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Old 02-22-08, 09:18 PM   #1
hockeyteeth
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Mountain front derailleur w/ road shifter - works, right?

I have a Deore LX front derailleur I want to use with a triple crankset and triple 105 shifter, but was told they had differing cable pulls. Before I buy a triple road derailleur I would like to know the consensus on compatibility.
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Old 02-22-08, 09:25 PM   #2
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They have different cable pulls (I think) but more importantly they have different pull directions. MTB derailleurs are top pull (because the cable runs along the top tube) and Road fronts are pulled from the bottom. You should probably spring for the road FD; they are relatively cheap. Should be around $25 or less.
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Old 02-22-08, 09:29 PM   #3
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The main points of concern with the Mountain/road compatibility is the radius of the cage(as viewed from the side). A road derailleur is made to have a radius compatible with a 48 tooth or higher large ring, while a mountain set is designed for the 42-44 tooth big ring range.
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Old 02-22-08, 09:57 PM   #4
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Yes, the front shifter/derailleur cable pull ratio between Shimano road and MTB/flat bar are different.

What kind of crank will you be using; more specifically, how many teeth on the outer ring? If it's 48 or above, just use a road front derailleur (Sora, Tiagra, 105, Ultegra, Dura Ace). If less than 48T, I'm not sure what you can do.

As a side note, not all MTB FDs are top pull. Some are bottom pull or dual pull.
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Old 02-22-08, 10:10 PM   #5
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Thanks for the responses. I totally forgot about the cable routing, ha. For the record, I'm using a mtb crankset with a 44 tooth big ring.

I suppose I'll try the road derailleur.
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Old 02-22-08, 10:25 PM   #6
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You can use the LX front derailleur with the 105 shifter if you use the last model on this page:
http://jtekengineering.com/shiftmate_straight.htm

Like mtbikerinpa mentioned, the curvature would be off between a 44T crank and road FD.
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Old 02-23-08, 10:11 AM   #7
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A mountain type FD should work better with your mtn. crankset if it will adjust low enough on your frame. If you have a braze-on type derailleur hander this could be a problem. If it is a clamp-on then no problem. You will need a bottom pull FD.
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Old 02-23-08, 04:21 PM   #8
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Originally Posted by mtbikerinpa View Post
The main points of concern with the Mountain/road compatibility is the radius of the cage(as viewed from the side). A road derailleur is made to have a radius compatible with a 48 tooth or higher large ring, while a mountain set is designed for the 42-44 tooth big ring range.
Yeah, but in practice it really doesn't make much difference.

I built my everyday user with an XT FD and a Dura-Ace triple (53-39-30) and it shifts flawlessly.
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Old 02-23-08, 04:30 PM   #9
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Yeah, but in practice it really doesn't make much difference.

I built my everyday user with an XT FD and a Dura-Ace triple (53-39-30) and it shifts flawlessly.
What kind of shifters?
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Old 02-23-08, 04:38 PM   #10
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What kind of shifters?
XT; as the other posters have observed, MTB FDs don't work with roadie shifters. (It's a flat-bar set-up.)

I built my wife an Orbea flat-bar all Ultegra with the Shimano 440 shifters & FD because they have lighter action than the MTB stuff; it works great, too.
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Old 02-23-08, 04:50 PM   #11
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XT; as the other posters have observed, MTB FDs don't work with roadie shifters. (It's a flat-bar set-up.)
I know; I was one of them.

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Originally Posted by rmfnla View Post
I built my wife an Orbea flat-bar all Ultegra with the Shimano 440 shifters & FD because they have lighter action than the MTB stuff; it works great, too.
My wife's former triple 8-speed flat-bar road bike came with the flat bar road shifters and matching FD, but I could never get it setup without there being a ton of cable slack when in the inner ring (it wasn't a big deal while riding but it took a lot longer to get the cable tension just right). I ended up using a regular road FD and though it still had to have a little slack, it wasn't nearly as bad as the original FD.
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Old 02-23-08, 05:03 PM   #12
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One additional problem with incompatability. MTB front derailleurs often won't fit between the seat tube and the rear tire when set for the big ring. The mechanisim for the cable is bent over more and moves into that space when it is pulled. The road derailleur has a more upright arm that stays out of the way. Touring and Cyclocross frames usually have enough room in there for it to work (as long as you use the right shifter or one of the travel agents.)
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Old 02-23-08, 10:59 PM   #13
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Good point!

On my "everyday user" the FD cable bolt touched the tire when shifted to the big ring. I drilled the washer countersink and used a beveled flat-head Allen bolt (an Egg Beater cleat screw) instead and it fits perfectly.

Looks cool, too.
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Old 02-25-08, 08:35 PM   #14
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Today I put a Tiagra FD on my bike to use with the triple mtb crankset. Works great! The max. tooth capacity is larger than 44t, but it still downshifts like a champ. I only had immediate access to a braze-on derailleur, so I used an adapter and shims to make it work.

I'm so excited to have finished my Long Haul Trucker. I've wanted a bike built with that frame for soooo long!
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