Campy FD or extra BB spacer to solve shifting problem?

Jens Kurt Heycke said:

I'm setting up an Aegis T2 time trial bike. The DA 7700 FD can't go inward
far enough
because its pivot runs into the FD mounting bracket. Thus, I can't use the 3
largest
cogs without the chain rubbing the FD.

The shop proposes that I add one or 2 extra 1mm BB spacer rings on the drive
side.
I'm thinking that this will mess up the chainline, so I'm looking for other
solutions.

I'm wondering if a Campy derailleur would be able to reach a little further
inward
without colliding into the mounting bracket. Anyone know?

I'd suggest starting by measuring the chainline to see if it's correct.
Standard chainline for a double is 43.5 mm.

See: http://sheldonbrown.com/chainline for details.

If the chainline is correct, and a normal front derailer won't work, the
frame may be defective. The spacers suggested may correct the problem
to the extent of making the bike usable even if it is defective.

Sheldon "Chainline" Brown
+------------------------------------------------------------------+
| Also, are you familiar with the PTF-PTM manufacturing technique? |
| (This term comes from the bridge-building industry.) Stands for |
| "pound to fit, paint to match." --Steve Palincsar |
+------------------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

"Sheldon Brown" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Jens Kurt Heycke said:

I'm setting up an Aegis T2 time trial bike. The DA 7700 FD can't go

inward

Quoted message said:

Quoted message said:

far enough
because its pivot runs into the FD mounting bracket. Thus, I can't use

the 3

Quoted message said:

Quoted message said:

largest
cogs without the chain rubbing the FD.

The shop proposes that I add one or 2 extra 1mm BB spacer rings on the

drive

Quoted message said:

Quoted message said:

side.
I'm thinking that this will mess up the chainline, so I'm looking for

other

Quoted message said:

Quoted message said:

solutions.

I'm wondering if a Campy derailleur would be able to reach a little

further

Quoted message said:

Quoted message said:

inward
without colliding into the mounting bracket. Anyone know?

I'd suggest starting by measuring the chainline to see if it's correct.
Standard chainline for a double is 43.5 mm.

See: http://sheldonbrown.com/chainline for details.

If the chainline is correct, and a normal front derailer won't work, the
frame may be defective. The spacers suggested may correct the problem
to the extent of making the bike usable even if it is defective.

Sheldon "Chainline" Brown

Thanks Sheldon. The chainline is 43.5 with one 1mm BB spacer ring. I think
everything would
work OK with a 53 chanring, but I'm using a 56 (it's a TT bike after all).
When the FD is
raised to clear the 56, the FD pivot ends up colliding with the mounting
bracket when
I shift to the inner chainring. So, in a sense, I suppose the frame is
defective.

A derailleur with a very slightly narrower pivot (or a slightly longer
pivot) would not have this problem.
We're talking maybe half a millimeter. That's why I'm wondering if any
derailleur out there has
a slightly narrower pivot than the DA 7700

thanks, Jens

Jens Kurt Heycke said:

Thanks Sheldon. The chainline is 43.5 with one 1mm BB spacer ring. I think
everything would
work OK with a 53 chanring, but I'm using a 56 (it's a TT bike after all).

No fair witholding important information!

Quoted message said:

When the FD is
raised to clear the 56, the FD pivot ends up colliding with the mounting
bracket when
I shift to the inner chainring. So, in a sense, I suppose the frame is
defective.

No, probably not. You still haven't revealed the size of the small
ring. If it's a 39, you're definitely exceeding the design range of the
derailer. The 56 requires mounting the derailer higher for clearance,
and this higher position would put it farther away from the small ring,
so it wouldn't be surprising that you'd have some chain rub issues.

Quoted message said:

A derailleur with a very slightly narrower pivot (or a slightly longer
pivot) would not have this problem.
We're talking maybe half a millimeter. That's why I'm wondering if any
derailleur out there has
a slightly narrower pivot than the DA 7700

Before replacing the derailer, I'd try reshaping the outer plate to make
it match the curvature of the 56 tooth chainring. This is easy as pi if
you have access to a bench grinder. I've had great success modifying
front derailers this way to work with chainring sizes outside of their
design parameters.

Sheldon "Couldn't Live Without My Bench Grinders" Brown
+-----------------------------------------------------+
| Once more upon the waters! yet once more! |
| And the waves bound beneath me as a steed |
| That knows his rider. Welcome to their roar! |
| Swift be their guidance, wheresoe'er it lead! |
| Though the strain'd mast should quiver as a reed, |
| And the rent canvas fluttering strew the gale, |
| Still must I on; for I am as a weed, |
| Flung from the rock, on Ocean's foam to sail |
| Where'er the surge may sweep, |
| the tempest's breath prevail. |
| --Lord Byron Child Harold's Pilgrimage |
+-----------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Thanks again Sheldon. I really appreciate the time you've taken to
respond. A few comments below.

"Sheldon Brown" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Jens Kurt Heycke said:

Thanks Sheldon. The chainline is 43.5 with one 1mm BB spacer ring. I

think

Quoted message said:

Quoted message said:

everything would
work OK with a 53 chanring, but I'm using a 56 (it's a TT bike after

all).

Quoted message said:

No fair witholding important information!

Quoted message said:

When the FD is
raised to clear the 56, the FD pivot ends up colliding with the mounting
bracket when
I shift to the inner chainring. So, in a sense, I suppose the frame is
defective.

No, probably not. You still haven't revealed the size of the small
ring. If it's a 39, you're definitely exceeding the design range of the
derailer. The 56 requires mounting the derailer higher for clearance,
and this higher position would put it farther away from the small ring,
so it wouldn't be surprising that you'd have some chain rub issues.

The small ring is a 42. Some more withheld information: Aegis has
front derailleur hanger isssues beyond this. When I first got the frame
the FD couldn't even shift into the small ring with a 53/39. Bicycle Sports
had to ship me a new mounting bracket that they had reshaped with a
vise. They tell me that 7/10 of the T2 frames have this problem.
So I'm wondering if I should just reject/return the frame.

Quoted message said:

Quoted message said:

A derailleur with a very slightly narrower pivot (or a slightly longer
pivot) would not have this problem.
We're talking maybe half a millimeter. That's why I'm wondering if any
derailleur out there has
a slightly narrower pivot than the DA 7700

Before replacing the derailer, I'd try reshaping the outer plate to make
it match the curvature of the 56 tooth chainring. This is easy as pi if
you have access to a bench grinder. I've had great success modifying
front derailers this way to work with chainring sizes outside of their
design parameters.

This sounds like a reasonable solution. In the meantime, I actually tried
two extra spacers, which does appear to work. I'm wondering how
bad it is to have the extra 2 mm in front?

--Jens