Even the short cage Jubilee has a surprisingly wide range, I'm using one wi th a 28T cog on my early 70's Raleigh Competition, and another on an even l arger cog, 32T I think, on my Raleigh Super Tourer.
However, I've found there are two considerations in regard to what gears an RD will shift. The first is how much chain the cage will wrap between the rear stop and the point where the cage becomes too near horizonal on the large-large combo to let the chain run smoothly. Simplex RD's hav e a range advantage because the sprung upper pivot allows the derailleur body to rotate further forward, so that the body rotation as well a cage ro tation wraps chain. How much chain an RD will wrap is a function of RD geometry and whether the upper pivot is sprung.
But the second consideration, which often is the limiting one, is whether the upper pulley will hit the large cog or come so close that the chain wo n't run smoothly. This one is a function not only of RD geometry, but also dropout geometry, chainstay length, chain length and front chainring s ize. If the pulley hits the large cog, it is often because the cage is near vertical, when the chain is on the large cog. This can often be solved by either lengthening or shortening the chain to rotate the cage eit her forward of back, and in either case down. But this can then cause the chain to be slack on the small-small combo or the cage to be near hor izonal on the large-large. One may then be forced to either use a larger small cog or a smaller large chainring. I find I usually choose to shor ten the chain and fit a smaller large chainring, typically substituting a 5 0T for a 52T or 53T. In fact, I just happened to go through this drill with a mid-70's Raleigh Gran Sport yesterday.
Regards,
Jerry Moos
Big Spring, Texas, USA
From: John Thompson <johndthompson@gmail.com> Subject: Re: [CR]Max sprocket for Huret Jubilee long cage? To: Cc: classicrendezvous@bikelist.org Date: Sunday, September 7, 2008, 9:25 PM
Mitch Harris wrote:
>> Has anyone here used a long cage Jubilee with anything larger than
>> 24T? If so, what's the largest toot count it can safely /
reasonably
>> handle?
> My short cage Jubilee der works easily with a 28 cog, and I remember
> them in the 70s specced on bikes with 28 large cogs.
I think this may also depend on the dropout. I have a short-cage Jubilee mounted on a Tange TR dropout (http://www.os2.dhs.org/~john/dropouts/tange-tr.jpeg) and it barely clears the upper pulley with a 23T cog.
Further accommodation may be possible by adjusting the "angle of the dangle" if your mounting bolt kit includes an adjusting screw, but changing the angle too much will adversely affect shifting.
--
-John Thompson (john@os2.dhs.org)
Appleton WI USA