Originally Posted by
Barrettscv
While the above is generally true, the current generation Tiagra 10-speed 4700 & 4703 is an exception to this rule and are not compatible with prior Shimano 10-speed components. The prior generation Tiagra 10-speed 4600 & 4603 is the most recent Shimano 10-speed group that is compatible with older 10 & 9 speed road and 9 speed mountain drivetrains.
Correct, thanks for pointing that out!
Apparently,
Tiagra 4700 has a cable pull of 2.8 mm, which is the same as Shimano 8 speed. The 4700 RD actuation ratio (cog spacing to cable pull ratio) seems the same as Shimano 11 sp which has 2.7 mm of cable pull but also proportionally closer cog spacing.
So the only RDs that will work with Tiagra 4700 shifters are:
- 4700 RDs (obviously)
- (if you're willing to sacrifice two gears, but there's no real point): Shimano 8, 9 or 10 speed (except-4700) RD with Shimano 8 speed cassette
- Shimano 5800/6800 RD with 10 speed cassette