Well, not exactly. The largest cog one can use is a matter of the upper jockey wheel being able to clear the largest cog when the chain is on that cog. This is indeed affected by the length of the parallelogram, but also by whether it is a drop, horizonal or slant parallelogram, the type of DO, the position of the wheel in the DO, and even the chain length, as one can sometimes gain clearance between jockey wheel and large cog by adding or removing chain links to rotate the jockey wheel down away from the large cog.
Another major factor is where the pivot of the jockey cage is located. The Campy NR and its predecessors had the pivot located about half way between the two jockey wheels, which tends to reduce the largest cog it can shift. The ideal design in this respect is to have the cage pivot through the center of the upper jockey wheel. This is exactly the design of the Huret Jubilee.
As a result, even the short cage Jubilee shifts a surprising large range and handles a 28T cog with ease. I have the original short cage Jubilee on my early 70's Raleigh Competition. I usually try to have a pretty low gear and I set the bike up with a 14-28 FW and I believe a 38T small chainring on the original TA Professional crank. Clearing the 28T cog was not an issue. Thinking the Jubilee range might be a problem I went with a smaller large chainring, I think 50T or even 49T. Once set up however, I found the setup had chain wrap to spare, and I probably could have used a 52-38 with the 14-28 FW, a setup I often use on French bikes with Stronglight cranks and Simplex RD's. The Simplex sprung upper pivot improves its range, but even lacking a spring upper pivot, the Jubilee, surprisingly, seems to have a similar range.
Regards,
Jerry Moos
Big Spring, Texas, USA
> From: r cielec <teaat4p@yahoo.com>
\r?\n> Subject: [CR] Huret Jubilee Rears and Rears in General ?
\r?\n> To: "Classic Rendezvous" <classicrendezvous@bikelist.org>
\r?\n> Date: Friday, September 11, 2009, 5:54 AM
\r?\n> Ahoy!
\r?\n> I've some questions, please, concerning Huret Jubilee rear
\r?\n> derailleurs and, rear ders. generally speaking. Yes, I am
\r?\n> trying to set-up a drive train incorporating a Huret Jubilee
\r?\n> short cage rear derailleur.
\r?\n>
\r?\n> Re: Huret Jubilee rear ders., short cage version
\r?\n> I am of the understanding that the max. rear sprocket is
\r?\n> 26t-28t, depending on one's specific set-up (that is: at
\r?\n> these limits, it's a trial and error as to whether a 26t or
\r?\n> a 28t can be handled).
\r?\n> Can anyone confirm this, please? Yes, I'm trying to get an
\r?\n> idea of what may work so I don't unecessarily purchase a
\r?\n> heap of FW's that can't be used.
\r?\n>
\r?\n> Re: Rear ders., generally speaking
\r?\n> I am of the understanding that (A) the length of the
\r?\n> parallelogram determines the max. size of the rear sprocket;
\r?\n> and, that (B) the length of the cage determines the amount
\r?\n> of chain take-up. Example: If the rear der. max. size of
\r?\n> rear sprocket is 26t then, doing a retro-fit of a longer
\r?\n> cage will allow for smaller (front) chain rings to be
\r?\n> installed because more chain can now be wrapped but, the
\r?\n> longer cage does not allow retro-fitting rear sprocket
\r?\n> larger than the 26t max. (that is: one is"stuck" with the
\r?\n> 26t rear sprocket).
\r?\n> Do I understand correctly?
\r?\n>
\r?\n> Thank you.
\r?\n>
\r?\n> Richard Cielec
\r?\n> Chicago, Illinois; U.S.A.