Rear Derailleur. Will I be Shunned?

si_c

Veteran
Location
Wirral
Do it, it'll work fine.

Shimano's new road groupsets have taken a lot of their design from their MTB ones anyway so you can pretend you are a trendsetter.
 

Venod

Eh up
Location
Yorkshire
Perhaps I could have got away with it, but the original rear mech had a 33 tooth capacity and the bike now has a 38 tooth range.
You can push the capacity and sprocket size a little bit, 32t is supposed to be max for the derailleur I have, but with the latest 105 medium cage will take a 34t and probably a bit larger at a push.
 

wafter

Über Member
Location
Oxford
Isn't there some compatability issue (cable pull ratios..?) that prevents the use of more modern Shimano MTB mechs with road shifters...?
 

freiston

Senior Member
Location
Coventry
It must be something to do with yellow bikes: back in the early 80s, I swapped out the Shimano 600 short cage RD on my yellow bike for a Suntour VGT long cage RD (after changing the block for something bigger). I was shunned before and after the swap so I cannot help with your query 😉
 

ColinJ

Puzzle game developer
Isn't there some compatability issue (cable pull ratios..?) that prevents the use of more modern Shimano MTB mechs with road shifters...?
I was told that my 10-speed Tiagra shifters would work well with a 9-speed XT rear mech and that turned out to be true. Shifting doesn't feel 100% accurate in that there is occasionally a slight hesitation going up onto a couple of the bigger sprockets but when that happens a very slight additional 'nudge' with the gear shift lever is enough to help the chain climb up to the next sprocket. Once the chain has settled on the new sprocket, it stays there. I've got used to it now and simply push the lever slightly beyond the click-stop and then release it.

PS It is possible to adjust the action so there isn't that hesitation, but the problem then is that the chain sometimes doesn't drop down onto smaller sprockets when shifting in the opposite direction. It works better the way I described above. Most shifts just work without any extra encouragement, but it isn't a big deal to push slightly further on the shift lever when that is needed.
 
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freiston

Senior Member
Location
Coventry
I was told that my 10-speed Tiagra shifters would work well with a 9-speed XT rear mech and that turned out to be true. Shifting doesn't feel 100% accurate in that there is occasionally a slight hesitation going up onto a couple of the bigger sprockets but when that happens a very slight additional 'nudge' with the gear shift lever is enough to help the chain climb up to the next sprocket. Once the chain has settled on the new sprocket, it stays there. I've got used to it now and simply push the lever slightly beyond the click-stop and then release it.

PS It is possible to adjust the action so there isn't that hesitation, but the problem then is that the chain sometimes doesn't drop down onto smaller sprockets when shifting in the opposite direction. It works better the way I described above. Most shifts just work without any extra encouragement, but it isn't a big deal to push slightly further on the shift lever when that is needed.
From the link I posted above, in relation to Shimano 6, 7, 8 & 9 speed rear mechs (both road and MTB):
BikeGremlin said:
Rear shift ratio is 1.7, that is for 1 mm of cable pull/release, RD is moved left/right by 1.7 mm. Shimano calls this 2:1 ratio for marketing reasons.

All these RDs are compatible and any 6 to 9 speed RD will work perfectly with either 6, 7, 8 or 9 speed shifter. Regardless whether it’s a MTB, or road shifter, or RD. They are also compatible with Shimano 10 speed road shifters, except the Tiagra 4700 series.
So I suppose it depends if your 10-speed Tiagra shifters are 4600 series or 4700 series.

Edit: From that linked artice, I understand that the 4700 series has a pull ratio of "around 1.4" and so is compatible with the following Shimano mechs - 11 speed road mechs, 10 speed Tiagra 4700 mechs and 10 speed GRX mechs, and Campagnolo "Old" mechs.
 
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