Compact cranks

I just bought a compact crank and am wondering if it will work with standard
(short cage) road rear and front derailleurs? The crank has 50/34 teeth --
it will replace a 50/39 setup.

Thanks

RJ Peterson wrote:
I just bought a compact crank and am wondering if it will work with standard
(short cage) road rear and front derailleurs? The crank has 50/34 teeth --
it will replace a 50/39 setup.

Thanks

Rear derailleurs are rated by capacity. Capacity equaling the
difference between the smallest and largest cassette cogs PLUS the
difference between largest and smallest chainrings. Pretend you have a
13-26 cassette and 50-34 chainrings. That is 13-26=13 PLUS 50-34=16.
Total equals 29. Short cage rear derailleurs are rated at roughly 27
capacity. Medium cage at roughly 30. Long cage roughly at 36.
Roughly meaning you can add 2-3 or so to these rough numbers and be
perfectly fine. If you exceed the capacity of the derailleur the chain
will droop in the small chainring-smallest 2-3 or so cog combinations.
Usually not a problem since you don't use these gears much. But if you
were using your 50-34 crank with a 13-29 cassette, total is 32, and a
short cage rear derailleur, you would probably have chain droop in your
smallest 3-4 or so cogs. That would be concern because if you use
these gears, and you probably would, the drooping chain could jump the
pulleys and catch on the derailleur cage. Its possible.

RJ Peterson wrote:
I just bought a compact crank and am wondering if it will work with standard
(short cage) road rear and front derailleurs? The crank has 50/34 teeth --
it will replace a 50/39 setup.


I ran an FSA Energy 50/34 with an 2004 Ultegra short cage and a 12-25
cassette, no problems. I ran the same derailleur with a Ultegra 600
53/39 and a 12-28 cassette, again no problems. Currently using same
derailleur and a Campy 52/42/30 and a 12-25 cassette, I get slight
chain rub on the rear derailleur cage when in the 30 (front) 12 (rear)
combo, so really no problems. This whole short cage/long cage is
completely overrated. In my experience short cage works for up to 28
teeth in the back, over that use an MTB GS.

-Nate

On Mon, 30 Jan 2006 14:03:05 -0600, "RJ Peterson"
wrote:

I just bought a compact crank and am wondering if it will work with standard
(short cage) road rear and front derailleurs? The crank has 50/34 teeth --
it will replace a 50/39 setup.

You won't have any problem in back. The front might possibly be a
problem, as most front derailleurs aren't really designed for the 16
tooth jump. I had an Ultegra 9 speed which I couldn't get to shift
smoothly and quickly. So I swapped it with an old Dura Ace 8 speed
off my circa 1990's bike and no problem. On my new build, I installed
a IRD compact specific front derailleur, but I really think the Dura
Ace worked better.

P.S. Think about installing a chain checker/keeper and take 2 links
out of your 53/39 chain

On Mon, 30 Jan 2006 20:10:52 -0500, Doug Taylor
wrote:

On Mon, 30 Jan 2006 14:03:05 -0600, "RJ Peterson"
wrote:

I just bought a compact crank and am wondering if it will work with standard
(short cage) road rear and front derailleurs? The crank has 50/34 teeth --
it will replace a 50/39 setup.

You won't have any problem in back. The front might possibly be a
problem, as most front derailleurs aren't really designed for the 16
tooth jump. I had an Ultegra 9 speed which I couldn't get to shift
smoothly and quickly. So I swapped it with an old Dura Ace 8 speed
off my circa 1990's bike and no problem. On my new build, I installed
a IRD compact specific front derailleur, but I really think the Dura
Ace worked better.

P.S. Think about installing a chain checker/keeper and take 2 links
out of your 53/39 chain

Don't just take the links out, without checking. Going from a 50 to a
50, there should be no reason to change chain length.


Life is Good!
Jeff

On Mon, 30 Jan 2006 14:03:05 -0600, "RJ Peterson"
wrote:

I just bought a compact crank and am wondering if it will work with standard
(short cage) road rear and front derailleurs? The crank has 50/34 teeth --
it will replace a 50/39 setup.

Depends on which front derailleur you have. Some do a much better job
than others.

On Mon, 30 Jan 2006 20:10:52 -0500, Doug Taylor
wrote:

The front might possibly be a
problem, as most front derailleurs aren't really designed for the 16
tooth jump. I had an Ultegra 9 speed which I couldn't get to shift
smoothly and quickly. So I swapped it with an old Dura Ace 8 speed
off my circa 1990's bike and no problem. On my new build, I installed
a IRD compact specific front derailleur, but I really think the Dura
Ace worked better.

My exact experience, The DA FD 77?? works expecially well. The IRD
compact is a lost cause. It does nothing well. Stiff springs and set
too high for a braze on fitting and you must use an adapter for a
clamp. Currrent Campy fronts work fine too.

On Mon, 30 Jan 2006 20:10:52 -0500, Doug Taylor wrote:
You won't have any problem in back. The front might possibly be a
problem, as most front derailleurs aren't really designed for the 16
tooth jump. I had an Ultegra 9 speed which I couldn't get to shift
smoothly and quickly.

So strange! I have the same (Ultegra 9v) and replacing 53-39 with FSA
50-34 works perfectly.

Sure, I should adjust it, since with 53-39 can work even not perfectly
aligned, while with 50-34 requires a perfect setup.

I mean, I placed chain on 53/13 (my hardest gear) then I aligned derailer
with *chain*, not with crank. Then I reduced clearances to minimum.
Finally I adjusted cable tension to have a proper trim-click, even if
with my setup I don't need trimming at all.

Cheers.

--
Massimo Bacilieri AKA Crononauta
ICQ:4005815

RJ Peterson wrote:
I just bought a compact crank and am wondering if it will work with standard
(short cage) road rear and front derailleurs? The crank has 50/34 teeth --
it will replace a 50/39 setup.

Thanks

Yes it will, just lower your front der, perhaps take one link out of
your chain(depends on how ell it was sized before) and go ride.

Paul Kopit wrote:
On Mon, 30 Jan 2006 14:03:05 -0600, "RJ Peterson"
wrote:

I just bought a compact crank and am wondering if it will work with standard
(short cage) road rear and front derailleurs? The crank has 50/34 teeth --
it will replace a 50/39 setup.

Depends on which front derailleur you have. Some do a much better job
than others.

We have tried some of the 'compact front ders, both IRD and Campag and
find the standard front derailleur for a double works the best for all
compact systems. A chain watcher and ....wait for
it....................Robert is your father's brother.