Originally Posted by
Grand Bois
The cable pull is not the same, but it's close enough. They sold 8 speed shifters as 7/8 speed when they first came out. I've been using Ultegra 8 speed shifters on a 7 speed cassette for years without ever missing a shift.
Nope, wrong.
7-speed was sold as 6/7-speed when Shimano first offered indexing bar-ends. (There was a little plastic shim to change the cable pull for 6-speed.) For eight-speed, there were 2 versions: Dura-Ace and everything else. 9-speed was standard across the board, and there's been 2 versions of 10-speed: one with friction option, 1 without.
I tried doing the opposite: using 7-speed shifters on an 8-speed cassette. I couldn't get it to shift correctly across the cassette. It's probably got something to do with free play and shifting tolerances.