Bicycle Mechanics - How to replace a dished chainring?

I have a bike with a single 44T 104 BCD Aluminum chainring on a Sturmey Archer crank (see pic). The chainring is 2mm thick and is dished by 2.1mm (see pic). The bike came with two chainring guards, that are also dished to have equal spacing from the chainring.

I would like to replace the 44T chainring with a 40T one but am not sure about the dishing. The chainrings I could find do not mention anything about dishing (e.g. http://amzn.com/B001IOPHIW).

Any suggestion where to find a dished chainring? If not, should I use spacers on the outer side (and live with larger spacing between the chainring and the inn130703130704er guard)?

Thanks,

Kam

Spacers are likely your best bet, at least for a non-ramped/pinned chainring. I know some Shimano chainrings are dished but they are not single-speed specific rings. Don't forget you'll need to make sure your chainring bolts are long enough to work with the spacers.

Usually, thin chainrings are dished that way to compensate for their thinness and put the teeth where they'd be if they were standard alloy chainrings, which are thicker, and whose teeth are centered outboard from the inner face.

If you replace it with an alloy ring, there's a high probability that you won't need any spacers, the "dish" being already built in. Otherwise if it's still off by 1-2mm don't sweat it, you're still well within working tolerances for chainline.

One note, there's a possibility that you'll need a new chainring bolt set. If you don't get decent thread engagement reusing your bolt set, replace it.

Looking closer at your drawing, FBinNY is likely correct about the dishing. Machined aluminum chainrings will be thicker at the mounting points and then machined down at the teeth. Your chainring was likely stamped and the offset was added to correct the geometry and/or stiffen the ring.

Thanks everybody for the feedback.

Is there a difference between a chainrings that are intended for a single chainring applications and the ones the are intended to be part of a dual or triple chainring set?

This one for example http://amzn.com/B001IOPHIW is specified as 'position: single'. What does it mean?

Kam

Thanks everybody for the feedback.

Is there a difference between a chainrings that are intended for a single chainring applications and the ones the are intended to be part of a dual or triple chainring set?

This one for example http://amzn.com/B001IOPHIW is specified as 'position: single'. What does it mean?

Kam

Most better chainrings intended for double or triple today have shifting gates. These are the cut down or skipped teeth, which along with ramps or pins are intended to improve FD performance.

For single speed (or 1x?) these gates are undesireable because there's no benefit to you, and they can be the cause of chains derailling. Look for a ring designated for single use, or any old fashioned (cheap) ring intended for mutiple use, but without the gates.

There are 3 different types of chainrings (someone correct me if I'm wrong though as I'm not that well versed in single speed/track tech):

track (designed for 1/8" track chains)
flat, single/multiple speed (3/32" chain)
ramped/pinned multiple speed (3/32" chain)

Given the measurement you provided earlier, you are not currently using a track chainring so that's out of the equation. That leaves you with the last two options either of which will work for your intended application. Because you won't be shifting up front, there is no need for a ramped/pinned chainring so any chainring described as single speed or just "flat" will work for your application.