Panza

I'm trying to get MTB gearing onto my road bike for the Mt. Washington Auto Road Hill Climb Race. A hiccup occurred.

I tried to pair my SRAM X1 32T mountain bike crankset to my road bike, Italian 70mm Threaded Dura Ace bottom bracket.

The SRAM X01 was too thin, though. Are the spindles in the cranksets different sizes? Or are they different between Shimano - SRAM?
How can I know what MTB cranks can fit my road bike BB?

Can I solve the issue by:
Replacing the crankset to a Shimano Deore XT? or
Replacing the bottom bracket with a SRAM GXP Italian threaded?

fietsbob

I have had an M730 XT triple crank on my 700c derailleur Touring bike
since the 80s.. my low 24:34

problem with the newer external cranks is you cannot change the spindle width..

Its part of the crank arms (but its lighter)

my Mt Tam hill climb bike another 80s project 36:28 , on an AlAn..
lots of out of the saddle time..





Have you gone by a bike shop, to someone who can see it?

others did not buy all the same parts as you ask about.


...

base2 

68mm bottom bracket width is "road.
73mm bottom bracket width is "mountain."
There is a fair degree of cross pollination depending on bike and date manufactured.

70mm you just discovered is Italian/French/weirdo/obsolete.
You'll need to do a full swap.

Depending on your particular bike, and combination of components...If you buy a 73mm mountain crankset, they (Shimano at least) will come with 2, 2.5 mm spacers that go between the external bearing and the bottom bracket shell. Math says you'll need 3mm of spacer. On an old bike I once had, the shell was 70mm but standard english threads, so I shaved 1mm off each spacer so that 70+2.5+2.5-1-1=73mm the Shimano hollowtech crankset wanted. You might find yourself in a similar situation/solution assuming thread direction and pitch is compatible. [edit: it's not, so disregard.]

Alternatively, if you have some basic hand tools, you can make a 3mm spacer with a hole saw, a belt sander and a trip to the local metal supply house. Hit their scrap bin for some by the pound goodness. You might be out $1, assuming they charge you at all. [edit: nevermind. Thread pitch & diameter not compatible.]

You might even see if the crankset you want comes with an Italian bottom bracket. That would be the easiest. Does this match the crankset you want?

Kontact 

There are lots of compatibility issues, but the most glaring one is trying to put a SRAM crank in a Shimano BB. That's like trying to put a Nissan transmission in a Ford - there's no reason to assume they should be compatible.

jlaw

As a previous poster said - you're biggest issue is the 70mm BB. Beyond that, as long as you can get a new BB (that is compatible with your new MTB crank) to fit your frame, I don't see why a 'mountain' crank can't be installed on a 'road' bike.

I recently purchased the SRAM x5 MTB crankset (39-26) along with a SRAM GXP BB (68mm english) and installed it on a mid-1980's road bike frame. The GXP BB comes with 2 spacers (2.5mm each?) - check the SRAM website. You can also purchase spacers of various thicknesses, but you may not need them.

Your idea of buying a GXP Italian-threaded BB is worth a try - the GXP isn't too expensive. If you buy the 68mm width it seems like you could install it with no shims into a 70mm shell. I say this because since the BB comes with 2 shims then it is meant to have enough flexibility to work with a 68mm (road) or 73mm (MTB) shell - you are right in the middle at 70mm. The shims are used to make the chainline for a MTB set-up more favorable. I am not an expert, but I think it would work. Check the SRAM website to make sure that the GXP BB is compatible with the SRAM X01 crankset you already have.

I really like the cruising and lower gearing that I now have available on my road bike with the 39-26 crankset - don't miss the 50T.

Jon T

I have a triple (32-42-52) on a Peugeot I've had for 34 years. I used the Peugeot spindle and bearings and just put the new cranks on the old spindle. Why can't you do the same? As long as the crank/spindle drive surfaces (the square drive) fit, you should be good to go. Don't over think it.
Jon

Kontact 

Because he doesn't have a square taper crank.