Mount front brakes on rear?

On Wed, 31 Oct 2007 16:56:13 -0700, Michael Press wrote:

In article ,
_ wrote:

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

"_" wrote in message
...
On Mon, 29 Oct 2007 09:33:12 -0700, wrote:

On Oct 28, 6:48 pm, 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?

Who is "jim beam"?

_ wrote:
On Thu, 01 Nov 2007 19:27:33 -0600, A Muzi wrote:

wrote:
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.
Michael Press wrote:
You seem to be talking about fork offset here.
When the fork rake is varied the fork tip and
fork crown move together; and therefore the
brake pad position wrt the wheel rim remains
invariant.
I assumed he meant the angle of the pad to the arm

You were correct. The following jim beam quote makes this clear:

"...shimano & campy dual pivot brake
calipers have a pivot action that increases toe on the pad as the
caliper closes."

eh? the pad doesn't change relative to the arm - the arm is responsible
for the angle swing. misunderstanding is no reason to misrepresent meaning.



He's not yet explained[1]:

a) why nobody else can measure see this; and/or

this is r.b.t, buddy. this is home to people that can't tell the
difference between rolled and cut thread, but feel free to argue about
thread fatigue. you have people that correctly identify the math
regarding camber thrust, but fail to make their point because they're
intent on personal disagreement, not the facts. and you have people
that claim to be able to eliminate metal fatigue while being ignorant of
100+ years of materials research proving the opposite.


b) just how these pivots change their axis of rotation

but i have.



[1] this assumes that the standard beamboy response of the form "f**king
moron f**ktard" does not qualify as "explanation".

you seem very intent on keeping that stuff alive. is your appearance at
the same time as "jambo"'s disappearance mere coincidence?

On Nov 2, 12:53 am, jim beam wrote:
_ wrote:
On Thu, 1 Nov 2007 14:08:07 +0100, James Thomson wrote:

What should I be measuring?
"jim beam" a ?crit:

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'm using the moulding seam of the brake block at the point it touches the
holder as a reference point on the Ultegra 6500 brakes, and (in the absence
of a convenient moulding mark) trying to pick a consistent point on the
Centaur pad holder. The measurements are repeatable to within about 1mm, and
I can't detect any sign of the effect you say is there.

James Thomson

Either beam's bushings are worn or the arms are loose on the pivots - that
was already pointed out.

no, these are new calipers - in perfect condition.

It's impossible for an arm to pivot on a
cylindrical bushing and change the axis of rotation without another pivot
(which is, in essemce, what beamboy is claiming).

no it's not. it's a simple geometry problem. you not figuring it out
doesn't mean it's impossible - after all, it is observed to be happening.

Yes, it's a very simple geometry problem. Far simpler than your
explanation of magic pivots describes. The brake pads are adjustable
in a number of directions, one of which is rotation about the pad
fixing bolt. Look at the brake from the side with the mounting bolt
horizontal, and if the brake is set up to go on the rear, the rear
ends of the pads are going to be sitting lower than the front ends.
Assuming everything is set up square and parallel when the pads are
about a rim width apart, this will will give the appearance of the
front ends of the pads pointing inwards when you open the caliper all
the way. The rear ends of the pads moved farther out horizontally
because they are father from the pivot axes. Close the caliper all
the way and the front ends of the pads will be pointed out, because
they traveled a shorter horizontal distance for the same angle. Re-
adjust the pads so that the front ends are sitting lower than the rear
when viewed from the side, and you get the exact opposite behavior.
Adjust them level, and you're back to boring old parallel motion,
which is what everyone who actually wasted their time obeying your
command to measure their brakes observed. This is why you need to
prove your magic pivot theory by measuring from the arms not the
pads. The pads may be fixed, but they are not always fixed in a
position that supports your theory. If the second pivot really is
angled, there will also be some fore-aft translation of the arm
attached to it. Another reason why common sense dictates that this
would be an incredibly stupid way to design a brake.

On Nov 2, 8:18 am, jim beam wrote:
_ wrote:
On Thu, 01 Nov 2007 19:27:33 -0600, A Muzi wrote:

wrote:
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.
Michael Press wrote:
You seem to be talking about fork offset here.
When the fork rake is varied the fork tip and
fork crown move together; and therefore the
brake pad position wrt the wheel rim remains
invariant.
I assumed he meant the angle of the pad to the arm

You were correct. The following jim beam quote makes this clear:

"...shimano & campy dual pivot brake
calipers have a pivot action that increases toe on the pad as the
caliper closes."

eh? the pad doesn't change relative to the arm - the arm is responsible
for the angle swing. misunderstanding is no reason to misrepresent meaning.



He's not yet explained[1]:

a) why nobody else can measure see this; and/or

this is r.b.t, buddy. this is home to people that can't tell the
difference between rolled and cut thread, but feel free to argue about
thread fatigue. you have people that correctly identify the math
regarding camber thrust, but fail to make their point because they're
intent on personal disagreement, not the facts. and you have people
that claim to be able to eliminate metal fatigue while being ignorant of
100+ years of materials research proving the opposite.



b) just how these pivots change their axis of rotation

but i have.



[1] this assumes that the standard beamboy response of the form "f**king
moron f**ktard" does not qualify as "explanation".

you seem very intent on keeping that stuff alive. is your appearance at
the same time as "jambo"'s disappearance mere coincidence?



You are replying to the infamous "jtaylor" of Canada, psychotic anti-
helmet nutcase extraordinaire. Rotsa ruck.

IMO, just ignore the insane lil' sack-o-****.

On Fri, 02 Nov 2007 08:16:12 -0700, wrote:

Yes, it's a very simple geometry problem. Far simpler than your
explanation of magic pivots describes. The brake pads are adjustable
in a number of directions, one of which is rotation about the pad
fixing bolt. Look at the brake from the side with the mounting bolt
horizontal, and if the brake is set up to go on the rear, the rear
ends of the pads are going to be sitting lower than the front ends.
Assuming everything is set up square and parallel when the pads are
about a rim width apart, this will will give the appearance of the
front ends of the pads pointing inwards when you open the caliper all
the way. The rear ends of the pads moved farther out horizontally
because they are father from the pivot axes. Close the caliper all
the way and the front ends of the pads will be pointed out, because
they traveled a shorter horizontal distance for the same angle. Re-
adjust the pads so that the front ends are sitting lower than the rear
when viewed from the side, and you get the exact opposite behavior.
Adjust them level, and you're back to boring old parallel motion,
which is what everyone who actually wasted their time obeying your
command to measure their brakes observed. This is why you need to
prove your magic pivot theory by measuring from the arms not the
pads. The pads may be fixed, but they are not always fixed in a
position that supports your theory. If the second pivot really is
angled, there will also be some fore-aft translation of the arm
attached to it. Another reason why common sense dictates that this
would be an incredibly stupid way to design a brake.

And as the pivots are not magical (except perhaps in jim beam's world) such
action is no support for his asserting that this magical pivoting action is
a reason for not putting a back brake on the front - or vice-versa.

All fixed! Got my new caliper in the mail. I was going to use the
washer/nut idea, but when I put the caliper through the hole in the
seatstay it was too short- only about 3 threads stuck out the other
side, and with a washer would have made matters worse.

I then considered either cutting more threads onto the bolt and
shortening it or changing it out with the one from the no-name caliper
I took off.

I was worried about tapping the bolt, as the existing threads looked
like they were formed on, and the unthreaded part of the bolt looked
like it might be too thick to cut threads into (?). I also worried
that if it didn't work, I'd have ruined the whole caliper.

So I dissassembled the old caliper. The bolt involved is actually
kinda complex, it goes from one size thread to a smaller about 1/3 of
the way along. I worried that the no-name bolt might not work on the
shimano, but to my surprise it worked just fine.

Other than pinching my palm with the spring as I dissassembled the old
caliper, it went fine.

I adjusted the pads after installation, and I cant percieve any
problem with toe in/out.
Thank you everyone for the help. Sweet!

J. Taylor wrote:

Who is "jim beam"?

I think its a bot.

--
Tom Sherman - Holstein-Friesland Bovinia
When did ignorance of biology become a "family value"?

wrote:
On Nov 2, 12:53 am, jim beam wrote:
_ wrote:
On Thu, 1 Nov 2007 14:08:07 +0100, James Thomson wrote:
What should I be measuring?
"jim beam" a ?crit:
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'm using the moulding seam of the brake block at the point it touches the
holder as a reference point on the Ultegra 6500 brakes, and (in the absence
of a convenient moulding mark) trying to pick a consistent point on the
Centaur pad holder. The measurements are repeatable to within about 1mm, and
I can't detect any sign of the effect you say is there.
James Thomson
Either beam's bushings are worn or the arms are loose on the pivots - that
was already pointed out.
no, these are new calipers - in perfect condition.

It's impossible for an arm to pivot on a
cylindrical bushing and change the axis of rotation without another pivot
(which is, in essemce, what beamboy is claiming).
no it's not. it's a simple geometry problem. you not figuring it out
doesn't mean it's impossible - after all, it is observed to be happening.

Yes, it's a very simple geometry problem. Far simpler than your
explanation of magic pivots describes. The brake pads are adjustable
in a number of directions, one of which is rotation about the pad
fixing bolt.

duh. and when that bolt is tightened, they remain fixed. from that
point on, it doesn't matter /what/ you do, the /delta/ measurements i
did, remain the same.


Look at the brake from the side with the mounting bolt
horizontal, and if the brake is set up to go on the rear, the rear
ends of the pads are going to be sitting lower than the front ends.
Assuming everything is set up square and parallel when the pads are
about a rim width apart, this will will give the appearance of the
front ends of the pads pointing inwards when you open the caliper all
the way. The rear ends of the pads moved farther out horizontally
because they are father from the pivot axes. Close the caliper all
the way and the front ends of the pads will be pointed out, because
they traveled a shorter horizontal distance for the same angle. Re-
adjust the pads so that the front ends are sitting lower than the rear
when viewed from the side, and you get the exact opposite behavior.
Adjust them level, and you're back to boring old parallel motion,
which is what everyone who actually wasted their time obeying your
command to measure their brakes observed. This is why you need to
prove your magic pivot theory by measuring from the arms not the
pads. The pads may be fixed, but they are not always fixed in a
position that supports your theory. If the second pivot really is
angled, there will also be some fore-aft translation of the arm
attached to it. Another reason why common sense dictates that this
would be an incredibly stupid way to design a brake.


says the guy that doesn't understand the concepts.

In article
,
_ wrote:

On Wed, 31 Oct 2007 16:56:13 -0700, Michael Press wrote:

In article ,
_ wrote:

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

"_" wrote in message
...
On Mon, 29 Oct 2007 09:33:12 -0700, wrote:

On Oct 28, 6:48 pm, 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?

Who is "jim beam"?

Accounts for you being trolled on the
great brake bolt thread controversy.

--
Michael Press

On Nov 2, 9:18 pm, jim beam wrote:
wrote:
On Nov 2, 12:53 am, jim beam wrote:
_ wrote:
On Thu, 1 Nov 2007 14:08:07 +0100, James Thomson wrote:
What should I be measuring?
"jim beam" a ?crit:
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'm using the moulding seam of the brake block at the point it touches the
holder as a reference point on the Ultegra 6500 brakes, and (in the absence
of a convenient moulding mark) trying to pick a consistent point on the
Centaur pad holder. The measurements are repeatable to within about 1mm, and
I can't detect any sign of the effect you say is there.
James Thomson
Either beam's bushings are worn or the arms are loose on the pivots - that
was already pointed out.
no, these are new calipers - in perfect condition.

It's impossible for an arm to pivot on a
cylindrical bushing and change the axis of rotation without another pivot
(which is, in essemce, what beamboy is claiming).
no it's not. it's a simple geometry problem. you not figuring it out
doesn't mean it's impossible - after all, it is observed to be happening.

Yes, it's a very simple geometry problem. Far simpler than your
explanation of magic pivots describes. The brake pads are adjustable
in a number of directions, one of which is rotation about the pad
fixing bolt.

duh. and when that bolt is tightened, they remain fixed. from that
point on, it doesn't matter /what/ you do, the /delta/ measurements i
did, remain the same.



Look at the brake from the side with the mounting bolt
horizontal, and if the brake is set up to go on the rear, the rear
ends of the pads are going to be sitting lower than the front ends.
Assuming everything is set up square and parallel when the pads are
about a rim width apart, this will will give the appearance of the
front ends of the pads pointing inwards when you open the caliper all
the way. The rear ends of the pads moved farther out horizontally
because they are father from the pivot axes. Close the caliper all
the way and the front ends of the pads will be pointed out, because
they traveled a shorter horizontal distance for the same angle. Re-
adjust the pads so that the front ends are sitting lower than the rear
when viewed from the side, and you get the exact opposite behavior.
Adjust them level, and you're back to boring old parallel motion,
which is what everyone who actually wasted their time obeying your
command to measure their brakes observed. This is why you need to
prove your magic pivot theory by measuring from the arms not the
pads. The pads may be fixed, but they are not always fixed in a
position that supports your theory. If the second pivot really is
angled, there will also be some fore-aft translation of the arm
attached to it. Another reason why common sense dictates that this
would be an incredibly stupid way to design a brake.

says the guy that doesn't understand the concepts.

And what concepts would those be? That the distance traveled by a
point on a rigid rotating body does not depend on that point's
distance from the axis of rotation? Because that's what you're trying
to claim, and you're exactly right that I don't understand it. You
would be hard pressed to find anyone with a passing knowledge of
geometry who would buy that one. If you change the relative distances
of the pad ends from the pivot axes (in whichever direction you
believe them to be pointing) the delta measurements you performed will
change. Front or rear, and I'm looking at it right now on a single
pivot caliper. The ends of the pads farthest from the pivot will
always be farther apart when the caliper is open, and closer together
when it's closed. How do you suppose it is that I can observe
something that you say absolutely has to be the result of one of a two
degree of freedom mechanism on a brake with only one degree of freedom?