Ineos are running XTR for Roubaix it looks like.
But using a road cassette?
Iām really curious if it works with a road cassette without any further modification (asking for a friendā¦)
1 Like
Maybe @Dave_Rome can let us now on geek warning 
Short answer is no.
Road and MTB are designed for different cassette geometries. Even the mid cage XTR is too long for for a typical road cassette (eg. an 11-34). The upper pulley will sit very far away from the cogs and lead to some very sloppy shifting.
Road and MTB are also designed for different chain lines (45 vs 55mm) and chain angles (boost vs non-boost), though you could probably spacer your way around that.
Road and MTB have a slightly different shift ratio that cumulates across the range (ie. How far does one click move the chain over).
As mentioned in my original comments, a system/combination that gets around those differences is kick ass and very common in gravel and on the road (see Ineos) these days. I personally have extensive experience with XTR Di2 (9250) SGS, with 12 speed MTB cassettes (native/non-native, 9-45 and 10-51), paired with GRX Di2 wireless shifters and a single chain ring. I swap cassettes depending on topography and/or course design. The 9-45 allows for very efficient chain lines and lovely, almost linear gaps around the mid block for flat-ish courses for example. The 10-51 is much more ājumpyā around the mid section.
Hope that helps.
Last year at Spoken - when wireless XTR was really new - one of the Shimano guys had the long cage RD and 10-51 on his gravel bike and said it was fine. IME Shimano RDs will always work with a larger or smaller casette than the specs say, but Iāve no idea how much tolerance there is with this generation; Iāve not had a chance to experiment. (I wouldnāt be at all surprised if 11-34/36 worked fine, but who knows?)
The one thing Iām confident about is that the specs only ever list things in the same group as compatible, which is untrue and unhelpful.
Really interested how Ineos, Total Energies etc. did this at Roubaix. Looks like a road 11-34/36 cassette. Would be a great setup for crits, but 10-45 and a big chainring is a safer bet I guess, I just hate the 10-12 jump.
1 Like
The 9-45 cassette is 9, 11, 13, 15, 17 and so on. If you mashed it together with the 10-45 cassette you could have single tooth gaps from 10 (or 9, if it fits on your bike) up to 19. Requires buying two cassettes, but XT level isnāt all that expensive.
Before anyone buys anything to sttempt this I suggest they look at the EVs (Exploded Views) of the casettes at si.shimano.com - itās almost certain to be impossible, but even if it was none of the shift ramps would line up. Most of the larger cogs are on a spider too, so thereād be a horrendous gap at some point, to go along with the terrible shifting.
1 Like
That is a good point about the ramps not lining up, I didnāt think about that!
The largest loose MS cog looks to be 19T after which there are large spiders 21-45T), so while it might be possible to cobble together a 9-19 cassette somehow, I think thatād be it. An 11-23 or 12-25 11 speed cassette plus an Ultegra RX RD would make more sense, assuming no low gears are needed. And no, the RX RD isnt rated for <11-28, but works fine with 11-40 & 2x so should be fine. (There are third party close ratio 12 speed cassettes too, for instance 11-26 from E. Dubied, Recon, etc.)