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PostPosted: Tue Feb 11, 2014 1:03 pm 
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Joined: Sun Sep 10, 2006 6:43 pm
Posts: 657
Location: Copenhagen, Denmark, Earth, Universe
Hi,

Instead of putting a larger cassette on when riding in the mountains I thought about putting a double mountainbike crankset on my Caad 9 roadbike with BSA bottom bracket.

This would save some weight (small cassette and small chainrings) and also give me a better gear-ratio.

Would there be any technical problems with that? I'm thinking about chainline differences and increased q-factor and that sort of stuff.

I'm running a Campagnolo 10 speed setup on my bike and the cranks that I'm considering are Lightning and the Raceface Next SL. But I'm not looked onto those if there are better suggestions.

thanks


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Posted: Tue Feb 11, 2014 1:03 pm 


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PostPosted: Tue Feb 11, 2014 1:16 pm 
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Joined: Thu Mar 28, 2013 4:42 pm
Posts: 113
Location: Pa USA
I've got a set of topline mtb ( granny removed) cranks on a Campy 9 spd bike. They work acceptably. The chainline is acceptable, even though the q is much different than standard campy cranks. I did it for ww reasons, it was one of the lightest affordable cranks out there when I built the bike.


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PostPosted: Tue Feb 11, 2014 2:25 pm 
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Formerly known as wassertreter

Joined: Tue Apr 12, 2011 8:08 am
Posts: 1946
Location: Pedal Square
Swapping the crank and readjusting the FD is way more hassle than switching cassettes (if the chain is long enough). If you're getting a crank anyway, you could also get a compact one, and run whatever chainrings you need for flat vs mountains (In case the in-between sizes don't cut it for you). Still need to adjust the FD, obviously.

Also Mtb cranks with typically 40-42 big ring spin out quickly, somewhat limiting the joy of a hard earned descent.

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Bikes: Raw Ti, 650b flatbar CX


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PostPosted: Tue Feb 11, 2014 6:24 pm 
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Joined: Sat Aug 29, 2009 4:30 pm
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I'm running a mtn triple on my winter commuter bike.
Most mtn bike cranks are designed to work on a 73mm bottom bracket, so mtn bike BB's include 2 x 2.5mm spacers to adapt to 68mm BBs. But the mtn cranks are also designed for a wider chain line.
So I put both spacers on the non-drive side of the BB and was able to get my road triple front derailleur adjusted to cover the extra required outward throw.

Bottom line: you can make it work, but be careful of chain line and front derailleur adustments.


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PostPosted: Tue Feb 11, 2014 10:43 pm 
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Joined: Fri Oct 28, 2011 3:25 am
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Location: United Kingdom of Great Britain and Northern Ireland
It is really not until you go to the trouble of fitting one that you will perhaps find it is outside of the limit of adjustment of your front derailleur.

I also use Campag 10 speed (old style) and remember trying a 36/42 double crankset (Stronglight Impact) for a while. I have found that you need at least a gap of 8 teeth between chainring sizes for a Campag FD to work properly, and you also need to be able to get the FD low enough down the seat tube - usually not possible if it is bracket-type fixing as opposed to clamp.

There is a reason why triple cranksets exist. I now use 26/36/46 triple road crankset (74/110BCD) with 13-29 cassette - and it gets me up >25% hills.


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PostPosted: Tue Feb 11, 2014 11:45 pm 
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Joined: Thu Mar 28, 2013 4:42 pm
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Location: Pa USA
Valbrona wrote:
It is really not until you go to the trouble of fitting one that you will perhaps find it is outside of the limit of adjustment of your front derailleur.

I also use Campag 10 speed (old style) and remember trying a 36/42 double crankset (Stronglight Impact) for a while. I have found that you need at least a gap of 8 teeth between chainring sizes for a Campag FD to work properly, and you also need to be able to get the FD low enough down the seat tube - usually not possible if it is bracket-type fixing as opposed to clamp.

There is a reason why triple cranksets exist. I now use 26/36/46 triple road crankset (74/110BCD) with 13-29 cassette - and it gets me up >25% hills.

Yeah, should have mentioned that I run 50/34 on the toplines


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PostPosted: Wed Feb 12, 2014 1:37 am 
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Joined: Tue Nov 11, 2003 9:47 pm
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Location: Santa Cruz, California, USA
If you have a braze-on derailleur mount it may not let the derailleur go low enough. They're usually sized for 50/34 being the smallest chainrings.


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PostPosted: Wed Feb 12, 2014 6:38 am 
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Joined: Sun Aug 02, 2009 6:59 pm
Posts: 141
Check the Specialites TA cranks:
http://www.specialites-ta.com/produits/ped_car_gb.htm

I have a Specialites TA Carmina 46/29 double crankset (94bcd spider) on a cyclocross bike running Campagnolo Record 10 shifters and f/r derailleurs. This bike has a 68mm bsa bottom bracket shell and 103mm Phil Wood bottom bracket. I measure the Q factor at 146mm. It shifts perfectly.

If you're opposed to a square taper bottom bracket, Sugino has a "super compact" road crank with a narrow q factor and external bottom bracket. This guy (not me) likes it:
http://www.gravelbike.com/?p=1799


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PostPosted: Wed Feb 12, 2014 8:52 am 
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Location: Copenhagen, Denmark, Earth, Universe
Thanks for all the input, I will look into it!

I have a clamp on front derailleur and the seattube on my Caad 9 has the same diameter further towards the bottom bracket so I think I can move it lover without a problem.


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PostPosted: Sat Feb 22, 2014 3:14 pm 
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Joined: Wed Feb 02, 2011 3:48 am
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You can also run a SRAM MTB spider on a road crank eg:
Image


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Posted: Sat Feb 22, 2014 3:14 pm 


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PostPosted: Mon Feb 24, 2014 9:20 pm 
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Joined: Mon Oct 13, 2008 11:20 am
Posts: 64
Location: Lausanne, Switzerland
You mentioned that you're considering Lightning cranks. They make a 94mm BCD double spider that can be mounted to their road cranks. I'm running this setup on one of my bikes right now. I've got a set of 32-46 rings and 29-42. I call this my "super-compact" crank. The 29-42 is basically a road triple without the large ring. I've also tried 29-46, but the cadence jump when going between the two rings is a bit extreme.

Chainline with the Lightning road crank and 94mm BCD double spider is just about spot-on what it should be for a road double crank (i.e., around 43mm), and the Q-factor is pretty minimal.

As mentioned by someone above, one problem with this kind of setup is whether you can get your front derailleur low enough for the smaller outer ring. I'm using an older SRAM Rival FD because it has two mounting holes, so using the upper hole gets the FD just about low enough for me, but YMMV.


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