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PostPosted: Tue Apr 24, 2012 3:17 pm 
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Joined: Thu Oct 26, 2006 8:54 pm
Posts: 471
Location: USA
Can someone who's tried and tested using a road front derailleur on a 2x10 mtb drivetrain enlighten me on some of the pros and cons? Obviously there's a lot of weight to be saved, but how much sacrifice is there to shifting under load? I'll be running XX shifters and a Hollowgram SL crank (39/26) on a 29er. It seems like the road FD might improve tire clearance compared to the much larger MTB FDs. The cage profile seems likely to be compromised since its designed for a much bigger 53 tooth ring... Anyway just wondering if this is the realm of weenie bikes that are designed for the scales and aren't really ridden on trails, or if its a good functional weight saving option....?

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PostPosted: Tue Apr 24, 2012 6:10 pm 
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Joined: Mon May 16, 2011 8:14 pm
Posts: 410
dwaharvey wrote:
Can someone who's tried and tested using a road front derailleur on a 2x10 mtb drivetrain enlighten me on some of the pros and cons? Obviously there's a lot of weight to be saved, but how much sacrifice is there to shifting under load? I'll be running XX shifters and a Hollowgram SL crank (39/26) on a 29er. It seems like the road FD might improve tire clearance compared to the much larger MTB FDs. The cage profile seems likely to be compromised since its designed for a much bigger 53 tooth ring... Anyway just wondering if this is the realm of weenie bikes that are designed for the scales and aren't really ridden on trails, or if its a good functional weight saving option....?


I'm very interested in this too. I would think the major factor would be the relative jump in teeth between the rings. For road, there's a 14t jump (for standard rings). For a 2x10; 39x26; its a 13t. So in that regard, perhaps it would work well. In actual design, a large difference in road/mtn FDs seem to be the size of the plate that pushes the chain up onto the big ring.. not sure what effect having a much smaller backplate would have on a 2x10.


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PostPosted: Tue Apr 24, 2012 6:51 pm 
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Joined: Fri Jul 25, 2008 7:18 pm
Posts: 93
Location: Sofia, Bulgaria
I am running both a dedicated double mountain front derailleur (SLX) and Dura Ace 7900 with Spleen adapter on different bikes with the same double chainring setup - RaceFace Next LP (old ISIS) with 24/38 Specialites TA rings.

Here are my observations:

The Dura Ace: Very light and very blink. Works very well - i.e. no misshifts, dropped chains, etc, but it tooks me some time to figure the correct setup - i.e. no rubbing, etc. It is almost impossible to fit on a modern full suspension frame. I am running it on a hardtail. Shifting under load - I think it is possible, but to be honest the setup does not give me confidence in doing it.

The Shimano SLX double front: 125g weight is not that bad, considering the price. Setup is very easy and it works very well - i.e. no misshifts, dropped chains, etc. It can fit a full suspension frame easily. I am running it on a Giant Trance. Shifting under load - it seems to be better than the Dura Ace. It gives more solid shifts.

As a conclusion I can say that both setups work well, but the SLX feels more "solid". Never tried SRAM XX, so I cannot give direct comparison. I think though that the main difference will come from the chainrings, not the front derailleur.

Stefan


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PostPosted: Tue Apr 24, 2012 8:12 pm 
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Posts: 380
I run a tuned Ultegra sl front and it shifts fine on FSA rings. You might want to use a gripshifter because of the stronger spring. Think about tuning it for correct reach, I had to because of running the rings very close to the frame for low Q-factor.

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PostPosted: Tue Apr 24, 2012 11:38 pm 
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Joined: Sat Dec 13, 2003 2:25 am
Posts: 4745
Location: Canada
I am running Record on a triple. It is very solid and shifts fine under load. Road derailleurs are routinely used in cyclocross, which is pretty demanding.


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PostPosted: Wed Apr 25, 2012 2:53 am 
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Joined: Sun Sep 13, 2009 4:22 pm
Posts: 41
I'm using a compact road crank, 50/34, so it's a 16t jump but it shifts well. Guess there won't be much penalty.


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PostPosted: Wed Apr 25, 2012 5:47 am 
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Joined: Mon Sep 15, 2008 4:39 pm
Posts: 22
Location: Singapore
DA7800 FD with M970 and XTR crank using middleburn 26T/38T works great. Shifting was spot on and lever spring felt good.

Similar setup but with DA7900 FD instead was not that well. The spring tension felt very hard. When downshift from big ring to small ring, it was very loud because of the cable tension.

Upgraded to XTR980 series with a SR2012 FD, there may be some chain rub but overall, it feels just as good as the original.

all of the frames were using bottom pull so no adaptor was needed.


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