Following on from the excellent post "The Definitive (But Wildly Inaccurate) Guide to Brake Cable Pull Ratios" I thought I'd do the same for gear cable but as gears are indexed (usually) it is a bit easier as the vagaries of lever size & throw are eliminated.
I started this as I’ve been putting together a 10 spd Campy shifter-Shimano geared bike (and I think I’ve come up with a simple, cheap fool-proof solution and I’ll post the info soon) so I needed to get a handle on the various shifters and how much they pull the cable.
First, there seems to a lot of misinformation and rumor about gear cable pull, not the least is the variation on the “campy cable pull is not linear but Shimano is..” see for example this (otherwise great) post
Art's Cyclery Blog » Science Behind the Magic | Drivetrain Compatibility
where it says “Campagnolo Ergo levers pull 2.5mm of cable five times, 3mm twice and 3.5mm twice” and this data seems to have been accepted as gospel and has spread far and wide.
But this bothered me. Why, if the derailleur is sweeping in a circular arc would it not be a more constant increase? And why would only Campy use non-linear movement and not Shimano, Sram et al? Surely their derailleurs all use similar geometry and would require non-linear pull or else they would end up moving the derailleur less and less with each shift.
So I measured my only Shimano shifter I have – a 9spd Durace downtube which would match any Shim 9spd shifter and if it holds for 9 spd, it would most certainly for 10 and 11 too. This I compared to my Campy 10 spd shifter. I measured Low gear (biggest cog) to high (smallest cog) last and did so by wrapping some tape around the cable and using digital calipers to measure the gap, resetting the caliper to zero after each shift.
The results are graphed below.
* Note: The first and last gear change is probably more influenced by the limit stops so can probably be ignored.
As you can see there is a clear downward trend for both levers. And, for the Campy, the average of shifts 1-9 is 2.81mm which closely matches the 2.8 given by Campagnolo. For the Shimano it’s 2.46 which is close to the advertised 2.5. This indicates my measurements are within reason. I suspect the reason the values jump around is more due to manufacturing intolerance as the detent springs sit in very precise indents and slight imperfections here could cause imprecise movement. My Campy lever was also brand new vs the Shimano which was older and on my beater bike so grit may also be an cause of its more random swings.
If anyone else has Sram or 11 spd, it would be great to see how they pull but I suspect it will be similar.