OK to fit MTB crankset to a road bike?

Eurostar

I want to fit an MTB crankset to a road bike. Any reason why I can't? The crankset will be square taper, if that matters.

Big Red S

It'll fit fine.

If you're using MtB-sized rings (big ring less than about 50 teeth) you'll want an MtB front mech (but a road shifter will work).

Eurostar

Ta very much!

Eurostar

Just thought of something else - if I get a Shimano MTB front mech will it work with an SIS road shift-cum-brake lever? (This would be for triple chainrings.)

Big Red S

I'm not sure exactly what you mean by "SIS road shift-cum-brake lever", but any Shimano left hand shifter will work with any Shimano front derailleur. All MtB derailleurs are for triple, but will obviously work in a double setup.

So you can fit an MtB front derailleur, like an XT or an LX, and it'll work with your Road STIs.

nicklouse

i would do a little bit of looking into on this as i was in a similar ish situation.
and things were not all that cut and dried.

my situation i wanted a braze on front mech to work with a mtb shifter (shimano trigger XT or a sram trigger X-9) and it resulted in that there was only one shimano front mech that Mr Shimano said would work. and that was the Tiagra tripple.

He was on about this and that and whatever that did not seem relavent. and i could not see why any mech would not work. but he was adamant that there was only one solution.

Unfortunatly i desided to not bother with a front mech.

i can see no reason why it would not work. and if BRS says it will then thata what i would go with as he knows way more about road parts than i do.

Big Red S

Some road mechs do (or certainly did) have a stronger spring in them (because STIs have such a long lever compared to MtB shifters) so there aren't many road front mechs that work well with MtB shifters (and I think Shimano list them as incompatible for this), but the other way round is quite common on touring and CX bikes where they have drop bars but MtB mechs.

nicklouse

cheers for that Avi.

that could have been what he was on about. but TBH it was wet and muddy at Fort Will last year. and all that stuck was could be problems...

Eurostar

Good news, thanks. I suppose Shimano developed just the one indexing system for road and off road groupsets? No point developing two different systems if one will do the job I suppose. Ideally I'd like to have triple 9 speed Dura Ace on a touring bike but with a particular crankset which is usually for an MTB. It's really useful that Shimano makes such a wide range of stuff.

John Stevenson

There are a couple of potential gotchas with this.

The inner ring bolts of a triple sit very close to the chainstays of a road bike.

Mountain bike chainstays are shaped to accommodate them; road bike stays usually aren't, and that can mean a long bottom bracket axle is needed to stop them scraping.

That in turn means you need a triple front mech that will reach all the way out to the big ring. Occasionally it just can't be made to work.

custom-freak

hello i think you may have aproblem, as far as i am aware the mtb front mechs font work with the road sti levers the cable pull is wrong as far as i know this is the only option at the minute http://harriscyclery.net/itemdetails.cf ... 39&id=2435 not sure about uk suppliers at the minute, am planning to get mine through a friend in the states.
Cf

cyclone

Shimano use the same 1:1 ratio on all front mechs and same 1:2 ratio for all rear mechs.

The only problem you may find is the reach to the big ring like John said.

Saying that, my XT front mech goes way past the big ring if you adjust the cable barrels and stoppers so you might be OK.

Just choose your axel length wisely.

Big Red S

custom-freak wrote:

hello i think you may have aproblem, as far as i am aware the mtb front mechs font work with the road sti levers the cable pull is wrong as far as i know this is the only option at the minute http://harriscyclery.net/itemdetails.cf ... 39&id=2435 not sure about uk suppliers at the minute, am planning to get mine through a friend in the states.

Deore mech, Tiagra STIs
XT mech, Tiagra STIs

And it can't be that only Tiagra STIs can deal with MtB mechs, since that'd stop them working with any road MtB mechs. And, besides, I know I've fitted MtB mechs to bikes with other STIs on.

Eurostar

The plot thickens!

Been reading more stuff about this on the web, written by our own John Stevenson http://tinyurl.com/2ttfd2 and the not quite so famous Chris Juden http://tinyurl.com/3ykcpt - scroll down to Mixing Road and Mountain. But both pages were written some years ago - is it still the case that the road STI lever pulls a different amount of cable from an MTB lever? From what Cyclone is saying the cable lengths are equal these days.

The frame is a custom which is not designed yet so I hope I can get the necessary chainstay clearance factored in. I want the axle length to be decided by the expert fitters at Cyclefit - I don't want to get knee problems from having them too far apart.