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I'm struggling to find a replace crank set to replace the SR Suntour set that came on my bike. The chain rings were riveted together so on bending one I had to replace the set. There's very few 7 speed crank sets for a 118mm spindle and separate chain rings. I would like to fit a Shimano M410 on a 113mm bb. This will alter the chain line by 2.5mm, will this be an issue?

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    You don not necessarily need a 7 speed crank -- 8 and 9 speeds should also work. As the chain blades get narrower the more sprockets you have in your cassette, a 7 speed chain will also fit on 8 or 9 speed chain rings. Maybe this will get you some more crank sets to chose from. A drawback could be that narrower chain rings wear out faster but I don't think this should make a huge difference. In fact, the lifetime difference between the different price segments would be larger than the one caused by the narrower chain rings, I guess. – Benedikt Bauer Dec 17 '12 at 7:58
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2.5mm would not be a serious issue. You may find the "sweet spot" in your gearing changes a little to favor the larger rear sprockets, but so long as you don't run a lot in your top-most gear this should not be a problem.

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    I agree. Besides, there are at most one "perfect line" gear per chainring, EVERY other gear combination runs offset, sometimes severly offset, and this is (or should be) accounted by the very chain design which allows for lateral flexing. As mentioned, there will only be a change on where the drivetrain "sweet spots" are. – heltonbiker Dec 17 '12 at 23:35

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