my son up in Newcastle is trying to convert his bike to singlespeed.

sounds simple enough.

chain is a new SRAM PC1051

cog & spacers are from PlanetX – & says – works with 3/32 or 1/8in chain

having put the chain on the bike it looks like the pitch of either the chain or the cog are incorrect.

see attached photo – also here https://photos.app.goo.gl/HXoCIFT9I9cIt0qF2

unfortunately he does not have the old chain or cassette to compare as I swapped them a few weeks ago.

Hé has a 10 speed chain. Maybe need 8 or 9 speed.

May not be the issue but I think a 10 speed chain is too narrow.

I always use 8 speed chains.

but as I said the cog is compatible with both 3/32 or 1/8in chain

& as far as I can tell the issue appears to be pitch & as far as I know the pitch of of 8, 9, 10 & 11 speed chains are the same.

Again may not be the issue but I had a Gusset SS sprocket that had teeth that fouled on the chain as they were too long. A quick file sorted that.

Bicycle chain pitch is 1/2″. There are some very rare exceptions to this but you’re not going to stumble across them by accident.

The measurements you’ve given, 1/8″ & 3/32″ are not specifications but names really. 1/8″ being single speed chain and 3/32″ being for multiple gear systems.

As more cogs are added at the back, the chain gets narrower but the name has remained.

Try a wider chain.

thanks all.

an 8 speed chain costs naff all – even for a student – so I might as well send him off to try that.