Originally Posted by
Racer Ex
Damn discs kill off a splined hub system for most folks. That's why I'm on the Miche adapter.
The 13 cog with a coating is kind of a reach if the papers I've read about friction losses on smaller radius gears with a chain is accurate. Not sure if folks confuse quiet with fast too. I can make a drive train that will be dead silent and suck power like crazy.
You'd figure if the chain line is right the friction from a cog is tiny, essentially the only "slip" you have is the fractional point of engagement and disengagement. Couple of milleseconds? If it's side loaded you're still not talking about a large event.
Big ass gears. Less RPM, less frictional loss.
Interesting discussion.
1+ to almost everything. The only exception I have is to the drivetrain noise. Noise energy is losses. You can coat the cog/chain in rubber or something and make it silent and dissipate the losses into heat, but all things being equal, a quiet drivetrain is less lossy than a loud one. But to get back to the point about differences in cog tooth profile: the cog tooth is an involute, meaning ideally there is no point where the chain roller is in sliding contact with the cog. Ideally, you cut a cog using a
hobbing process which makes the involute shape nearly exactly. Less expensive cogs use an approximate shape programmed into a CNC machine tool. The really cheap cogs are stamped. But getting back to the point about noise; some or all of this noise from cog engagement is from non-ideal sliding contact with the chain.
But all this is getting more into the mental aspects of the sport than physics. People want things quiet because they
sound more efficient, which puts them in a better state of concentration for the event. It's one of the things I've grown to enjoy about track. Everything's so simple and elegant about the equipment that competition really is stripped down to its basics. The losses in the drivetrain really are very small (unless you put your chain too tight!).
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Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --
the tiniest sprinter