Chainrings and chain tension

amaferanga

Unshipped the chain from my fixed bike (Specialized Singlecross) yesterday going at ~20mph downhill. Fortunately I was going in a dead straight line so I quite serenely skidded to a stop. Chain was mashed up and a real bugger to remove, but I got it all untangled eventually and walked the remaining couple of miles to work.

I know why it happened - chain too loose, but the trouble is there's a huge variation in tension as the cranks rotate. I'm about to try the Sheldon method to help even things out, but I'm none too optimistic that it'll make much of a difference. I've now tightened the chain, but it's a bit tight at its tightest point in order for it not to sag too much at the loosest point.

I'm guessing it must be the chainring that's the problem as I've tried a sprocket I had on another bike where the tension was nice and even and it makes no difference.

So can anyone recommend a chainring that's not too expensive that's more likely to be round than oval?

And does anyone else with a Singlecross have this issue?

Thanks.

pete.whelan

It may not be the chainring, but the sprocket that is the cause of the tension changes.

What make of sprocket are you using. If it a Cyclo- one, then bin it as they are just a bit of punched metal and almost always off centre.

amaferanga

Both sprockets are from Spa Cycles I think. But like I said, I tried a sprocket from another bike where the chain tension is nice and even and it was tight/slack on the Tricross.

barrybaines

How old is the chain? How well has it been looked after? And is it a reasonable one?

Many chains will wear unevenly especially if not looked after to well, and once they start to go, every little stretch from there on in will appear magnified

stickman

It's common for chainrings not to perfect circles.

amaferanga

I know its common for chainrings not to be round, hence why I asked for recommendations for a round one :roll:

PapaZita

amaferanga wrote:

recommendations for a round one

I can recommend a Thorn one from SJS. Nice and round. Made from a big thick lump of metal which I'm sure is stiff and strong but might require you to adjust your chainline by a mm or two.

PZ.

System_1

PapaZita wrote:

amaferanga wrote:

recommendations for a round one

I can recommend a Thorn one from SJS. Nice and round. Made from a big thick lump of metal which I'm sure is stiff and strong but might require you to adjust your chainline by a mm or two.

PZ.

+1. Just got one of these last week and they really are fantastic for the money. Miles better than the FSA Vero ring of cheese it replaces. I finally have consistent tension and a silent drivechain. Bliss.

Like PapaZita says, they're quite chunky and well built, with nice tall teeth so unshipping chains should be a thing of the past. Reversible too so should last twice as long. I'm very impressed and will be buying another when this one wears out.

stickman

amaferanga wrote:

I know its common for chainrings not to be round, hence why I asked for recommendations for a round one :roll:

yes, I meant that in the context of be aware that you could end up buying chainring after chainring and not find a perfectly round one. (but now one has been mentioned)