70sSanO

I’ve used alternate cable routing when I switch out a 7401 RD for an M910 RD and the shifters were 7401 7 speed.

In a nutshell changing the attach point alters the distance to the RD pivot point; closer moves it more and further away moves it less.

I call it a 10% rule. It was originally a DA 7400 work around. Because the RD actuation difference between standard 1.7 and DA 1.9 was roughly 10% using the “alternate” routing moved the RD laterally about 10% more.

Since 10 speed cog spacing is 3.95mm and 9 speed is 4.35mm, using the alternate routing with a 10 speed shifter moves the RD an internet extra 10% so in theory it should work. Likewise, in theory, you could just slap an 8 speed DA 7402 RD, with a 1.9 actuation, use 10 speed shifters, and use a 9 speed cassette and no alternate routing.

In reality, I have found that you may have to tinker with the alternate routing a bit to get the best shifting. I’m guessing there is less margin of fudge or slop in the routing with closer cog spacing.

It is not something I would ever consider using unless I already had the components and didn’t want to buy the correct ones.

In my case I already had the 7 speed DA shifters (spring loaded left) and just wanted to use a RD with the capacity for a wider range freewheel.

John