Deore XT M8000 11 spd and 105 (5800) 11 spd cassette compatibility?

[uart]

A friend currently has a 1x11 speed setup on his MTB. I think it's probably a Deore XT M8000 cassette and it's absolutely massive (11-46T). However he mostly rides on the road , and doesn't need the real low gears. So he wants to change the cassette for something a little less outrageous. I was going to suggest a 105 (5800) 11 spd in 11-32T, but just wondering if there are any compatibility issues.

[Duck!]

If it's on a MTB hub, it won't fit. MTB 11-sp cassettes are dished in the back to enable them to fit on a regular 8/9/10-sp. hub. The tightest cassette that will fit is an Ultergra-level HG800 or soon-to-be-released 105-level HG700 11-34, as these cassettes are also shaped to fit the standard freewheel body. Road cassettes of 11-32 or less need a longer (by 1.85mm) freewheel body.

[uart]

If it's on a MTB hub, it won't fit. MTB 11-sp cassettes are dished in the back to enable them to fit on a regular 8/9/10-sp. hub. The tightest cassette that will fit is an Ultergra-level HG800 or soon-to-be-released 105-level HG700 11-34, as these cassettes are also shaped to fit the standard freewheel body. Road cassettes of 11-32 or less need a longer (by 1.85mm) freewheel body.

Ok thanks or the info Duck.

So if he doesn't need the 11 speed, would a standard 10 speed 105 cassette fit it?

[Duck!]

It would fit the hub, but wouldn't work with 11-sp. shifter because the index spacing is wrong.

The second consideration is that the MTB derailleurs are designed with massive cassettes in mind; as they shift in to the lower gears, the body swings down as well to ensure clearance, but with tighter cassettes this means a lot more clearance than is ideal. This can result in the chain flexing more rather than shifting smoothly, and gets worse as the chain wears.

I'd suggest go for the 11-34 cassette and if it's still not tall enough, change to a larger chainring. Or change crank & add a front derailleur & shifter and go 3x....