Changing to 48 x 34 - help with front derailleur problem?



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Argyll Bob

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I am in the process of trying to change from 53 x 39 to 48 x 34 in order to get a gearing range more
compatible with my ability and expected terrain. I found a Ritchey 110 bcd crankset which allows me
to use the smaller inner ring, so that is not a problem. It's now on the bike, and the gear ranges
for both rings are where I want them. While I could get most of the same gears with 53 x 39, I had
some high gears I couldn't use and would have to use some very large cogs to get the low gearing I
want with a 39. Here's the problem - My bike is a 1997 Softride Powerwing - a beam bike with the
tall (tapering from about 3" to 2") aluminum chainstays rather than the normal small round ones.
1. Moving the derailleur down the braze-on tab enough to get the proper distance between the cage
and chainring causes the rear of the cage to hit the chainstay.
2. The cage on a standard road derailleur doesn't curve enough to match the smaller 48t ring. It
seems that my ideal solution might be a braze-on (has to be a braze-on as this bike has no
seat tube), MTB (would have a cage curvature close to what I need, and maybe enough metal that
I could make small changes with a grinder), with a shorter than normal cage. I haven't seen
anything like this, so I'm assuming that I will have to start with an existing derailleur and
make modifications. As far as cage length is concerned, it looks like I will need to cut
enough off the bottom of an existing derailleur cage to clear the chainstay, then make some
type of cross brace to regain the stiffness. For the curvature question, I see two
possibilities: Either start with a derailleur that has enough metal in the side plates so I
can grind the outer plate to match the ring shape, or tilt the derailleur back on the mounting
tab to get the tail of the cage closer to the ring. The second option would require reshaping
the mounting ear and/or shimming above the mounting bolt - not sure if that approach would be
strong or rigid enough. So i'm looking for suggestions from the experts - what derailleur
should I start with, and how do I make it work?

Thanks, Bob Leckron Indianapolis
 
P

Paul Southworth

Guest
In article <[email protected]>, Argyll Bob <[email protected]> wrote:
> I am in the process of trying to change from 53 x 39 to 48 x 34 in order to get a gearing range
> more compatible with my ability and expected terrain. I found a Ritchey 110 bcd crankset which
> allows me to use the smaller inner ring, so that is not a problem. It's now on the bike, and the
> gear ranges for both rings are where I want them. While I could get most of the same gears with
> 53 x 39, I had some high gears I couldn't use and would have to use some very large cogs to get
> the low gearing I want with a 39. Here's the problem - My bike is a 1997 Softride Powerwing - a
> beam bike with the tall (tapering from about 3" to 2") aluminum chainstays rather than the
> normal small round ones.
> 1. Moving the derailleur down the braze-on tab enough to get the proper distance between the
> cage and chainring causes the rear of the cage to hit the chainstay.
> 2. The cage on a standard road derailleur doesn't curve enough to match the smaller 48t ring.

Bob, if you get into cutting up the front derailleur cage you are going to be farting around with
this bike for days. I think the quickest way out may be a 50t chainring. If the 16t jump between the
rings is too big for your front derailleur, get a bz-on road triple front derailleur or use a 36t
small ring. I think if you compromise that amount then it should all go together a bit easier and
hopefully the cage will not hit the stay.

Campy sells a crank in the 30-40-50 format and their road triple derailleur works pretty well on it.

--Paul
 
T

The Pomeranian

Guest
Argyll Bob wrote:
>
> I am in the process of trying to change from 53 x 39 to 48 x 34 in order to get a gearing range
> more compatible with my ability and expected terrain. I found a Ritchey 110 bcd crankset which
> allows me to use the smaller inner ring, so that is not a problem. It's now on the bike, and
> the gear ranges for both rings are where I want them. While I could get most of the same gears
> with 53 x 39, I had some high gears I couldn't use and would have to use some very large cogs
> to get the low gearing I want with a 39. Here's the problem - My bike is a 1997 Softride
> Powerwing - a beam bike with the tall (tapering from about 3" to 2") aluminum chainstays rather
> than the normal small round ones.
> 1. Moving the derailleur down the braze-on tab enough to get the proper distance between the
> cage and chainring causes the rear of the cage to hit the chainstay.
> 2. The cage on a standard road derailleur doesn't curve enough to match the smaller 48t ring.
> It seems that my ideal solution might be a braze-on (has to be a braze-on as this bike has
> no seat tube), MTB (would have a cage curvature close to what I need, and maybe enough metal
> that I could make small changes with a grinder), with a shorter than normal cage. I haven't
> seen anything like this, so I'm assuming that I will have to start with an existing
> derailleur and make modifications. As far as cage length is concerned, it looks like I will
> need to cut enough off the bottom of an existing derailleur cage to clear the chainstay,
> then make some type of cross brace to regain the stiffness. For the curvature question, I
> see two possibilities: Either start with a derailleur that has enough metal in the side
> plates so I can grind the outer plate to match the ring shape, or tilt the derailleur back
> on the mounting tab to get the tail of the cage closer to the ring. The second option would
> require reshaping the mounting ear and/or shimming above the mounting bolt - not sure if
> that approach would be strong or rigid enough. So i'm looking for suggestions from the
> experts - what derailleur should I start with, and how do I make it work?

I suppose I would be surprised if the arc is that big of a deal for the 48t as opposed to a 53t.
I've used 48t rings with "regular" front derailleurs with no difficulty.

I'm not sure of the total cage length, but I do know that the inside arc/plate and plate screw &
cylinder (for the brace at the "back" of the cage) of a Campy f-der is "cut" along a larger arc than
Shimano's is. I don't know what the total cage length between the two is, so if the Campy is longer
it would tend to eliminate the benefit you need. If not, the Campy would help a bit, but I'm not
sure how much. If you have a bike shop nearby that tends to hold onto some old stuff, you might find
and old derailleur is better suited. Something like an old half-step for race bikes would likely
have a fairly short cage and have the inner plate quite high. Sometimes you can find old stuff with
plenty of life left.
 
B

Bluto

Guest
[email protected] (Argyll Bob) wrote:

> 1. Moving the derailleur down the braze-on tab enough to get the proper distance between the
> cage and chainring causes the rear of the cage to hit the chainstay.
> 2. The cage on a standard road derailleur doesn't curve enough to match the smaller 48t ring.

Have you tried leaving the front derailleur higher than spec to see if it works? Try placing it as
low as you can without the clearance problem, and test whether it will shift properly.

Any up-to-date front derailleur intended for a smaller ring will have a deeper cage, which sounds
like it would exaggerate your problem.

Chalo Colina
 
P

Paul Kopit

Guest
I know that a regular Campy front derailleur will handle 48T w/o a problem. I'm not sure that a MTB
rear derailleur is short where you want it to be. If you cut and brace, you will get chain drag on
the bottom of the front derailleur with many of the 34t combinations, which you will need to use.
Consider a 50t ring and a cassette with 13 as the smallest cog. You'd have to try different front
derailleurs to find out which will handle the 16t cog difference.

On 27 Jan 2003 06:44:37 GMT, [email protected] (Argyll Bob) wrote:

> 1. Moving the derailleur down the braze-on tab enough to get the proper distance between the cage
> and chainring causes the rear of the cage to hit the chainstay.
> 2. The cage on a standard road derailleur doesn't curve enough to match the smaller 48t ring. It
> seems that my ideal solution might be a braze-on (has to be a braze-on as this bike has no
> seat tube), MTB (would have a cage curvature close to what I need, and maybe enough metal
> that I could make small changes with a grinder), with a shorter than normal cage. I haven't
> seen anything like this, so I'm assuming that I will have to start with an existing
> derailleur and make modifications.
 
D

David L. Johnso

Guest
On Mon, 27 Jan 2003 01:44:37 -0500, Argyll Bob wrote:

> I am in the process of trying to change from 53 x 39 to 48 x 34 in order to

I have a 46/30 for the same purpose.

> 1. Moving the derailleur down the braze-on tab enough to get the proper distance between the
> cage and chainring causes the rear of the cage to hit the chainstay.

Give a little extra distance between the cage and the chainring, so it clears, or bend the end
of the cage

> 2. The cage on a standard road derailleur doesn't curve enough to match the smaller 48t ring.

Big deal. I've used mine for years, no trouble.

> It seems that my ideal solution might be a braze-on (has to be a braze-on as this bike has no
> seat tube), MTB (would have a cage curvature close to what I need, and maybe enough metal that
> I could make small changes with a grinder), with a shorter than normal cage. I haven't seen
> anything like this, so I'm assuming that I will have to start with an existing derailleur and
> make modifications.

Possibly, but less than ideal on a front derailleur would probably work just fine. Now, Shimano may
be fussier than Campy, because of their adaptation for a no-trim front shifter, but still it should
be doable.

> As far as cage length is concerned, it looks like I will need to cut enough off the bottom of
> an existing derailleur cage to clear the chainstay, then make some type of cross brace to
> regain the stiffness.

The end of a Shimano cage is a hole on the outside, and a threaded hole on the inside. Cut it down,
shape it, drill new holes, and tap.

> For the curvature question, I see two possibilities: Either start with a derailleur that has
> enough metal in the side plates so I can grind the outer plate to match the ring shape, or tilt
> the derailleur back on the mounting tab to get the tail of the cage closer to the ring.

What about a mountain-bike derailleur that is meant for this size chainring?  If you _have_ to have
the curvature match, do that. Don't grind it to death.

--

David L. Johnson

__o | Some people used to claim that, if enough monkeys sat in front _`\(,_ | of enough
typewriters and typed long enough, eventually one of (_)/ (_) | them would reproduce the
collected works of Shakespeare. The internet has proven this not to be the case.
 
D

David L. Johnso

Guest
If you really believe that a derailleur whose curvature matches a 53-tooth chainring would not shift
a 48, then how is it possible for that same derailleur to shift between the two inner chainrings of
a triple? It is also higher than "spec", but, strangely, still works.

Try the derailleur you have, at a height that clears the stay, and see if it can't be made to
work well.

--

David L. Johnson

__o | As far as the laws of mathematics refer to reality, they are not _`\(,_ | certain, and as
far as they are certain, they do not refer to (_)/ (_) | reality. -- Albert Einstein
 
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