Or only single ring up front?
Cheers

Yes you can, providing the rear mech can deal with the range.

what groupset is it? I think XT is max 40T for 2×11. You also need to consider the size of your front chainrings

Cheers.
Mechs I have are either long cage XT or medium SLX, what’s the biggest size chainring I can run?

Forgot to say it’s 10 speed gears if anyone can advise on size chainrings I can use with either 40 or 42 on the back ta

I’ve run a 40t on the back with 34 middle ring and XT, SLX, and Zee mechs. Long or medium. The Zee was less happy, but xt and SLX no problems.

You may need to experiment with the rings that you have available as it is unlikely that many people have tried combining an 11-40 (or 42) with 2 rings. Try a search of forums.mtbr.com there could be info there.

The long cage mech is probably your best bet as it has the ability to accommodate more slack in the chain created by the different size rings. The closer in size the rings are the better chance you have that it will work.

It would be worth fitting a Wolf Tooth hanger things (can’t recall the proper name), too.

Not much help, but something I’ve pondered myself in the past.

Yes.

I ran a 10-42 with 28/38 up front. Xx1 rear mech. Chain length wouldn’t work with big/big very well but it coped with more than advertised.

I did have 22 gears but the more extreme chain crossing wasn’t that good

Interesting. What cranks and rings were you using? Was it a tripe with 2 rings, or a double?

Edit:

I think what I’m really asking is, did you use 10 speed rings with 11 speed chain?

I am still using….
10speed SLX triple, with Race Face 30t NW ring and little used granny ring….
XT 10speed rear mech.
10 speed chain.
10 speed cassette with Hope Expander.

Works fine, although my ‘Granny ring’ is something i don’t use very often. In fact, so infrequently, i don’t even have a front mech. I just kick it onto the granny on the very rare occasions that i encounter some sort of unmanageably steep climb. Then whilst stopped, popping my lungs back in at the top of said climb, i just put the chain back onto the 30t with my fingers (or foot).

It’s not very Enduro, but works for me.

Cheers guys more food for thought.