Bicycles Asked by Adam Jones on October 7, 2020
OK, so I have a rough and ready road bike (Planet X London Road) that is not shifting right….
It is running:
Shimano Tiagra 4600 Shifters (3 x 10) but running it a 1×10 with one front chainring
Shimano Deore RD-M610 (RDM610SGSL) 10 Speed Derailleur
Shimano Tiagra 4700 10 speed rear cassette
It shifts through the first 7 gears without issue but uses all 10 clicks to get there. It does not reach up to the last/top 3 gears (even though it will when I move the derailleur manually by hand).
I have tried with another Tiagra road shifter and it produced the same results.
I have set up the high/low limit screws correctly, tightened the cable multiple times and set the jockey wheel height correctly. No difference.
I have connected a MTB 10 speed shimano thumb shifter and it goes through all 10 gears perfectly.
Any ideas? It is driving me quite mad!
I believe your problem is a mismatch of cable pull ratios between the shifter and derailleur.
The rear derailleur actuation ratio is how far the shifter cage moves for a unit length of cable pulled. The amount of cable a shifter needs to pull for each gear shift is determined by the actuation ratio and the spacing between the cassette sprockets.
Generally, Shimano road 10 speeds and below and mountain 9 speeds and below used the same pull ratio (the exception being Tiagra 4700). Road 11 speed and MTB 10 and 11 speeds require more cable to be pulled for each gear shift as it makes it easier to get the accuracy required out of the shifters to index more closely spaced sprockets.
Because you have a 10 speed MTB shifter it's mismatched with the road derailleur. Presumably you got the MTB derailleur because you wanted to be able to run a wide range cassette, but you are using a road cassette anyway. Simplest fix is to get any Shimano 10 or MTB 9 speed derailleur (but not Tiagra 4700) that can accommodate the largest cassette sprocket you want to run.
Correct answer by Argenti Apparatus on October 7, 2020
You need a shimano 9 speed MTB mech to work with shimano 10 speed road shifters.
(The exception to the rule is Tiagra 4700 shifters)
Answered by Andy P on October 7, 2020
You already got great answers here is some other good reading. http://blog.artscyclery.com/science-behind-the-magic/science-behind-the-magic-drivetrain-compatibility/
Answered by Jim on October 7, 2020
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