i recently bought a smaller rear cog for my dirt jumper and since the cog is smaller it rubs against the little wall on the right of the cog. if i were to move the cog more inwards (to the left) technically the chain wouldn’t rub anymore but would the chain be out of line from the chain ring? or would it be fine?
if i moved it over it would only be about 3mm out of line.
i hope i didn’t make this too confusing for you guys to understand lol i didn’t know how to word it better.
by cheese_deliverer35
2 Comments
3mm wouldn’t be the end of the world, but it would wear everything faster. I would think it would only take 1mm or less. What chain are you using?
If you know the chainline you have is perfect and worth preserving, the first step from here is determining whether you’ll still have acceptable thread engagement on the lockring (or another lockring) if you just add cassette spacer under it. It looks like this may be possible here because it appears there’s even some FHB poking out from the lockring.
If you don’t actually know (beyond eyeballing) how good the existing chainline is, step one is take the chainline measurements to see how bad it actually is. For the front, that’s the distance from the tooth centerline to the ST plus half the diameter of the ST. For the back it’s half the OLD minus the distance from the dropout to the tooth centerline. Once you have the numbers you can see what you’re working with. Most bikes aren’t perfect to start with, plus this isn’t the stock cog and that can make a difference as well. If you did shuffle spacers to move the cog in, there’s also the possiblity of tuning the sprocket/chainring in to match with some cranks.
The consequences of bad chainline depend a lot on the chain. Singlespeed chains in general, and especially chunkier BMX chains, do run smoother with very good chainline. If it’s a 3/32 cog and sprocket and a derailleur chain, 3mm is irrelevant.