There's no practical reason why you can't use a 1/8" chain with a 3/32" cog and/or chainring. It's very, very common for road-riding singlespeeders to use road cranks, and you pretty much can't get 1/8" chainrings for a 130mm bolt circle. It's easy to get chains and cogs in both sizes, so it's less common to use a cog that doesn't match the chain size, but there's no reason you can't do it. It will be a little noisier than if they matched, but as was mentioned before, it can give you a little wiggle room if your chainline isn't great. If you plan on swapping wheels with other bikes, or think you might need to borrow an emergency wheel sometime with a cog of unknown size, that's a good argument for using the 1/8" chain since a 3/32" one won't get over the teeth on a 1/8" cog. Practically speaking, there's no reason beyond aesthetics, weight savings, or being cheap (BMX chains are dirt cheap, and come in bright colors) to go with one size or the other. If you're running a singlespeed or fixed gear and you're not doing stupid stuff like breaking your chain all the time and reassembling it without the master link, you're not going to break it even if it is a "wimpy" little 3/32". I suppose a wider chain on narrower gears probably wears faster (slides around a little more) than if they matched. But those nickel-plated 1/8" chains sure are nice and low-maintenance in that they pretty much don't rust.
I use 1/8" chain and cog on my Raleigh Pro fixed gear more out of habit than anything else; with the comoponents I use I am certainly not going for period-appropriate.
Emily O'Brien Medford, MA
> From: "Mitch Harris" <mitch.harris@gmail.com>
> To: "Dr. Paul Williams" <castell5@sympatico.ca>
> Subject: Re: [CR]On-topic single-speed: Should I use a single-speed chain?
>
> The visual difference between a 1/8" track/single speed chain and a
> 3/32" chain is very noticeable, and is one of the attractive features
> of any bike with only one ring and cog. Like Mark I always use a 1/8"
> in this situation (assuming it is period correct). I've found no
> problem using a 1/8" chain with a 3/32" ring, but haven't tried it
> with a 3/32" cog--I've heard that others say you can use a 1/8" chain
> on the 3/32" cog just fine but I haven't tried it and, for me, that
> would be the only hesitation I'd have in your situation.
>
> Mitch Harris
> Little Rock Canyon, Utah