My 9spd drivetrain is worn out, and I’m tempted to go to a 2×11 speed set-up.
The 11spd XT groupset has some strange ratios – only 10t difference in chainring size, but the smallest cassette is 11-40. This seams to have a big range available at the the back, and a lot of overlap in the two sprockets at the front.

I already have an XT M785 chainset with 24t & and 38t rings, and I think if this was matched to a close ratio 11spd cassette (say 11-36) then I’d have my ideal set-up.

I know that 11spd road cassettes use a different, longer freehub body. Is there a 6-bolt disc compatible hub with 135mm OLD that means I could use one on an MTB? Would this work with MTB shifters and mech (probably XT)?

Alternatively, is there an narrow range XD driver cassette compatible with an MTB wheel?

Is there a 6-bolt disc compatible hub with 135mm OLD that means I could use one on an MTB?

Yes, there are plenty. Hope for instance.

Would this work with MTB shifters and mech (probably XT)?

Yes

I know that 11spd road cassettes use a different, longer freehub body. Is there a 6-bolt disc compatible hub with 135mm OLD that means I could use one on an MTB? Would this work with MTB shifters and mech (probably XT)?

Road disc hubs are 135 OLN. I have a 6-bolt Novatec on mine.

I’m going to say why not just go 1×11? If you don’t feel you need any more range than a double with 11-36 offers, then a 1×11 with a 10-42 or a 10-44 is going to give you plenty enough gears but with a lot less weight and added simplicity!

If you don’t feel you need any more range than a double with 11-36 offers, then a 1×11 with a 10-42 or a 10-44 is going to give you plenty enough gears but with a lot less weight and added simplicity!

And annoying, larger jumps between gears and aluminium large sprocket to wear out quickly.

mboy
32t x 11-42t 1x11spd has a range of 282%.
24-38t x 11-32t 2x9spd has a range of 361%.
The steps between gears are similar, but the range is quite different.

Now whether I need the top end of the range is debatable, I didn’t miss it when I ran 22-32t x 11-32t 2x9spd, which has a range 323%.

Will a 42t aluminium rear sprocket wear out much more than the front sprocket, which is also aluminium?

With shimano 11 spd, i don’t think there is compatibility to use mtb shifter and mech with a 11 spd road cassette, nor an 11spd mtb shifter with a road mech. There’s not a lot of cross-compatibility between them unfortunately

I know that 11spd road cassettes use a different, longer freehub body

because the gap between cogs is different from mtb versions, presumably ?

(i.e. what Dr Faustus says ^ 😳 )

because the gap between cogs is different from mtb versions, presumably ?

No. It’s because Shimano with mtb have fitted 11 cogs on a 10spd freehub by offsetting the largest sprocket towards the spokes (probably explained badly!)

so the pitch is the same then SimonD ?

(so that just some fiddling with limit screws might allow swappage ?)

Yes, the massive sprockets on the MTB cassettes overlap the spoke flange. To get smaller sprockets needs a longer freehub.

so the pitch is the same then SimonD ?

Yes

32t x 11-42t 1x11spd has a range of 282%.
24-38t x 11-32t 2x9spd has a range of 361%

I’m not sure how you are working that out and I don’t have a calculator handy but I’m sure it’s not right . 11-42 is just shy of 400% .

I’m not sure how you are working that out and I don’t have a calculator handy but I’m sure it’s not right . 11-42 is just shy of 400% .

me neither – unless google works things out weirdly, I’m getting more like 460% for the double and 380% for the single (although the differences between the 2 “wrong” and the 2 “right” figures are probably similar, somehow)

I recently rebuilt a a wheel for my CX bike using an XT M8000 11 sped hub, with the intention of using it with a 11-32 Ultegra 11 speed cassette, oop’s the road cassette is too long.
I’ve now rebuilt the wheel using a Hope Pro 4 hub and the cassette fits a treat.

Hmmm, maybe my calcs are following a dodgy method:

32t x 42t = 0.76 turns of wheel per turn of crank.
32t x 11t = 2.91 turns of wheel per turn of crank.
2.91/0.76 = 282%

Is that the way to do it?

2.91/0.76 = 282%

That is your error 🙂

Just divide 42 by 11

Ok, math corrected and the wider range cassette put in:

34t x 11-46t 1x11spd has a range of 418%.
24-38t x 11-32t 2x9spd has a range of 423%.

Looks like 1×11 might be the choice.

11-46t

do **** off ! surely that doesn’t exist, does it ? 😆

24-38t x 11-32t 2x9spd has a range of 418%

Top gear then = 38/11 (=3.45) and bottom = 24/32 (=0.75)

top / bottom = 3.45 / 0.75 = 4.6

or a meringue ?

scaredypants – yes, i was looking at the wrong column on my spreadsheet. Not a good day for figures for me 🙁

Corrected:

34t x 11-46t 1x11spd has a range of 418%.
22-32t x 11-32t 2x9spd has a range of 423%. (my old set-up)
24-38t x 11-32t 2x9spd has a range of 461%. (my current set-up)

and yes:
http://bike.shimano.com/content/sac-bike/en/home/components11/mountain/deore-xt-m8000/cs-m8000.html