Do you know of engineering papers for what people call brake rotor'warp'?

On 02/15/2013 06:35 PM, Scott Dorsey wrote:
> Joe Mastroianni > wrote:
>> All these (which are decidedly NOT engineering papers!) say rotors
>> aren't warping, but as you noted, it might just be advertising.
>
> Rotors warp for the same reason that lugs break off: idiots with lug wrenches.
> It is correct that rotors do not warp by themselves, but I have seen plenty
> of cases of warped rotors,

did you mic them?


> all of which can probably be traced to some idiot
> mistorquing lugs.
> --scott
>

right, but that's not warping in the permanent sense that you can
measure off the vehicle, only in the elastic distortion sense that
disappears again as soon as you sort the wheel interface out properly.


--
fact check required

On Fri, 15 Feb 2013 18:34:14 -0800, jim beam wrote:

> i'll try to look at the rest, but seriously, most people who don't know
> are chasing their tails. those that do know aren't going to say much
> because they're not going to do two things:
>
> 1. they're /definitely/ not going to kill a cash cow which is selling
> new disks way before they're worn.
>
> 2. they're not going to stop using single-sided calipers because they're
> essential to macpherson strut suspension being able to have a negative
> scrub radius.

I'm reading those papers, as you are, and they talk about hot and cold
judder and they speak of high and low speed judder (mostly we're talking
around 100Hz here so that's low speed judder).

There's a lot of stuff about hot spots (I 'think' that's thermoelastic
instability) and disc thickness variation (I 'think' that's uneven
pad deposition) and axial runout (I think that's plane old runout).

It will also take me a while to read them all, but I don't see anything
(yet) about the single piston caliper design.

jim beam wrote:

> that's doesn't in the least explain how i go to a shop for tire
> replacement, and driving home, my disks are "warped". i take the wheels
> off, clean up the hub, torque with a three-stage sequence, and then my
> disks are unwarped again.

Just to be clear, I never said the disks actually warped.

Anyone who says that rotors commonly warp is clearly heading back
to the village missing its idiot.

However, to be 'fair', a lot of what people call warp is simply
runout, which is what I think you're referring to (since you could
never correct true warp short of machining the rotors).

A lot of other times, what people call warp is merely uneven pad
deposition, which, oftentimes, a rebedding run (especially one
with very harsh pads) will scrape clean & eliminate the judder.

Whatever they 'call' it, it's not warp because you can MEASURE
warp and they never ever measure it! Those who do, find out that
it's not warp. It's really that simple. Those who insist it's
warp seem to have no resistance with the q-tips in the ears.

This thread seems to be going in the right direction which is
to find the true cause of judder.

I will also try to read those scientific papers that were posted.

http://www.researchgate.net/publicat...7d38711887.pdf
http://sem-proceedings.com/20i/sem.o...-Roughness.pdf
http://sem-proceedings.com/14i/sem.o...Prevention.pdf
http://www.mecheng.osu.edu/adl/files/adl/C12-1.pdf
http://www.ehu.es/compmech/welcome/d...mputations.pdf
http://researchbank.rmit.edu.au/eser.../Rodriguez.pdf
http://eprints.hud.ac.uk/3878/1/2008-01-0818.pdf
http://cdn.intechweb.org/pdfs/5380.pdf
http://www.acoustics.asn.au/conferen...papers/p46.pdf
http://www.hitachi.com/ICSFiles/afie...009_07_107.pdf
http://ejum.fsktm.um.edu.my/article/1146.pdf
http://eprints.hud.ac.uk/3797/1/10_P...l_D_Bryant.pdf
http://www.mecheng.osu.edu/adl/files/adl/J187.pdf
http://pid.sagepub.com/content/217/6/419.full.pdf

On 02/15/2013 07:20 PM, Zen wrote:
> jim beam wrote:
>
>> that's doesn't in the least explain how i go to a shop for tire
>> replacement, and driving home, my disks are "warped". i take the wheels
>> off, clean up the hub, torque with a three-stage sequence, and then my
>> disks are unwarped again.
>
> Just to be clear, I never said the disks actually warped.
>
> Anyone who says that rotors commonly warp is clearly heading back
> to the village missing its idiot.
>
> However, to be 'fair', a lot of what people call warp is simply
> runout, which is what I think you're referring to (since you could
> never correct true warp short of machining the rotors).

indeed.


>
> A lot of other times, what people call warp is merely uneven pad
> deposition,

as said before, that's comparatively uncommon [and very rare on bmw!]
and pursuit of that as an explanation is not going to yield meaningful
results to a big picture understanding other than being something some
people will latch onto if there's any visible clues. ordinary looking
disks without deposition are the norm, and any explanation has to be
able to account for them too.


> which, oftentimes, a rebedding run (especially one
> with very harsh pads) will scrape clean & eliminate the judder.
>
> Whatever they 'call' it, it's not warp because you can MEASURE
> warp and they never ever measure it! Those who do, find out that
> it's not warp. It's really that simple. Those who insist it's
> warp seem to have no resistance with the q-tips in the ears.
>
> This thread seems to be going in the right direction which is
> to find the true cause of judder.
>
> I will also try to read those scientific papers that were posted.
>
> http://www.researchgate.net/publicat...7d38711887.pdf
> http://sem-proceedings.com/20i/sem.o...-Roughness.pdf
> http://sem-proceedings.com/14i/sem.o...Prevention.pdf
> http://www.mecheng.osu.edu/adl/files/adl/C12-1.pdf
> http://www.ehu.es/compmech/welcome/d...mputations.pdf
> http://researchbank.rmit.edu.au/eser.../Rodriguez.pdf
> http://eprints.hud.ac.uk/3878/1/2008-01-0818.pdf
> http://cdn.intechweb.org/pdfs/5380.pdf
> http://www.acoustics.asn.au/conferen...papers/p46.pdf
> http://www.hitachi.com/ICSFiles/afie...009_07_107.pdf
> http://ejum.fsktm.um.edu.my/article/1146.pdf
> http://eprints.hud.ac.uk/3797/1/10_P...l_D_Bryant.pdf
> http://www.mecheng.osu.edu/adl/files/adl/J187.pdf
> http://pid.sagepub.com/content/217/6/419.full.pdf
>


--
fact check required

On 02/15/2013 07:06 PM, Joe Mastroianni wrote:
> On Fri, 15 Feb 2013 18:34:14 -0800, jim beam wrote:
>
>> i'll try to look at the rest, but seriously, most people who don't know
>> are chasing their tails. those that do know aren't going to say much
>> because they're not going to do two things:
>>
>> 1. they're /definitely/ not going to kill a cash cow which is selling
>> new disks way before they're worn.
>>
>> 2. they're not going to stop using single-sided calipers because they're
>> essential to macpherson strut suspension being able to have a negative
>> scrub radius.
>
> I'm reading those papers, as you are, and they talk about hot and cold
> judder and they speak of high and low speed judder (mostly we're talking
> around 100Hz here so that's low speed judder).
>
> There's a lot of stuff about hot spots (I 'think' that's thermoelastic
> instability) and disc thickness variation (I 'think' that's uneven
> pad deposition) and axial runout (I think that's plane old runout).
>
> It will also take me a while to read them all, but I don't see anything
> (yet) about the single piston caliper design.

well, it's pretty obvious if you consider the relative masses as a
dynamic system being agitated by a waving disk sat in its middle.


--
fact check required

On 2/15/2013 5:06 PM, Joe Mastroianni wrote:
>
> I'm reading those papers, as you are, and they talk about hot and cold
> judder and they speak of high and low speed judder (mostly we're talking
> around 100Hz here so that's low speed judder).
>
> There's a lot of stuff about hot spots (I 'think' that's thermoelastic
> instability) and disc thickness variation (I 'think' that's uneven
> pad deposition) and axial runout (I think that's plane old runout).

I believe that what happens is that there's some transference of pad
material onto the iron disk at a molecular level. You can't measure it
because we're not able to measure tolerances to that level. It does,
however effect the frictional coefficients between the two surfaces at
localized areas. This causes the hot spots. Well, that's my
understanding about it anyway.

The pad material transference occurs mostly when the pads are hot. As a
practical matter, I try to ease up on the brake pressure after coming to
a stop after heating up the brakes.

>
> It will also take me a while to read them all, but I don't see anything
> (yet) about the single piston caliper design.
>
>
>

On 02/15/2013 10:53 PM, dsi1 wrote:
> On 2/15/2013 5:06 PM, Joe Mastroianni wrote:
>>
>> I'm reading those papers, as you are, and they talk about hot and cold
>> judder and they speak of high and low speed judder (mostly we're talking
>> around 100Hz here so that's low speed judder).
>>
>> There's a lot of stuff about hot spots (I 'think' that's thermoelastic
>> instability) and disc thickness variation (I 'think' that's uneven
>> pad deposition) and axial runout (I think that's plane old runout).
>
> I believe that what happens is that there's some transference of pad
> material onto the iron disk at a molecular level.

dude, absolutely there's transference "at the molecular level" - you
can't have friction without it. but to be grasping at straws as if
there's some kind of ghost in the machine that can't be explained any
other way is just ridiculous.


> You can't measure it
> because we're not able to measure tolerances to that level.

nothing personal to you, but that's complete b.s.


> It does,
> however effect the frictional coefficients between the two surfaces at
> localized areas.

only in some cases, with some kinds of pads. maybe 10% at most. all
the rest is plain old mechanical misalignment coupled [literally] to
poor dynamics of an unevenly weighted caliper.


> This causes the hot spots. Well, that's my
> understanding about it anyway.

it seems this is another one of those hose flap and antifreeze
electrolysis topics - a knowledge gap into which some people feel
compelled to inject good old underinformed guessing.


>
> The pad material transference occurs mostly when the pads are hot. As a
> practical matter, I try to ease up on the brake pressure after coming to
> a stop after heating up the brakes.
>
>>
>> It will also take me a while to read them all, but I don't see anything
>> (yet) about the single piston caliper design.
>>
>>
>>
>


--
fact check required

On 2/16/2013 5:29 AM, jim beam wrote:
> On 02/15/2013 10:53 PM, dsi1 wrote:
>> On 2/15/2013 5:06 PM, Joe Mastroianni wrote:
>>>
>>> I'm reading those papers, as you are, and they talk about hot and cold
>>> judder and they speak of high and low speed judder (mostly we're talking
>>> around 100Hz here so that's low speed judder).
>>>
>>> There's a lot of stuff about hot spots (I 'think' that's thermoelastic
>>> instability) and disc thickness variation (I 'think' that's uneven
>>> pad deposition) and axial runout (I think that's plane old runout).
>>
>> I believe that what happens is that there's some transference of pad
>> material onto the iron disk at a molecular level.
>
> dude, absolutely there's transference "at the molecular level" - you
> can't have friction without it. but to be grasping at straws as if
> there's some kind of ghost in the machine that can't be explained any
> other way is just ridiculous.
>
>
>> You can't measure it
>> because we're not able to measure tolerances to that level.
>
> nothing personal to you, but that's complete b.s.

I'll regret it but OK, I'll bite - how would you measure rotor runout
that's only a few molecules thick?

>
>
>> It does,
>> however effect the frictional coefficients between the two surfaces at
>> localized areas.
>
> only in some cases, with some kinds of pads. maybe 10% at most. all
> the rest is plain old mechanical misalignment coupled [literally] to
> poor dynamics of an unevenly weighted caliper.
>
>
>> This causes the hot spots. Well, that's my
>> understanding about it anyway.
>
> it seems this is another one of those hose flap and antifreeze
> electrolysis topics - a knowledge gap into which some people feel
> compelled to inject good old underinformed guessing.
>
>
>>
>> The pad material transference occurs mostly when the pads are hot. As a
>> practical matter, I try to ease up on the brake pressure after coming to
>> a stop after heating up the brakes.
>>
>>>
>>> It will also take me a while to read them all, but I don't see anything
>>> (yet) about the single piston caliper design.
>>>
>>>
>>>
>>
>
>

Zen wrote:

> However, to be 'fair', a lot of what people call warp is simply
> runout,

If it does not mean "run out" what else would warp mean?

On Sat, 16 Feb 2013 11:01:24 -0600, jim wrote:

> If it does not mean "run out" what else would warp mean?

Warp and runout are totally different things (to me, anyway)!

1. Warp means, to me, the rotors are 'wavy' (like a potato chip).
2. Runout merely means, to me, the rotors aren't spinning on
on the same axis as the hub is.

So, for example, let's assume a PERFECT ROTOR!
If you put it on the hub crooked, it will have runout but not warp.

How could you put it on crooked?
I don't know all the ways, but one way is to have uneven
rust on the hub. That 'tilts' the rotor so that the hub
and the rotor aren't spinning on the same axis.

The results in runout - which you measure with a dial gauge
firmly affixed to something relative to the hub center axis.

The way I understand warp, you'd NEVER be able to measure it
on the vehicle (not anywhere near accurately, anyway).

You measure warp on the bench. I suppose it's something that every
rotor manufacturer measures as part of their quality control.

The faces need to be parallel to each other.

Now, having said that (which is pretty obvious stuff), I must
then ask you (or anyone else) what THEY think the difference is
between warp and runout - as it's pretty simple stuff (to me).