Bigger rear or smaller front.

4 replies to this topic
  • loudarbs

Posted February 07, 2008 - 09:12 AM


I know that they say you lose more mechanical advantage if you go with a smaller sprocket. Keeping the gearing ratio that I want the same, should I go with a smaller front sprocket or a bigger rear sprocket? Also assuming that the rear axle position will stay the same. What's everyones thoughts? Does extra chain wt make a difference?. Does added friction in the chain guides make a difference? Just a couple primer questions.

  • grayracer513

Posted February 07, 2008 - 09:40 AM


Given the same gear ratio, for example, 13/49 vs. 14/52, there is no difference in the two setups from the standpoint of the "leverage" the engine has over the rear wheel at all.

The smaller front sprocket will produce a very small increase in frictional losses within the chain due to the increased rotational angle of the links passing over it, but it's such a small difference that it's negligible from a practical standpoint. I seriously doubt it could be reliably detected on a dyno. A bigger issue is that the sprocket and chain will wear faster over sprockets having 12 or fewer teeth.

In the rear, larger sprockets are necessarily heavier, but here again, what really is the weight difference in two otherwise identical sprockets, one a 49 and the other a 52? Drag at the lower guide can become a factor if the sprocket is so large that the chain must deflect over the back edge of the guide in order to run down to the sprocket. This, however, is more of a problem because of the wear it causes the guide than for the power loss involved.

Chain weight is also not significant between the two setups, since at most, it would require a difference of not more than one link; two pins one way or other out of 114 is less than one percent.

So, IMO, it's functionally immaterial which way one does it, as long as both sprockets are within practical limits as to their size.

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  • loudarbs

Posted February 07, 2008 - 10:05 AM


Great response Gray except you forgot one important factor, $$ Price $$. Just kidding. Thanks. Great info. Do you think going with the larger rear sprocket and added chain length will affect rotational mass enough that it could be noticed by seat-of-the-pants?

  • grayracer513

Posted February 07, 2008 - 10:08 AM


Machinery designed to measure such things would find it virtually undetectable. Whether you feel it or not (and realistically, you won't be able to) depends on what you convince yourself of. That's why the black feather worked for Dumbo.

  • loudarbs

Posted February 07, 2008 - 10:13 AM


Amazing the power of the mind, I think?:busted:

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