This seems like the way to go. I’m running x2 9sp atm, which is great..but I’d like to loose the front mech.

I assume it’s like the old roadie 9sp to 10sp – 10sp will fit/work on a 9sp cassette with the shim?

No need for a shim behind the cassette on MTB 10 speed- road and MTB 10 speed aren’t interchangeable.

It won’t work. The cassettes are the same width and the ratios are all different. To upgrade you need a new cassette, chain, mech and shifter. And possibly a new chainring although probably not.

Sorry, didn’t explain that well at all. I didn’t plan to use a road cassette on an MTB freehub. On my old road bike, (9sp) I upgrade to 10sp drive train. The 10sp could be used on the 9sp freehub with a shim behind it.

I was wondering if the same method applied to MTB, that one could use a 10sp mtb cassette on a 9sp MTB freehub.

But they won’t fit, would this be correct? I understand the shifter and other bits.

Thanks for getting back, sorry about the confusion

I was wondering if the same method applied to MTB, that one could use a 10sp mtb cassette on a 9sp MTB freehub.

You can, no shim required.

Unlike on the road though you will need a new rear mech (and shifter and chain as above).