Splic

Hello everyone.

So I've been running a single speed that has inconsistent chain tension. It has been that way ever since I got it new from the LBS, and they told me it was simply due to an un-round chainring. I accepted this and was about to buy a nicer brand but stumbled upon chainring centering.

I read Sheldon's article on how to do it and attempted to do this myself. After literally about an hour of trial and error, I got too frustrated to continue. No matter how I did it I could never get it to be consistent. I tried a hundred times. I adjusted how tightly I would keep the bolts, how hard I would strike the chain and how tight the chain was at its tightest. No matter what combination of those three variables I used, I couldn't get it to center properly.

Eventually I just gave up. Is there anything that I can do? The only thing that I could think of is that maybe the chainring really is quite out of round... but I doubt that - it's a stock Truvativ and I don't think they'd let something that bad slip (but I could be wrong).

Please let me know what I'm doing wrong. This tight spot in my crank rotation is really bugging me and I'm tired of just letting it be.

Thanks,

Calvin.

Bill Kapaun

Some chain rings are "oval" by design. Shimano Bio Pace for example. I think it's probably more typical on road bikes, but my old TREK 820 has one that is stock.

https://sheldonbrown.com/biopace.html

I don't quite understand what you mean by "centered".

JanMM

Have you taken the ring off and compared it to other "round" rings? To see if the problem is the ring itself. Is the rear sprocket perfectly OK? The teeth look identical all the way around on both chainring and cog?
Centering rings is done on the synchronizer side of tandem cranks, too. I've done it a couple of times with some success but it seems to be an inexact science with a large component of trial and error.

Wordbiker

It could also be a crank with a spider that is offset.

Have you tried rotating the chainring on the bolts?

Bill Kapaun

https://www.sram.com/en/service/truva...D=1&subcatID=5

BCRider

My single has issues like this as well. I long ago gave up worrying about it. My motorcycles do just fine with a lot more slack than my single has and they don't throw chains. In fact racing motorcycles run the chain tension within the limits but on the loose side of the slackness spec. Another mountain bike single I put together some years ago had the same issue. After fretting over it and trying all the tricks to center them I just plain gave up.

On my single I look for the tightest spots as the set runs around and as long as I can easily see about 1/2 inch of slack I'm happy. That means that when it's really slack I may see as much as an inch or even 1 1/4 inch of slack when I lift up and push down on the chain at the mid point. It hasn't been any trouble at all.

roadfix

Try re-orienting the ring on the spider arm. You should definitely see a change in variance in tension....could be for the better, or worse.

roadfix

Round chainrings are usually never perfectly machined round. Same goes for crankarms. This affects chain tension when running a singlespeed or fixed drivetrain.
This is a non-issue on a derailleured bike.

Splic

I haven't tried rotating the ring, but I'll do that soon. I never even considered the spider being off... as for the rear cog, I know that's not the issue because the inconsistency is tied to the crank arm position. It's definitely not Biopace, though. I have a few of those and know not to use them on a singlespeed (even though Sheldon says it still works...?).

Anyway, thanks for all the suggestions! I'll let you know if it works.

tellyho

How about your freewheel? Does it have any wobble? Cheap Dicta freewheels have quite a bit; this could cause changes in chain tension.