Wide range cassette on CX bike

sean1515 Posts: 2
edited June 2016 in Workshop
Hi, I want to convert my cyclocross bike with STI road shifters into a single 1x 36t chainring system with a 10-speed, 11-42 (or 11-40) wide range cassette for long gravel rides with steep climbs. I am trying to figure out what I will do for a rear derailleur. Will a 9-speed mountain bike derailleur work with the STI shifters and the wide-range (11-42) cassette? Can anyone recommend a 9-speed mountain derailleur (that is mid-to low range cost) that would work for me? Thanks.


  • It depends on the model of shifter. The pull ratio changes between (some) models, and the ratio needs to match between the shifter and derailleur.

    What exact model of shifter do you have? Not just the name, eg: "Ultegra" or "105", but the series number too. If you peel pack the rubber hood on the shifter, the full Shimano model number will be there.
  • Monty Dog
    Monty Dog Posts: 20,614
    Shimano changed the cable-pull actuation ratios between their 10 speed road and MTB groups i.e. 9 speed MTB mech will work with a 10-speed road STI - no need to worry about model series. Suitable mech is Shimano XT M772 medium cage -but you don't get a clutch so you'll probably want to use a narrow-wide chainring to hold the chain in place. Setting-up a 40 tooth cassette may need some tweaking too and maybe a longer B-screw or a Lindarets Goatlink adaptor.
    Make mine an Italian, with Campagnolo on the side..
  • Nick Payne
    Nick Payne Posts: 288
    My wife's bike has 10-speed XT components with an M786 RD, and I put a range extender 42t cog on the bike for a trip to the Pyrenees. I had to screw the B adjustment screw all the way in for the top jockey pulley to clear the large cog, and the curved arm that the cable clamps to is perilously close to the 42t cog when on the smallest cog on the cassette, but it's worked fine so far for almost 2000km over all sorts of terrain.