arangov3

but wouldn't it not match up with the brifter using the mtb crank with its non modified spacing?

nfmisso

the spacing on the crank is not the issue, it is the pull ratio of derailleur.

And as others have suggested, I'd get a 48T outer ring for your crank set; 104mm BCD 4 bolt 48T rings are widely available: Amazon, eBay, etc. Leaving the inner rings as is.

mconlonx

Other issues I didn't see mentioned... (but might have missed)

Chainline. When you get your road crank to the point where it clears the chainstays with a longer BB, your chainline will be sub-optimal. At which point, big/big combo, normally not a good idea anwyay, becomes even more problematic.

FD throw. When you get the chainring out far enough to clear the chainstays, you may very well be approaching the end of usable travel of the front derailleur via limit screws.

arangov3

I'd hate to go through all that to run into that thank you for being the guinea pig. The bike I'm doing this to is a late 80s Univega and there is not much room for a larger road crank but there is room for the rings to have there spacing changed to match that of a rd bike.

fietsbob

Clearance for fat tires and that chainstay Bend, may limit the size of the big chainring .
then moving the whole crank outboard, to get clearance makes the chainline goofy.

lopek77

Did that on one of my bikes. Big chain ring is now 48. Didn't change derailleurs, cassette or chain. I just adjusted everything and it works great. Rear cassette is 12-34. It's a pretty common setup like on many hybrid bikes. It's far from being a road bike, but with 28mm tires, it's plenty fast. Hopefully your bike will be an easy project like mine was. Have fun!

arangov3

What did you do? Move it out farther or adjust the spacing also what are you using for shifting, brifters?

forgive me for pelting you with questions I would like to learn from your experience.

xenologer

forseeable problem
you cant make your crank spider thinner to put rings closer, and even if you could your chain wouldn't fit w/o rubbing



note
mtb and road sprockets have the same spacing, the compatibility issue is in the derailer cable pull
mtb long pull, road short pull

assuming you have a mtb crankset and mtb derailer , a brifter will not pull enough cable
may be possible to modify derailer cable clamp to shorten lever arm and reduce required cable pull
try routing cable to other side of clamp bolt, dremel may be involved

lopek77

I found crank that matches my chain line, and I used that with my old BB. If I just bought a new crank without matching it to my existing BB, I would spend additional $30-$50 for BB, so it's well worth to do your research first. Then I adjusted my front derailleur (moved it higher). I'm still using all my existing gear shifters and mountain bike handlebar. I also replaced my wheels and put 28mm tires on them. This setup gives me more speed and more fun on roads.

bicyclridr4life

My mountain bikes have a 28/38/48 (Bio-Pace, on two of the bikes) and 22/32/48 (Bontrager) rings. Where can I get a 38 or 40 tooth outer ring - or even a 36 tooth outer ring for the one I'm making into a long distance touring bike (pulling a trailer, on and off road.) the 32 to 48 is quite a jump, and I don't need a 48 tooth big ring, since I'm not racing. I figure gravity alone will get me going way fast enough on the down-hills.

hybridbkrdr

That's useful to know. Guess I won't be buying a Nashbar mountain frame for my Sora crankset.

LesterOfPuppets

I love my MTB with road crank. Steel frame with slim chainstays probably helps with clearance. 9speed in back and the straight chainline from the 5 cog is with the inner chainring instead of between the rings, so chainline is slightly off but hasn't manifested itself in any real world problems. Had to try out a couple of square taper BBs to see what the right spindle length would be.

The 52 really helps when running 1.4 or 1.5" tires but I even kinda like having it with 1.75" tires.



Used the same crank for STXC this year but kept it in the 42 little ring the whole time while racing. I rode to and from the track so the 52T big ring was nice for the road miles to and fro.



- Lester

krobinson103

I've put a 48-38-26 on just about all my frames including a hardtail fuji. Work great. Doubt you could go over 48 easily though. The FD isn't set up for it.

XXLHardrock

Wow, very informative thread. I was told that 12 teeth difference was the max for a FD, when I asked the LBS about replacing the 42 with a 46 or 48 on my 22/32/42 triple. But my FD-H screw is almost all the way in to keep the chain from falling off the big ring. So I'm wondering if this indicates that there is sufficient travel available for a 16 tooth difference (32-48).

JamadianSparrow

Heheh….'Velo-Alchemy' hybrid heresy never goes out of style!

I…have possession of a Scott Scale LTD mountain frame; lightly used & never abused and vice free! Cost me a 10th of its original list price from the proprietor of the shop.

My project: fit a 54T/38/26 road triple crank/ring on a 68 x 122.5 or 127 BB and run a 7 or 8spd cluster possiblywith grip shifters.

So far, the signature challenge with Scott CF mtb frames is a HUGE seat tube OD of 38.2 mm, making finding a front derailleur with capacity and mounting options near impossible. These are usually spec'd E-bracket mounts for Shimano XT and SRAM XX.
There also exists the option of employing an 'after-market' carbon or aluminum braze-on clamp made for this girth seat-tube and fitting a Shimano DA7700 braze on FD. However the unexpected expense here is not the actual derailleur equipment, but the oversize clamp mount: they are incredibly light CF at 8 gr. but they are special order and cost between $70 - 105!!!
This is to ensure your clamp mounting is not tightening down in a manner that crunches the CF seat tube

I am not willing to spend that much on a chunk of carbon & alloy smaller than a wristwatch!?! Thinking there HAS to be a cheaper, satisfactory approach, I finally determined that a generic, stainless steel 'T-Bolt, "V"-clamp' could do the trick, if its tightening bolt & screw are modified to retain the braze-on derailleur.

It is sufficiently wide and flush fitting to distribute compression loads without crushing the carbon beneath!
Obtained four in size 1.5 in./38 mm; it fits beautifully and at a height midway bewteen the water bottle mount-lugs. I have 5, inexpensive but reliable braze-on derailleurs awaiting modes to mate with this clamp.

Details and pics to follow, along with 650C tri wheels to round out my 'urban rocket'…a configuration I've used before.

RoadGuy

OP, it would probably be easier (and might be less expensive) to just go out and buy a reasonably priced used road bike for on-road adventures.

You could probably find something that's rideable for $100 or less (or depending on how picky you are $200).

In the past few months I've got four (4) Trek road bikes (88-97), three of which cost me $100 or less, all oof which needed the expendables replaced and all of which are basically sound and just in need of TLC.

My latest is a Trek 1100 road bike with a triple crank. It needed attention to the rear wheel, tires, and inner tubes. I'm doing a bunch of upgrades (upgrading from a 7-speed rear freewheel wheel to a 8-speed rear cassette wheel) since I only paid $40 for it. This past week, someone else reported that he bought a Trek 1100 for $10 (and crashed it riding it home). These are both instances of road triple crank bikes that cost less than the changes that would be required to run a road triple on your mountain bike (compromising the utility of the mountain bike).

jralbert

Okay, I have a kinda related question - forgive me if I've missed it having been answered already in this thread, there's a lot of details flying back and forth! I've got a Specialized TriCross, which runs a 50/34 compact double crankset (on a 68mm english threaded external bearing bb) with a SRAM Apex FD against an 11-30 cassette, and while it works really well in all paved and gravel contexts, I'd really like to be able to outfit it for more aggressive back-country trekking, which in my geographic region means a lot of very steep climbing and descending.

It had occurred to me that if things were as simple as taking the 50/34 off and installing a (say) 22/34 MTB double crank, or even a 28t single, and an appropriate chain, I could fairly quickly switch the machine back and forth from commuter mode to logging-road-exploration mode and finally achieve true happiness.

Based on what I've read in this thread it sounds like it isn't that simple - but shouldn't it be? Will the chainline just be massively wrong because of the difference in BB shell width from road to mtb - and if so, could I get away with this if I just used an mtb bottom bracket? So many questions...

grampa.sjb

Hey Bill

This isn't a direct answer to your mechanical question, more to your progress as a rider overall.

The differences between a road bike and mountain bike is more than just gear ratios. Rider position is a big one. A mountain bike puts you more upright - necessary to quickly apply body "english" when encountering rapid changes in direction, obstacles, etc. The road bike body position emphasizes low air drag, especially when in the drops of the handlebar.

No matter what changes you make to your mountain bike, it's still not going to be a road bike, and you still won't be really happy with it, especially if you ride with roadies who will inherently have at least a 4+ mph advantage on you just because they are riding on road bikes.

My advice would be to spend as little $$$ as possible to change your mountain bike (maybe change the cassette on your road wheels, and change your big ring to a 48t), then save your money to get an actually road bike. It's the road bike itself which will really make the big difference, not just the gears.

I'm saying this cuz I went down the same road you're riding, and wasted too much time and $$$ before I got a real road bike. Trust me on this: it's the bike that will make the real difference!