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Chain Ring (Newbie Question)(2 posts)

Chain Ring (Newbie Question)Borg
Mar 28, 2003 12:41 PM
While riding on a flat road, will you typically generate more power by using the large chain ring or the small chain ring (on a double crank)? Or does it matter?
Mar 28, 2003 1:36 PM
If the particular combinations of front ring/rear cog results in the same gear ratio, your pedalling efficiency is the same; put another way, if you're able to acheive the same road speed, using the same effort to turn the cranks at the same rate, in either ring, your efficiency should be the same. An example of this would be a 51 front/17 rear (resulting in three revolutions of the wheel for each pedal rotation) and 42 front/ 14 front (same 3:1 ratio). In the real world, however, you'll rarely be able to acheive the same ratios (and you wouldn't want to, anyway).

You start to lose efficiency, however, when your chain line starts to get extreme: asking the chain to go from the outer front ring to the inner rear cog (or vice versa) results in frictional losses as the chain bends laterally. (It also causes premature chain wear.) The ideal chain line is as close to parallel to the bike's long axis as possible.

Keeping the chain line straight could therefore effect your choice of which chainring to use for maximum efficiency.