I’m searching for options for running a 2 x 9 with M970 XTR cranks on say a 40 / 28. Has anyone done this ?

No, but run a 36/22 on 970’s, and had a 36/24 on there. Have a look at TA Chinook chainrings, SJS and others sell them.

You should be able to get 40 to fit it, but as the XTR grany is different to “normal” granny rings then you’ll probably need to buy a normal mtb inner (again I’d look at TA for a 28T) and will need to space it out a few mm’s with some washers . Should be able to find plenty of threads on it if you do a search 😉

I do.
Using Specialites TA rings, in the granny and middle position. Be aware that you will need something like this to space out the ring in the granny position.

Forgot to say – using a 28T granny ring (64PCD) and 40T middle ring (104PCD). I think they’re TA Chinooks.

Yep, I used to, as Schmiken said. 2mm spacers on the granny ring, short bolts, and TA Chinook 28/40 rings.

Njee – The 40T ring is that a middle as can only see that size online as such.. ? Thanks

As above, I’m on 22/32 on my 970 at the moment (29er) but was using 24/36 previously (26″) – I’m not really sure what you’re asking though – just get the right sized 4-bolt chainrings (with 2mm spacers for the inner ring) and bolt them on!

The 40T is a middle ring. Clee cycles and sjsc sell them.

plenty here

http://weightweenies.starbike.com/forum/viewtopic.php?f=1&t=53945

Yes it is a middle as ac282 said, check Starbike in Germany too, not sure how the prices work out, but they often have better stock than any of the UK dealers.

Used MRP Podium Chainring 40 and inner ring TA 28. MRP stiff and looks good! 2mm spacers.

I’ve done it, 42/28 with TA rings, in the outer/middle position. Massively improved the chainline.
2mm spacers were hard to find, but I managed to find some eventually. I had to buy a bag of 50, so have a few spares knocking about. If you need some send me an email, page134 at hotmail dot com