First of all, I thought the OP was asking about vintage front derailleurs with a deep enough cage to handle the big wheel jump inherent in a compact crankset. I'm not sure anyone has addressed that. Many vintage bikes had half-step gearing, which if anything does not require a deep cage, quite the opposite. What did need a deep cage in the late '60s and early '70s were the entry to mid-range bikes like the UO-8, that often were equipped with Alpine gearings with a 52/36 or so in front -- hey, sound familiar? These bikes used Simplex front derailleurs, at least when I had Peugeot lust back in high school! I'm not sure if there is a more rugged alternative. Maybe the Huret derailleur of the Allvit era? or the one that was twinned with the DuoPar?
Wide gear range or not, the '70s designed Huret DuoPar and EcoDuoPar are some of the best shifting rear derailleurs ever. They are long cage, so with your compact you could easily end up needing to wrap a lot of chain. Campy recommends the use of long cages with their compacts and freewheel spreads of any significant size. Chain wrap is a key requirement.
It's not a slant paralellogram, but a dual parallellogram. One is the standard lateral parallellogram that we know and in some cases love. The second is a vertical parallellogram that moves the entire cage subsystem up and down in response to the change in chain tension as the cog size changes. The motion is passive, but it is driven by the cage spring. The result is that the free length of chain between the cog and the jockey wheel is kept constant for all cog sizes, at least 13 through 34, where I've used it. I can't say if it will or won't adapt well to an 11.
The shifting result is that the overshift and undershift are minimal to non-existent, in either direction. With a good tooth profile, such as a Shimano or a Sachs or Maillard Aris, the chain shifts essentially instantly with no feathering required, at least if your hand on the friction lever knows where to go. The dual parallelogram design is a LOT more effective than the offset jockey wheel employed in the Campy NR or the Tourismo (hope I remembered that name right!). I'm not that familiar with the Rallye variations.
Folks have often claimed them to be fragile or unreliable, but I have not seen a problem. If you back-pedal when the derailleur is sufficiently out of position, the chain can hang up. It's not hard to free the chain, and I've even done it kinda spontaneously while pedaling on rare occasion. But there is a little flex in the cage. I've also found this problem can be avoided by maintaining the shift lever friction screw suitably tight, but that's really just one of our friction shifting skills, right?
Ken Freeman Ann Arbor, MI USA
On Thu, May 7, 2009 at 10:41 AM, Jan Heine <firstname.lastname@example.org> wrote:
> Taking the plunge into compact gearing for my vintage touring project. No
>> less an authority than the late Sheldon Brown (see his Hetchins) recommends
>> it, but he uses a modern long cage rear derailleur, which I'd like to avoid
>> if possible.
> I can go either way, Campy or Simplex/Huret. I'll be running a TA or
>> Stronglight 50/34 on the front, and would like to know from members who use
>> such a setup about best derailleurs. Have followed the posts here about
>> Rallys with interest. That's one way I'm might go, either with a pure
>> Rally or a NR fitted with a Rally cage. I've got many replies about this.
> You want a rear derailleur where the cage swings around the upper pulley.
> That means that front shifts don't affect the rear at all. If you don't have
> a huge range on the freewheel, you don't need a long cage.
> Most Huret derailleurs are that way. My Alex Singer uses a TA 48-32 on the
> front, and a 13-24 on the rear, with a Huret Jubilee short cage. It works
> very well, shifts reliably into every gear (even the cross-chained ones),
> and has lasted 30 years before I replaced it last year. (Most of those 30
> years were under its first owner, who must have ridden at least 100,000
> miles on the bike.)
> The Jubilee doesn't shift as well as a true cyclotouring derailleur like a
> Nivex or Cyclo, nor as well as some modern derailleurs when set up well, but
> it shifts well enough that it has never bothered me. And I ride that bike
> more than any other I own.
> Jan Heine
> Bicycle Quarterly
> 140 Lakeside Ave #C
> Seattle WA 98122