Originally Posted by
feejer
hmm. What I don’t understand is that from what I have read, derailleurs don’t have a pull ratio, the pull ratio is controlled by the shifter. The DR only has a range of motion, and the indexing within that range of motion is set by the shifter. So, if a DR has the appropriate range of motion, how can there be a road and mtn difference in a derailleur? The only way I can think of if a shifter doesn’t function with a DR is if the crankset doesn’t match up in some way. Confusing stuff.
Good tip on the cable, I would not have thought of that.
Both derailers and shifters have a pull ratio (the ratio between how much the cable moves and how much the derailer moves). The indexing is built into the shifter (that is, the number of clicks and how far those clicks are apart). As long as the shifter and derailer have the same pull ratio, the indexing will work. For example, Shimano 7- and 8-speed rear derailers have the same pull ratio, and the cog spacing on 7- and 8-speed cassettes is so close (
1.85mm v. 1.8mm) that 8-speed shifters work with 7-speed derailers and cassettes.
One other advantage of bar-end shifters is that the front shift usually isn't indexed, so it will work with pretty much any front derailer and crankset, 2x or 3x, regardless of chainring spacing or pull ratio.