maximum cog size with ultegra short cage rear derailleur?

I have an older ultegra rear derailleur (RD-6401, early-mid 90's
vintage). What's the largest cog that derailleur will ACTUALLY
accommodate? The specs for it say 27, but can one use a 28 on it w/o
problems?

On 22 Sep 2005 14:32:16 -0700, "damyth"
wrote:

I have an older ultegra rear derailleur (RD-6401, early-mid 90's
vintage). What's the largest cog that derailleur will ACTUALLY
accommodate? The specs for it say 27, but can one use a 28 on it w/o
problems?

Twenty-eight or 30t even will work fine. Don't forget to size the
chain for the larger cog.

I have a 2004 Ultegra short Cage (SS) I've used it with a 28, works
well with a few mm to spare. I tried a 32 and it hits the cog. I would
bet 30 is the limit.

-n

On 22 Sep 2005 14:32:16 -0700, damyth wrote:
I have an older ultegra rear derailleur (RD-6401, early-mid 90's
vintage). What's the largest cog that derailleur will ACTUALLY
accommodate? The specs for it say 27, but can one use a 28 on it w/o
problems?

Hallo.

AFAIK it's not the single size the problem, but the total "amount of
teeth". It means that you should sum teeth difference in cranks with
teeth difference from smallest to biggest cog.
For a short cage derailer max difference is 29.

I.e.: crankset 53-39 has a difference of 14 teeth.
A 27-12 cassette has a 15 teeth difference.
Total difference that cage must accomodate is 14+15= 29 teeth.

So, 27 is max cog size only if you have a 12 smallest cog.

But if you find i.e. a cassette 14-29, derailer is perfectly enough,
because difference it's always 29-14 = 15 and sum with cranks is always
29.

Cheers.

--
Massimo Bacilieri AKA Crononauta
Ravenna, Italy

damyth wrote:

I have an older ultegra rear derailleur (RD-6401, early-mid 90's
vintage). What's the largest cog that derailleur will ACTUALLY
accommodate? The specs for it say 27, but can one use a 28 on it w/o
problems?

28t is a safe bet. I've run a 28t on that derailer. Some say a 30t cog
works, some say it doesn't. I suppose the derailer mount on your frame
might have some impact on this.

--
Dave
dvt at psu dot edu

Crononauta wrote:
On 22 Sep 2005 14:32:16 -0700, damyth wrote:
I have an older ultegra rear derailleur (RD-6401, early-mid 90's
vintage). What's the largest cog that derailleur will ACTUALLY
accommodate? The specs for it say 27, but can one use a 28 on it w/o
problems?

Hallo.

AFAIK it's not the single size the problem, but the total "amount of
teeth". It means that you should sum teeth difference in cranks with
teeth difference from smallest to biggest cog.
For a short cage derailer max difference is 29.

I.e.: crankset 53-39 has a difference of 14 teeth.
A 27-12 cassette has a 15 teeth difference.
Total difference that cage must accomodate is 14+15= 29 teeth.

So, 27 is max cog size only if you have a 12 smallest cog.

The big problem with equations. a 12-28 is no problem with a short cage
rear derailleur, cuz many of us have actually tried it.



But if you find i.e. a cassette 14-29, derailer is perfectly enough,
because difference it's always 29-14 = 15 and sum with cranks is always
29.

Cheers.

--
Massimo Bacilieri AKA Crononauta
Ravenna, Italy

Qui si parla Campagnolo wrote:
a 12-28 is no problem with a short cage
rear derailleur, cuz many of us have actually tried it.

or even an 11-28.

--
Dave
dvt at psu dot edu