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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 1x10 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!

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    What happens if you pull on the cable by hand rather than moving the derailer by hand? – Daniel R Hicks Oct 24 '18 at 11:43
  • Pulling the cable by hand only moves it through 7 gears. Moving the derailleur by hand moves it through 10 gears :( – Adam Jones Oct 24 '18 at 11:47
  • (I gather from the interweb that Tiagra and Deore have different pull ratios.) – Daniel R Hicks Oct 24 '18 at 11:48
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    If you can't pull the cable and go through all 10 gears then your limits screws need adjusting. – Daniel R Hicks Oct 24 '18 at 11:49
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    Is the derailleur cable damaged? I once had a badly frayed cable where the fraying was not visible because it was frayed inside the housing. It would only give me the first four gears. Had I not replaced it, it probably soon would have given me nothing. – Michael Hampton Oct 24 '18 at 15:37
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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.

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    Ah now it makes more sense! I will see if I can find another derailleur and give that a go. Thanks! – Adam Jones Oct 24 '18 at 13:42
  • PERFECT! So a specific Tiagra derailleur solved this issue. Bring on the hills! – Adam Jones Oct 30 '18 at 11:46
  • @AdamJones Glad to help. I'd appreciate it if you would mark the answer as accepted – Argenti Apparatus Oct 30 '18 at 12:31
  • I know Tiagra 4700 rear derailleur systems use the actuation ratio of Shimano's 11 speed, and this is why the 4700 is often mentioned when discussing road-mountain mixes. Anyway, I'm wondering how that affects the 4700's cassette and if that also may be a complicating factor here?? – Jeff Nov 5 '18 at 20:33
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    @Jeff 4700 uses the same sprocket spacing all other 10 speed groups. The derailleur actuation ration is lower, but the cable pulled by the shifter per click is greater, resulting is the same derailleur movement per click as other Shimano 10 speed groups. – Argenti Apparatus Nov 5 '18 at 20:45
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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)

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  • Do you think a Tiagra 10 speed rear derailleur would solve the problem? – Adam Jones Oct 24 '18 at 11:58
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    It would have to be a Tiagra 4600, and the tooth count of your cassette would have to be within the allowable range. You should also check into the comment by Daniel R Hicks as he is quite correct that the RD should move through its full range when manually pulling the cable. – Andy P Oct 24 '18 at 12:02
  • Thanks for the input and I shall check the limit screws again to see if that helps. :) – Adam Jones Oct 24 '18 at 12:43
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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/

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    This is a link-only answer. Can you summarize the salient points here? meta.stackexchange.com/questions/8231/… – Vladimir F Sep 18 '20 at 21:06
  • Link-only answers aren't useful when the remote site vanishes, or reorganises. Its better to duplicate the main points into your answer, and leave the link as further information. That way the answer stands by itself in the future. Check out the tour for more info on how SE is a bit different. – Criggie♦ Sep 18 '20 at 23:08

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