wverdsha

Hi,

I have a mountain bike that I love (Trek 8500 LT). I have two wheelsets....one for road, and one for off-road. I notice that I don't have the correct gearing when I ride on the road (approx 80% of the time). I am thinking about going with a triple road crank. This way I still retain many of the gears I use off road with the middle and lower rings, while I have the larger chainring, for the flat/down hill road riding. It appears to be logical to make this change. Am I missing anything? I figure I will need the crank set & possibly a new chain that is a little longer.

I appreciate any insight - Thanks.

Bill

capwater

Most likely a new bottom bracket depending on the crank you plan on using.

metabike

Have you considered a more aggresively geared cassette on your road wheels? Might be less $$ than a new crankset & BB.

DMF 

Is your current crank have two chainrings or three?

HillRider

I see a few potential problems:

1. MTB's cranks usually have a 42 or 44T big chainring and a 20 or 22T granny while road cranks have 50 to 53T big rings and a 30T granny. The larger chainrings may not clear the frame's chainstays since MTB frames often have fat chainstays that are flaired to clear fat tires.

2. You will probably need a different bottom bracket. Your bb shell may be either 73 or 68 mm wide. All road cranks are made for a 68 mm bb shell so your chainline may be off.

3. You will almost certainly need a longer chain to make up the 6 to 11T big chainring difference.

4. Your front derailleur cage won't be curved to match the larger chainring and will have to sit way too high to clear it so shifting will be very poor. A road fd will be needed to shift properly but won't index correctly with your MTB shifters.

There may be other items i can't think of but those are what come to mind immediately.

well biked

As already mentioned, there's a good chance you'll need a different bottom bracket. But the big thing might be chainring clearance, because mountain bike frames aren't usually designed for road-sized chainrings, the chainstays flare out too much to accomodate fat tires. Also, the current front derailleur will need to be moved up on the seat tube to reposition it for the larger big ring, and the cage won't be shaped optimally for the larger ring, either. I've used a dremel tool to re-shape front derailleurs. It's the chainring clearance that might be a deal breaker-

wverdsha

I should have put more details in. I have as 3 ring 22-44 currently and xtr components except for the Crank it's the Icon stock one. The bike shifts very well now and I am really happy with the bike. I don't remember the exact cassette size, but I know that I have 9 speed arrangement with 11 on the smallest and I believe 34 or 35 on the largest. I am new to cycling, but generally mechanically inclined. I don't want to screw the bike up any, just looking for a little more out of it on the road. Changing to the slicks was a good first step. I appreciate your help everyone.

cyccommute 

If you crank is a 4 bolt 104mm BCD, you can easily get a 48 tooth outer ring from BikeMan. Shimano is making a trekking crank that is a 48/36/26 so that ring is available. Nashbar carries an LX version of the whole crank for octalink for around $70, which is pretty reasonable. They also carry an external bearing version for much more. You'd have a better chance of not having interference issues with the chainstay with the 48 over a 52. And your front derailer should work better with it.

maddmaxx 

If you get big enough that you think about changing to a front road derailleur, you will not have the proper ratio on the existing MTB shifters.

The 26/36/48 touring crank works pretty well on an MTB on asphault. You will still have gear left above 30mph.

Gonzo Bob

Hillrider covered most everything... except...

5. If your FD is bracket mount, you might not be able to raise it high enough for the bigger ring.

well biked

But I said that!!!

wverdsha

Thanks everyone for your help.

I really appreciate it.

Bill

cs1

This is the most important reason you won't be able to use a road triple. The other reasons can be worked around easily. You can't change the chainstays though.

What you might want to try is a Shimano LX crank with a 48 tooth big ring. It will give you more top end than standard MTB gearing. If you are using a Shimano crank now you shouldn't need a new BB either. The ft der might work also, try it first. The chain is the only other change you might need. Sounds like a winner, good luck.


Tim

erader

do you really need more than 44 x 11 ?

ed rader

DMF 

I sometimes wish I had more than 52:11.

HillRider

To do what with? Can you really pedal at 38 mph?

DannoXYZ 

I say just get a 48t chainring for the existing crank. Then a narrow-range road cassette in the rear. A 11-24t should be fine. You're really not going to get more speed from changing your gearing, that's a matter of air-resistance vs. power. To make more power, you'll need to improve fitness (aerobic capacity & muscle efficiency).

cyccommute 

I put it more at 34 mph @90 rpm, but yes there are situations where something larger than a 52/11 would be handy...not many and most of them involve doing something really, really stupid...but it could be handy

HillRider

I certainly admire your honesty.

DMF 

Sure! Downhill.


But that's when you store energy for the next up grade. So my 52:11 helps my climbing.

HillRider

I find tucking in to reduce drag is more efficient at conserving momentum for the next up hill than pedaling wildly on the downhills.

DMF 

Depends on the length of the hill, doesn't it?

When do you start pedaling again, when you've slowed down to grinding speed? Your advantage is long gone by that time. Adding energy *as* you slow down is where it's most effective. The higher gear lets you start adding sooner (while you're going faster).

arangov3

Zombie thread bump


Would there be any foreseeable problems if you were to dissemble a mtb front crank and modify the spacing to match the spacing of a road bike so that it would work with brifters?

nfmisso

Easier to fit a road FD - try a Shimano A 073 - very inexpensive.

hueyhoolihan

the previous zombie thread failed to directly mention the experience i had when trying to run a road crank on a 97 gary fisher tassahara.

i removed the square tapered shimano deore crank and brought out one of my 80's vintage road cranks. i put the drive side crank arm on and as previously mentioned the inner chainring hit the chainstay. i removed it (was for SS setup anyway), and found that the OUTSIDE chainring hit the chainstay too. so i found a smaller chainring that barely cleared and thought i was home free.

i went to the trouble of setting up the chainline and all the rest. then, i finally tried to mount the non drive-side arm. guess what? DIDN'T CLEAR THE CHAINSTAY (MTB crank arms are bent out, i now know, creating a much larger Q-factor than road cranks). called it a day, and put the old one back on.

end of experiment...