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Old 12-26-12, 10:57 AM   #1
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What front derailleur for a smaller-than-compact chainset?

I'm planning to set up my steel rando bike with a 44/26 or 42/26 chainset. I'd prefer an indexing front derailleur, but it's not a requirement. Seat tube is 28.6 mm, so I need a conventional clamp on or I can get a bracket to simulate a braze-on fitting. But what will it take to shift this well? I'm using DT friction now, but will probably change to a brifter of some sort (drop bar) in the future.
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Old 12-26-12, 11:06 AM   #2
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Are you sure a standard road FD won't work?

If not, I'd use a mountain bike FD. Shimano Deore or similar, pretty cheap used. Second choice, a road triple FD.

An indexing FD is uncommon and not necessary.
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Old 12-26-12, 11:07 AM   #3
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MTB's use 42~44t big chainrings.. good luck you are in a fringe territory,

cage plates wont follow the outside radius of the big chainring,
but it will still force it to move sideways, de railing it.

so will be kludging things together.. drop bar , Have the left lever friction, as in Bar end shifter kits.

then the shifting is in your hands,

not an engineer making parts for OEM build packages.. that you wont be using

of course a SRAM dual drive moves the triple crank into the rear hub,internal gear + Cassette .
then you don't need any front derailleur at all, or more than 1 chainring .

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Old 12-26-12, 11:13 AM   #4
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You can get a 1-1/8" (28.6 mm) clamp-on adapter to use a braze-on fd so either option will work. Here's one choice:

http://www.amazon.com/Origin8-MaxFit...d_sim_sbs_sg_4

If you stick with friction, any current MTB front derailleur will match the curvature of your new smaller "big ring". If you want to use road brifters you will need a road fd and the shifting won't be quite as good.
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Old 12-26-12, 02:48 PM   #5
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I would go with an older XT or something, made for a triple but the plates are pretty flat and shapeless. I have used them for doubles before, only time it's a problem is when running a large inner ring as the inner plate of the derailleur hangs pretty low.
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Old 12-26-12, 06:03 PM   #6
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I'd use an mtb or road compact derailleur since the angle and curve of the cage is better matched to smaller rings. With a band mount, it's easy to get the height correct.

If you have good hand skills, especially if you're good with a file, you can buy a braze on and adapter clamp. Then you can reshape the front to customize cage angle so it follows the curve of the chainring.
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Old 12-26-12, 06:25 PM   #7
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The indexing is in the shifter, not the derailler.
There is no advantage to indexing with a double crankset.
The best choice for an FD will depend on the particular chainrings used.
Having synchronized rings with ramps and pins on the big ring will help if using STI type shifters.
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Old 12-26-12, 06:34 PM   #8
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The indexing is in the shifter, not the derailler. ...
True, but it's a consideration. If the designed pull ratio of the derailleur is less than the lever, there may be inadequate travel with an index lever.

OTOH, if the travel is greater than the levers call for, that's no problem since the inner limit locates the FD on the slack side.
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Old 12-26-12, 07:28 PM   #9
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Having synchronized rings with ramps and pins on the big ring will help if using STI type shifters.
It helps a lot with friction shifting too. Shifting under load is much better and faster.

A few years ago I switched one of my bikes from an old style "flat" chainring crank to a newer crank intended for index shifting. Using the same friction shifters, the improvement in shift speed and accuracy was dramatic.
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Old 12-26-12, 09:16 PM   #10
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True, but it's a consideration. If the designed pull ratio of the derailleur is less than the lever, there may be inadequate travel with an index lever.
On a front derailleur the ratio is usually not much of a problem. If there is a problem with inadequate travel it will more likely be due to inadequate offset from the seat post. Front derailleurs are relatively cheap and I'm assuming that the OP can recognize real obvious problems like clamp diameter size or unusual geometry weirdness.
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Old 12-26-12, 09:18 PM   #11
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So, Road Fan, what are you using for shifters?
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Old 12-26-12, 09:45 PM   #12
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It helps a lot with friction shifting too. Shifting under load is much better and faster.

A few years ago I switched one of my bikes from an old style "flat" chainring crank to a newer crank intended for index shifting. Using the same friction shifters, the improvement in shift speed and accuracy was dramatic.
Yeah, I was also thinking that the ramp and pin shift assists would make it unnecessary to overshift to force the chain onto the big ring.
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Old 12-26-12, 11:36 PM   #13
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So, Road Fan, what are you using for shifters?
Right now they're DT friction, mid-80s Campy Retrofriction, probably C-record but a bit ratty.

The rear mech at this point is a Deore LX 9-speed, the cassette is Ultegra 6700 11-28. The rear derailleur is a lot longer than I need, and besides I like a shiny road bike look, and the rest of the bike is shiny-parts. I'm looking for an Ultegra 6600 GS rear derailleur, but I may settle for a 105, or I may install my 1st generation Chorus.

The front der I've removed is a SunTour XC-pro. It has a really long cage and is s pretty decent fit to the ring radius, but the tail of the cage is only 1/16" from the chainstay and it will not accommodate being moved any lower on the seat tube. The frame builder did not use a braze-on, probably because the tubing is standard-diameter OX-Plat with 0.4 mm walls. I just did a test install of a Huret Jubilee front der, and it fits quite well with the 46 tooth triple. It has about 12 mm clearance between the tail of the cage and the chainstay.

Tomorrow I'll remove the triple rings and install the 44/26 super compact rings. It'll take a little while to experiment with BBs and shims to nail the chainline and balance the Q as well as possible.

I'd certainly prefer to have index-compatible front rings, and I may go to Velo Orange or Ticino rings at some point, if they have sizes I want. I've used a Campy Racing Triple with the matching front derailleur with friction shifters, and it shifted like it was indexed. Even if I never go to brifters, better shifting is better.
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Old 12-27-12, 06:58 PM   #14
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You don't want to put a Campy RD on there if you plan to have a Shimano shifters and/or Shimano compatible cassette. The Campy RD actuation ratio won't be compatible.
The Deore 9-speed RD is fully compatible with the Shimano 10-speed road cassette.
Most road front shifters are not actually indexed anyway.
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Old 12-27-12, 07:13 PM   #15
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Chill, I know! I have the proper Jtek sitting in my parts box, and I like Ergos a lot better than Shimano. Besides, near term I will be using friction, and I guess you're not familiar with the 1st gen Campy Chorus, but it's pretty much friction only, being such an odd design.
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Old 12-28-12, 12:13 AM   #16
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Right now they're DT friction, mid-80s Campy Retrofriction, probably C-record but a bit ratty.
With friction shifters, then, you're pretty open to using any 9-speed MTB bottom-pull front derailleur with the right contour for a 42/44 big ring. Since these cages are made for larger middle rings, you 26 will not be a problem. Understand that Shimano chain ring spacing is different between MTB cranks and road cranks. There may be travel agents to compensate for this. This is for a 9-speed cassette, right?
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Old 12-28-12, 12:11 PM   #17
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Oldbobcat,

The contour is the part of the question I can't answer. Do you know of any cages shaped to fit a big ring near 42 teeth in size? One of the issues I've had with trying to make this work with vintage to late model road derailleurs is that some times the chain wants to sneak under the tail of the cage, especially on upshifts. I've seen some form of this on a Jubilee, a vintage Nuovo Record, a Shimano 600-6207, and small assortment of Cyclones and LePrees floating around in my derailleur box. The only thing so far that does not do this is a SunTour XC Pro - very rigid and a pretty tight fit, but the tail of the cage prevents this unit from being fit to a smaller chainring than 46 teeth. I have an IRD Alpine to try. For both of these the inner cage plate is quite deep and does a better job of engaging the chain when its on the granny ring, than the Huret Jubilee or any of the other plain road FDs.

Any thoughts on how a modern Ultegra 6703 might work?

My rear end is 10 speed: an Ultegra 6700 cassette and currently a Deore LX rear derailleur. I'm thinking of going Campy 1st gen Chorus, a Campy Racing Triple, or a Shimano RD-6703-GS here.

But the number of speeds in the back does not matter until I buy indexing levers, which will probably not be until next Fall. Right?
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Old 12-28-12, 12:49 PM   #18
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RF, The FD won't matter if you continue to use a friction shifter, either down tube or bar end. To index the rear the shifter, RD and cassette spacing have to be compatible or able to be compensated for. For the front derailleur just buy a compact FD, if available, compatible with your proposed integrated shifter.

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Old 12-28-12, 07:02 PM   #19
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Brad, I have to disagree. The FD choice will matter to my setup because the cage shape and design will affect how well it lifts the chain up the 18 tooth gap from the granny to the main ring. This affects riding quality regardless of whether you are using friction levers or indexing controls.

That 18 tooth gap is greater than what is specified for most road derailleurs.

I am intrigued by what you mean by "just buy a compact FD." If you have a specific one in mind, please tell me. I've been on a number of the major manufacturers' sites, and I don't think I saw any parts called "compact front derailleur."
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Old 12-28-12, 09:23 PM   #20
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RF, I come up with Shimano RSX, Shimano R770(?) and the FSA Energy. I would preferably buy one intended for a triple because the cage design might help deal with the 18T difference. Chainrings designed to shift with an integrated shifter for the best possible shifts...still might not be the smoothest upshift on the planet. If you stay with a friction front shifter most any mountain bike FD will work.

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Old 12-28-12, 10:48 PM   #21
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Roadguy, I was going to recommend something like an Alivio FD-M431, but I'm seeing problems. First, you might need to mount it so low that the cage would hit the chain stay. Second, it's made for MTB triples that use longer (118-122mm) BB spindles and 135mm rear hubs. With a short spindle it won't swing close enough to the frame to drop the chain, and with a long spindle you might raise chain line issues. Third, it still might not be all that happy trying to jump the chain up a 16-18t gap, because its humps and bumps really have 12-14t gaps in mind.

Ultegra 6703 is for triples. You could knock the chain off the big ring with the outer plate, but then you'd have to do some sort of double shift to get it off the granny, which would not have enough lift to get it up to 42. Or if it did, it might push it right over the top.

Why are you doing this? No, don't answer, I really don't want to know. Truth is, there isn't a front derailleur made for the chain ring configuration you envision. They all need either a smaller gap or that intermediate step called a middle ring. Why not just get a triple? Or a dual-sport or hybrid bike with a triple? Or one of those new 2x10 MTBs?

Last edited by oldbobcat; 12-28-12 at 10:58 PM.
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Old 12-29-12, 08:08 AM   #22
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Roadguy, ...

mount it so low that the cage would hit the chain stay. Second, it's made for MTB triples that use longer (118-122mm) BB spindles and 135mm rear hubs. With a short spindle it won't swing close enough to the frame to drop the chain, and with a long spindle you might raise chain line issues. Third, it still might not be all that happy trying to jump the chain up a 16-18t gap, because its humps and bumps really have 12-14t gaps in mind.

Ultegra 6703 is for triples. You could knock the chain off the big ring with the outer plate, but then you'd have to do some sort of double shift to get it off the granny, which would not have enough lift to get it up to 42. Or if it did, it might push it right over the top.

Why are you doing this? No, don't answer, I really don't want to know.

Truth is, there isn't a front derailleur made for the chain ring configuration you envision. They all need either a smaller gap or that intermediate step called a middle ring. Why not just get a triple? Or a dual-sport or hybrid bike with a triple? Or one of those new 2x10 MTBs?
Ok, too bad, I'm gonna tell you why I'm doing this and why a cheap-ass hybrid is not in my future.

I'm building a 650b road rando bike based on a Terraferma Corsa 650b frame. I am not building for indexing at this point, so issues with mismatched cog pitch or cable pull ratios are irrelevant at this point. The essentials of good shifting such as cage shape and chain free length are critical. Ditto for clearances, lateral throw, chainline, Q, and chainstay clearances, not to mention gearing range and progression. I think the 42-26 with a Shimano 11-28 10 speed cassette will be just fine for me, thank you.

The person I bought the Terraferma frame from ordered it custom from Mike Terraferma, who mainly builds custom anyway. His usual design choices, while they result in a really nice and efficient steel frame, are in my way as far as crank choice: deep BB, wide chainstay tubes, no dimpling of chainstay tubes. Great handling and a very stiff rear end, but limited space for modern cranksets. The bike is designed to accept 650b x 42 mm tires, and has a 130 mm OLD and a 73 degree seat tube angle. BB drop is 79 mm.

The clearance between the chainstays is about 58 mm at the widest point of the tire (adequate), and across the chainstays the width is 108 mm at the point where the crankarm swings (challenging). I like low-q, so I have fit a vintage TA cyclotourist crankset as a double with a 122.5 mm BB and have also tried it as a triple with a 127.5. The Q as a double is will be about 140 to 144, and as a triple it was 149. The chainline for the double is just a little wide at 45 mm, and it was 45 for the triple. So as far as offset of the chainrings goes, I have a standard road bike with the Q about as optimized as possible. I'm going to trial-fit a 118 mm BB, too, to see if I can nail the chainline without causing chainstay interference.

As some of you know, TA's can deliver a Q as low as the upper 130s if you compromise down the chainline. My wide chainstays prevent that from being done on this bike.

The BB drop is rather deep for a 650b, at 79 mm. Because of the large diameter of the 42 mm tire, this is ok as far as cranklength goes. The tire diameter is bigger than a narrow 700c clincher or tubular. But the chainstay has a steep upsweep due to the low BB. Terraferma also builds with large-diameter chainstays. The result is that derailleur vertical positioning is limited by the tail of some front mechs scraping on the chainstay.

I tried several, and the best shifting resulted (46/36/26 triple) with a SunTour XC Pro with a long cage tail and a somewhat deep inner cage plate, but its tail is only 1/16" above the chainstay. It can't go any deeper. Not as deep as a triple mech or a Shimano M770, but a lot deeper than a traditional road part like a Nuovo Record or a Huret Jubilee. With my double setup, as I've said many times, I'm using a 42-26 or a 44-26. Trial fitting with the 44-26 shifts downward decently with a Huret Jubilee (which has good chainstay clearance!), but it is flexy and won't always lift the chain up to the big ring with "alacrity." It needs a derailleur with a deep inner cage but a short tail.

What am I looking for?

a top-pull (like a road bike) low-normal (with no cable tension the cage is over the granny ring) front derailleur

braze-on or preferably 28.6 mm clamp

with a cage with a deep inner plate like a triple mech and

a short cage tail, like a vintage part


I don't know much about the other styles of front mech design, such as bottom-pull. I'm not a pro mechanic nor have ever ridden much less owned or tweaked on a MTB. I've been a road bike rider (in traffic!!!) since my early teens, 45 years ago.

I appreciate all the help so far, but I hope the above bike-building novelette will help you understand my assumptions and ground rules. This is what I'm building.
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Old 12-29-12, 10:16 AM   #23
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Technically a traditional road derailleur is bottom pull. not top pull. Any pictures of bike with said Suntour derailleur mounted? I have never measured but from memory the older Shimano mountain triple F-deralleurs have shorter cages in length than the Suntour.

If you need to acquire some derailleurs for testing just ask, I have a giant pile of them.
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Old 12-29-12, 02:53 PM   #24
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It's good to have unique problems to solve. Keeps the gray matter exercised.

I think the "deep inner plate" and "short tail" requirements will be hard to reconcile on one FD -- hope someone can prove me wrong. The 16-18 tooth difference itself shouldn't be a problem for any FD spec'd for a compact crankset. If you're not averse to modifying a part for your use, perhaps you could grind off a little from the outer cage wall toward the front so that when you move it down, it fits the 42-44T front ring better and sits closer to the 26T inner ring.

Another thought (since typing is cheap ) -- if you switch to the 12-30 Tiagra cassette, that would allow you to run slightly larger chainrings (like 46T and 28T) and keep the same gearing.
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Old 12-29-12, 03:13 PM   #25
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yeah, top pull means the cable comes from above and pulls up to shift into the bigger ring, this is more common on mountain bikes than on road bikes which are almost always bottom pull, eg the shift cable comes up from the BB and pulls downwards to shift towards the big ring.

the other option on FD's of late I've found is top vs bottom swing. a normal/bottom swing front derailleur the clamp is *above* the cage, while a top swing FD, the clamp is approximately level with the the cage so the seat tube is less cluttered.
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