Hi ,,,My FSA chainset has given up on me , so i need to fit a new chainset to my ON ONE DIRTY DISCO ive got an XTR M785 double chainset is there any reason this wont work ,, ie chain line etc

Thanks in advance

I’ve been researching this too as I want to put a mountain double on my touring bike – looks like chainlike will be off slightly and front mech alignment might be affected. I’d be interested in a definitive answer if anyone’s done it successfully!

You’ll need some extra spacers to move your bottom bracket cups out too. Plus adjusting the front mech. Probably be able to do that by moving the band and tweaking the limit screws.

I run an mtb crank on my CX bike which works fine

The axle is 5mm longer, so the chainline is out by 2.5mm, and the front mech likely won’t reach the outer ring without modification, or running the chainset offset. MTB mech will do it, although the cable pull is slightly different to road STIs.

My all city cx bike has the sram Chainset that came off my enduro just used a mtb bb and road front mech to match the ring sizes. All works fine but I do use bar end shifters so the left one is non-indexed

No issues with front mech not reaching the outer ring

I now run a Sram X5 28-42 on my CAADX. Works really well. No option with BB30 to alter chainline but I’ve had no dropped chains. Front mech won’t go down quite as far as I would like as the seat tube on my bike flares slightly before it meets the BB shell. Having said that I spend a lot more time in the 42 and the 28 is really only for STEEEEEP hills

As above, you can do it and make it work but IME it’s never quite spot on. Fine to get you out for a weekend but not a longterm option that I’d go for.

Is it better to go with a triple and just use the inner and middle positions, or will a double be OK?

forgot to mention the chainrings are 44/30 , dont no if that makes a difference or not

Thanks for the comments so far

Just to tap into the expertise. Is it also true for 9 speed that the cable pull for a front mech is different road vs mtb

If I get a cx for touring I’ll need lower ratios than a compact…

been running mtb “touring” 9 speed triple for a few years on my kinesis pro6 with ultrega sti’s and a standard mtb hollowtech bearing set up, xt front and rear mechs

need a bit of jiggery pokey with a wooden wedge to hold front mech in correct position to get cable tension correct and have in line adjusters to keep it shifting smooth – at the limits of what the front mech will do and won’t absolutely always drop to granny first time if set to avoid chain rub on big ring/smallest rear but can ride up virtually anything without any mtfu

pretty sure won’t work with 10/11 speed due to different pull and will be going compact on a new build

edit wooden wedge isn’t permanent – just to hold mech in correct position when clamping cabling

Sram x7 chain set, XT front mech and 105 10 speed for the rest works for me.

I had a deore on my old cx for years no problems at all i had to use a road front mech tho as mtb one didnt play nice. I used an mtb bb btw. I also had an mtb cassette and mtb rear mech on it too along with road stis

Yep been running a triple XT with 26, 34, 48 for a while. Bit of messing around with BB spacers to get the chain line right, but no problems at all

the axle length is different (longer) so you need to mess about with spacers, then you need to be careful that the spacers allow the bottom bracket to screw in far enough and not risk causing the threads to wear over a period of time, rendering the bb shell useless !! as i found out. you would probably be better building up a suitable chain set from middle burn

Is it also true for 9 speed that the cable pull for a front mech is different road vs mtb

yep. MTB cable pull is greater. If you run a mtb mech and road STI then the mech won’t move far enough per click. Ditto, the other way round (road mech on mtb pod) it moves too much.

You can often get round this with alternative cable routing and cunning use of the limit stops but only really for double setups.

reggiegasket

Thanks

Does an MTB triple chainset have a different chain line to a road triple chainset? In other words is it easier to convert a triple as you can use the same front mech?

Full XT drivetrain on my crosser with no problems

Usually used for touring and MTB-Lite but survives the odd cross race as well

As i said above i just stuck an mtb bb in with an mtb crank and a road mech it worked fine. Chainline isnt a real issue tbh as its all over anyway with the cassette. Its not like its a fixie where its really important

Again thanks folks

My only concern ion chain line was the reach of the front mech…