Well, the ring doesn't necessarily have to be new! But yeah, something round would be good - and I think biopace rings are 130bcd, but don't quote me on it. Also, I haven't looked back through the thread, so forgive me if it's already been covered/if you already know, but you'll need a ring that matches your chain width - so if you have bought a 3/32 cog/chain to use with the biopace, you won't be able to use a new 1/8 ring, but as I say, I'm sure you realise that already. You can of course use a 3/32 chainring with a 1/8 chain/cog - it's not ideal, but it works. Hope that helps.
I've got the wider rear cog / chain. It was just the lack of roundness I was unaware of. I've had a quick look on eBay and there's plenty to chose from. Just need to confirm pcd size.
I've got the wider rear cog / chain. It was just the lack of roundness I was unaware of. I've had a quick look on eBay and there's plenty to chose from. Just need to confirm pcd size.