Originally Posted by
Dutch Jazz
Correct me if I'm wrong here; but if you are saying that friction = power lost, doesn't that mean that 45x12 is better than 52x14, because the chain makes contact with fewer teeth. Fewer contact points = less friction = less power losses?
The 45T has both a higher tension chain and less teeth to deal with it. The force on the 45T tooth is about 33% higher than on the 52T ring (did a quick Excel calc.). A 52T has a radius 15% bigger than 45T. The chain is under 15% less tension on the 52T. For easy math I assumed the chain contacts just 26T on the 52T ring and 22.5T on the 45T ring (it is slightly different based on rear derailleur pulley position and top of rear cog).
Experience shows smaller gears and rings wear faster.
But the friction I'm concerned about is in the chain. That between the rollers and pins and between the plates. I want less tension and a straight shot from rear cog to front ring whenever I can get it.
How much does this all matter? Hard to tell but chain optimization through different lubes seems to save 4-5W in testing. I guess its in that realm.