Mount front brakes on rear?

[Gary Young]

On Tue, 30 Oct 2007 20:48:24 -0700, jim beam wrote:

> Gary Young wrote:
>> On Sun, 28 Oct 2007 20:01:29 -0700, jim beam wrote:
>>
>>> [email protected] wrote:
>>>> Nashbar has a good deal on ultegra brake calipers; I mounted them on
>>>> my front wheel. My rear caliper is kinda corroded, and I was
>>>> considering mounting another front caliper on the rear wheel... Is
>>>> this a good idea?
>>>>
>>> as pointed out by others, the bolt length thing is not a big deal.
>>> however, you need to be aware that shimano & campy dual pivot brake
>>> calipers have a pivot action that increases toe on the pad as the
>>> caliper closes. [easily observed for yourself if you have the caliper
>>> in your hand - simply squeeze and note how the relative angles of the
>>> pads change as the lever arms move through their arc.] if a front
>>> caliper is used on the rear, the toe is towards the rear of the pads,
>>> not the front, relative to rim direction.
>>
>>
>> According to Shimano spare parts lists (http://tinyurl.com/2kecg9), the
>> front and rear brakes are identical except for a bolt, a nut and a washer
>> or spacer.
>
> no, that's the parts list for the nuts and bolts, not the caliper arms.
>

Much as I hate to admit it, you are right that those lists are
inconclusive -- they list all the parts but the arms.

>
>> How is this magical effect achieved?
>
> "magical"??? how about you ask an objective question rather than a
> sarcastic one that presupposes ******** instead? you could also take
> the time to look for the shimano mounting instructions which do indeed
> advise against switching front/rear calipers.
>
> the answer is pivot angle. buy a campy or shimano dual pivot caliper
> and observe for yourself.
>
>>
>>> will you notice any effect in practice? maybe some brake squeal, but
>>> probably not. is it correct in theory? no. and iirc, there's a
>>> warning in the shimano literature to the effect that each caliper is
>>> specific to front or rear application and should not be interchanged.

 

[_]

On 30 Oct 2007 17:40:37 -0700, philcycles wrote:

> _ wrote:
>>
>> Or run a die down the longer bolt and cut the excess off.
>
> Not really a good idea. These bolts are commonly chromed and the
> chrome will ruin the die.
> Phil Brown

Not for one bolt. It's not a very thick plate, and while the wear on the
die will be greater unless you are looking at production quantities it
won't matter.

 

[_]

On Tue, 30 Oct 2007 10:09:43 -0700, Kerry Montgomery wrote:

> "_" <[email protected]> wrote in message
> news:[email protected]...
>> On Mon, 29 Oct 2007 09:33:12 -0700, [email protected] wrote:
>>
>>> On Oct 28, 6:48 pm, [email protected] wrote:
>>>> Nashbar has a good deal on ultegra brake calipers; I mounted them on
>>>> my front wheel. My rear caliper is kinda corroded, and I was
>>>> considering mounting another front caliper on the rear wheel... Is
>>>> this a good idea?
>>>
>>> If you have an old bolt for the rear, you can disassemble the brake
>>> and replace the longer front bolt with a shorter one required for the
>>> rear. I believe this is even easier to do with dual pivot sidepulls
>>> than the old style single pivots, but it's been a while since I've
>>> taken one of these apart.
>>
>> Or run a die down the longer bolt and cut the excess off.
>
> But then you'd have cut threads instead of the superior rolled threads
> (vastly superior if they're Italian rolled threads).
> Kerry

For the strength required of a brake bolt, it makes no difference.

 

[James Thomson]

"jim beam" <[email protected]> a écrit:

>>>> shimano & campy dual pivot brake calipers have a pivot action that
>>>> increases toe on the pad
>>>> as the caliper closes. [easily observed for yourself if you
>>>> have the caliper in your hand - simply squeeze and note
>>>> how the relative angles of the pads change as the lever
>>>> arms move through their arc.]

> since you presumably have these things laying about your store,
> new in box, why not dig out both brake calipers and measuring
> calipers and measure what i describe?

What should I be measuring? I have new (previous generation) Campag Centaur
and Shimano Ultegra calipers here on my desk, and I can't see or measure any
change in angle between the pads relative to the plane of the rim. In fact I
can't readily see how that would be possible, as the pivot of one arm is
co-axial with the brake bolt in each case (and that's true of all dual-pivot
brakes I've seen).

James Thomson

 

[[email protected]]

On Oct 30, 11:48 pm, jim beam <[email protected]> wrote:
> Gary Young wrote:
> > On Sun, 28 Oct 2007 20:01:29 -0700, jim beam wrote:
>
> >> [email protected] wrote:
> >>> Nashbar has a good deal on ultegra brake calipers; I mounted them on
> >>> my front wheel. My rear caliper is kinda corroded, and I was
> >>> considering mounting another front caliper on the rear wheel... Is
> >>> this a good idea?
>
> >> as pointed out by others, the bolt length thing is not a big deal.
> >> however, you need to be aware that shimano & campy dual pivot brake
> >> calipers have a pivot action that increases toe on the pad as the
> >> caliper closes. [easily observed for yourself if you have the caliper
> >> in your hand - simply squeeze and note how the relative angles of the
> >> pads change as the lever arms move through their arc.] if a front
> >> caliper is used on the rear, the toe is towards the rear of the pads,
> >> not the front, relative to rim direction.
>
> > According to Shimano spare parts lists (http://tinyurl.com/2kecg9), the
> > front and rear brakes are identical except for a bolt, a nut and a washer
> > or spacer.
>
> no, that's the parts list for the nuts and bolts, not the caliper arms.
>
> > How is this magical effect achieved?
>
> "magical"??? how about you ask an objective question rather than a
> sarcastic one that presupposes ******** instead? you could also take
> the time to look for the shimano mounting instructions which do indeed
> advise against switching front/rear calipers.
>
> the answer is pivot angle. buy a campy or shimano dual pivot caliper
> and observe for yourself.
>
>
>
> >> will you notice any effect in practice? maybe some brake squeal, but
> >> probably not. is it correct in theory? no. and iirc, there's a
> >> warning in the shimano literature to the effect that each caliper is
> >> specific to front or rear application and should not be interchanged.

No, the answer is that either your pivot bolts are loose or the
bushings are worn. The effect you're describing is geometrically
impossible with fixed pivots no matter what angle they're at. There's
slop in the pivots, and it looks like the arms are twisting because
the cable attachments and springs are out of plane. The mechanism was
most certainly not designed to move that way.

 

[[email protected]]

On Oct 30, 11:48 pm, jim beam <[email protected]> wrote:
> Gary Young wrote:
> > On Sun, 28 Oct 2007 20:01:29 -0700, jim beam wrote:
>
> >> [email protected] wrote:
> >>> Nashbar has a good deal on ultegra brake calipers; I mounted them on
> >>> my front wheel. My rear caliper is kinda corroded, and I was
> >>> considering mounting another front caliper on the rear wheel... Is
> >>> this a good idea?
>
> >> as pointed out by others, the bolt length thing is not a big deal.
> >> however, you need to be aware that shimano & campy dual pivot brake
> >> calipers have a pivot action that increases toe on the pad as the
> >> caliper closes. [easily observed for yourself if you have the caliper
> >> in your hand - simply squeeze and note how the relative angles of the
> >> pads change as the lever arms move through their arc.] if a front
> >> caliper is used on the rear, the toe is towards the rear of the pads,
> >> not the front, relative to rim direction.
>
> > According to Shimano spare parts lists (http://tinyurl.com/2kecg9), the
> > front and rear brakes are identical except for a bolt, a nut and a washer
> > or spacer.
>
> no, that's the parts list for the nuts and bolts, not the caliper arms.
>
> > How is this magical effect achieved?
>
> "magical"??? how about you ask an objective question rather than a
> sarcastic one that presupposes ******** instead? you could also take
> the time to look for the shimano mounting instructions which do indeed
> advise against switching front/rear calipers.
>
> the answer is pivot angle. buy a campy or shimano dual pivot caliper
> and observe for yourself.
>
>
>
>
>
> >> will you notice any effect in practice? maybe some brake squeal, but
> >> probably not. is it correct in theory? no. and iirc, there's a
> >> warning in the shimano literature to the effect that each caliper is
> >> specific to front or rear application and should not be interchanged.- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -

Hi,
I took a look at the instructins,
Not to put too fine a point on it, but the instructions actually say
"Brakes designed for use as rear brakes should not be used as front
brakes." Oddly, they do not contain a similar prohibition against
using front brakes as rear brakes...

regards,
dan

 

[A Muzi]

>>>> [email protected] wrote:
>>>>> Nashbar has a good deal on ultegra brake calipers; I mounted them on
>>>>> my front wheel. My rear caliper is kinda corroded, and I was
>>>>> considering mounting another front caliper on the rear wheel... Is
>>>>> this a good idea?

>>> jim beam wrote:
>>>> as pointed out by others, the bolt length thing is not a big deal.
>>>> however, you need to be aware that shimano & campy dual pivot brake
>>>> calipers have a pivot action that increases toe on the pad as the
>>>> caliper closes. [easily observed for yourself if you have the caliper
>>>> in your hand - simply squeeze and note how the relative angles of the
>>>> pads change as the lever arms move through their arc.] if a front
>>>> caliper is used on the rear, the toe is towards the rear of the pads,
>>>> not the front, relative to rim direction.

>> Gary Young wrote:
>>> According to Shimano spare parts lists (http://tinyurl.com/2kecg9), the
>>> front and rear brakes are identical except for a bolt, a nut and a washer
>>> or spacer.

> jim beam <[email protected]> wrote:
>> no, that's the parts list for the nuts and bolts, not the caliper arms.

>> Gary Young wrote:
>>> How is this magical effect achieved?

> jim beam <[email protected]> wrote:
>> "magical"??? how about you ask an objective question rather than a
>> sarcastic one that presupposes ******** instead? you could also take
>> the time to look for the shimano mounting instructions which do indeed
>> advise against switching front/rear calipers.
>> the answer is pivot angle. buy a campy or shimano dual pivot caliper
>> and observe for yourself.

>>>> will you notice any effect in practice? maybe some brake squeal, but
>>>> probably not. is it correct in theory? no. and iirc, there's a
>>>> warning in the shimano literature to the effect that each caliper is
>>>> specific to front or rear application and should not be interchanged.

[email protected] wrote:
> I took a look at the instructins,
> Not to put too fine a point on it, but the instructions actually say
> "Brakes designed for use as rear brakes should not be used as front
> brakes." Oddly, they do not contain a similar prohibition against
> using front brakes as rear brakes...

I believe that's merely because your average human would forget to
reverse the brake shoes.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

 

[_]

On Wed, 31 Oct 2007 15:33:32 +0100, James Thomson wrote:

> "jim beam" <[email protected]> a écrit:
>
>>>>> shimano & campy dual pivot brake calipers have a pivot action that
>>>>> increases toe on the pad
>>>>> as the caliper closes. [easily observed for yourself if you
>>>>> have the caliper in your hand - simply squeeze and note
>>>>> how the relative angles of the pads change as the lever
>>>>> arms move through their arc.]
>
>> since you presumably have these things laying about your store,
>> new in box, why not dig out both brake calipers and measuring
>> calipers and measure what i describe?
>
> What should I be measuring? I have new (previous generation) Campag Centaur
> and Shimano Ultegra calipers here on my desk, and I can't see or measure any
> change in angle between the pads relative to the plane of the rim. In fact I
> can't readily see how that would be possible, as the pivot of one arm is
> co-axial with the brake bolt in each case (and that's true of all dual-pivot
> brakes I've seen).
>

Exactly - as another poster has said, it is geometrically impossible to
produce two degrees of freedom with one pivot axis.

 

[Michael Press]

In article <[email protected]>,
_ <[email protected]> wrote:

> On Tue, 30 Oct 2007 10:09:43 -0700, Kerry Montgomery wrote:
>
> > "_" <[email protected]> wrote in message
> > news:[email protected]...
> >> On Mon, 29 Oct 2007 09:33:12 -0700, [email protected] wrote:
> >>
> >>> On Oct 28, 6:48 pm, [email protected] wrote:
> >>>> Nashbar has a good deal on ultegra brake calipers; I mounted them on
> >>>> my front wheel. My rear caliper is kinda corroded, and I was
> >>>> considering mounting another front caliper on the rear wheel... Is
> >>>> this a good idea?
> >>>
> >>> If you have an old bolt for the rear, you can disassemble the brake
> >>> and replace the longer front bolt with a shorter one required for the
> >>> rear. I believe this is even easier to do with dual pivot sidepulls
> >>> than the old style single pivots, but it's been a while since I've
> >>> taken one of these apart.
> >>
> >> Or run a die down the longer bolt and cut the excess off.
> >
> > But then you'd have cut threads instead of the superior rolled threads
> > (vastly superior if they're Italian rolled threads).
> > Kerry
>
> For the strength required of a brake bolt, it makes no difference.

Do you skip messages that are in jim beam debate threads?

--
Michael Press

 

[jim beam]

James Thomson wrote:
> "jim beam" <[email protected]> a �crit:
>
>>>>> shimano & campy dual pivot brake calipers have a pivot action that
>>>>> increases toe on the pad
>>>>> as the caliper closes. [easily observed for yourself if you
>>>>> have the caliper in your hand - simply squeeze and note
>>>>> how the relative angles of the pads change as the lever
>>>>> arms move through their arc.]
>
>> since you presumably have these things laying about your store,
>> new in box, why not dig out both brake calipers and measuring
>> calipers and measure what i describe?
>
> What should I be measuring?

distance between the front tips of the brake pads with the caliper open
vs. caliper closed, and for the rear tips, open vs closed. when open,
the front tips are further apart than the rears. when closed, the front
tips are closer than the rears. [front caliper]


> I have new (previous generation) Campag Centaur
> and Shimano Ultegra calipers here on my desk, and I can't see or measure any
> change in angle between the pads relative to the plane of the rim. In fact I
> can't readily see how that would be possible, as the pivot of one arm is
> co-axial with the brake bolt in each case (and that's true of all dual-pivot
> brakes I've seen).
>
> James Thomson
>
>

 

[jim beam]

A Muzi wrote:
>>>>> [email protected] wrote:
>>>>>> Nashbar has a good deal on ultegra brake calipers; I mounted them on
>>>>>> my front wheel. My rear caliper is kinda corroded, and I was
>>>>>> considering mounting another front caliper on the rear wheel... Is
>>>>>> this a good idea?
>
>>>> jim beam wrote:
>>>>> as pointed out by others, the bolt length thing is not a big deal.
>>>>> however, you need to be aware that shimano & campy dual pivot brake
>>>>> calipers have a pivot action that increases toe on the pad as the
>>>>> caliper closes. [easily observed for yourself if you have the caliper
>>>>> in your hand - simply squeeze and note how the relative angles of the
>>>>> pads change as the lever arms move through their arc.] if a front
>>>>> caliper is used on the rear, the toe is towards the rear of the pads,
>>>>> not the front, relative to rim direction.
>
>>> Gary Young wrote:
>>>> According to Shimano spare parts lists (http://tinyurl.com/2kecg9), the
>>>> front and rear brakes are identical except for a bolt, a nut and a
>>>> washer
>>>> or spacer.
>
>> jim beam <[email protected]> wrote:
>>> no, that's the parts list for the nuts and bolts, not the caliper arms.
>
>>> Gary Young wrote:
>>>> How is this magical effect achieved?
>
>> jim beam <[email protected]> wrote:
>>> "magical"??? how about you ask an objective question rather than a
>>> sarcastic one that presupposes ******** instead? you could also take
>>> the time to look for the shimano mounting instructions which do indeed
>>> advise against switching front/rear calipers.
>>> the answer is pivot angle. buy a campy or shimano dual pivot caliper
>>> and observe for yourself.
>
>>>>> will you notice any effect in practice? maybe some brake squeal, but
>>>>> probably not. is it correct in theory? no. and iirc, there's a
>>>>> warning in the shimano literature to the effect that each caliper is
>>>>> specific to front or rear application and should not be interchanged.
>
> [email protected] wrote:
>> I took a look at the instructins,
>> Not to put too fine a point on it, but the instructions actually say
>> "Brakes designed for use as rear brakes should not be used as front
>> brakes." Oddly, they do not contain a similar prohibition against
>> using front brakes as rear brakes...
>
> I believe that's merely because your average human would forget to
> reverse the brake shoes.

andrew, you have stock of dual pivot brakes, and measuring calipers.
please perform the measurements i requested. i can do it, but i have to
strip a bike and that's going to have to wait until the weekend.

 

[jim beam]

[email protected] wrote:
> On Oct 30, 11:48 pm, jim beam <[email protected]> wrote:
>> Gary Young wrote:
>>> On Sun, 28 Oct 2007 20:01:29 -0700, jim beam wrote:
>>>> [email protected] wrote:
>>>>> Nashbar has a good deal on ultegra brake calipers; I mounted them on
>>>>> my front wheel. My rear caliper is kinda corroded, and I was
>>>>> considering mounting another front caliper on the rear wheel... Is
>>>>> this a good idea?
>>>> as pointed out by others, the bolt length thing is not a big deal.
>>>> however, you need to be aware that shimano & campy dual pivot brake
>>>> calipers have a pivot action that increases toe on the pad as the
>>>> caliper closes. [easily observed for yourself if you have the caliper
>>>> in your hand - simply squeeze and note how the relative angles of the
>>>> pads change as the lever arms move through their arc.] if a front
>>>> caliper is used on the rear, the toe is towards the rear of the pads,
>>>> not the front, relative to rim direction.
>>> According to Shimano spare parts lists (http://tinyurl.com/2kecg9), the
>>> front and rear brakes are identical except for a bolt, a nut and a washer
>>> or spacer.
>> no, that's the parts list for the nuts and bolts, not the caliper arms.
>>
>>> How is this magical effect achieved?
>> "magical"??? how about you ask an objective question rather than a
>> sarcastic one that presupposes ******** instead? you could also take
>> the time to look for the shimano mounting instructions which do indeed
>> advise against switching front/rear calipers.
>>
>> the answer is pivot angle. buy a campy or shimano dual pivot caliper
>> and observe for yourself.
>>
>>
>>
>>>> will you notice any effect in practice? maybe some brake squeal, but
>>>> probably not. is it correct in theory? no. and iirc, there's a
>>>> warning in the shimano literature to the effect that each caliper is
>>>> specific to front or rear application and should not be interchanged.
>
> No, the answer is that either your pivot bolts are loose or the
> bushings are worn. The effect you're describing is geometrically
> impossible with fixed pivots no matter what angle they're at. There's
> slop in the pivots, and it looks like the arms are twisting because
> the cable attachments and springs are out of plane. The mechanism was
> most certainly not designed to move that way.
>

brand new dura-ace, i.e. no loose pivots or worn bushings, says you need
to check your facts. supposition or disbelief are no a basis for
"certainly" statements.

 

[jim beam]

_ wrote:
> On Wed, 31 Oct 2007 15:33:32 +0100, James Thomson wrote:
>
>> "jim beam" <[email protected]> a �crit:
>>
>>>>>> shimano & campy dual pivot brake calipers have a pivot action that
>>>>>> increases toe on the pad
>>>>>> as the caliper closes. [easily observed for yourself if you
>>>>>> have the caliper in your hand - simply squeeze and note
>>>>>> how the relative angles of the pads change as the lever
>>>>>> arms move through their arc.]
>>> since you presumably have these things laying about your store,
>>> new in box, why not dig out both brake calipers and measuring
>>> calipers and measure what i describe?
>> What should I be measuring? I have new (previous generation) Campag Centaur
>> and Shimano Ultegra calipers here on my desk, and I can't see or measure any
>> change in angle between the pads relative to the plane of the rim. In fact I
>> can't readily see how that would be possible, as the pivot of one arm is
>> co-axial with the brake bolt in each case (and that's true of all dual-pivot
>> brakes I've seen).
>>
>
> Exactly - as another poster has said, it is geometrically impossible to
> produce two degrees of freedom with one pivot axis.

and with a _dual pivot_ brake caliper you have, wait for it, _two_ pivot
axes! now, that gives /how/ many degrees of freedom?

 

[jim beam]

jim beam wrote:
> A Muzi wrote:
>>>>>> [email protected] wrote:
>>>>>>> Nashbar has a good deal on ultegra brake calipers; I mounted them on
>>>>>>> my front wheel. My rear caliper is kinda corroded, and I was
>>>>>>> considering mounting another front caliper on the rear wheel... Is
>>>>>>> this a good idea?
>>
>>>>> jim beam wrote:
>>>>>> as pointed out by others, the bolt length thing is not a big deal.
>>>>>> however, you need to be aware that shimano & campy dual pivot brake
>>>>>> calipers have a pivot action that increases toe on the pad as the
>>>>>> caliper closes. [easily observed for yourself if you have the
>>>>>> caliper
>>>>>> in your hand - simply squeeze and note how the relative angles of the
>>>>>> pads change as the lever arms move through their arc.] if a front
>>>>>> caliper is used on the rear, the toe is towards the rear of the pads,
>>>>>> not the front, relative to rim direction.
>>
>>>> Gary Young wrote:
>>>>> According to Shimano spare parts lists (http://tinyurl.com/2kecg9),
>>>>> the
>>>>> front and rear brakes are identical except for a bolt, a nut and a
>>>>> washer
>>>>> or spacer.
>>
>>> jim beam <[email protected]> wrote:
>>>> no, that's the parts list for the nuts and bolts, not the caliper arms.
>>
>>>> Gary Young wrote:
>>>>> How is this magical effect achieved?
>>
>>> jim beam <[email protected]> wrote:
>>>> "magical"??? how about you ask an objective question rather than a
>>>> sarcastic one that presupposes ******** instead? you could also take
>>>> the time to look for the shimano mounting instructions which do indeed
>>>> advise against switching front/rear calipers.
>>>> the answer is pivot angle. buy a campy or shimano dual pivot caliper
>>>> and observe for yourself.
>>
>>>>>> will you notice any effect in practice? maybe some brake squeal, but
>>>>>> probably not. is it correct in theory? no. and iirc, there's a
>>>>>> warning in the shimano literature to the effect that each caliper is
>>>>>> specific to front or rear application and should not be interchanged.
>>
>> [email protected] wrote:
>>> I took a look at the instructins,
>>> Not to put too fine a point on it, but the instructions actually say
>>> "Brakes designed for use as rear brakes should not be used as front
>>> brakes." Oddly, they do not contain a similar prohibition against
>>> using front brakes as rear brakes...
>>
>> I believe that's merely because your average human would forget to
>> reverse the brake shoes.
>
> andrew, you have stock of dual pivot brakes, and measuring calipers.
> please perform the measurements i requested. i can do it, but i have to
> strip a bike and that's going to have to wait until the weekend.

ok, i found a caliper still in a box. dura-ace, 7700 rear:

open, front tips, 26.2mm, rear tips, 28.8mm, i.e. rear tips further apart.

closed, front tips, 4.3mm, rear tips, 0mm [touching], i.e. front tips
further apart.

the change in toe is /clearly/ visible in operation.

 

[jim beam]

A Muzi wrote:
>>>>>>> [email protected] wrote:
>>>>>>>> Nashbar has a good deal on ultegra brake calipers; I mounted
>>>>>>>> them on
>>>>>>>> my front wheel. My rear caliper is kinda corroded, and I was
>>>>>>>> considering mounting another front caliper on the rear wheel... Is
>>>>>>>> this a good idea?
>>>
>>>>>> jim beam wrote:
>>>>>>> as pointed out by others, the bolt length thing is not a big deal.
>>>>>>> however, you need to be aware that shimano & campy dual pivot brake
>>>>>>> calipers have a pivot action that increases toe on the pad as the
>>>>>>> caliper closes. [easily observed for yourself if you have the
>>>>>>> caliper
>>>>>>> in your hand - simply squeeze and note how the relative angles of
>>>>>>> the
>>>>>>> pads change as the lever arms move through their arc.] if a front
>>>>>>> caliper is used on the rear, the toe is towards the rear of the
>>>>>>> pads,
>>>>>>> not the front, relative to rim direction.
>
>>>>> Gary Young wrote:
>>>>>> According to Shimano spare parts lists
>>>>>> (http://tinyurl.com/2kecg9), the
>>>>>> front and rear brakes are identical except for a bolt, a nut and a
>>>>>> washer
>>>>>> or spacer.
>
>>>> jim beam <[email protected]> wrote:
>>>>> no, that's the parts list for the nuts and bolts, not the caliper
>>>>> arms.
>
>>>>> Gary Young wrote:
>>>>>> How is this magical effect achieved?
>
>>>> jim beam <[email protected]> wrote:
>>>>> "magical"??? how about you ask an objective question rather than a
>>>>> sarcastic one that presupposes ******** instead? you could also take
>>>>> the time to look for the shimano mounting instructions which do indeed
>>>>> advise against switching front/rear calipers.
>>>>> the answer is pivot angle. buy a campy or shimano dual pivot caliper
>>>>> and observe for yourself.
>
>>>>>>> will you notice any effect in practice? maybe some brake squeal,
>>>>>>> but
>>>>>>> probably not. is it correct in theory? no. and iirc, there's a
>>>>>>> warning in the shimano literature to the effect that each caliper is
>>>>>>> specific to front or rear application and should not be
>>>>>>> interchanged.
>
>>> [email protected] wrote:
>>>> I took a look at the instructins,
>>>> Not to put too fine a point on it, but the instructions actually say
>>>> "Brakes designed for use as rear brakes should not be used as front
>>>> brakes." Oddly, they do not contain a similar prohibition against
>>>> using front brakes as rear brakes...
>
>> A Muzi wrote:
>>> I believe that's merely because your average human would forget to
>>> reverse the brake shoes.
>
> jim beam wrote:
>> andrew, you have stock of dual pivot brakes, and measuring calipers.
>> please perform the measurements i requested. i can do it, but i have
>> to strip a bike and that's going to have to wait until the weekend.
>
> Campagnolo are variegated (SP rear) and the Tektro are indeed identical
> front to rear except bolt length.
>
> In The Olden Days calipers were bent slightly to correct pad angle, new
> calipers have orbital shoe adjustment washers. Am I missing something
> here?

repost:

dura-ace, 7700 rear:

open, front tips, 26.2mm, rear tips, 28.8mm, i.e. rear tips further apart.

closed, front tips, 4.3mm, rear tips, 0mm [touching], i.e. front tips
further apart.

the change in toe is /clearly/ visible in operation.


> Mounting a 'front' brake on a classic rear bridge with a nylock
> nut is 'bad' because... ??

 

[A Muzi]

>>>>>> [email protected] wrote:
>>>>>>> Nashbar has a good deal on ultegra brake calipers; I mounted them on
>>>>>>> my front wheel. My rear caliper is kinda corroded, and I was
>>>>>>> considering mounting another front caliper on the rear wheel... Is
>>>>>>> this a good idea?
>>
>>>>> jim beam wrote:
>>>>>> as pointed out by others, the bolt length thing is not a big deal.
>>>>>> however, you need to be aware that shimano & campy dual pivot brake
>>>>>> calipers have a pivot action that increases toe on the pad as the
>>>>>> caliper closes. [easily observed for yourself if you have the
>>>>>> caliper
>>>>>> in your hand - simply squeeze and note how the relative angles of the
>>>>>> pads change as the lever arms move through their arc.] if a front
>>>>>> caliper is used on the rear, the toe is towards the rear of the pads,
>>>>>> not the front, relative to rim direction.

>>>> Gary Young wrote:
>>>>> According to Shimano spare parts lists (http://tinyurl.com/2kecg9),
>>>>> the
>>>>> front and rear brakes are identical except for a bolt, a nut and a
>>>>> washer
>>>>> or spacer.

>>> jim beam <[email protected]> wrote:
>>>> no, that's the parts list for the nuts and bolts, not the caliper arms.

>>>> Gary Young wrote:
>>>>> How is this magical effect achieved?

>>> jim beam <[email protected]> wrote:
>>>> "magical"??? how about you ask an objective question rather than a
>>>> sarcastic one that presupposes ******** instead? you could also take
>>>> the time to look for the shimano mounting instructions which do indeed
>>>> advise against switching front/rear calipers.
>>>> the answer is pivot angle. buy a campy or shimano dual pivot caliper
>>>> and observe for yourself.

>>>>>> will you notice any effect in practice? maybe some brake squeal, but
>>>>>> probably not. is it correct in theory? no. and iirc, there's a
>>>>>> warning in the shimano literature to the effect that each caliper is
>>>>>> specific to front or rear application and should not be interchanged.

>> [email protected] wrote:
>>> I took a look at the instructins,
>>> Not to put too fine a point on it, but the instructions actually say
>>> "Brakes designed for use as rear brakes should not be used as front
>>> brakes." Oddly, they do not contain a similar prohibition against
>>> using front brakes as rear brakes...

> A Muzi wrote:
>> I believe that's merely because your average human would forget to
>> reverse the brake shoes.

jim beam wrote:
> andrew, you have stock of dual pivot brakes, and measuring calipers.
> please perform the measurements i requested. i can do it, but i have to
> strip a bike and that's going to have to wait until the weekend.

Campagnolo are variegated (SP rear) and the Tektro are indeed identical
front to rear except bolt length.

In The Olden Days calipers were bent slightly to correct pad angle, new
calipers have orbital shoe adjustment washers. Am I missing something
here? Mounting a 'front' brake on a classic rear bridge with a nylock
nut is 'bad' because... ??
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

 

[[email protected]]

On Oct 31, 8:55 pm, jim beam <[email protected]> wrote:
> jim beam wrote:
> ok, i found a caliper still in a box. dura-ace, 7700 rear:
>
> open, front tips, 26.2mm, rear tips, 28.8mm, i.e. rear tips further apart.
>
> closed, front tips, 4.3mm, rear tips, 0mm [touching], i.e. front tips
> further apart.
>
> the change in toe is /clearly/ visible in operation.

I tried this with two types of Shimano dual pivot brakes
and I can't see any cammed toe-in effect, either on or
off a bike. I think I might be able to get one end to
touch first on the off-bike pair if the pads are
rotated up (no longer parallel to the brake bolt)
but that isn't how they are usually used.

Further, in usage, brakes are never closed to 0mm, since
rims are of order 18-20mm wide. Also, one arm of the
dual pivot brake pivots on the brake bolt and is surely
tracking straight, not canted.

I can't see this as a valid safety argument against
exchanging rear and front brake. You just have to
be careful to change around cartridge pads if you
have them to avoid pad ejection. And to make sure
the nut engages enough threads on the bolt, of course.
Naturally, when mounting any brake, you should
try to get the toe-in correct as the pads hit the
rim. The toe-in when the pads are off the rim only
affects brake clearance.

Ben

 

[_]

On Wed, 31 Oct 2007 20:37:23 -0700, jim beam wrote:

> _ wrote:
>> On Wed, 31 Oct 2007 15:33:32 +0100, James Thomson wrote:
>>
>>> "jim beam" <[email protected]> a �crit:
>>>
>>>>>>> shimano & campy dual pivot brake calipers have a pivot action that
>>>>>>> increases toe on the pad
>>>>>>> as the caliper closes. [easily observed for yourself if you
>>>>>>> have the caliper in your hand - simply squeeze and note
>>>>>>> how the relative angles of the pads change as the lever
>>>>>>> arms move through their arc.]
>>>> since you presumably have these things laying about your store,
>>>> new in box, why not dig out both brake calipers and measuring
>>>> calipers and measure what i describe?
>>> What should I be measuring? I have new (previous generation) Campag Centaur
>>> and Shimano Ultegra calipers here on my desk, and I can't see or measure any
>>> change in angle between the pads relative to the plane of the rim. In fact I
>>> can't readily see how that would be possible, as the pivot of one arm is
>>> co-axial with the brake bolt in each case (and that's true of all dual-pivot
>>> brakes I've seen).
>>>
>>
>> Exactly - as another poster has said, it is geometrically impossible to
>> produce two degrees of freedom with one pivot axis.
>
> and with a _dual pivot_ brake caliper you have, wait for it, _two_ pivot
> axes! now, that gives /how/ many degrees of freedom?

One for each arm. You were saying that each arm changes angle as it
pivots; as another poster has stated, that is geometrically impossible with
a single axis.

Time to weasle again, beamboy.

 

[jim beam]

[email protected] wrote:
> On Oct 31, 8:55 pm, jim beam <[email protected]> wrote:
>> jim beam wrote:
>> ok, i found a caliper still in a box. dura-ace, 7700 rear:
>>
>> open, front tips, 26.2mm, rear tips, 28.8mm, i.e. rear tips further apart.
>>
>> closed, front tips, 4.3mm, rear tips, 0mm [touching], i.e. front tips
>> further apart.
>>
>> the change in toe is /clearly/ visible in operation.
>
> I tried this with two types of Shimano dual pivot brakes
> and I can't see any cammed toe-in effect, either on or
> off a bike.

well, i've observed this on both campy and shimano. hence the above
measurements.


> I think I might be able to get one end to
> touch first on the off-bike pair if the pads are
> rotated up (no longer parallel to the brake bolt)
> but that isn't how they are usually used.
>
> Further, in usage, brakes are never closed to 0mm, since
> rims are of order 18-20mm wide.

full open to full close exaggerates the effect for sure, but the point
is that this operation is a design feature. i can only presume that
it's for increasing toe in operation.


> Also, one arm of the
> dual pivot brake pivots on the brake bolt and is surely
> tracking straight, not canted.

indeed, but the other pivot on the short arm isn't. and as it swings
through its arc, it tilts the axis angle for the "c" arm.


>
> I can't see this as a valid safety argument against
> exchanging rear and front brake. You just have to
> be careful to change around cartridge pads if you
> have them to avoid pad ejection.

well /that/ is a given - and not relevant to pivot angles.


> And to make sure
> the nut engages enough threads on the bolt, of course.
> Naturally, when mounting any brake, you should
> try to get the toe-in correct as the pads hit the
> rim.

my personal experience of this is that toe simply acts as a trap for
grit - all my bikes have orbital pad holders and i take the toe out.
and the caliper having its own toe action makes it even more unnecessary
imo.


> The toe-in when the pads are off the rim only
> affects brake clearance.
>
> Ben
>

 

[[email protected]]

On Oct 31, 11:37 pm, jim beam <[email protected]> wrote:
> [email protected] wrote:
> > On Oct 30, 11:48 pm, jim beam <[email protected]> wrote:
> >> Gary Young wrote:
> >>> On Sun, 28 Oct 2007 20:01:29 -0700, jim beam wrote:
> >>>> [email protected] wrote:
> >>>>> Nashbar has a good deal on ultegra brake calipers; I mounted them on
> >>>>> my front wheel. My rear caliper is kinda corroded, and I was
> >>>>> considering mounting another front caliper on the rear wheel... Is
> >>>>> this a good idea?
> >>>> as pointed out by others, the bolt length thing is not a big deal.
> >>>> however, you need to be aware that shimano & campy dual pivot brake
> >>>> calipers have a pivot action that increases toe on the pad as the
> >>>> caliper closes. [easily observed for yourself if you have the caliper
> >>>> in your hand - simply squeeze and note how the relative angles of the
> >>>> pads change as the lever arms move through their arc.] if a front
> >>>> caliper is used on the rear, the toe is towards the rear of the pads,
> >>>> not the front, relative to rim direction.
> >>> According to Shimano spare parts lists (http://tinyurl.com/2kecg9), the
> >>> front and rear brakes are identical except for a bolt, a nut and a washer
> >>> or spacer.
> >> no, that's the parts list for the nuts and bolts, not the caliper arms.
>
> >>> How is this magical effect achieved?
> >> "magical"??? how about you ask an objective question rather than a
> >> sarcastic one that presupposes ******** instead? you could also take
> >> the time to look for the shimano mounting instructions which do indeed
> >> advise against switching front/rear calipers.
>
> >> the answer is pivot angle. buy a campy or shimano dual pivot caliper
> >> and observe for yourself.
>
> >>>> will you notice any effect in practice? maybe some brake squeal, but
> >>>> probably not. is it correct in theory? no. and iirc, there's a
> >>>> warning in the shimano literature to the effect that each caliper is
> >>>> specific to front or rear application and should not be interchanged.
>
> > No, the answer is that either your pivot bolts are loose or the
> > bushings are worn. The effect you're describing is geometrically
> > impossible with fixed pivots no matter what angle they're at. There's
> > slop in the pivots, and it looks like the arms are twisting because
> > the cable attachments and springs are out of plane. The mechanism was
> > most certainly not designed to move that way.
>
> brand new dura-ace, i.e. no loose pivots or worn bushings, says you need
> to check your facts. supposition or disbelief are no a basis for
> "certainly" statements.

Allow me to clarify, since there seem to be some differences in the
ways that engineers and pretend metallurgists approach problems. A
few of the things that I considered.
1) In all of the press releases, web copy, and magazine reviews I've
ever seen, all filled with outlandish claims of technical achievement,
neither Campy nor Shimano has ever said anything about variable toe
in. This is not terribly surprising, as I'm looking at the Campy
installation manual right now, and they don't seem to believe that the
pads should be toed in to begin with. Also, despite all manner of
uptight safety warnings, there's no mention of not interchanging front
and rear calipers.
2) Two pivots do not always mean two degrees of freedom. This is the
kind of thing that we teach the real engineers to stop and think about
before they rip machines apart to see how they work. We teach it to
them before they reach legal drinking age, so I'll understand if
you're a bit behind the curve. In a dual pivot brake, one of the arms
is only rotating around one axis. If the second pivot were somehow
being used to twist one arm relative to one that's fixed in plane, the
result would be bad for pad wear, and potentially bad for the rim.
Now on to fact checking and supposition of fact as a basis for
"certainly" statements
1) My assumption of worn/loose pivots was based on my assumption that
you understand what you're talking about. I promise not to make that
mistake again.
2) You absolutely cannot presume from your measurements of pad
spacing that the brake arms are twisting. This assumes that the front
and rear edges are exactly the same distance from the pivot axis. In
practice, this is going to vary depending on things like fork rake,
rear dropout design, and how well the brakes are set up. It will in
fact vary from front to rear, but not because of any difference in the
calipers. Now, before instructing other people to take their bikes
apart to make the same useless measurements, perhaps you should take
the pads off of those shiny new Dura-Ace brakes and make some
measurements that actually prove some caliper twist that's different
between front and rear.