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modifying MTB for road use

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modifying MTB for road use

Old 03-18-08, 04:02 PM
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a_n
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modifying MTB for road use

Hi,
I first posted this on the recreational riding page: http://www.bikeforums.net/showthread.php?t=398767, but was referred here. So, if you would kindly share your experiences.
I've recently started using my Cannondale M300 commuting bike for road riding (got skinnier tires on it). Problem is that on flat ground I run out of high gears. So I would like to switch out the crankset to a road crank (was thinking of Sora or Tiagra). The kids at two local shops said that this is not possible, but I get the feeling they just don't know. Plus they want to sell me a new road bike instead.
The bike has 8-speed Alivio cassette and chain that I'd like to keep if possible. So, would a road crank fit on Cannondale mountain frame and work with other components? Will there be problems with chainline when going from MTB to road crank?

Any other suggestions/words of caution would be appreciated.
Thank you,
AN
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Old 03-18-08, 04:21 PM
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Deanster04
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Check to see if there are any chairings available to increase the number of teeth on the large ring. Also, you can buy a cassette with an 11 and you will get a pretty decent high gear. I have a MTB and put a set of Continental Road MTB tires so I can go either way.
If you have money to spend upgrading to a 9 spd would be worth the $$$. It will be a compromise bike and as such not a "real" road bike. The young LBS guys are probably trying to steer you in the direction of a road bike for a better ride "in their mind trying to help you...not just trying to sell you something. Go to the Sheldon Brown website for some ideas. Harris Cyclery can send you stuff by mail and probably will give you advice. Call them up! Good Luck. Deanster,
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Old 03-18-08, 04:24 PM
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You'll need a new chain. It needs to be longer to fit around the larger chainrings. But other than that there's no issues. Depending on what cranks you get and what you have now you MAY need a new bottom bracket with the correct axle length to position the arms and rings correctly.

And of course you'll need to move the front derraileur up higher on the frame so if you have a bottom pull version you'll need a new shifter cable since it likely won't be long enough.

That's about it. And if you find out the bottom bracket length and pick your cranks to match it then you can avoid replacing the BB.

I wish I still had the strength of youth. I'm looking at MTB cranks for my road bikes instead of the other way around like you're doing just because I can't push the tall gearing for long...
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Old 03-18-08, 04:36 PM
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I had a triple with a 28/38/48 on my Kuwahara Cascade and a 12-28 in the rear...that was pretty insane and fun gearing for an mtb / touring bike as it had 103 gear inches at the top end.

If you can run a 44:11 top gear on your mtb (ir it's equivalent) you'll have 103 gear inches which is enough for most human beings... I ran this for quite a while when my Trek 6700 was serving commuting duties and running slicker tyres.
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Old 03-18-08, 05:30 PM
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According to the Cannondale site, that bike comes with a 42T large ring and an 11-30 cassette.
Caveats to watch are clearence between the chain ring and chain stay, Sometimes there isn't room, unless you use a longer BB.
IF you have room, you should be able to find a "donor" 28-38-48 somewhat easily.
IF you need bigger than a 48T, you pretty much have to go to a road crank. That may have other caveats?
I would think a 48 from 42 should be sufficient? That's almost 15%! It would be like going to a 9.6T cog on your current ring.
Assuming you have 1.5" tires, you currently would have about 96 gear inches. I think maybe you need to increase your cadence some? If you can't, I'd think your cranks are probably too long. IF so, you might look for a crank that's 5MM shorter than your current cranks. If your current cranks are 170MM, you'll probably have to go to a road crank to get shorter.
Another caveat is that with a bigger ring that you might have too high of a gear. If that's the case, you'll have to use the next lower gear and you'll be worse than you are currently! a 48/13 gear is only 93 gear inches. Your 42-11 is 96! That means you'd probably need a new cassette for things to actually improve. IF you "study" 8 speed cassettes, you'll see there aren't any 11-12-13... combos. 11-12-14----or 12-13-14----. Missing the 13 on the first instance, will leave a pretty big "hole" in that range. And, a 48-12 isn't a huge amount higher than your current 42-11.
Shorter cranks! See the link for my experience with shorter is better for me
http://www.bikeforums.net/showthread.php?t=361045
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Old 03-18-08, 10:00 PM
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Thank you all! You guys have been really generous and helpful. Regars, AN
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Old 03-18-08, 10:09 PM
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42/11 gives you ~3.82:1
I've often found that the gearing on a MTB is somewhat lacking on the road.

However:
I'm riding SS @ 28/13 (~2.15:1) on my city MTB and I can keep up with traffic.
Albeit I do have to sprint and coast.

If you're looking for speed ...
Get a larger front ring. 44-46-48
Adjust the f.derailer.
You also might need a longer chain.

But for real, and for serious speed, try a road bike.
The position you ride in just makes you feel faster!

Pushing the 52/11.
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Old 03-19-08, 09:25 AM
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Road cranks have narrower Q factors which may cause the arms to strike the fat C'dale chainstays. You could fit a longer spindle it the road arms are square taper but then the chainline may get messed up.

Race Face and Salsa make larger rings for 4 bolt MTB arms. The Salsas are not ramped and pinned. The Race Face are $pendy, but may be the best rings made.
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