[BeniBoy]

Kind of reminded me of the traditional wisdom that you should select chains and sprocket to avoid patterned wear. I don't know if there is an effect (especially with bikes and their low torque),but I always think about it when changing my chain. I suppose this only applies to single sprocket bike.

[jstanley]

This is called "hunting tooth". It applies to any system of gears or timing belts.

In gears, if you make sure the number of teeth of mating gears is coprime then you wear the teeth of one gear evenly against the other gear. If there are low factors, then each tooth of one gear only engages with a small number of teeth on the other gear, exacerbating wear.

With belts, if the number of teeth on the belt shares low factors with the number of teeth on either of the pulleys then you get the same effect: any given tooth on the belt only ever meshes with a small number of teeth on the pulley.

[dredmorbius]

You've just made me realise that several of the more popular freewheel / sprocket combinations are in fact prime: 11, 13, 17, 23.

Usually contrasted against the decidedly non-prime 52 (2 * 2 * 13) and 42 (2 * 3 * 7) chainrings. 38 if you're old-school triple (2 * 2 * 7).

My chain lengths would vary and I never counted them specifically, though I'd typically remove a few links for fit.

[fyhn]

Isn't this only relevant for fixed gear bikes, where you can skid the rear wheel to brake, and you want maximize the number of possible "skid patches", or orientations of the rear wheel while the pedals are in a fixed position?

[analog31]

It could also apply to the wear on the chainring and cog if their teeth are in a perfect proportion to one another, but without thinking too hard about it, I'm guessing that's actually rare. For instance a 2:1 ratio would be awkward for most cyclists riding on pavement (too low) and 3:1 too high, if they had to choose exactly one ratio.

I ride 46:19, because those are the parts that were in my bin when I built the bike, and it's a pretty good all-round ratio for city riding unless you're a lot more athletic than I am.

Also, those components wear out soon enough anyway -- a chain lasts 2 to 3 thousand miles, and a cog lasts a few chains.

[namdnay]

"I suppose this only applies to single sprocket bike."