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I’m working on a mate’s bike Monday and he’s switching from a 36 tooth chainring to a 38. How many extra links do you reckon I will need ? 2 or more ? Obviously it’s a brand new chain, cassette et all.
You may not need any - certainly no more than one. Its a complex geometry thing that I don't really grasp but 2 teeth extra does not equal two links extra
not that complex - roughly speaking the chain goes round half the chainring. So a 2T increase on a chainring means 1T extra is actually engaged which is a 1/2 link. But if you're using a normal chain you can't do 1/2 a link, it'll be a full link (inner and outer) which is 2T worth
Assuming it isn't a ss with a half link already to make it exactly the right size, chances are that to be long enough the original will be on the side of caution and I suspect that an extra 1T on half the chainring will be OK. If not - then one pair will certainly be enough.
If you're fitting a new chain, just follow the manufacturer's instructions on chain length rather than basing it on the old chain. It used to be to wrap the chain around the big ring and big sprocket and add one full link (with the suspension worked through the range of travel). I haven't fitted 12 speed, but I gather that it's a bit more finicky, so just see what the manufacturer recommends.
Like TJ says, rationally it's 2 but in practice it depends if it was right before.
People like formulas and rules for setting chain length, it's all bollocks, just undo the shock and cycle it through the suspension travel. Guaranteed to be right, dead easy, why do anything else?
<p>Cheers guys. Yeah I never wanted to go away from 8 speed when chain length was easy to set up - and a lot cheaper. If it was mine I’d just add the links and change if needed but my mate can ride a bike but that’s it ! Just trying to make my life easier. I’ll set it up then give it a ride. What could possibly go wrong ??</p>