Join Date: Feb 2004
Location: St Peters, Missouri
Bikes: Rans Rockst (Retro rocket) Rans Enduro Sport (Retro racket) Catrike 559, Merin Bear Valley (beater bike).
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Originally Posted by VeganRider
Changed my chain and rear cassette and now Im thinking maybe the chain should be shorter? The new cassette is 12/25 the old was 12/27. Is there a rule of thumb I could go by say for instance if the bike is in 3rd gear what position the wheels on the rear derailleur would be in? Figure there has to be a method. thanks......
I'd leave well enough alone.
The big issue with chain length is that your chain is long enough to safely cover the big/big combination. If it's not and you inadvertantly shift into that combination, you'll twist your rear derailleur cage into the spokes. That can be a hyper expensive mistake not to mention a long walk home (if you're able).
A less serious potential problem is when your chain is too long. If your rear derailleur doesn't have adequate chain slack take up capability, your chain will go slack in the little/little combination and bounce off of either the front or rear sprocket.
If you had enough slack take up with a 12/27, you'll have enough with a 12/25 too. If your chain was long enough for a 12/27, it'll be long enough for a 12/25 too.