I am building up a fixie and, as you can tell from my questions, I'm new at this.

I got a Jamis Sputnik. It has 120mm track 'dropouts' and I'm using Sugino RD cranks with a Sugino 103mm bottom bracket (as recommended for that crankset by Sheldon Brown).

I am going to use a regular road 42T 130bcd chainring--everything is 3/32". I thought any road chainring (without pins and ramps) would be ok. But a couple of people have told me that I need a track specific chainring or my chainline will be off. This doesn't make sense to me...I thought anything that fits on the crank would have the teeth aligned properly.

Can someone educate me on this?

thanks

Although very tiny, chainline difference between 3/32" & 1/8" chainrings is insignificant. Your drivetrain won't notice the difference.

I understand that but what about the chainring? Not whether it's 3/32 vs 1/8 but using any road chainring?

Track specific is 1/8" thick cogs & chainrings. Road chainrings are thinner and your chainline won't be affected. Yes, you can use most any road chainring, no problem.

Track specific is 1/8" thick cogs & chainrings. Road chainrings are thinner and your chainline won't be affected. Yes, you can use most any road chainring, no problem.

+1 what he said....,.

so here's another question: if a road chainring is thinner (ie: 3/32 vs 1/8) I presume that the teeth on both are centred in the metal of the chainring so chainline remains constant.

I know that 3/32 is almost the same as 1/8 as far as chainline is concerned. However, I bought a Blackspire chainring from Mtn Equipment Coop in Toronto and then noticed that it seems thicker than any other chainring I have.
So, I emailed the company and this is their reply:

"The ring you bought is not a single speed ring. It is offset for road double.
So you will have to adjust your chainline to accomodate this offset."

This is what has generated my concern. Even if the chainring seems thicker (and it sure doesn't flex, which is good), wouldn't the teeth still be centred on the rim?

I think you're over-thinking this too much. Is this chainring causing any trouble?

I'm sure you're right about me overthinking.
I haven't assembled it yet so it can't be causing a problem...I just want to avoid problems.

Basically, are you saying 'a chainring is a chainring'?

a chainring is a chainring as long as you don't try to use a 3/32 chain on a 1/8" ring..other than that, no worries...

When you say thick, are the teeth thick as well? If they are, a standard 3/32" multi-speed chain may not work. You'll need to get a 1/8" BMX or track chain.

no the teeth seem quite the same as any 3/32 chainring. The 'wheel' that the teeth are attached to (I'm sure there's a techiical name for it) is thicker. What worried me is that the distance from the crank to the centre of the teeth may be off if the wheel is thicker aluminum. But perhaps the teeth are simply centred appropriately so that doesn't happen...although, as I noted above, the manufacturer said I should not use that chainring.

Ah yes, I'm obsessing!

no the teeth seem quite the same as any 3/32 chainring. The 'wheel' that the teeth are attached to (I'm sure there's a techiical name for it) is thicker. What worried me is that the distance from the crank to the centre of the teeth may be off if the wheel is thicker aluminum. But perhaps the teeth are simply centred appropriately so that doesn't happen...although, as I noted above, the manufacturer said I should use that chainring.

Ah yes, I'm obsessing!

Start thinking quantitatively. How much thicker is the ring? maybe a millimeter? So the center of the teeth will be displaced by half that? A chainline that's within a millimeter of perfect is, effectively, perfect. Yours may not be that perfect, but it won't be because of the thick ring.

One other thought. How thick are the tabs that bolt to the spider? If they're "normal" (thinner than the ring) then your placement won't be affected at all.

that's exactly the point. The tabs are indeed thicker. I spoke to the manufacturer and they are 1.5mm thicker, which would, I think, place the teeth 1.5mm farther in or out.
Which doesn't sound like a lot but I thought that a fixie had to be pretty close to perfect.

A detailed photo of this chainring would be nice.

here's the best I can do for now (picture wise). you will note that they mention that it is cut from 'thick .190 material'. To look at it is is noticeably thicker.
I am talking about a middle ring so there are no pins.

http://www.blackspire.com/chain-rings/super-pro-series-road-chainrings

I know what you are saying about offset but I really don't think it's going to me a problem. If it becomes an issue, run a 1/8" chain... The wider width helps make up for small chainline issues....

On a real track bike with 120mm OLD, the chainline is 42.5mm from the centerline of the bike. It doesn't matter if it's 1/8" or 3/32" because the rings are the same thickness where they bolt onto the crank arms and the only thing that is different is that the teeth are cut slightly narrower for 3/32".

Your big problem is using a road crank which will have a chainline around 43.5mm. But that's an imaginary point between the two rings. You'll probably get the best alignment running the ring on the inside of the spider, but that won't look as good.

3/32 vs 1/8 is 1/32 of an inch difference. That part doesn't matter at all.

Fred, I still think you are worrying about nothing.. I'm looking at two bikes right now.

1. Phil 120mm hubs. 3/32 DA cog. Cranks are road cranks using a 3/32 42t road ring on the inside position. 3/32 chain. Bike is wisper quiet..

2. Dura Ace 120mm hubs. 3/32 DA cog, DA track cranks/BB with 3/32 Superbe track chainring. I'm running 1/8" chain because of slight noise when I run 3/32" chain....

All track stuff doesn't guarantee a perfect chainline..

Try your current set up and see how it works... Also remember that few drivetrains are wisper quiet from the start...With what you described, you'll ver very close if not spot on...

the spec I've seen is that chainline should be within +/- 3mm (or 1/8"), and this has worked out in my experience, bikes with chainline in that range have run quiet and smooth...sounds like you will be within those limits

that's exactly the point. The tabs are indeed thicker. I spoke to the manufacturer and they are 1.5mm thicker, which would, I think, place the teeth 1.5mm farther in or out.
Which doesn't sound like a lot but I thought that a fixie had to be pretty close to perfect.

If the ring is 1.5 mm thicker, the center of the teeth will be displaced by only .75mm, I think. As Ukiahb notes, anything within 3mm is usually fine. I think you're okay.