Originally Posted by
70sSanO
Actually chain wrap on a correctly sized chain only effects the small-small. Maybe the 1st and 2nd position depending on how far over capacity someone goes.
On the large large the wrap is “closer” to zero, depending on the extension of the cage, since the chain is “almost” going straight from the cog to the chainring.
On the small-small the derailleur cage folds back on the derailleur until the chain sags.
John
True... although if your chain goes slack enough to drag on the front derailleur cage, I could see bad things happening if it was slack enough to wrap itself up in the derailleur or seat tube under load. I wouldn't have a problem doing this on my own bike, because I'd know that it was there and would never ride in those gears, but I hesitate to suggest it to anyone else. Especially if someone other than the builder is going to be riding the bike.
A little bit beyond specs with a proven combo, no problem, as the specs are very conservative. Once you get past a couple of teeth beyond spec, I start getting nervous. (Especially because tolerances stack. 2 extra teeth of big cog, a couple more teeth of chainwrap, and then a few extra teeth of chainring difference, and you can end up with combos that are 6-8 teeth too much, and then it can suddenly become a Very Bad Thing. ) Locking up your drivetrain at speed tends to really, really suck.
--Shannon