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PostPosted: Thu Nov 03, 2011 1:57 pm 
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Joined: Thu Oct 07, 2004 7:33 pm
Posts: 243
Location: Barcelona/Torino
Hello,

I use my road bike (caad8) as a touring bike, and I feel I need lower gears. Today I'm using 50.34 compact road crankset, paired with a 12-27 road cassette (10v).
I'm considering a double mountain crankset, a 40.28 Shimano XT or Sram x5 42.28, to replace the UltegraSL I have.
I'd leave a pair of pedals on each crankset: courrent road pedals to the 50.34 and mountain pedals to the 40.28.

The question is: Will this worK? I mean, will It shift properly? I'm worried about the FD performance.

I don't want triple drivetrain because I don't want to change STi (limited budget)

This is an alternative to 10s mountain cassette, with big jumps between cogs that I don't like. A 11-34 may be, and changing RD to a shimano preshadow 9v. And longer chain of course.

thankyou!

_________________
flat transitioner shimanoist


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PostPosted: Thu Nov 03, 2011 2:05 pm 
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Joined: Sat Mar 19, 2011 10:50 pm
Posts: 659
40 isn't big enough for the road. do it with the cassette. The big jumps on the low gears aren't going to be a big deal because you aren't generating a ton of torque when you're in those gears. Also dont cross chain.


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PostPosted: Thu Nov 03, 2011 2:44 pm 
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Joined: Tue Aug 05, 2008 1:15 am
Posts: 156
For touring 40 would def work. Currently I'm running 46-36 w/12-27 and thinking about stepping down to 42-28ish range w/a 11-32/34. I haven't looked into if the mountain cranks would work w a cross bike, as far as OKish chain line and etc.


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PostPosted: Thu Nov 03, 2011 4:21 pm 
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Joined: Wed Feb 25, 2009 7:58 pm
Posts: 320
Location: Lancaster, UK
the issue is the FD

an MTB FD will shift well with a MTB double c/set but your road STI does not pull enough cable per click to work the FD properly. In other words, you'll be under-shifting.

A road FD will work fine with your STI but probably won't shift very well with the c/set.

I've run a Sram red FD on a 32/44 MTB chainset (mtb triple minus the granny) in the past and it was okay. Not brilliant but okay.


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PostPosted: Thu Nov 03, 2011 5:00 pm 
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Joined: Thu Oct 07, 2004 7:33 pm
Posts: 243
Location: Barcelona/Torino
the two things that worry me are:
chainline: It seems to me that mountain cranksets put de rings further than the road ones,
FD performance: I'm not sure if the shifting is going to be "enough" precise.


The "super cassete" option is mean to be troublefree, I suppose...but, if I leave the mountain RD installed and go back to road cassette, will it shift ok?

_________________
flat transitioner shimanoist


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PostPosted: Sun Nov 06, 2011 9:44 pm 
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in the industry

Joined: Sun Nov 21, 2004 2:45 pm
Posts: 2871
Location: London, UK
Velozirrapt0r wrote:
Hello,

I use my road bike (caad8) as a touring bike, and I feel I need lower gears. Today I'm using 50.34 compact road crankset, paired with a 12-27 road cassette (10v).
I'm considering a double mountain crankset, a 40.28 Shimano XT or Sram x5 42.28, to replace the UltegraSL I have.
I'd leave a pair of pedals on each crankset: courrent road pedals to the 50.34 and mountain pedals to the 40.28.

The question is: Will this worK? I mean, will It shift properly? I'm worried about the FD performance.

I don't want triple drivetrain because I don't want to change STi (limited budget)

This is an alternative to 10s mountain cassette, with big jumps between cogs that I don't like. A 11-34 may be, and changing RD to a shimano preshadow 9v. And longer chain of course.

thankyou!
How much lower do you need to go? By changing to an 11-28 cassette and a 33 inner you'll be almost as low as you'd be on 30x27 with none of the fuss of swapping out cranks, BB & pedal system. Nor would it be necessary to readjust the front mech.

I ride with a semi-fused ankle but manage fine with a 34x25 unladen. Of you're climbing with panniers then a triple may be a better solution.


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