Originally Posted by
Retro Grouch
I'm from Missouri. You'll have to explain that one to me.
FWIW, I'm a devotee of the big/big school of chain sizing and I don't care how far forward it pulls the derailleur arm. That's how it's designed to work.
Although 4 teeth is 2 inches of sprocket circumference, a sprocket that is four teeth larger requires only 1 inch more chain length since the chain only wraps half way around the sprocket. If you use the big/big method with a 12-23 and later want to use a 12-27, the chain will be 1-inch too short. If the little/little method was used, the chain would be 1 inch longer and work with either cassette, or even an 11-21.
As an interesting note, I've used the same 53 inch chain length on my LOOk frames, with a 53/39/28 triple crank, a 53/39 double or 50/34 compact. With this length and a medium cage RD, any Campy road cassette except a 13-29 could be used. That requires 1 inch more chain length (and a long cage RD with the triple).