between the spokes and cassette, and it looks like parts of the spokes and hub have been ground away, too. Also, the ordeal stressed the rear derailleur, so there's a fair chance that that's damaged, too, though hopefully it's no more than bent—derailleurs can be bent back into alignment. Strangely, through all of this, none of the spokes broke outright.

I own four bikes. Of the other two not mentioned in this post, one is a triathlon bike and the other is an $80 junker. Why couldn't this have happened to the triathlon bike instead?

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