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cross chaining

Accepted wisdom is that is bad and that we should never do it. However, most of us set up our bikes so that we can run any gear combination. Invariably, I'll occasionally look down and see that I'm running my big chainring against one of the bigger cogs.

Is there any measurement of how much faster equipment will wear out from cross chaining, or energy loss or whatever?

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It's like crossing the streams in Ghost Busters -- it's will end the universe as we know it, except when it saves the universe. (Don't worry to much about it. The main problem with a big/big or small/small combo is that your derailer may not have the tooth capacity for it, plus you're apt to get more chain noise, and possibly some skipping. Avoid it over the long run, but don't worry about it for a minute or three, if the derailer handles it.) –  Daniel R Hicks May 29 '12 at 15:19
    
@DanielRHicks I admit I've had an inkling that it's not as bad as some folks let on. –  user973810 May 29 '12 at 15:45
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It used to be worse, before derailers were designed to handle larger tooth ranges, et al. But that's been 20-30 years. –  Daniel R Hicks May 29 '12 at 16:25
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(Though note that if you do it a lot that's a sign that you're not taking the best advantage of your gearing options. Or perhaps your front derailer is simply too "fussy" and you avoid mucking with it, suggesting that you need to get your bike tuned up.) –  Daniel R Hicks May 29 '12 at 16:28

1 Answer 1

up vote 3 down vote accepted

The problem with cross-chaining is that you put more stress on the chain which causes wear and tear on cassette teeth, eventually leading to the chain slipping gears.

The chain line is one factor. The chain should ideally run in a plane from the front derailleur teeth back to the rear derailleur. It shouldn't be forced into a line on the teeth, and then angle as soon as it clears the teeth to get to the cassette as happens when cross-chaining because that causes teeth to wear. You're not going to fix the chain line except by making the chain and gear spacing narrower which requires weaker chains at a given price.

The length of the rear derailleur cage determines how much slack it can pick up in the chain. If you size your chain big-to-big, and have a derailleur capable of picking up the slack then shifting into big-big shouldn't do damage. Shimano XT rear derailleurs have a 43 tooth capacity which should cover just about anything, but I had a touring bike with a wide range of gears that exhausted it. I managed to wedge things pretty well when my shifters got pushed into awkward positions on a train and I started riding without checking.

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