dual pivot brake caliper toe progression



A Muzi wrote:
> jim beam wrote:
>> jim beam wrote:
>>> for the skeptics.
>>>
>>> http://www.flickr.com/photos/38636024@N00/1928128941/
>>> http://www.flickr.com/photos/38636024@N00/1928128939/
>>> http://www.flickr.com/photos/38636024@N00/1928128923/
>>
>> based on viewer stats, it seems some people are only looking at the
>> first link. you'll need to look at all three to see the
>> progression.
>
> I saw a photo series of a rear caliper whose shoes ended up angled
> the wrong way at full compression. I'm sorry I can't help with that.
>
> Brakes on bicycles here seem to not have any complex mechanism to do
> such a complex movement - all DPs here have a pair of simple sleeve
> pivots for the arms. Modern shoes have orbital mounts for toeing.
>
> In fact if our rear calipers on bikes moved like your rear brake
> photos, we would know it. The pads would be noisy, hitting the rim
> backwards.
>
> Again, perplexing photos which I don't understand and cannot explain.
> If you find no solution, check with Shimano or get some genuine
> Campagnolo calipers.

I can think of a couple of possibilities to explain the apparent motion.
One is motion parallax error caused by the camera position. Another
is that the brakes are laying freely on a surface and may move slightly
as the brakes close. Note that there are two sets of photos that appear
to show contradictory evidence. Hence my suggestion that the brakes
should be mounted to a planar surface to provide a reference. If I
owned a dual pivot brake, I'd do it, but unfortunately all my bikes have
cantilevers, single pivots or hub brakes.
 
In article <[email protected]>,
jim beam <[email protected]> wrote:
>> Now, you can call names all you want, but it doesn't make anything
>> that you've said or shown us evidence of front/rear non-
>> interchangeability. I'll let you back up, split some hairs, and claim
>> that Shimano changed their design for dual pivots between my old RX100
>> and your new Dura-Ace. I'll even accept it if you can figure out a
>> way to prove that the second pivot on your brake is off axis with the
>> mounting bolt, but I will not take pictures of brake pads as
>> evidence. They don't prove anything.
>>
>
>but your caliper still shows toe progression!!!

These photos show quite clearly that the same front caliper can
have toe-in or toe-out as the caliper closes with just the change of the
pad angle. This is not a function of front calipers being different from
rear calipers as you've claimed, it's a matter of the pads being
mounted at different angles in either application.

>compare with single pivot!!!

No difference.

http://www.OCF.Berkeley.EDU/~tee/rbt/toe/DSC01855.JPG
http://www.OCF.Berkeley.EDU/~tee/rbt/toe/DSC01851.JPG

The phenomenon is weaker for single pivot calipers, but still
exists, and functions as I described it previously. What accentuates
it for dual pivot calipers is that the offset pivot is lower, making a
larger relative difference in the radiii on which the front and back
ends of the pads pivot.

-Luns
 
In article <[email protected]>,
jim beam <[email protected]> wrote:
>> Now, you can call names all you want, but it doesn't make anything
>> that you've said or shown us evidence of front/rear non-
>> interchangeability. I'll let you back up, split some hairs, and claim
>> that Shimano changed their design for dual pivots between my old RX100
>> and your new Dura-Ace. I'll even accept it if you can figure out a
>> way to prove that the second pivot on your brake is off axis with the
>> mounting bolt, but I will not take pictures of brake pads as
>> evidence. They don't prove anything.
>>
>
>but your caliper still shows toe progression!!!

These photos show quite clearly that the same front caliper can
have toe-in or toe-out as the caliper closes with just the change of the
pad angle. This is not a function of front calipers being different from
rear calipers as you've claimed, it's a matter of the pads being
mounted at different angles in either application.

>compare with single pivot!!!

No difference.

http://www.OCF.Berkeley.EDU/~tee/rbt/toe/DSC01855.JPG
http://www.OCF.Berkeley.EDU/~tee/rbt/toe/DSC01851.JPG

The phenomenon is weaker for single pivot calipers, but still
exists, and functions as I described it previously. What accentuates
it for dual pivot calipers is that the offset pivot is lower, making a
larger relative difference in the radiii on which the front and back
ends of the pads pivot.

-Luns
 
In article <[email protected]>,
Tim McNamara <[email protected]> wrote:
>Luns Tee wrote:
>> In article <[email protected]>, Tim
>> McNamara <[email protected]> wrote:
> >
>>> It's difficult to tell from the photos, but it appears that there
>>> is an eccentric motion to the pad on the right. As the brake
>>> closes, the right pad not only moves towards the other pad but also
>>> forward (down, in the photo). This could be explained by the
>>> pivots not being parallel to each other.
>>
>> It's not a matter of the pivots: the same thing happens with
>> single-pivot brakes with both brake arms pivoting on the same bolt.
>>
>> This is a matter of the brake pads not being parallel to the brake
>> pivots. A rear brake has its pads mounted with their rear end farther
>> from the pivots than the front end. Being at a larger radius from the
>> pivot, the rear end moves more than the front. A front brake, thanks
>> to the offset off the fork, has its pads more parallel to its pivot.
>
>That doesn't suffice to explain the apparent movement shown in "jim's"
>photos in which one pad appears to move forward relative to the other.
>That could just be an artifact of the brake laying on an open book,
>hence my suggestion to "jim" to mount the brake on a planar surface to
>provide a reference.

I'm sorry, I missed your point on first reading, and wrote
addressing the phenomenon of changing toe.

I think what you're seeing is a combination of foreshortening
and parallax. As the centre-pivot arm closes in on the rim, the pads
move down towards the hub. The offset-pivot arm does the opposite, with
the pivot being outboard of the pad rather than inboard (this is the
cosine effect that Jobst dislikes with these brakes). What this means is
that in the photos, one pad is retreating away from the camera, while
the other gets closer. The movement you're seeing is just the effect of
parallax as you see this motion.

>> It's a stretch of the imagination to to think that this is a
>> deliberate effect though. More to the point of what started this
>> discussion, a front brake mounted on the rear has its pads at the
>> same angle relative to its pivots as a rear brake mounted on the
>> rear.
>
>Calipers can be swapped front for back and always have been
>interchangeable; the only difference is the lengths of the pivot bolts.

Agreed.

-Luns
 
In article <[email protected]>,
Tim McNamara <[email protected]> wrote:
>Luns Tee wrote:
>> In article <[email protected]>, Tim
>> McNamara <[email protected]> wrote:
> >
>>> It's difficult to tell from the photos, but it appears that there
>>> is an eccentric motion to the pad on the right. As the brake
>>> closes, the right pad not only moves towards the other pad but also
>>> forward (down, in the photo). This could be explained by the
>>> pivots not being parallel to each other.
>>
>> It's not a matter of the pivots: the same thing happens with
>> single-pivot brakes with both brake arms pivoting on the same bolt.
>>
>> This is a matter of the brake pads not being parallel to the brake
>> pivots. A rear brake has its pads mounted with their rear end farther
>> from the pivots than the front end. Being at a larger radius from the
>> pivot, the rear end moves more than the front. A front brake, thanks
>> to the offset off the fork, has its pads more parallel to its pivot.
>
>That doesn't suffice to explain the apparent movement shown in "jim's"
>photos in which one pad appears to move forward relative to the other.
>That could just be an artifact of the brake laying on an open book,
>hence my suggestion to "jim" to mount the brake on a planar surface to
>provide a reference.

I'm sorry, I missed your point on first reading, and wrote
addressing the phenomenon of changing toe.

I think what you're seeing is a combination of foreshortening
and parallax. As the centre-pivot arm closes in on the rim, the pads
move down towards the hub. The offset-pivot arm does the opposite, with
the pivot being outboard of the pad rather than inboard (this is the
cosine effect that Jobst dislikes with these brakes). What this means is
that in the photos, one pad is retreating away from the camera, while
the other gets closer. The movement you're seeing is just the effect of
parallax as you see this motion.

>> It's a stretch of the imagination to to think that this is a
>> deliberate effect though. More to the point of what started this
>> discussion, a front brake mounted on the rear has its pads at the
>> same angle relative to its pivots as a rear brake mounted on the
>> rear.
>
>Calipers can be swapped front for back and always have been
>interchangeable; the only difference is the lengths of the pivot bolts.

Agreed.

-Luns
 
[email protected] (Luns Tee) writes:

> In article <[email protected]>,
> jim beam <[email protected]> wrote:
>>> Now, you can call names all you want, but it doesn't make anything
>>> that you've said or shown us evidence of front/rear non-
>>> interchangeability. I'll let you back up, split some hairs, and claim
>>> that Shimano changed their design for dual pivots between my old RX100
>>> and your new Dura-Ace. I'll even accept it if you can figure out a
>>> way to prove that the second pivot on your brake is off axis with the
>>> mounting bolt, but I will not take pictures of brake pads as
>>> evidence. They don't prove anything.
>>>
>>
>>but your caliper still shows toe progression!!!
>
> These photos show quite clearly that the same front caliper can
> have toe-in or toe-out as the caliper closes with just the change of the
> pad angle. This is not a function of front calipers being different from
> rear calipers as you've claimed, it's a matter of the pads being
> mounted at different angles in either application.
>
>>compare with single pivot!!!
>
> No difference.
>
> http://www.OCF.Berkeley.EDU/~tee/rbt/toe/DSC01855.JPG
> http://www.OCF.Berkeley.EDU/~tee/rbt/toe/DSC01851.JPG

These would be slightly easier to compare if you hadn't rotated one of
them 180 degrees.

--
Joe Riel
 
[email protected] (Luns Tee) writes:

> In article <[email protected]>,
> jim beam <[email protected]> wrote:
>>> Now, you can call names all you want, but it doesn't make anything
>>> that you've said or shown us evidence of front/rear non-
>>> interchangeability. I'll let you back up, split some hairs, and claim
>>> that Shimano changed their design for dual pivots between my old RX100
>>> and your new Dura-Ace. I'll even accept it if you can figure out a
>>> way to prove that the second pivot on your brake is off axis with the
>>> mounting bolt, but I will not take pictures of brake pads as
>>> evidence. They don't prove anything.
>>>
>>
>>but your caliper still shows toe progression!!!
>
> These photos show quite clearly that the same front caliper can
> have toe-in or toe-out as the caliper closes with just the change of the
> pad angle. This is not a function of front calipers being different from
> rear calipers as you've claimed, it's a matter of the pads being
> mounted at different angles in either application.
>
>>compare with single pivot!!!
>
> No difference.
>
> http://www.OCF.Berkeley.EDU/~tee/rbt/toe/DSC01855.JPG
> http://www.OCF.Berkeley.EDU/~tee/rbt/toe/DSC01851.JPG

These would be slightly easier to compare if you hadn't rotated one of
them 180 degrees.

--
Joe Riel
 
One more while I'm at it:

http://tinyurl.com/yobozb

This is the same single-pivot Shimano 600EX caliper in my previous
photos.

The lines drawn show the angle of the pads relative to the
pivots as installed on the rear of a bike. The toe of the brake pads is
clearly closer to the pivot axis than the rear. Thus, the toe of the
brake pads move less than the heels do as the caliper is actuated.

-Luns
 
One more while I'm at it:

http://tinyurl.com/yobozb

This is the same single-pivot Shimano 600EX caliper in my previous
photos.

The lines drawn show the angle of the pads relative to the
pivots as installed on the rear of a bike. The toe of the brake pads is
clearly closer to the pivot axis than the rear. Thus, the toe of the
brake pads move less than the heels do as the caliper is actuated.

-Luns
 
[email protected] wrote:
> The dual pivot caliper is a dud. Brake centering can be
> accomplished with a properly designed return spring, one that is
> coiled about the center post rather than the common coils offset
> to either side.

SunTour built that long ago, my GPX stay centered...


> Such a brake was shown at InterBike by an unknown Vietnamese
> producer.

Would be nice to have that again on the market, in at least decent
quality.

--
MfG/Best regards
helmut springer panta rhei
 
[email protected] wrote:
> The dual pivot caliper is a dud. Brake centering can be
> accomplished with a properly designed return spring, one that is
> coiled about the center post rather than the common coils offset
> to either side.

SunTour built that long ago, my GPX stay centered...


> Such a brake was shown at InterBike by an unknown Vietnamese
> producer.

Would be nice to have that again on the market, in at least decent
quality.

--
MfG/Best regards
helmut springer panta rhei
 
On Sat, 10 Nov 2007 12:14:37 -0600, Tim McNamara
<[email protected]> wrote:

>No, no. Get it straight. You're the lightweight. I'm the retard.
>Krygowski's the idiot. Jobst is satan in "jim's" little world, as far
>as I can tell. I can't remember the rest of "jim's" little pet names.

He seems to use "moron" on a fairly regular basis.
 
Helmut Springer writes:

>> The dual pivot caliper is a dud. Brake centering can be
>> accomplished with a properly designed return spring, one that is
>> coiled about the center post rather than the common coils offset to
>> either side.

> SunTour built that long ago, my GPX stay centered...

>> Such a brake was shown at InterBike by an unknown Vietnamese
>> producer.

> Would be nice to have that again on the market, in at least decent
> quality.

I would have included a link if I had one. I think the problem of the
return spring is so blatantly obvious on any dual pivot caliper that
it is better to see it in person. The return spring articulates about
a theoretical point in the center of the return spring coil, the
foreshortening is visible as the caliper is exercised in that the
spring moves substantially in the plastic sleeve. Single pivot brakes
have two of these sliding places encrusted in the road dirt where
their ends bear on the caliper. These points do not change in sliding
friction identically, so one arm retracts, the other doesn't.

What more do you want. A coil about the center-bolt causes neither
end of the spring to foreshorten, articulating about the same pivot
caliper arms do. Basta!

Jobst Brandt
 
Helmut Springer writes:

>> The dual pivot caliper is a dud. Brake centering can be
>> accomplished with a properly designed return spring, one that is
>> coiled about the center post rather than the common coils offset to
>> either side.

> SunTour built that long ago, my GPX stay centered...

>> Such a brake was shown at InterBike by an unknown Vietnamese
>> producer.

> Would be nice to have that again on the market, in at least decent
> quality.

I would have included a link if I had one. I think the problem of the
return spring is so blatantly obvious on any dual pivot caliper that
it is better to see it in person. The return spring articulates about
a theoretical point in the center of the return spring coil, the
foreshortening is visible as the caliper is exercised in that the
spring moves substantially in the plastic sleeve. Single pivot brakes
have two of these sliding places encrusted in the road dirt where
their ends bear on the caliper. These points do not change in sliding
friction identically, so one arm retracts, the other doesn't.

What more do you want. A coil about the center-bolt causes neither
end of the spring to foreshorten, articulating about the same pivot
caliper arms do. Basta!

Jobst Brandt
 
On Nov 10, 8:16 pm, [email protected] wrote:

[snip]

> What more do you want. A coil about the center-bolt causes neither
> end of the spring to foreshorten, articulating about the same pivot
> caliper arms do. Basta!
>
> Jobst Brandt

Dear Jobst,

With our dangerously fragile wheels and perilously over-priced
bicycles, are any brakes a good idea?

"There are many arguments for and against it, but one thing is certain
and that is that the brake is not a popular attachment. Few riders of
experience use it, and a novice is inclined to look upon it as an
unnecessary article. An expert has said that many of this year's
wheels are so constructed as to make the addition of brakes very
undesirable. He points out that many wheels are not strong enough to
withstand the use of brakes, and refers to the cost as an obstacle to
many. The minimum expense would seldom be less than $1.50, while the
average would be nearer $3."

--NYT Feb. 2, 1896, "Gossip of the Cyclers"

http://query.nytimes.com/gst/abstract.html?res=9A0CE4DD143BEE33A25751C0A9649C94679ED7CF

Cheers,

Carl Fogel
 
On Nov 10, 8:16 pm, [email protected] wrote:

[snip]

> What more do you want. A coil about the center-bolt causes neither
> end of the spring to foreshorten, articulating about the same pivot
> caliper arms do. Basta!
>
> Jobst Brandt

Dear Jobst,

With our dangerously fragile wheels and perilously over-priced
bicycles, are any brakes a good idea?

"There are many arguments for and against it, but one thing is certain
and that is that the brake is not a popular attachment. Few riders of
experience use it, and a novice is inclined to look upon it as an
unnecessary article. An expert has said that many of this year's
wheels are so constructed as to make the addition of brakes very
undesirable. He points out that many wheels are not strong enough to
withstand the use of brakes, and refers to the cost as an obstacle to
many. The minimum expense would seldom be less than $1.50, while the
average would be nearer $3."

--NYT Feb. 2, 1896, "Gossip of the Cyclers"

http://query.nytimes.com/gst/abstract.html?res=9A0CE4DD143BEE33A25751C0A9649C94679ED7CF

Cheers,

Carl Fogel
 
On Nov 11, 1:56 am, [email protected] wrote:
> On Nov 10, 8:16 pm, [email protected] wrote:
>
> [snip]
>
> > What more do you want. A coil about the center-bolt causes neither
> > end of the spring to foreshorten, articulating about the same pivot
> > caliper arms do. Basta!
>
> > Jobst Brandt
>
> Dear Jobst,
>
> With our dangerously fragile wheels and perilously over-priced
> bicycles, are any brakes a good idea?
>
> "There are many arguments for and against it, but one thing is certain
> and that is that the brake is not a popular attachment. Few riders of
> experience use it, and a novice is inclined to look upon it as an
> unnecessary article. An expert has said that many of this year's
> wheels are so constructed as to make the addition of brakes very
> undesirable. He points out that many wheels are not strong enough to
> withstand the use of brakes, and refers to the cost as an obstacle to
> many. The minimum expense would seldom be less than $1.50, while the
> average would be nearer $3."
>
> --NYT Feb. 2, 1896, "Gossip of the Cyclers"
>
> http://query.nytimes.com/gst/abstract.html?res=9A0CE4DD143BEE33A25751...
>
> Cheers,
>
> Carl Fogel

I think CarbonSports is the only company to step right up and tell
customers to lay off the brakes.

"The "L'Alpe d'Huez" wheelset has been developed specifically for the
demands of uphill time trials. To achieve the least possible rotary
mass, the rim's brake surfaces have been lightened. Thus, the brakes
must be used sparingly and not with brute force. Only use these wheels
in flat or uphill sections. They are not designed for the braking
forces encountered when riding downhill."

At $5500 a pair retail, a panic stop could get expensive.
 
Andrew Price wrote:
> On Sat, 10 Nov 2007 12:14:37 -0600, Tim McNamara
> <[email protected]> wrote:
>
>> No, no. Get it straight. You're the lightweight. I'm the retard.
>> Krygowski's the idiot. Jobst is satan in "jim's" little world, as far
>> as I can tell. I can't remember the rest of "jim's" little pet names.
>
> He seems to use "moron" on a fairly regular basis.

I wonder if "jim" would be so free with the insults if he/she/it had to
use his/her/its real name? (Of course, that never stopped Mr. Ed the Grate.)

--
Tom Sherman - Holstein-Friesland Bovinia
Tradition is the worst rational for action.
 
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