Double/triple front deraileur difference

Drew Eckhardt said:

What are the differences between double and triple front derailleurs?

The triple has a lower lip to force the chain off the small ring. The
double has plates that are more or less at the same height, i.e., they look
kinda symmetrical.

I've adjusted the height to about

Quoted message said:

1/8" above the outer ring, cage to parallel the chain rings, and
cannot set a high limit screw that consistantly upshifts and doesn't
drop the chain - either I loose upshifts in some gear combinations or
drop the chain.

It sounds like you may not be holding your front shifter long enough to
complete the shift. You might need to hold the shifter past the click for a
1/2 second or so.

Quoted message said:

I have not angled the derailleur to match the chain-line in the
big/small combination; and am wondering if this is all that's needed
or if there's

A cage parallel to the chainrings is a happy cage, unless your chainline is
far from normal.

Quoted message said:

a mechanical difference between double and triple derailleurs that
matters.

I used a 34.9 clamp MTB top-swing front triple derailleur on my 31.8 dia
seat-tubed double road bike, and it shifted fine... until the derailleur
began to get sucked into the rear tire because it was a top swing...

Quoted message said:

Obviously the outer plate matches the big ring curvature (the
Racing-T front should be designed for a 52 big ring and 30 small
ring) and inner plate height/shape matches the intended small ring
(34 isn't too different
from 30).

If it looks close, it should work. If it happens to have a spot where the
chain doesn't hit the derailleur cage on the imprint that pushes it up to
the big ring, adjust the derailleur up or down on the seat tube to try to
get it where it belongs.
--
Phil, Squid-in-Training

On Wed, 17 Nov 2004 16:24:26 -0700, [email hidden] (Drew

Eckhardt) said:

Obviously the outer plate matches the big ring curvature (the Racing-T front
should be designed for a 52 big ring and 30 small ring) and inner plate
height/shape matches the intended small ring (34 isn't too different
from 30).

Are there geometry other geometry differences (say the triple's larger
horizontal gap between small/big than the doubles) which are giving
me trouble?

Shifts into the little ring are real consistent.

The Racing-T rear derailleur should work fine and can be even closer
to the big ring. It should be parallel to the 50t ring when sighted
from above.

The 50t ring needs some decent shift assists. If it is flat on the
inner side with no pins, ramps, or upward bevel, shifting will be
difficult.

The cable to the front derailleur should be in back of the attachment
screw and not in the front.

You aren't trying to use the Racing-T crank with a 50t x 135 bolt
pattern and a 34t x 74 ring? If you try that, you'll need to put the
50t ring in the place of the middle ring.

In article <[email hidden]>,

Phil said:

It sounds like you may not be holding your front shifter long enough to
complete the shift. You might need to hold the shifter past the click for a
1/2 second or so.

I've twiddled the upper limit screw between index clicks. Once it's
enough to get the chain to shift while slowly turning the cranks the
chain drops off if the rear derailleur is on one of the smallest cogs.

Quoted message said:

If it looks close, it should work. If it happens to have a spot where the
chain doesn't hit the derailleur cage on the imprint that pushes it up to
the big ring, adjust the derailleur up or down on the seat tube to try to
get it where it belongs.

The derailleur bumps hit the chain where they should.

I was playing with shimming a bit beyond normal spacing (the FSA crank having
.3mm less between rings than Campy 9 speed suggested this might help); backing
off a bit there should get better engangement between the pins and ramps.
I'll also try the new compact derailleur and see how that works.

I know some rub is common in the last gear, although with the first rub-free
gear 34x15 falling between my last two big-ring gears of 50x21 and 50x23
I wanted a bit more noise-free overlap.

--
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Life is a terminal sexually transmitted disease.