Road crank on MTB
 

Hey guys I'm planning on running a 1x9 setup on my giant NRS this season. Ive already ordered a chainguide (MRP 1.X) and I'm thinking of running a road compact crankset with a 34 tooth ring. Do you guys think this is a good idea? or will i just end up breaking it? My crank of choice is a sram rival and im planning on facing down the bb shell to accommodate the chain guide for the available 68mm width. Has anyone ever done this?

Thanks..

Not that you can't do it, but...why?

The weight loss is likely marginal - and if you are running an older NRS, there are other things you could do to lose weight before swapping on a road crank. There are a ton of light mtb cranks that will let you use a 34T ring, without having to face down your shell, or screw with your chainline set up. As well, you may run into clearance issues at the chainstays - mtbs have wider stays to take fatter tires.

I mean, unless you just have the parts around and want to experiment, there isn't a lot of point to it. Hell, unless you have a really funky setup already, you ought to be able to set your current crankset up to work just fine with the 34T ring and MRP guide.

Short cage rear, unramped ring, short chain, MRP guide and you'll be good to go. You don't even need to run the shorter rear mech and unramped ring, they'll just help more with a cleaner and less problem prone setup.

I'm betting the road crank axle isn't long enough for the MTB BB shell.

Also i'm betting the inner chainring on the double won't clear the chainstay...

nah, the spindle would fit fine, it's the arms possibly not clearing the chainstays tha tis the bigger problem. considering his bb is a 68mm, and most road are also 68mm, that part is at least a non-issue.

shouldn't have any trouble with the chainring tabs, either. it's the arms that may or may not be the problem.

using a road crank on a mtb is a solution looking for a problem that dosn't exist, unless you just feel like running some odd gearing combos.

The time I tried the R700 from my cross rig on my XC bike it wasn't even close, but I can recall no measurements to support my claims. It seemed like way more than a 5mm miss.

Thanks for the help. The reason I'm doing this is mainly for light weight (I'm building a weight weeny bike) But also i like the sleekness of a road crank and the absence of granny gear tabs, and i just want to try something different. A have an FSA gossamer lying around and just might try that, but its a 130 bcd so ill have to get something else for the final build.

If you already had it laying around...I'd say do it, break it, replace it with something designed for the rigors. But...since you're gonna go out and buy the thing...don't be a closet roadie...climb a few more feet per ride and roll with an XT. A couple oz of non rotating weight won't be noticed.

Ah, Paul. I told you it wasn't a great idea. Your NRS is already plenty light. Stick with a mountain crank; it will look better anyway.