I keep an old 3x6-geared MTBSO near work, and the front shifter is currently broken (smashed plastic gripshift). It will be a few weeks before I can get it home to replace it with a spare, so I've currently used the FD limit screws to fix it into the middle chainring. This leaves the gearing a bit low -- I don't have much accleration once I'm spinning over 100rpm which makes keeping up with traffic hard -- so I'd like to fix it in the big ring, but then for pulling away I'd be geared big-big.

Is this likely to significantly increase wear on the gears themselves? It's only a BSO so I wouldn't mind, except I don't think the sprockets are ever coming off, and if they did, replacements would cost about as much as the bike is worth.

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    Sprockets typically last 5000+mi, sure you'll wear them a little more running cross chained, but the damage you can achieve in a few weeks will be negligible in the grand scheme of things. – Andy P Oct 9 at 14:14
  • @AndyP on that bike it might well be true, though I have no measure for whether the increase in wear is 10%, 100%, or 1000%. On one of my others I expect to ride >10% of your sprocket life estimate (with which I concur) in the next few weeks. – Chris H Oct 9 at 14:20
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    The Difference between theory and practice is that in theory hell freezes over if you cross the chains, in practice nothing bad happens. The extra wear is statistically insignificant compared to the wear variation caused by difference levels of maintenance. – mattnz Oct 10 at 1:16
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    Yeah, this isn't a huge issue. I'd worry about more important things. Like lunch. – Batman Oct 10 at 3:36
  • Big-big cross chaining not as significant as small-small, I've heard it said. – Jeff Oct 17 at 7:52
up vote 0 down vote accepted

I would not be concerned in the short term, say 6 months to a year. There are several things in your favor. A six speed chain is wider than a modern 10 speed chain. Wider equals more material equals longer wear. On a MTBSO parts are used that are cheap. Cheap means steel instead of lighter alloys. So I think you will see some wear but it will be minimum.

  • I'm not convinced by your reasoning, here. The question is about wear to the cogs, not the chain, but you're saying that the chain is wider so the chain has more material so can have more worn off it before there's a problem. How does that affect the cogs? – David Richerby Oct 11 at 15:36
  • The wearing of the chain influences the wear on the cogs, The chain is what causes cog wear. The more wear in the chain the faster the cogs will wear. – mikes Oct 11 at 20:57
  • Stretch on the chain wears the cogs, but this isn't about stretch. Wear on the cogs from a bad chainline shouldn't depend on how worn the chain is, because it's about the chain rubbing against one side of the teeth rather than being in a straight line. – David Richerby Oct 11 at 21:27

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