MTB cassette on Road Bike with Road rear derailleur

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  • MTB cassette on Road Bike with Road rear derailleur
  • Should also mention that the correct solution would be to fit a triple but the current setup is fine for the majority of my normal riding and i cannot afford to replace the chainset and shifters!


    the top jockey wheel might interfere with the big sprocket.

    you might be able to mod it with a longer b screw.

    some of this depends on the geo of the hanger. best bet is to try it.

    and are you talking 9/ 10 speed? 10 speed isn’t that simple.

    Mister P

    A Tiagra rear mech isn’t designed to clear a 34t sprocket. Plenty of B tension should move the mech far enough out to get away with it but I would be tempted to lob a cheap 9 speed Deore mech on to make sure.


    What generation of Tiagra and what mech cage length? It will do 30T for sure but 34 is probably too much, I’d stick with 30 anyway TBH as an MTB 11-34 will give big jumps in gears which is a lot more noticeable on the road when you’re trying to maintain a consistent cadence.


    Like Mister P, Just swap out the cassette and fit a MTB mech, problem sorted.
    I have run MTB mechs on road bikes to be able to fit larger cassettes for a long time.

    Does anyone know the capacity of a Shimano Tiagra rear mech. Will be undertaking my first Dartmoor Classic 100 mile in two weeks and i’m looking for lower gears for a bit of a safety buffer..

    Currently have a compact chainset and a 28t largest rear cog which is fine for the 60-70 mile rides i have been doing recently around Dartmoor but i would really like a couple of lower gears to give me a bit of breathing room on some of the steeper climbs on the route (especially as most of my training rides take in one or two of the steep / long climbs used for the Classic and i’m nervous about tackling them all in one ride!)

    Have a spare 34t MTB cassette and a longer chain, any reason this won’t work. I’m guessing i will have to avoid big-big gear combinations.

    Many thanks

    Thanks all, hadn’t thought of clearance to the jockey wheel, will rob the rear mech from the wife’s bike and swap the cassette.

    Happy days


    My Planet X has a SRAM Rival rear mech and an 11-34 rear cassette standard from the factory – works fine!!


    Sheldon Brown’s got some useful stuff on this. Basically no such thing as an “mtb” mech or a “road” mech it’s only cage length. I’ve run an 8sppd set up with a 9spd XT mech and ancient sora shifters. Works fine and a 32 sprocket is very helpful in the winter when I’m fat and unfit (as opposed summer when just fat!)

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