When to replace a sprocket

[Tom B]

(reposting this as it seems to be off the radar elsewhere)

With derailleur systems a common reckoning says that more than a certain amount of chain stretch (1/8") means that the cassette needs replacing as well as the chain. Can one apply a similar reckoning to a fixed drivetrain? LBS thinks so.

Given that fixed sprockets can be higher or lower quality, steel or alloy, 1/8" or 3/32" and do not have the ramps / differently-shaped teeth of cassette sprockets, I feel less sure. Is there a ready way to tell when a fixed sprocket needs replacing?

[Simon Galgut]

Somewhat earlier than I did last time on the Rohloff.  Shark's teeth and three teeth MIA. A new chain also felt rough and made a horrible noise under pressure.

[iakobski]

No. You need to replace the cassette when it's worn a bit because a new chain may jump. That won't happen on a single-speed setup unless your chain is stupidly slack, so it's not the same rule of thumb.

You can keep using a sprocket until it looks very worn, as long as the chain runs smoothly don't bother changing it.

[rogerzilla]

You can run the whole lot into the ground and then change the sprocket, chain and possibly chainring - but it will have gone on working aeons longer than a derailleur system - or just change your chain regularly and change the sprocket when it first grumbles with a new chain.

[TimO]

On my singlespeed it's getting a bit noisy, so I really need to replace the chain, sprocket, and chainring, but if I could live with the clicking under pressure, it would go on working for a while longer.

I've used it for something like 6500 miles, mostly commuting, and didn't really oil it as often as I should have.

[teethgrinder]

I try to keep my chain in good condition and replace it before it gets badly worn, so that it doesn't wear the sprocket and chainring as fast. That meas that everything stays compatable if I use a different sized sprocket or chainring. But if I wear the chain over the threshold and the sprocket starts to wear, I run the whole lot until it gets rough and the teeth on the sprocket and chainring are very worn. Then replace the lot.