03 March, 2011

Front Derailleurs

We've recently seen a number of questions regarding the choice of front derailleur for 50.4bcd and compact double cranks. As one of my college professors quipped before explaining some obscure point, "I cannot stress strongly enough how unimportant this is."

What I mean is that front derailleurs were perfected decades ago and there has been virtually no significant progress since. Front derailleurs just work and there is no point in agonizing over which to use. I've seen ancient Campy Nuevo Records shift modern triple cranks on touring bikes without issue and MTB derailleurs on compact doubles. Remember that the only significant difference between a double and triple front derailleur is that the inner cage plate on the triple is deeper to better pick up the chain on the granny ring. In short, getting the ideal derailleur may improve shifting, but probably not by enough for most to notice.

So in choosing a front derailleur for a compact double or wide range double I'd consider the following, in order of importance:
  • Make sure the clamp fits the frame.
  • If you use index shifting be sure it's compatible
  • A front derailleur designed for a compact double is nice because the curve of the plate better matches the outer chainring, but I can't feel much performance difference. If I already owned a regular double or triple front derailleur I'd just use it.
  • On 50.4bcd cranks there can be an issue with derailleurs that have a "sculpted" outer cage, as in the photo on the right. These cages can brush the crank arm. It's safer to stick with derailleurs with flat outer plates.
    • Modern derailleurs with flat outer cages are hard to find, though, so I use a Tiagra front derailleur with the Grand Cru 50.4bcd crank, but mount it with around 8.5mm of clearance between the teeth and the outer cage, instead of the usual recommended 2-3mm
    • With this kind of setup, you need to adjust the limit screws just right, but if you're careful with the setup it shifts well and runs fine.
So what new front derailleur would I buy for my own bike, any Campy double, or a Shimano 105, or one of the Micro Shift compact doubles that have been imported by FSA, IRD, and Forte (Performance). We may import our own version of the latter; it's well made, shifts nicely, and is cheap.

22 comments:

Gunnar Berg said...

I'm always a little surprised when someone gives straight-up advice that I actually agree with. Which probably says more about me than you.

Brian @ OBB said...

Yikes, I normally agree with everything you post, but not here.

1. The front derailleur has the hardest job on the bike (shifting while the chain is under direct load), and running a road double shifter on a mountain bike (even with just 2 rings) is usually finicky because of the lack of lower inner cage as well as...

2. No mention of the different pull ratios between mtb and road? Lots of touring bikes come specced with brifters matched to mountain bike derailleurs and gearing... but shifting always sucks.

Nate Knutson said...

Er, um, you forgot all about minimum tooth difference, an issue that often rears its head when using Shimano 10-speed front derailers on setups they're not intended for. (A number specified for any given triple derailer that specifies the minimum tooth difference required to prevent the inner cage from hitting the top of the middle ring when you're shifted onto the big ring, and the reason why triple derailers don't work with half-step or similar chainring setups. Sometimes the spec is conservative by 1 tooth, but not usually. And grinding is an option but it's a big hassle in practice).

Kevin Mulcahy said...

FYI: Shimano just announced a cyclocross specific group, with 4 front derailleurs built to work with compact cranks with a 46t outer ring.

Chris Kulczycki said...

Just to be clear, this post is about derailleurs for wide-range and compact doubles, not triples.

Nate, I've never had an issue with minimum tooth difference on double cranks. But then I've not tried every combination. We have no problems shifting from a 30t to a 46t ring using any number of road derailleurs.

Brian, It is true that you may need to have derailleurs compatible with your index shifting system. That's why I like my Campy brifters with non-indexed front.

I should also have said that a 10 speed derailleur on a wide chain won't work, but I've successfully used 8 and 9-speed derailleurs with 10 speed.

philcycles said...

I'm clearly a retro guy-see-but I seem to find that an oldish front derailleur works best. I currently have old Campy Record, Simplex and a Suntour. One thing I like-because I am, if I do say so myself, a pretty good mechanic-is that I can tweak them to perfection.
Phil Brown

philcycles said...

After I hit send realized that the website might be construed as an ad. It isn't. I'm not longer building.
Phil Brown

Nate Knutson said...

Chris - My bad; I kind of have "50.4 = triple-able" burnt into my mind and forgot that VO isn't doing that (yet?).

Ray Warns said...

I agree that many of the past front derailleurs work as well as anything since, and the best of the best (in my view)is the Simplex Super LJ, as shown. It works with most cranks, 5 speed through 10 speed chains, anything. Coming in second are the Suntour products from 1987-1992.

Anonymous said...

Nuovo Record

eaglerock said...

I'm with you, Nate; 50.4 triples are my standard, and I want the GC components made available for that purpose. Chainrings and bolts especially.



Unlike the compact double+wide-range cassette people, some of us are using older frames that can't take the spread of a 8/9/10-speed cassette/freehub without unacceptable risk. We adapt 3x6/3x7 to produce roughly equivalent results.



As for the subject of the thread, flat-cage FDs seem to work fine for 50.4 triples. I normally use the cheap and durable Campy Nuovo Records; I haven't had any trouble coming off 30T grannies to 46T middles. I'll gladly try 26T or 28T grannies, if VO will stock them.

mpetry912 said...

+1 on the old Campy FD, which I think is a mod. 1052. One of the best bike components ever made! Shifts just about any combination of chainrings, from wide range compact to triple to close ratio, no muss no fuss.

However I think some of the discussion around what front derailleur is best comes from the use of brifters as opposed to downtube levers. Remember that the brifter does not have quite as much cable take up and does not "trim" in quite the same way as an analog downtube lever. This is part of the reason for the differentiated FD cage shapes atmo.

doug in seattle said...

I've run into one problem while using various different derailleurs on different frames:

If you use a smallish big ring with a long-cage triple derailleur on an old frame with the rear derailleur cable travelling along the top of the chainstay, you run the risk of interference between the cable and the bottom of the derailleur. Annoying!

Anonymous said...

Is anyone using a Simplex or similar front derailleur with Ergo shifters? I'm wondering how they would pair up.

Nate Knutson said...

I love VO and hate to pick nits, but there's something that's been bothering me about this post/thread: as a working mechanic and someone who's often ran unusual gearing/speed/chainring setups on my own bike, I find that you do almost always have to be pretty selective about front derailers if you want to bring the chance of chain drop ever occurring as close to zero as possible without using a chain catcher and with good overall performance. I think it's often pretty easy to make an error in FD selectivity that most will notice if you don't get the right one.

frank said...

would an old shimano deerhead designed for half-step gearing work with a 46-30?

NatMc said...

Unfortunately, it seems like modern obseletism has finally caught up with the devil-may-care world of front derailers. I just bought a campy 11-speed FD to go on my 9-speed drive train. It was actually one of the better-priced models and certainly the best looking in my price range. But none of that mattered once I installed it and found that the cage's depth is too narrow for non-eleven-speed chains. No matter how perfectly I adjusted it, with my campy indexed brifter, it rubbed in either the large or small ring. No way around it other than to bend the hell out of it.

So, not just any front derailer will do. alas.

Anonymous said...

Hi, I'm wondering if you have any suggestions for which front derailleur to use with a compact triple with a low Q-factor. I'm having trouble finding a replacement that doesn't rub the arms of the Mavic 637 crank on my tourer. Thanks!

John B said...

Just installed the VO 50.4 crank (46/30) on my Ellis Briggs Randonneur (shimano 105, 10 speed, swapping out the triple) and felt my experiences may be of interest or help.

No way was the 105 triple derailleur going to work. The sculpting of the plates fouls the crank arm before it would up-shift. Clearly derailleur choice is of some importance.

Tried the the new Shimano CX70 cyclocross front derailleur designed for a 46 tooth crank with a range of 16. Unfortunately the braze on mount location on the cx70 is much (7mm or so) shorter than the 105 and so I was unable to mount low enough (now i understand why clamp on may be preferable)

So, decided to simply drill the cx70 derailleur with a new mount bolt hole 7mm above the original and tapped it with and M5 tread to mount at the correct height.

Result? Works perfectly, the width and shape of the CX70 matches well and shifts crisply with no issues so far...

Johan said...

Every new front derailer I've seen with my own eyes have had shaped and too wide outer plates to work with my old 50.4 bcd Stronglight and TA cranks. They'd hit the crank arm whem shifting. Also, some derailers that do have a flat outside, have been made for road doubles with rather large small rings, and have had a cage that doesn't extend low enough for the chain to run free with a small second front ring. I've only been able to use a few selected older front derailers.

All this makes me think it's a pretty strange attitude that this is an "unimportant" issue? In my experience the large majority of front derailers doesn't work at all with these older cranks. I'd be very glad to get to know if there are any new and available front derailers that work with old French 50.4 bcd cranksets with a 48/26 or 52/28 setup.

Rnager1942 said...

Much as I love the styling of the Gran Cru, I may be ordering the polyvlant.
I tried the gran cru and regardless of what was tried there were issues with the crank arm rubbing (jamming into at one point)the rx100 front derailleur and the vintage 105 (which as as flat a plate as one can get)FD.
More of an issue was the unacceptable chain deflection with the chain ou the outer CR and outer Sprocket (46/13)
The Polyvlant (I believe at least one other place offers the same setup)has the arms which sit farther out from the spider (and thus from the derailleur cage)as well as having the entire chainring setup out farther allowing a much straighter chainline (The crank is based on a triple {ie:Sugino rd600)wsith the outer ring removed and a bash guard in its place.
May not look as great but with this rider function outweighs form

Rnager1942 said...

While the triple based Polyvlant with its outer bash guard,may not have the 'bling' of the gran cru it the mechanic at my local LBS says :"it's the way to go" if I want to avoid all the constant tweaking"
The newer school design of the crank arms and spider erase the issues with the crank arm/derailleur cage and the nasty chain deflection issues.