Mixing ultegra with dore set up

[1982john]

Due to a crash (not my fault), I need to replace the rear derailer on my road bike which is a standard ultegra set up.

Instead of replacing like for like can I switch to the DEORE M8000 XT 11SPEED and a 11-40 11 speed cassette without needing to change or order other specialist parts? Other than a new chain.

Would an lbs likely install this for me or would they not mess about with this sort of stuff.

Thanks

[nsew]

Can’t mix newer Shimano road and mtb. Just replace the derailleur.

[AndyA]

Shimano GRX RD-RX812-GS rear mechs allow a 42t max rear sprocket and are compatible with road 11 speed shifters

[1982john]

Shimano GRX RD-RX812-GS rear mechs allow a 42t max rear sprocket and are compatible with road 11 speed shifters

So I could add this derailer Shimano GRX RD-RX810 2x11
https://www.bike-discount.de/en/buy/shi ... eur-847411

And then any sprocket - brand doesn't matter - up to 42t?

[1982john]

Using a 50/34 upfront if that matters....

[AndyA]

Shimano GRX RD-RX812-GS rear mechs allow a 42t max rear sprocket and are compatible with road 11 speed shifters

So I could add this derailer Shimano GRX RD-RX810 2x11
https://www.bike-discount.de/en/buy/shi ... eur-847411

And then any sprocket - brand doesn't matter - up to 42t?

Nah, its got to be the rd-rx812 variant, the link has the rd-rx810 which has a max 34t I think. I'm fairly sure spacing is consistent across brands of 11 speed cassettes, but no reason not to use Shimano SLX in my view

[Brucey]

Would an lbs likely install this for me or would they not mess about with this sort of stuff.

depends on the LBS.

As noted above a MTB RD won't work with your shifters, but the GRX RD will.

FWIW the pitch (spacing) of 11s sprockets varies slightly with different makes and (some say) varies slightly between 'road' 11s and MTB 11s even if you stick with shimano, with 11s MTB cassettes having a slightly wider pitch (which I have always supposed is to make room for more mud in the workings...?). But this a) may not matter much in practice (the difference is small and folk do mix and match) and b) I'm not 100% sure if the cassettes which are in the GRX groupset fall into one category or the other, (but logically, they ought to match the 'road' shifter/GRX mech combination perfectly).

There is also the matter of freehub body length; 'road' 11s freehub bodies and cassettes are (where they fit together, somewhat couterintuitively) longer than MTB 11s cassettes and freehub bodies. This means that you can't fit a road 11s cassette to a MTB freehub body and you usually need a spacer if you fit a MTB cassette to a 'road' 11s freehub body. It also means that you can fit a MTB 11s cassette to a 10s 'road' freehub body. Just to confuse the issue further, Shimano also make a few cassettes which are 'road' 11s cassettes but have short bodies like MTB cassettes so they fit 10s freehub bodies too.

Needless to say you will need a new, longer, chain, even if the old one is brand new.

cheers

[AndyA]

LBS is much more likely to want to do this if you buy the parts from them too!