thanks for the explainer (genuinely) but you totally lost me here
also, out side of the ss world, the rotational inertia difference of the small/small doesn’t factor because you’re still spinning all your cogs and all your chainrings, right?
i forgot you’re new to tarck so you need a bit of a refresher on previously confirmed information. the issue here is that odd toothed chainrings with even cogs don’t match up each chain link. remember when we used to calculate skidpads for our fixies? it’s like the same thing, but you actually want FEWER. you need the same chain link to be touched by the same cog tooth every time. this way the wear patterns on the chain and the wear patterns on the teeth eventually match up. this means less friction on every rotation.
the real problem is with the odd-toothed wide/narrow chainrings. this is such a big issue that they actually stopped making odd-toothed wide/narrow chainrings because it was causing so much extra chain wear. a few of us still have some old odd tooth wide/narrow chainrings from back when wolftooth was the only company still making them at all, before they discovered this problem. it’s fine as long as your cog is odd toothed, because then the math works out fine. but having an odd-toothed wide/narrow is annoying because then you have to match it to the proper cog tooth count, whereas if your wide/narrow is even, then you’re fine.
what’s super super weird (and this part i don’t even totally understand) is that below the equator, you have to reverse it, so all the aussie wide/narrow rings are odd-tooth counts!
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i’m gonna need a sec to grok this
but in the mean time, a simpler question:
how do they handle the “last” tooth on a wide/narrow odd-toothed cr? is there a part where it goes wnwnwwn or something?
yeah, and you need a wnwnwwn chain, so you have to use a special link. that’s what half links are for.
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This is why it doesn’t work at the North Pole as well.
Most places you can pull out your compass and bear NNW or WWN but at the pole every direction is S, so you’re best off running single speed, or SS.
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and that wnwnwwn motif is repeated every T links (where T is the number of teeth)?
I honestly can’t tell if you’re taking the piss right now, this seems insane to me.
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Close. T= B - S + 2*
Where: B = total number of teeth @ big-big
And S = # @ small-small.
*2 for Shimano, 1 for Sram.
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man, fuck mountain bikes.
Mountian bikes? That equation is for road.
Is your mtb 1x or 2x? Full squish or front boinger only? If full squish, what’s the travel and chain growth? Wheel size? Super boost, boost, or normal? I hope it’s not quick release.
I don’t ride mountain bikes
Just assumed mtb because why on earth would I bother with all this shit for a road bike? My chains aren’t lemmings
wait you guys are def taking the piss
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You’re right, for a road bike just use my chain adaption formula I posted above. You can also look up the article on Sheldon Brown.
Um, thanks? Is this some Australian slang I’m too right-side-up to understand?
it means “taking me for a ride,” it’s just a sort of false friend because if you are taking the piss, then you are taking me for a ride.
Yes, I certainly hope you’re going to take your bike for a ride, mate! 
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With a smaller cog the chain links have to rotate against each other more, and thus creates more friction. Bigger is more efficient here.
Smaller cogs are lighter and use less chain and the reduction in mass makes for theoretical quicker acceleration (nothing to do with torque).
But does the reduced mass advantage overcome the increased friction? I have no idea.
Smaller cogs also may reduce wind resistance but it’s really hard to say for sure, way too many things interacting to know, aerodynamics can be counterintuitive.
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This is where you look for marginal gains after doing absolutely everything else, is what you’re saying.
It only applies to prime numbered chain rings.
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Does that lead to asymmetrical tire wear though?
hence oval chainrings
Was going to say this before we got derailed with narrow/wide chat again. What Kyle was saying sounds like it’s technically true but unlikely to make a noticeable difference in most cases outside of tiny BMX cogs.
The context I heard it in was that bmx kids liked the smaller cogs so they could get more torque and faster acceleration for tricks. And track/TT folks liked big rings/cogs so they could more easily spin when up to speed. I always thought that maybe these could be true, but there were probably many other reasons that were more likely.