Vic Smith wrote:

> I agree that rotors don't warp "as in a potato chip."
> Rotors do warp "as in a warped rotor."

Assuming you actually believe that, allow me to explain why intuition is a
terrible thing if people trust their own intuition far more than they do
facts. Me? I don't trust my intuition at all. I trust in facts.

Facts from reliable sources, like this PDF from Carroll Smith:
*The 'Warped' Brake Disc & Other Myths of the Braking System*
�<https://centricparts.com/getmedia/bd69395a-b65c-481d-93f7-b26b1bd0638d/Centric_and_APC_Technical_Whitepaper_B1-Warped-Brake-Disc-8-2018_1.pdf>
"In more than 40 years of professional racing, including the
Shelby/Ford GT 40s - one of the most intense brake development
programs in history - I have never seen a warped brake disc."

Like I said from the start, he goes on to explain what it usually is:
"In fact every case of "warped brake disc" that I have investigated,
whether on a racing car or a street car, has turned out to be
friction pad material transferred unevenly to the surface of the disc.
This uneven deposition results in thickness variation (TV)
or run-out due to hot spotting that occurred at elevated temperatures."

As I rather patiently explained multiple times in this thread:
"The driver can feel a 0.0004" deposit or TV on the disc. 0.001" is
annoying. More than that becomes a real pain. When deposit are present,
by having isolated regions that are proud of the surface and running
much hotter than their neighbors, cementite inevitably forms
and the local wear characteristics change which results in ever
increasing TV and roughness."

Notice it's not coincidence or happenstance that what I said in this thread
from the start is what the experts say, because I don't say it if it's not
fact (which is what _all_ well educated adults should do, by the way).

I understand that the vast majority of posters to Usenet are childish.
I mostly deal with iKooks whom I've taken on to prove what they are.

Hence, I deal with the iKooks all the time - so I'm well aware that people
will believe anything that marketing feeds them to believe, since marketing
preys on people's intuition (which is the intuition of a monkey).

If the word "warp" means, to you, vibration/shudder/judder under braking,
then sure, the braking system can cause all sorts of vibratory pulsations.

If the word "warp" really means runout, then, sure, rotors have runout.
If the word "warp" means, to you, DTV, then, sure, rotors get DTV.

If you can find a reference that backs up your intuition, I'll read it.
Otherwise, we're stuck with the references I already provided for you.
*What causes warped brake rotors?*
<https://ricksfreeautorepairadvice.com/warped-brake-rotors/>
"A typical street vehicle can't possibly generate enough heat
to warp a brake rotor."

Why not?
"First: The brake pads and rotors in a street vehicle can't possibly
generate enough heat to warp a brake rotor. As you can see later in
this post, the pads would disintegrate long before the rotors reached
a high enough temperature to distort."

Furthermore:
"Second: The heating and cooling that people refer to when
discussing "warped brake rotors" would cause cracking, not warping."

Yet more evidence:
"Third: High quality brake rotors that pass SAE J2928 Brake Rotor Thermal
Cracking Procedure for Vehicles below 4,540 kg GVWR proves they
don't warp."

The article discusses that test but all we need to know is the physics.
"To get cast iron hot enough to soften the metal you'd need to
generate almost 2,300°F range. There isn't a factory stock
automotive brake system in the world that's capable of generating
that kind of heat. In fact, you would experience brake pad fade,
pad disintegration, brake fluid boiling and rotor discoloration
long before you reached 1,000°F."

They go on by citing reliable references at the brake companies, where
prior to that they explain the basic physics which makes it impossible.
"Even if you're traveling straight down the side of a mountain with
your brakes applied the entire way. Your brake pads will fade and
start to disintegrate long before you come close to heating your
rotors enough to soften them to the point where they could possibly warp"

In summary, I deal with iKooks all the time who believe the strangest
things, where I believe they strongly believe what they believe; but the
fact is their belief system is completely imaginary, and most of the time
it's provided to them, gratis, courtesy of their local marketing outfit.

Marketing preys on the fact people own the intuition of a monkey.
If you truly believe rotors distort enough to call it warp, all you need to
do is provide a reliable cite (as I did above) backing your belief system.

You won't.
Because you can't.
But you'll learn by trying.

If your belief system isn't completely imaginary, you would be able to.
However, I don't expect it because people believe in their intuition only.
Not in facts.

However, I promise to read any reliable cites you can provide that back up
your belief system, where, rest assured, I know what's out there on warp.
--
Sometimes on Usenet you can find people who know more than you do.

On 11/5/2022 8:00 pm, NY wrote:
> "Vic Smith" <thismailautodeleted@comcast.net> wrote in message
> news:2b4m7hp2le1tl7anjbnleua0jiu1qsmfep@4ax.com...
>> I agree that rotors don't warp "as in a potato chip."
>> Rotors do warp "as in a warped rotor."
>
> Is "warp" the right word to use for a rotor (disc) that remains as a
> flat plane but with a surface that is not uniformly smooth over the

Short answer - no.

> whole area? I'd always thought that a warped disc had a wavy surface
> like a potato chip (aka potato crisp in the UK) or a vinyl LP - ie where
> the pads had to move parallel to the rotor axis to remain in contact
> with the disc that was not a perfectly flat plane.

The most common type of warped disc I have seen is more like a buckle.
Think of it like a bicycle wheel that doesn't run true in the lateral
plane. I have measured it and I have seen it when truing it on the brake
lathe. I have not seen a warp at opposite sides of the disc and in the
same plane - like a potato chip. Note however, there are a number of
causes of this, some not related to heat. The two most common are
incorrect/excessive tightening of wheel nuts and/or grit lodged between
disc and hub at the mounting surfaces. If the disc has been warped and
shows signs of severe overheating but no other cause can be determined,
it's the heat.
>
> Presumably if the surface becomes glazed in some parts and/or roughened
> in some parts that causes different amounts of wear in the different
> areas, exacerbating the problem.

That causes *thickness variation* and will appear as (possibly) pedal
pulsations or simply a shudder under braking. Most common cause of that
is the creation of *hard spots* caused by excessive hard braking over
extended periods of time. The driver needs educating on brake use.
>
> What is the advice for avoiding rotor warping? How should one brake
> differently to avoid it? I presume using engine braking (selecting a
> lower gear) when going down a long hill reduces the amount and/or time
> that the pads have to be in contact with the discs. I've also heard it

Yes, I do that. It is also the recommended procedure. What I do not do
is use the transmission gears to *slow* *down*, that's what the *service
brakes* are for.

> said that if you hold the car on the footbrake (rather than applying the
> handbrake or transmission lock) after braking to a halt, the area of the
> disc that's in contact with the hot disc will not be able to cool as
> much as the rest of the disc, leading to "rotor warping" - which is
> another reason (in addition to dazzling the person behind with your
> brake lights) for applying the handbrake whenever you come to a stop. As
> my driving instructor drummed in to me: "footbrake to stop the car;
> handbrake to *stay* stopped" - I can still "hear" him saying that 40
> years later ;-)

That sounds fair! ;-)

--
Xeno

Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

NY wrote:

> Is "warp" the right word to use for a rotor (disc) that remains as a flat
> plane but with a surface that is not uniformly smooth over the whole area?
> I'd always thought that a warped disc had a wavy surface like a potato chip
> (aka potato crisp in the UK) or a vinyl LP - ie where the pads had to move
> parallel to the rotor axis to remain in contact with the disc that was not a
> perfectly flat plane.
>
> Presumably if the surface becomes glazed in some parts and/or roughened in
> some parts that causes different amounts of wear in the different areas,
> exacerbating the problem.
>
> What is the advice for avoiding rotor warping? How should one brake
> differently to avoid it? I presume using engine braking (selecting a lower
> gear) when going down a long hill reduces the amount and/or time that the
> pads have to be in contact with the discs. I've also heard it said that if
> you hold the car on the footbrake (rather than applying the handbrake or
> transmission lock) after braking to a halt, the area of the disc that's in
> contact with the hot disc will not be able to cool as much as the rest of
> the disc, leading to "rotor warping" - which is another reason (in addition
> to dazzling the person behind with your brake lights) for applying the
> handbrake whenever you come to a stop. As my driving instructor drummed in
> to me: "footbrake to stop the car; handbrake to *stay* stopped" - I can
> still "hear" him saying that 40 years later ;-)

Everything you ask is explained in this one PDF from Carroll Smith:
*The 'Warped' Brake Disc & Other Myths of the Braking System*
<https://centricparts.com/getmedia/bd69395a-b65c-481d-93f7-b26b1bd0638d/Centric_and_APC_Technical_Whitepaper_B1-Warped-Brake-Disc-8-2018_1.pdf>

As I said from the start when I said "don't get me started" as most people
are incredibly gullible in that they believe things that just aren't true.

Even me.
I believed "gravity" was a force, for example because it's seems intuitive
that it's a force, just as it seems intuitive there's no gravity when
someone is weightless, and yet, all that intuition is dead wrong.

I believed we were whirring through the universe at around 400 kilometers
per second compared to the cosmic background radiation, but even _that_ is
dead wrong since we're actually moving at the speed of light all the time!
*How fast is the earth moving?*
<https://www.scientificamerican.com/article/how-fast-is-the-earth-mov/>

There is no other speed in our universe _but_ the speed of light.
Everything moves at the speed of light, in fact.
*Do we really travel through time with the speed of light?*
<http://backreaction.blogspot.com/2020/08/do-we-really-travel-through-time-with.html>

Now that's just not intuitive, right?
What you have to do is realize that intuition is a terrible thing indeed.

That's why I said that people intuit that cellphones _must_ be causing an
increase in the accident rate, which is yet another of the various and
sundry myths that people strongly believe simply because they intuit them.

An intelligent person, IMHO, doesn't trust his own intuition.
If he did trust his intuition, then he couldn't possibly be intelligent.

Even Einstein was dead wrong on a large part of his intuition (e.g., his
intuition caused what he referred to as "the biggest blunder in my life").

Einstein's intuition was wrong on many things (e.g., the Copenhagen
interpretation), but luckily his intuition was right on spacetime being
four dimensional and that we all moved through it at the speed of light.

I say all this to shows that humans have the intuition of monkeys.
We have to realize that if we're ever become intelligent beings.

I will answer your questions now, but I'm not going to use precise English
as that would make it as complicated as a discussion about gravity.

Q: Is "warp" the right word to use...
A: Warp implies a distortion that can't happen; however, if you use the
word to simply mean "something is fucked up", then it's perfectly ok.

Q: Is "warp" the right word to use for a rotor (disc) that remains as
a flat plane but with a surface that is not uniformly smooth
over the whole area?
A: I think a better word would be "thickness variation", although the
term "uniformly smooth" could also be related to "gouges" & "cracks".

Q: I'd always thought that a warped disc had a wavy surface...
A: That can't happen because the physics won't allow that to happen.

Q: Presumably if the surface becomes glazed in some parts and/or
roughened in some parts that causes different amounts of wear
in the different areas, exacerbating the problem.
A: It's not "exacerbating" the problem so much as being its own problem.

Q: What is the advice for avoiding rotor warping?
A: The simplest way to avoid it is to read the references which say
you already avoided it because it can't happen (physics won't let it).

Q: What is the advice for avoiding thickness variation then?
A: Proper pad bedding (which is almost never done in practice); and, as
I explained very patiently to Michael Trew, cognizance that it's your
own foot which is causing the thickness variation in the first place.

Q: How should one brake differently to avoid it?
A: I explained this in gory detail multiple times already, and you seem
to have already understood that it's your foot doing the damage here.

In summary, if you read this one reference, I think it answers your
questions. It comes from a far more reputable source than I can ever be.

*The 'Warped' Brake Disc & Other Myths of the Braking System*
<https://www.ipdusa.com/Articles/528/The-Warped-Brake-Disc-and-Other-Myths-of-the-Braking-System>
--
The smartest people I know do not trust their intuition more than they do
facts to the contrary.

Xeno wrote:

>> If a vehicle shudders while braking, people intuit that their rotors
>> warped, and, I don't blame them for thinking that any more than I blame
>
> I, for one, know that warped rotors do not necessarily *shudder*. What's
> more, I can differentiate between *shudder* and the myriad other
> symptoms that manifest themselves from brake faults.

Hi Xeno,
I respect your experience, where I am never afraid to admit when I don't
know something since there is an almost infinite amount of knowledge that I
don't have. You have much of that knowledge that I do not have.

I respect you for that.

One thing that always confuses me is "other people's terminology".

For example when my wife explains the taste of wine, and I can never
understand what she means by the "bouquet of slight hints of pear and
lavender", etc., where the problem is the far more simple and more
scientifically descriptive words I tend to use are "sweet, salty, sour,
bitter, and umami" (which is pretty much all our tongue _can_ taste).

Likewise when she talks of colors, where she has an almost infinitely
vibrant vocabulary whereas I only have RGBIV type color descriptions.

Which brings me to shudder, shake, judder, and vibrate in terms of braking.
*Brake Judder In Detail* by Jurid (who makes my OEM BMW rear brake pads)
<https://www.jurid.com/technical-support/light-vehicles/technical-tips/brake-judder.html>
"Brake judder is the vibration felt through the steering wheel
and suspension when the brakes are applied at certain speeds
and pressures. It can vary from a barely noticeable vibration
to a violent judder - experienced either through the brake
pedal or steering wheel."

If that's "judder", then what's "shudder"?
*Brake Shudder: Why Your Car Vibrates When You Brake*
<https://www.sundevilauto.com/brake-shudder-why-your-car-vibrates-when-you-brake/>
"You step on the brake pedal and you feel a vibration coming
from the brake pedal or worse, through the steering wheel.
You hold on tight to the steering wheel as you come to a stop.
You've just experienced brake shudder, also known as brake judder."

And then what's "shake" while braking?
*Why does my car shake when I brake?*
<https://www.tiresplus.com/blog/brakes/car-shakes-when-i-brake/>
Where at least this guy put "warped rotors" in quotes. :)
>> The only difference with me is I don't trust my intuition.
>> Most people trust their intuition well neigh more than they do the facts.
>
> Intuition, for the most part, *develops* from experience.

I agree even more than you realize, because intuition is _only_ from
experience, where that's why I keep harping on the fact that we own the
innate intuition of a monkey, where, luckily, monkeys needed good depth
perception and the ability to calculate whether or not they could get to
that next branch without it cracking under the combined weight of their
body and the added force their momentum based on weight & speed incurs.

There are _many_ things I've intuited that turned out to be wrong, Xeno.
An example is I intuited (like everyone else) that cellphones are a
distraction (they are) and they're a _big_ distraction (which they are),
and that they're a big _added_ distraction (which they are), so, duh, of
course the accident rate must have shown something of an effect between the
times that cellphones didn't exist, during the times that they skyrocketed,
and then plateaued.

And yet... the accident rate didn't even change by a blip.
That's just a fact. A decidedly non intuitive fact. But still a fact.
A fact in _all_ the reliable USA (and Australia) data sets.

The accident rate only seems to change in the bullshit data sets, almost
all from those who politically and financially benefit from stating that
they go up, such as from lawyers, police, and insurance companies.

Those are the datasets that the bullshitters (like Steve) always use.

Given I agree with you that intuition _develops_ from experience, I'm not
saying intuition is always wrong. But people who trust more in their
intuition than in facts are _often_ wrong because intuition itself is
limited.

I already said even Einstein was wrong as much as he was right, and he was
one of the most intelligent intuitive observers of physics who ever lived.

It's intuitive that brake rotors could warp just as it's intuitive that
we're moving at different speeds through spacetime, but the fact is that
brake rotors can't warp (the physics won't let them) and that we can't move
at any _other_ speed but the speed of light (the physics won't let us).

People who trust their intuition _more_ than they trust facts to the
contrary are often wrong (trust me, I am well aware the iKooks do just
that).

>> My intuition says that rotors should get hot and start "warping"; but the
>> facts say otherwise, just as my intuition says that cellphones must be
>> causing increased accident rates; but the facts say otherwise.
>
> You tell that to the warped rotors I have discarded.

If the rotor met thickness, cracking, gouging specs, then you wasted a good
rotor.

Wasting rotors _always_ solves what people think is warp.
But the "warp" will come back simply because the cause of the warp is your
foot.

What people call "warp" is explained on gory detail in my half dozen
respectable references, but mostly it's simple TV which can be solved two
ways:
a. Remove the TV
b. Junk the rotors

Your choice.

HINT: If "warp" was truly a wavy rotor, then why does rebedding often work?

> FWIW, when you machine rotor, you can actually *see* the warp right up
> until they clean up.

If the experts tell me that a rotor can't warp, and if you tell me not only
can they warp, but you can _see_ the warp, then we have a conflict of data.

Rest assured, I'm extremely well educated in some of the most complex
fields of endeavor, so I'm rather familiar with conflicts of information.

When there is a conflict of information such as you presented, you have to
weigh the discordant information based on a myriad set of ancillary data
points, one of which is what you say happened is what the most experienced
racers on this planet say can't possibly happen.
*The 'Warped' Brake Disc & Other Myths of the Braking System*
<https://www.ipdusa.com/Articles/528/The-Warped-Brake-Disc-and-Other-Myths-of-the-Braking-System>

When it's inconsonant, whose mutually exclusive opinion should I believe?

>> If marketing gold plates the letters on the marquee, people "think" it's
>> better, or, more to the point, if a car simply has DTV caused by pad
>> deposition, the shop tells them they need new rotors and pads (and maybe
>> even new calipers and a few other things too).
>
> I grew up and did my apprenticeship in a relatively poor area. You
> couldn't suggest such expensive fixes to people , they couldn't afford
> it. You were forced to do what was necessary to make the car serviceable
> and *safe* to use.

Trust me on that. I have an income of zero for the past 10 years, so I keep
my expenses low and one of the ways I do that is to repair my own vehicles.

What I do NOT do though, is hold down on the brake pedal after a long hard
stop, so as to avoid (as much as I can) the TV that can occur due to a pad
footprint.

Often I'm asked to 'fix the brakes' of my wife's car or those of my kids
though, where I take it for a nice fast and hard rebedding procedure, which
almost always 'fixes' the "warped" rotors in about a dozen 60 to 10
applications on the highway at night.

Some people actually put (supposedly) more abrasive pads on temporarily, to
scrape off the TV; but I don't know where the heck they get them. Do you?

>> "By declaring a customer's brake pedal pulsation complaint is caused �by
>> warped rotors is like saying the earth is flat. Both are cases where
>> �the observation of the person is based on a tiny piece of evidence
>> �that is false in nature and application."
>
> I never say that! Pedal pulsations can be caused by *hard spots* on
> rotors. Warped disks are more likely to cause symptoms akin to a
> *shimmy* in the steering under braking.

Bearing in mind I mount and balance my own tires at home, I'm well aware
there are a billion causes of "vibrations" while driving, where only some
of those causes are even related to the brakes (see this chart for others).
*Vehicle Vibration Diagnosis Chart - Tire Rack*
<https://www.tirerack.com/images/tires/vibechart.pdf>

>> Doesn't matter if the rotor is solid or not, if they're sold in the USA,
>> they meet a spec that makes it impossible - as the fluid would boil well
>> before the rotor could get hot enough, and the rest of the brake system
>> components would disintegrate well before the rotor ever got hot enough.
>
> Hmmm, I only needed to replace my periphery melted rotor. Everything
> else worked just as well as before and I didn't even get *brake fade*.
> My intuition is telling me something.

On 11/5/2022 9:48 pm, Andy Burnelli wrote:
> Xeno wrote:
>
>>> If a vehicle shudders while braking, people intuit that their rotors
>>> warped, and, I don't blame them for thinking that any more than I blame
>>
>> I, for one, know that warped rotors do not necessarily *shudder*.
>> What's more, I can differentiate between *shudder* and the myriad
>> other symptoms that manifest themselves from brake faults.
>
> Hi Xeno,
> I respect your experience, where I am never afraid to admit when I don't
> know something since there is an almost infinite amount of knowledge that I
> don't have. You have much of that knowledge that I do not have.
>
> I respect you for that.
>
> One thing that always confuses me is "other people's terminology".
>
> For example when my wife explains the taste of wine, and I can never
> understand what she means by the "bouquet of slight hints of pear and
> lavender", etc., where the problem is the far more simple and more
> scientifically descriptive words I tend to use are "sweet, salty, sour,
> bitter, and umami" (which is pretty much all our tongue _can_ taste).
>
> Likewise when she talks of colors, where she has an almost infinitely
> vibrant vocabulary whereas I only have RGBIV type color descriptions.
>
> Which brings me to shudder, shake, judder, and vibrate in terms of braking.
> *Brake Judder In Detail* by Jurid (who makes my OEM BMW rear brake pads)
> <https://www.jurid.com/technical-support/light-vehicles/technical-tips/brake-judder.html>
>
> "Brake judder is the vibration felt through the steering wheel  and
> suspension when the brakes are applied at certain speeds  and pressures.
> It can vary from a barely noticeable vibration  to a violent judder -
> experienced either through the brake  pedal or steering wheel."
>
> If that's "judder", then what's "shudder"?
> *Brake Shudder: Why Your Car Vibrates When You Brake*
> <https://www.sundevilauto.com/brake-shudder-why-your-car-vibrates-when-you-brake/>
>
> "You step on the brake pedal and you feel a vibration coming  from the
> brake pedal or worse, through the steering wheel.  You hold on tight to
> the steering wheel as you come to a stop.  You've just experienced brake
> shudder, also known as brake judder."
>
> And then what's "shake" while braking?
> *Why does my car shake when I brake?*
> <https://www.tiresplus.com/blog/brakes/car-shakes-when-i-brake/>
> Where at least this guy put "warped rotors" in quotes. :)
>
>>> The only difference with me is I don't trust my intuition.
>>> Most people trust their intuition well neigh more than they do the
>>> facts.
>>
>> Intuition, for the most part, *develops* from experience.
>
> I agree even more than you realize, because intuition is _only_ from
> experience, where that's why I keep harping on the fact that we own the
> innate intuition of a monkey, where, luckily, monkeys needed good depth
> perception and the ability to calculate whether or not they could get to
> that next branch without it cracking under the combined weight of their
> body and the added force their momentum based on weight & speed incurs.
>
> There are _many_ things I've intuited that turned out to be wrong, Xeno.
> An example is I intuited (like everyone else) that cellphones are a
> distraction (they are) and they're a _big_ distraction (which they are),
> and that they're a big _added_ distraction (which they are), so, duh, of
> course the accident rate must have shown something of an effect between the
> times that cellphones didn't exist, during the times that they skyrocketed,
> and then plateaued.
>
> And yet... the accident rate didn't even change by a blip.
> That's just a fact. A decidedly non intuitive fact. But still a fact.
> A fact in _all_ the reliable USA (and Australia) data sets.
> The accident rate only seems to change in the bullshit data sets, almost
> all from those who politically and financially benefit from stating that
> they go up, such as from lawyers, police, and insurance companies.
>
> Those are the datasets that the bullshitters (like Steve) always use.
>
> Given I agree with you that intuition _develops_ from experience, I'm not
> saying intuition is always wrong. But people who trust more in their
> intuition than in facts are _often_ wrong because intuition itself is
> limited.

You don't trust intuition, you listen to it, you make some assessments,
and then you *test* what it is telling you.
>
> I already said even Einstein was wrong as much as he was right, and he was
> one of the most intelligent intuitive observers of physics who ever lived.
>
> It's intuitive that brake rotors could warp just as it's intuitive that
> we're moving at different speeds through spacetime, but the fact is that
> brake rotors can't warp (the physics won't let them) and that we can't move
> at any _other_ speed but the speed of light (the physics won't let us).
>
> People who trust their intuition _more_ than they trust facts to the
> contrary are often wrong (trust me, I am well aware the iKooks do just
> that).
>
>>> My intuition says that rotors should get hot and start "warping"; but
>>> the
>>> facts say otherwise, just as my intuition says that cellphones must be
>>> causing increased accident rates; but the facts say otherwise.
>>
>> You tell that to the warped rotors I have discarded.
>
> If the rotor met thickness, cracking, gouging specs, then you wasted a good
> rotor.

Nope, they were warped and wouldn't clean up *before* they went below
minimum thickness. In the early days I tried a few, found I was wasting
my time machining them, then started relying on *measurements* to
determine serviceability after machining. It's only involves simple
arithmetic. Discs these days are like spark plugs - the cost of repair
due to time involved is outweighed by the low cost of new items.
>
> Wasting rotors _always_ solves what people think is warp. But the "warp"
> will come back simply because the cause of the warp is your
> foot.

Again, you are confusing warp with deposition. Don't do that. Look at
the *symptoms*, then measure.
>
> What people call "warp" is explained on gory detail in my half dozen
> respectable references, but mostly it's simple TV which can be solved two
> ways:
> a. Remove the TV
> b. Junk the rotors
>
> Your choice.
>
> HINT: If "warp" was truly a wavy rotor, then why does rebedding often work?

Because people cannot discern or determine the *difference* in symptoms.
As I said, *measurement* will tell you where matters have gone awry.
While I am at it, I must say I dislike the term *wavy rotor* as that
gives the incorrect intimation. In my experience, a warped rotor is
usually best described as *buckled* and a buckled rotor will just as
likely not judder, not shudder, not vibrate, etc. but it will likely
*shimmy*. Measurement, and a check of the rest of the suspension, will
determine the exact cause and the exact cure. Measurement with the
correct tools and methods will tell you, the diagnostician, so much.
Intuition may provide you with a lead but testing your intuition
determines the reality you are confronted with.
>
>> FWIW, when you machine rotor, you can actually *see* the warp right up
>> until they clean up.
>
> If the experts tell me that a rotor can't warp, and if you tell me not only
> can they warp, but you can _see_ the warp, then we have a conflict of data.

I can *measure* the warp. I can then machine the warp and the process of
machining makes it very self evident what has happened to that
particular disc. Measurement will also tell you if the disc will clean
up or require discarding. Go watch someone machining discs and you'll
get what I mean.
>

--
Xeno

Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

"Andy Burnelli" <spam@nospam.com> wrote in message
news:t5g136$11db$1@gioia.aioe.org...
> Again, I'm going to repeat I'm highly educated, intelligent, and I've
> researched this subject for years, so just saying "I measured it" is like
> saying "I measured the earth and it's still flat, dammit".
>
> Having taken on the iKooks with facts, rest assured I believe a lot of
> people strongly believe a lot of things that just aren't the case.
>
> If a vehicle shudders while braking, people intuit that their rotors
> warped, and, I don't blame them for thinking that any more than I blame
> people for thinking the earth is flat, since it makes sense in terms of
> the
> intuition of a smart monkey - which is the intuition we _all_ have.

OK, so what you (and all the sources you are quoting) are saying is that
brake discs *don't* warp by any measurable amount because they are designed
not to do so and must conform to a standard that means they don't.

And when people feel their car juddering (and maybe the pedal vibrating)
during braking, that's not caused by a disc which is "warped" in the
conventional sense of "not a plane disc but one which is wavy like a potato
chip", but is instead caused by the surface being more or less "sticky" in
different parts because of local roughness and/or glazing from pad deposits?

That all sounds very sensible. I think you've settled the debate by quoting
sources. The problem is that there are also sources which still use the term
"warped discs/rotors" to describe discs which have localised
roughness/glazing. That word "warped" is misleading because it makes people
think "wavy".

"Andy Burnelli" <spam@nospam.com> wrote in message
news:t5g3bk$1qs$1@gioia.aioe.org...

> They go on by citing reliable references at the brake companies, where
> prior to that they explain the basic physics which makes it impossible.
> "Even if you're traveling straight down the side of a mountain with your
> brakes applied the entire way. Your brake pads will fade and start to
> disintegrate long before you come close to heating your rotors enough to
> soften them to the point where they could possibly warp"

I saw a demonstration in a TV program(me) about physics in the early 1980s,
in which a car was repeatedly braked from high speed (and then accelerated
back up to speed) over a very short time. A camera mounted so it could see
one of the front discs showed the disc was glowing cherry red after n
iterations (for unknown n!). They were demonstrating the conversion of
kinetic energy into heat.

I wonder what effect that high temperature had on the pads once they were
red hot. Would you want to ride in that car afterwards - would the pads have
been made less effective? How hot do discs get if you descend a long hill
(let's say a mile long, average 1:4 aka 25%) using brakes only. My wife
remembers a friend descending such a hill (Porlock Hill in Devon, England)
in a motor caravan which may have had a mixture of discs and drums. By the
end of the hill, there was smoke coming from the wheels (brake pads,
presumably) - the driver learned an important lesson: to engage a low gear
on a long steep hill so there is a bit of transmission braking to supplement
the normal friction braking.

Incidentally, I can vouch for the fact that if the pads wear through to the
mounting studs and these start to score the discs, the braking effect is a
lot less. (Yikes!) My car had passed its MOT test (annual safety test in the
UK for all vehicles once they reach 3 years old) a few months earlier, and
braking was acceptable at that time. And nothing had been picked up when the
car was serviced. And yet the pads wore through to the studs. The first I
knew was a loud scraping metal-on-metal noise and the car didn't brake as
effectively as it should. I drove very cautiously to the nearest garage that
fitted brakes and got them to replace the relevant pads and discs. I *think*
it may have been only the front brakes that were affected, so I had working
rear brakes. I don't like to think what would have happened if all four
brakes had worn through at the same time. It turned out that the pads
*should* have triggered a warning light (wires embedded in the pads making
contact with the disc) before the pads wore down to the studs, but the
sensor wire had corroded. The warning bulb itself was working - it still
came on briefly as part of the self-test whenever the ignition is first
turned on.

I was rather horrified than the brakes had got to that state without
anything being picked up. Nowadays I always explicitly ask a garage to check
the discs and pads when my car is being serviced - because pad thickness is
not an easy thing to check yourself unless you know what to look for - and
unless you have a ramp, it means taking each wheel off in turn.

NY wrote:

> OK, so what you (and all the sources you are quoting) are saying is that
> brake discs *don't* warp by any measurable amount because they are designed
> not to do so and must conform to a standard that means they don't.

You are correct that I'm only saying what the reliable sources are saying,
as I don't know offhand what temperature brake fluid boils at, for example,
but _they_ do (the people who made the references); and I trust them.
*The 'Warped' Brake Disc & Other Myths of the Braking System*
<https://www.ipdusa.com/Articles/528/The-Warped-Brake-Disc-and-Other-Myths-of-the-Braking-System>

What _they_ say is that "warp" doesn't happen. Period.
In fact, what _they_ say is that it's usually caused by simple TV:
"In fact every case of "warped brake disc" that I have investigated,
whether on a racing car or a street car, has turned out to be friction
pad material transferred unevenly to the surface of the disc.
This uneven deposition results in thickness variation (TV)
or run-out due to hot spotting that occurred at elevated temperatures."

(The fact they say "runout" in the same sentence as "TV" will be something
that Xeno and I could hash out, because at first that seems incongruent.)

> And when people feel their car juddering (and maybe the pedal vibrating)
> during braking, that's not caused by a disc which is "warped" in the
> conventional sense of "not a plane disc but one which is wavy like a potato
> chip", but is instead caused by the surface being more or less "sticky" in
> different parts because of local roughness and/or glazing from pad deposits?

Bumpy more than sticky.

The thickness variation is _started_ by a single pad imprint, but, of
course, it grows over time, which is the part that gets too complicated for
most people to intuit (because, as Xeno stated, intuition is borne of
experience, but few people have the experience of these experts).

I suspect it's "intuitive" for people to believe their rotors 'warped',
instead of the fact that their own foot caused the TV in the first place.

> That all sounds very sensible. I think you've settled the debate by quoting
> sources. The problem is that there are also sources which still use the term
> "warped discs/rotors" to describe discs which have localised
> roughness/glazing. That word "warped" is misleading because it makes people
> think "wavy".

As you can tell, I'm well aware of almost every article on the Internet
about "warped" rotors (not the articles, per se, but what they claim),
simply because I've looked it up many times in the past (but not recently).

Unless new data has arisen, there are fundamentally two types of articles
that will use the word "warp", namely...
a. Those that _know_ warp doesn't happen, and,
b. Those that don't know warp doesn't happen.

For the articles that know warp doesn't happen, they will always explain
how the shudder occurs (e.g., TV or runout or whatever), while those that
don't know will be clueless. They'll call _everything_ warp.

Now, this isn't the first time we've discussed "warp" on this newsgroup,
nor will it be the last, and, in fact, almost every car forum that exists
has covered this topic in gory detail (ask me how I know).

The result is always the same:
a. Of the 100% of people who will vehemently claim they have warp,
exactly 0% of them will have _measured_ that warp (and probably
95% of them don't even know _how_ they would measure that warp).

b. Of the 100% of people who claim there is no warp, exactly 100% of
them will know that it's almost always thickness variation,
where about 10% of them (I'm guessing on that) will actually
_understand_ how that happens.

I'm in the 90% who don't really completely understand how a teeeny tiny
single footprint of pad can end up being a bump large enough to make a
difference but still so teeny tiny that you can barely see it can make
_that_ much of a difference.

However... I've had many times a claimed "warp" (as in TV) which "went
away" when I "scrubbed" the rotors (using the classic 60-to-10 re-bedding
procedure), so if _that_ was true warp, no way would a rebedding procedure
ever have worked.

The fact that re-bedding works in many cases, indicates that what
re-bedding fixed couldn't possibly have been warp.

The solution, by the way, is simple.
The cause is your foot.

If you recognize that fact, you'll _instantly_ know the solution:
a. Don't let your pad imprint on the rotor, and,
b. If it does, scrub it off as soon as you feel it.

If someone can find a reference that claims I'm wrong, I'll be _happy_ to
read it, as I'll change my opinion on a dime if the facts point that way.
--
Sometimes on Usenet you can find people who know more than you do.

Xeno wrote:

> You don't trust intuition, you listen to it, you make some assessments,
> and then you *test* what it is telling you.

I'm all for testing, as my cars are a quarter of a century old and when
they break, I form an hypothesis and then I test that hypothesis so as to
replace the part that needs to be replaced.

One place I need your intuition on is this sentence in this reference:

*The 'Warped' Brake Disc & Other Myths of the Braking System*
<https://www.ipdusa.com/Articles/528/The-Warped-Brake-Disc-and-Other-Myths-of-the-Braking-System>
"In fact every case of "warped brake disc" that I have investigated,
whether on a racing car or a street car, has turned out to be friction
pad material transferred unevenly to the surface of the disc.
This uneven deposition results in thickness variation (TV)
or run-out due to hot spotting that occurred at elevated temperatures."

The fact they say "runout" in the same sentence as "TV" seems incongruent
to me, where I think I understand what they're saying, but the reason it's
disconcerting is that "normally" the solution for runout is _different_
than the solution for DTV.

Of course, TV will cause an "apparent runout" on the dial gauge, but it's
not the same kind of runout you'd get with, oh, say, rust around the hub.

The reason the semantics matter is that the _solution_ to each problem is
different, where, for example, the solution to a truly warped rotor (as in
potato chip) would be to junk that rotor, while the solution to DT is
typically to smooth out the bumps, and the typical solution to runout is to
figure out what caused the roter to be mounted off kilter (in most cases).

All show up, eventually, as "runout" but each cause has a different
remedial solution so the fact you can measure an out-of-spec variation on a
dial gauge doesn't tell you _which_ problem caused the runout.

>> If the rotor met thickness, cracking, gouging specs, then you wasted a good
>> rotor.
>
> Nope, they were warped and wouldn't clean up *before* they went below
> minimum thickness. In the early days I tried a few, found I was wasting
> my time machining them, then started relying on *measurements* to
> determine serviceability after machining. It's only involves simple
> arithmetic. Discs these days are like spark plugs - the cost of repair
> due to time involved is outweighed by the low cost of new items.

I agree on the cost factor weighing in as I've replaced perfectly good
rotors for kids who no longer live at home even though the rotors were
within specs because I had to buy the parts ahead of time and because I
knew that a new rotor will last longer for the kids than an old rotor (even
though the old rotor was within thickness specs).

I get rotors for $15 to about $35 each, although I'm well aware they can
easily cost many times that (especially for the bullshit drilled and
slotted rotors - which are sold to morons who are intuitive people).

>> HINT: If "warp" was truly a wavy rotor, then why does rebedding often work?
>
> Because people cannot discern or determine the *difference* in symptoms.

Yup.

That's why it matters what _word_ we use.
a. If it truly warped, then any sane person would junk the rotors.
(Because the conditions to cause warp would have been horrendous.)
b. If it's simply pad deposits, then a sane person might try to
"scrape" them off with a simple re-bedding process.
(Or machine them off.)
c. If it's simply that there is rust buildup between the rotor and the
hub or maybe lug bolts/nuts torqued too tightly on one side, then
the runout can be cured by cleaning up the rust & retorquing the nuts.

What I've seen on innumerable forums is people replace not only the rotors
and then _blame_ the new rotors for "warp" but on some forums, they resort
to _larger_ calipers and rotors, thinking that their vibration was "warp"
caused by the brakes being designed to be too small.

I'm sure you're well aware, for example, of the infamous "Tundra upgrade"
to Toyota SUVs. There's zero chance of convincing them that it's a myth.

> As I said, *measurement* will tell you where matters have gone awry.

The main problem with the measurement is we're looking at puny differences
which are extremely difficult to measure in terms of pad imprints.

> I can *measure* the warp.

Did you read in the references how puny the DTV is for a sensible vibration
while braking? I have really nice dial gauges and calipers and yet even I
can't measure to that accuracy & precision (for a variety of reasons).

What's the best accuracy and precision of your measurement equipment?

On 5/11/2022 3:35 AM, Xeno wrote:

<snip>

where the pads had to move parallel to the rotor axis to remain in
>> contact with the disc that was not a perfectly flat plane.
>
> The most common type of warped disc I have seen is more like a buckle.
> Think of it like a bicycle wheel that doesn't run true in the lateral
> plane. I have measured it and I have seen it when truing it on the brake
> lathe. I have not seen a warp at opposite sides of the disc and in the
> same plane - like a potato chip. Note however, there are a number of
> causes of this, some not related to heat. The two most common are
> incorrect/excessive tightening of wheel nuts and/or grit lodged between
> disc and hub at the mounting surfaces. If the disc has been warped and
> shows signs of severe overheating but no other cause can be determined,
> it's the heat.

What has happened, over the years, is that vehicle manufacturers have
made the rotors as thin as possible to reduce the rotating mass of the
wheel in order to increases fuel economy slightly. IMVAIO it was not a
worthwhile tradeoff but they're up against government fuel economy
mandates and will do whatever they can to increase fuel economy. It's
also how we ended up with 2.5MPH bumpers in the U.S.
<https://www.upi.com/Archives/1982/05/14/The-Reagan-administration-Friday-eased-federal-standards-to-require/3390390196800/>.

Unfortunately, just replacing the warped rotors with the same OEM rotors
is not a long-term fix, the problem will come back. As someone else
mentioned, over-tightening the lug nuts, and not tightening them in the
right sequence, can also cause warped rotors.

"The process of slowing and stopping your vehicle relies on brake pads
pressing against the flat metal of your brake rotors. This braking
causes friction, which generates heat and makes the metal of your brake
rotors more malleable. Then, the contact of your brake pads can warp the
structure of your rotors. When your brake pads are pressing against a
warped rotor, this will cause shaking or vibrations to run through your
vehicle."
<https://www.chapelhilltire.com/tire-alignment-vs-warped-brake-rotors/>.

"Warping" may be the wrong word, sometimes. Sometimes the rotors end up
with uneven thickness but they are still straight and true.

Sometimes it's not the rotors but uneven hubs.

Sometimes junky pads, that overheat, deposit material that fuses onto
the rotors so the rotor surface is uneven but the rotor itself is not
warped, called "pad imprinting."

I recall back in the 1990's when my relative had a repair shop that
mainly did a lot of brake jobs. There was one U.S. brand of vehicles
(now defunct) that had terrible issues with warped rotors and every
brake job required replacement rotors, there was no way to put them on a
lathe to resurface them, they were just way too thin, and you can't fix
actual warping on a lathe anyway. Often the pads were fine but the
vehicle was shuddering while braking due to the warped rotors.

On 5/11/2022 11:37 AM, sms wrote:
> On 5/11/2022 3:35 AM, Xeno wrote:
>
> <snip>
>
>  where the pads had to move parallel to the rotor axis to remain in
>>> contact with the disc that was not a perfectly flat plane.
>>
>> The most common type of warped disc I have seen is more like a buckle.
>> Think of it like a bicycle wheel that doesn't run true in the lateral
>> plane. I have measured it and I have seen it when truing it on the
>> brake lathe. I have not seen a warp at opposite sides of the disc and
>> in the same plane - like a potato chip. Note however, there are a
>> number of causes of this, some not related to heat. The two most
>> common are incorrect/excessive tightening of wheel nuts and/or grit
>> lodged between disc and hub at the mounting surfaces. If the disc has
>> been warped and shows signs of severe overheating but no other cause
>> can be determined, it's the heat.
>
> What has happened, over the years, is that vehicle manufacturers have
> made the rotors as thin as possible to reduce the rotating mass of the
> wheel in order to increases fuel economy slightly. IMVAIO it was not a
> worthwhile tradeoff but they're up against government fuel economy
> mandates and will do whatever they can to increase fuel economy. It's
> also how we ended up with 2.5MPH bumpers in the U.S.
> <https://www.upi.com/Archives/1982/05/14/The-Reagan-administration-Friday-eased-federal-standards-to-require/3390390196800/>.
>
>
> Unfortunately, just replacing the warped rotors with the same OEM rotors
> is not a long-term fix, the problem will come back. As someone else
> mentioned, over-tightening the lug nuts, and not tightening them in the
> right sequence, can also cause warped rotors.
>
> "The process of slowing and stopping your vehicle relies on brake pads
> pressing against the flat metal of your brake rotors. This braking
> causes friction, which generates heat and makes the metal of your brake
> rotors more malleable. Then, the contact of your brake pads can warp the
> structure of your rotors. When your brake pads are pressing against a
> warped rotor, this will cause shaking or vibrations to run through your
> vehicle."
> <https://www.chapelhilltire.com/tire-alignment-vs-warped-brake-rotors/>.
>
> "Warping" may be the wrong word, sometimes. Sometimes the rotors end up
> with uneven thickness but they are still straight and true.
>
> Sometimes it's not the rotors but uneven hubs.
>
> Sometimes junky pads, that overheat, deposit material that fuses onto
> the rotors so the rotor surface is uneven but the rotor itself is not
> warped, called "pad imprinting."
>
> I recall back in the 1990's when my relative had a repair shop that
> mainly did a lot of brake jobs. There was one U.S. brand of vehicles
> (now defunct) that had terrible issues with warped rotors and every
> brake job required replacement rotors, there was no way to put them on a
> lathe to resurface them, they were just way too thin, and you can't fix
> actual warping on a lathe anyway. Often the pads were fine but the
> vehicle was shuddering while braking due to the warped rotors.

Hondas... improper lug torquing plus thin-ish rotors led to warping.

On Wed, 11 May 2022 13:37:53 +1000, Xeno <xenolith@optusnet.com.au> wrote:

>
>Yeah, "as in a potato chip" would be a bit too extreme. OTOH, I have
>*measured* warped rotors that were warped sufficiently to have an effect
>on the *steering*, even some that were too far gone to machine whilst
>still retaining minimum thickness. Note, not seen warping on ventilated
>discs that I can recall, just the old solid discs. The ventilated discs
>seem rather more robust.

Ventilated rotors warp too. After a period of severe braking I unintentionally drove
though a long, deep puddle. Went from a smoothly braking car to a shuddering
beast at the next stoplight.

On Wed, 11 May 2022 12:48:10 +0100, Andy Burnelli <spam@nospam.com> wrote:
>
>Which brings me to shudder, shake, judder, and vibrate in terms of braking.
> *Brake Judder In Detail* by Jurid (who makes my OEM BMW rear brake pads)
> <https://www.jurid.com/technical-support/light-vehicles/technical-tips/brake-judder.html>
> "Brake judder is the vibration felt through the steering wheel
> and suspension when the brakes are applied at certain speeds
> and pressures. It can vary from a barely noticeable vibration
> to a violent judder - experienced either through the brake
> pedal or steering wheel."
>
The author quoted above says - in the same article - "The excessive heat from the pads can
cause the discs to overheat, resulting in disc warping."

>If that's "judder", then what's "shudder"?
> *Brake Shudder: Why Your Car Vibrates When You Brake*
> <https://www.sundevilauto.com/brake-shudder-why-your-car-vibrates-when-you-brake/>
> "You step on the brake pedal and you feel a vibration coming
> from the brake pedal or worse, through the steering wheel.
> You hold on tight to the steering wheel as you come to a stop.
> You've just experienced brake shudder, also known as brake judder."
>
This author also says in the same article, "Brake rotors become warped over time from the
heat generated from the friction produced when braking."
>And then what's "shake" while braking?
> *Why does my car shake when I brake?*
> <https://www.tiresplus.com/blog/brakes/car-shakes-when-i-brake/>
> Where at least this guy put "warped rotors" in quotes. :)
>
Yes, "If one or more of your brake rotors becomes 'warped,' you might experience that
dreaded vibration when you brake."
>
>Me? I don't trust my intuition more than I trust facts to the contrary.

You'll probably find this study interesting:
https://link.springer.com/article/10.1007/s11665-012-0397-7#article-info
Let me know what you think of it.

Xeno wrote:

>> Is "warp" the right word to use for a rotor (disc) that remains as a
>> flat plane but with a surface that is not uniformly smooth over the
>
> Short answer - no.

Longer answer, verbatim...
*Brake Rotors Warp From Heat -- Myth Busted*
<https://www.hansonsubaru.com/service/information/brake-myths.htm>

5. Brake Rotors Warp From Heat -- Myth Busted
Damaged brake rotors can cause your car to shudder and shake under braking,
and that's often attributed to "warped" brake rotors. The suggestion goes,
under intense, emergency, both-feet-on-the-pedal-type braking, the brakes
get so hot that the brake rotor warps and deforms. Since it's not perfectly
flat anymore, it causes your car to shake when you engage the brakes.

But that's a myth -- there's simply no way that a brake rotor can get hot
enough to warp or deform on an ordinary passenger car. However, this idea
of a 'warped' rotor is commonly used in reference to the surface that the
brake pads contact. This surface can become uneven and this is most
commonly caused by heat from emergency or aggressive braking. As the brake
pads are held against an uneven rotor surface, the vehicle may shake or
shudder while stopping or you may notice that your brake pedal has
something of a bounce to it.

So, while it's usually not technically accurate to say that a brake rotor
is warped, that term is still used to indicate that the surface of your
brake rotors is not even.

On 2022-05-11 3:32 a.m., Andy Burnelli wrote:
> Vic Smith wrote:
>
>> I agree that rotors don't warp "as in a potato chip."
>> Rotors do warp "as in a warped rotor."
>
> Assuming you actually believe that, allow me to explain why intuition is a
> terrible thing if people trust their own intuition far more than they do
> facts. Me? I don't trust my intuition at all. I trust in facts.
>
> Facts from reliable sources, like this PDF from Carroll Smith:
> *The 'Warped' Brake Disc & Other Myths of the Braking System*
> ���<https://centricparts.com/getmedia/bd69395a-b65c-481d-93f7-b26b1bd0638d/Centric_and_APC_Technical_Whitepaper_B1-Warped-Brake-Disc-8-2018_1.pdf>

Empiricism:

<https://youtu.be/fFY2MPylrS4>

See the big dark patch as that rotor is slowly being turned on the brake
lathe?

That's warp.

As is this:

<https://youtu.be/eEpYifYWV5k?t=250>

On 2022-05-11 12:22 p.m., Andy Burnelli wrote:
> Xeno wrote:
>
>>> Is "warp" the right word to use for a rotor (disc) that remains as a
>>> flat plane but with a surface that is not uniformly smooth over the
>>
>> Short answer - no.
>
> Longer answer, verbatim... *Brake Rotors Warp From Heat -- Myth Busted*
> <https://www.hansonsubaru.com/service/information/brake-myths.htm>
>
> 5. Brake Rotors Warp From Heat -- Myth Busted
> Damaged brake rotors can cause your car to shudder and shake under braking,
> and that's often attributed to "warped" brake rotors. The suggestion goes,
> under intense, emergency, both-feet-on-the-pedal-type braking, the brakes
> get so hot that the brake rotor warps and deforms. Since it's not perfectly
> flat anymore, it causes your car to shake when you engage the brakes.
>
> But that's a myth -- there's simply no way that a brake rotor can get hot
> enough to warp or deform on an ordinary passenger car. However, this idea
> of a 'warped' rotor is commonly used in reference to the surface that the
> brake pads contact. This surface can become uneven and this is most
> commonly caused by heat from emergency or aggressive braking. As the brake
> pads are held against an uneven rotor surface, the vehicle may shake or
> shudder while stopping or you may notice that your brake pedal has
> something of a bounce to it.
>
> So, while it's usually not technically accurate to say that a brake rotor
> is warped, that term is still used to indicate that the surface of your
> brake rotors is not even.

Empiricism:

<https://youtu.be/fFY2MPylrS4>

See the big dark patch as that rotor is slowly being turned on the brake
lathe?

That's warp.

As is this:

<https://youtu.be/eEpYifYWV5k?t=250>

On 2022-05-11 11:35 a.m., Vic Smith wrote:
> On Wed, 11 May 2022 12:48:10 +0100, Andy Burnelli <spam@nospam.com> wrote:
>>
>> Which brings me to shudder, shake, judder, and vibrate in terms of braking.
>> *Brake Judder In Detail* by Jurid (who makes my OEM BMW rear brake pads)
>> <https://www.jurid.com/technical-support/light-vehicles/technical-tips/brake-judder.html>
>> "Brake judder is the vibration felt through the steering wheel
>> and suspension when the brakes are applied at certain speeds
>> and pressures. It can vary from a barely noticeable vibration
>> to a violent judder - experienced either through the brake
>> pedal or steering wheel."
>>
> The author quoted above says - in the same article - "The excessive heat from the pads can
> cause the discs to overheat, resulting in disc warping."
>
>> If that's "judder", then what's "shudder"?
>> *Brake Shudder: Why Your Car Vibrates When You Brake*
>> <https://www.sundevilauto.com/brake-shudder-why-your-car-vibrates-when-you-brake/>
>> "You step on the brake pedal and you feel a vibration coming
>> from the brake pedal or worse, through the steering wheel.
>> You hold on tight to the steering wheel as you come to a stop.
>> You've just experienced brake shudder, also known as brake judder."
>>
> This author also says in the same article, "Brake rotors become warped over time from the
> heat generated from the friction produced when braking."
>
>> And then what's "shake" while braking?
>> *Why does my car shake when I brake?*
>> <https://www.tiresplus.com/blog/brakes/car-shakes-when-i-brake/>
>> Where at least this guy put "warped rotors" in quotes. :)
>>
> Yes, "If one or more of your brake rotors becomes 'warped,' you might experience that
> dreaded vibration when you brake."
>>
>> Me? I don't trust my intuition more than I trust facts to the contrary.
>
> You'll probably find this study interesting:
> https://link.springer.com/article/10.1007/s11665-012-0397-7#article-info
> Let me know what you think of it.

I guarantee Arlen will find some reason why he understands the subject
better than the authors.

On 2022-05-09 8:39 a.m., Andy Burnelli wrote:
> Xeno wrote:
>
>>> You can't test warp on the vehicle (not reliably anyway).
>>> It has to be tested on a known flat bench (or using known flat tools).
>>
>> Or mounted on a brake lathe
>
> Agreed. All you need is a long flat edge and feeler gauges as a minimum.
>
> I'm all about facts. I'll change my mind in a split second if that's
> where the facts lead.
>
> Let's look at the facts in this discussion between two adults on Usenet.
>
> My point is that nobody who says warp (as in potato chip) measures that
> warp (as in potato chip), where I already know that warp (as in potato
> chip) isn't what happens when a brake rotor is subject to intense heating &
> cooling cycles.
> "High quality brake rotors that pass SAE J2928 Brake Rotor Thermal
>  Cracking Procedure for Vehicles below 4,540 kg GVWR proves
>  they don't warp"
>
> As I said, intuition is a terrible thing indeed.
> "Calling it brake rotor warp demonstrates a complete misunderstanding
>  of the metallurgy and the braking process"
>
>> I wasn't saying anything about rebedding at all.
>
> OK. But the fact that rebedding works sometimes means that what it fixed
> wasn't warp (as in potato chip). What it fixed wasn't runout either.
>
> What it fixed is the only thing it _could_ fix, which is deposit buildup.
>
> Intuition is a terrible thing indeed.
> "The brake pads and rotors in a street vehicle can't possibly  generate
> enough heat to warp a brake rotor."
>
>>> Almost nobody could machine a warped rotor (as in potato chip) back to
>>> perfection simply because the amount of metal needed isn't going to be
>>
>> Depends on the amount of warp and whether the rotor still meets
>> minimum specs afterwards. It only takes a very small amount of warp
>> for the driver to be able to sense it.
>
> Agreed.
> However, any rotor that was subject to enough heat to truly warp it (as in
> potato chip) was subject to _tremendous_ heat - almost impossible to attain
> in a passenger vehicle (again, I'm not talking about the space shuttle
> here).
> "The heating and cooling that people refer to when discussing  'warped
> brake rotors' would cause cracking, not warping."
>
> There are half a dozen materials rotors are made of though, so we'd have to
> look up the melting point of each of them to be more precise about melting.
> 1. cast iron
> 2. steel
> 3. stainless steel
> 4. laminated steel
> 5. high carbon iron (e.g., Sparta CX3.5)
> 6. ceramic
>
>> The car showed *symptoms* of warp, the rotors, when measured showed
>> *evidence* of warp. I drove the car, I felt the symptoms, I measured
>> the rotor warp.
>
> I'll leave it at that since I respect your experience.
>
> Read this please, though (it's just one random hit of many of course):
> *What causes warped brake rotors?*
> <https://ricksfreeautorepairadvice.com/warped-brake-rotors/>
> "brake rotors DO NOT WARP from  normal driving or even race track use.
>  Yes, you read that correctly. A typical street vehicle can't possibly
>  generate enough heat to warp a brake rotor."
>
> All the quotes in this one post are from that reference, but I can easily
> find more because I know what I know and most people are intuitive.
>
> Did I mention yet that intuition is a terrible thing?
>
>>> I doubt it. Rotors are made of a variety of steels (e.g., motorcycle
>>> rotors
>>
>> I don't, I saw the evidence.
>
> Again, I respect your experience.
> However, you have to respect my knowledge that _reliable_ sources say
> otherwise and that runout isn't warp (as in potato chip) and that if
> rebedding worked, it wasn't warp (as in potato chip) after all.
> "Even if you're traveling straight down the side of a mountain with your
> brakes applied the entire way. Your brake pads will fade and start to
> disintegrate long before you come close to heating your rotors enough to
> soften them to the point where they could possibly warp"
>
> I even doubt machining could fix any appreciable warp (as in potato
> chip), and even if it did, I wouldn't want any rotors from _that_ shop. :)
> "In addition, if your brake system is working properly, it's applying
> equal pressure to both sides of the rotor which means BOTH SIDES are
> heating at the same rate. To warp a brake rotor, you must have more heat
> on one side of the rotor than the other."
>
>>> are often stainless steel) but even for the worst quality cast iron
>>> rotors,
>>> look up the temperature it takes to melt them.
>>
>> Automotive rotors were pretty much all cast iron back in the era
>> concerned. And the rotor did *melt* at the periphery, as I stated. It
>> had been damn hot all over but the periphery was clearly melted.
>
> I'm not going to argue with you on that as cast iron has a relatively low
> melting point where our question is can a rotor typically get to that point
> on a passenger vehicle whose owner suspects his rotor warped (as in potato
> chip).
>
> "To get cast iron hot enough to soften the metal you'd need to generate
>  almost 2,300�F range. There isn't a factory stock automotive brake
>  system in the world that's capable of generating that kind of heat.
>  In fact, you would experience brake pad fade, pad disintegration,
>  brake fluid boiling and rotor discoloration long before you  reached
> 1,000�F."
>
>>> I'm not saying it's impossible. But I doubt it happens for normal
>>> passenger
>>> vehicles (I'm not talking space shuttle stuff or fighter plane stuff).
>>
>> Nor am I. I wasn't and never have been an aviation mechanic.
>
> The only thing I harp on is I've never met a person who claimed it was
> "warp" (as in potato chip) who actually measured it, and, worse, the remedy
> often is something (like rebedding) which couldn't possibly have fixed warp
> (as in potato chip).
>
> Worse than even that, is all the reliable sources say passenger vehicle
> rotors can't warp (as in potato chip) simply because brakes can't generate
> enough heat.
>
>>> Look it up.
>>
>> No need, I saw the evidence directly.
>
> I knew what I'd find in brake warp when I just looked it up as I did my
> research long ago (just as I did with cellphone caused accident rates).
>
> Most people work solely on intuition.
> Humans have the intuition of evolved monkeys.
>
> Intuition serves humans well... sometimes.
> But not always.
>
> Read this _one_ reference for a starting point on fixing that intuition.
> <https://ricksfreeautorepairadvice.com/warped-brake-rotors/>
>
> If you don't like it, find another (there are plenty).
>
>>> Yes. I know. But did you measure warp (as in potato chip)?
>>
>> Yes, I did, with a dial indicator. Definitely warp.
>
> "To pass the J2928 rotor test, rotors must withstand at least  150 heat
> cycles on a dynamometer without cracking or showing  any structural or
> dimensional failure. "
>
>>> You can't measure warp without a known straight surface to compare
>>> against.
>>> A mic won't measure warp.
>>> A dial gauge won't measure warp (unless it's a special setup).
>>
>> It was a special setup - a brake lathe. Runout and warp shows up very
>> clearly when the hub and rotor assembly is correctly mounted.
>
> Note that the link I am giving you has information from the brake rotor
> manufacturers who themselves claim that their rotors can't warp (as in
> potato chip) in passenger vehicles under _any_ circumstances.
>
> Raybestos video titled "Rotors Can't Warp":
> <https://youtu.be/LVRVe1cEBDI>
>
>>> HINT: I've never seen anyone who did who said their rotors warped
>>> when what
>>> really happened was something else (e.g., runout or pad deposition).
>>
>> Depending on the site, runout can be a symptom of warp. You verify it
>> as warp by checking both sides.
>
> I'm not going to harp on the issue other than to repeat my salient points.
> a. Rotors don't warp (as in potato chip) in passenger vehicles. Period.
> b. People who _say_ they did, didn't measure warp (as in potato chip).
> c. The temperatures needed are unattainable in passenger vehicles.
>
>>>> If they wouldn't clean up and still remain within specs, they would
>>>> be replaced, and that could be determined from the measurements.
>>>
>>> I seriously doubt an actual warp (as in potato chip) could be
>>> machined, but
>>> if it's only slight, then maybe, but what fool would want rotors that
>>> were
>>> actually warped (as in potato chip) even after they were machined?
>>
>> Well, these days the rule is discard and renew, don't machine.
>> Procedures have changed.
>
> OK. But I can _easily_ find industry references that say rotors can't warp
> (as in potato chip) simply because they are designed _not_ to warp (as in
> potato chip), and, because the temperatures to cause warp (as in potato
> chip) are unattainable.

On 2022-05-09 6:30 p.m., Andy Burnelli wrote:
> sms wrote:
>
>> But the mass of thick rotors negatively affected fuel economy so much
>> thinner rotors began to be used, and they usually can't be resurfaced
>> even once, they have to be replaced at the same time the brake pads
>> are replaced.
>
> Bullshit.
> The time to replace rotors is when they no longer meet the specs, and there
> are a few specs that they need to meet (cracks, thickness, gouges, etc.),
> but the main spec is the thickness.
>
> I've seen many people say the bullshit you say but the fact is you measure
> them, like Xeno and I do, and if they're within specs, you keep them.
>
> It doesn't matter how many brake pads you replaced.
>
>> They also warp much easier. It also actually became not that uncommon
>> to replace warped rotors, but not the pads, since the pads were fine.
>
> More bullshit.
>
> Read this before you bullshit us please.
> <https://ricksfreeautorepairadvice.com/warped-brake-rotors/>
>
> It's impossible for rotors to warp (as in potato chip), and everyone who
> says they do, has _never_ measured it, least of all you, Steve.

<https://www.youtube.com/watch?v=DiuwzN2mQuA&t=122s>

NY wrote:

> I saw a demonstration in a TV program(me) about physics in the early 1980s,
> in which a car was repeatedly braked from high speed (and then accelerated
> back up to speed) over a very short time. A camera mounted so it could see
> one of the front discs showed the disc was glowing cherry red after n
> iterations (for unknown n!). They were demonstrating the conversion of
> kinetic energy into heat.

There's no doubt rotors get hot during braking.
That's what friction is all about.

Black body radiation is well studied, which is what you were seeing.
Everything glows "red" (but usually in the infrared which our eyes can't
easily see but interestingly, digital cameras generally see it better).

Try this:
a. Point a TV remote at your face and click the button.
b. Point a TV remote at your phone and look at the screen.

See any difference?

BTW, FUN fact. Do you know _why_ friction works?
HINT: Why don't we fall thru the earth when we stand on it?
Doublehint: It's not what most people intuit it to be.
Triplehint: Rutherford Model of the atom (it's almost all empty space).

> I wonder what effect that high temperature had on the pads once they were
> red hot. Would you want to ride in that car afterwards - would the pads have
> been made less effective? How hot do discs get if you descend a long hill
> (let's say a mile long, average 1:4 aka 25%) using brakes only. My wife
> remembers a friend descending such a hill (Porlock Hill in Devon, England)
> in a motor caravan which may have had a mixture of discs and drums. By the
> end of the hill, there was smoke coming from the wheels (brake pads,
> presumably) - the driver learned an important lesson: to engage a low gear
> on a long steep hill so there is a bit of transmission braking to supplement
> the normal friction braking.

*Six Brake Rotor Myths Debunked*
<https://www.onallcylinders.com/2017/05/19/6-biggest-brake-rotor-myths-debunked/>
Brake Rotors Warp - Rotors don't warp.
Back in the 1970s, in what was probably a scene right out of the
movie Dazed and Confused, someone came up with a theory about
brake-rotor "warping," and it totally stuck. Why? Probably because,
in layman's terms, it makes sense.

But then real life happens and this faulty explanation doesn't
hold up to scientific scrutiny.

What is often described as "warping" is actually the presence of
two separate phenomena that can happen in isolation or in combination
with each other, and neither has anything to do with warping.
These phenomena are:
a. Brake torque variation (BTV), and
b. Disc thickness variation (DTV)

BTV is a variation of torque across the rotor's face which causes
the rotor to slip and catch as the brake caliper is engaged.
The differences in torque across the rotor may be caused by
inconsistencies in the rotor's finish or metallurgy.

BTV can be caused by uneven deposits of friction material.
This might not cause a pulsation in pedal feel, but it will cause
vehicle judder or vibration.

DTV, on the other hand, is the result of measuring the thickness
of the rotor surface in multiple spots around the rotor.
DTV measurement can be found simply by finding the difference
between the thickest part of the rotor from the thinnest.

As the rotor's variable thicknesses pass through the restricted
caliper, the piston moves in and out, causing pulsations in
the brake pedal while stopping."

> Incidentally, I can vouch for the fact that if the pads wear through to the
> mounting studs and these start to score the discs, the braking effect is a
> lot less. (Yikes!) My car had passed its MOT test (annual safety test in the
> UK for all vehicles once they reach 3 years old) a few months earlier, and
> braking was acceptable at that time. And nothing had been picked up when the
> car was serviced. And yet the pads wore through to the studs. The first I
> knew was a loud scraping metal-on-metal noise and the car didn't brake as
> effectively as it should. I drove very cautiously to the nearest garage that
> fitted brakes and got them to replace the relevant pads and discs. I *think*
> it may have been only the front brakes that were affected, so I had working
> rear brakes. I don't like to think what would have happened if all four
> brakes had worn through at the same time. It turned out that the pads
> *should* have triggered a warning light (wires embedded in the pads making
> contact with the disc) before the pads wore down to the studs, but the
> sensor wire had corroded. The warning bulb itself was working - it still
> came on briefly as part of the self-test whenever the ignition is first
> turned on.

*The myth of warped brake discs*
<https://alconkits.com/technical-info/brake-tech/56-the-myth-of-warped-brake-discs>
"Have you ever heard someone say they had warped brake discs?
Typically someone had the discs resurfaced to cure the problem
and after a relatively short time the roughness or vibration came back.
In almost every case, this problem is not caused by a warped discs,
but that the brake pad material transferred unevenly to the surface
of the disc. This uneven deposition results in thickness variation
or run-out due to hot spotting that occurred at elevated temperatures."

> I was rather horrified than the brakes had got to that state without
> anything being picked up. Nowadays I always explicitly ask a garage to check
> the discs and pads when my car is being serviced - because pad thickness is
> not an easy thing to check yourself unless you know what to look for - and
> unless you have a ramp, it means taking each wheel off in turn.

*Stop the "Warped" Rotors Myth and Service Brakes the Right Way*
<https://www.brakeandfrontend.com/warped-rotors-myth/>
"Myths take hold �because either A) they seem completely logical or
B) they are so often repeated that they just become common knowledge.
The warped rotor myth is a little bit of both. A rotor that
contributed to a pulsation condition certainly appears 'warped.'
Plus, everyone says it - even technicians that know the rotor isn�t
really warped will say it as shorthand. Rotors are cast in extreme heat
at three to five times greater than the most aggressive braking
situation. Physically 'warping' a rotor would require a similar
application of extreme heat, which is impossible."

News wrote:

> Hondas... improper lug torquing plus thin-ish rotors led to warping.

Everybody wants a simple answer, but as Xeno & Vic Smith are showing, a
simple answer isn't always going to be the answer to your issue.

In your case, improper torquing certainly can cause runout, as everyone
here has been saying; however while warp causes runout, runout doesn't
cause warp, so we have to be careful what we attempt to intuit.

Almost nothing about what people call 'warp' is intuitive bearing in mind
that almost all of this "unexplained warp" is simply pad buildup...
"As little as 0.0004 inch can be felt through the pedal,
and 0.001 inch can be downright annoying"
<https://www.motortrend.com/how-to/1808-nuts-and-bolts-warped-rotor-myth/>

See also:
*Warped Brake Rotors - Vibrating Reality or Internet Myth?*
<https://blog.fcpeuro.com/warped-brake-rotors-vibrating-reality-or-internet-myth>
"Traditionally, this was blamed on warped rotors, and the prescription
was to either get the rotors machined or to replace the rotors.

Technically this wasn't wrong, but it's not completely right either.

To understand what is going on, lets examine how the brake pads
and rotors interact. It's not as simple as it seems on the surface,
and relies on complex interaction between friction materials.

Technically yes, the rotor is warped because the buildup of pad deposits
is a few thousandths of an inch thick. To restore proper smooth braking
performance, the uneven deposits need to be removed, and a fresh uniform
layer of friction material needs to be laid down."

Vic Smith wrote:

> After a period of severe braking I unintentionally drove
> though a long, deep puddle. Went from a smoothly braking car to a shuddering
> beast at the next stoplight.

Nothing wrong with anecdotal evidence but here is what the pros say.

*Nuts & Bolts: Warped Rotor Myth*
<https://www.motortrend.com/how-to/1808-nuts-and-bolts-warped-rotor-myth/>
"It's exceedingly rare to actually warp a rotor. Instead, the cause
of the shudder you feel through the pedal is an uneven buildup
of brake pad material on the rotor itself. As little as 0.0004 inch
can be felt through the pedal & 0.001 inch can be downright annoying"

*Warped Brake Rotors - Vibrating Reality or Internet Myth?*
<https://blog.fcpeuro.com/warped-brake-rotors-vibrating-reality-or-internet-myth>
"Traditionally, this was blamed on warped rotors, and the prescription
was to either get the rotors machined or to replace the rotors.

Technically this wasn't wrong, but it's not completely right either.

To understand what is going on, lets examine how the brake pads
and rotors interact. It's not as simple as it seems on the surface,
and relies on complex interaction between friction materials.

Technically yes, the rotor is warped because the buildup of pad deposits
is a few thousandths of an inch thick. To restore proper smooth braking
performance, the uneven deposits need to be removed, and a fresh uniform
layer of friction material needs to be laid down."

*Stop the 'Warped' Rotors Myth and Service Brakes the Right Way*
<https://www.brakeandfrontend.com/warped-rotors-myth/>
"Myths take hold �because either A) they seem completely logical or
B) they are so often repeated that they just become common knowledge.
The warped rotor myth is a little bit of both. A rotor that
contributed to a pulsation condition certainly appears 'warped.'
Plus, everyone says it - even technicians that know the rotor isn�t
really warped will say it as shorthand. Rotors are cast in extreme heat
at three to five times greater than the most aggressive braking
situation. Physically 'warping' a rotor would require a similar
application of extreme heat, which is impossible."

sms wrote:

> Unfortunately, just replacing the warped rotors with the same OEM rotors
> is not a long-term fix, the problem will come back.

The "problem" most of the time is the driver's own foot, so, yeah.
It will come back.

It will continue to come back until the driver learns that warped rotors
(as in potato chip) are a myth.

> Often the pads were fine but the
> vehicle was shuddering while braking due to the warped rotors.

Verbatim...

*Six Brake Rotor Myths Debunked*
<https://www.onallcylinders.com/2017/05/19/6-biggest-brake-rotor-myths-debunked/>
Brake Rotors Warp - Rotors don't warp.
Back in the 1970s, in what was probably a scene right out of the
movie Dazed and Confused, someone came up with a theory about
brake-rotor "warping," and it totally stuck. Why? Probably because,
in layman's terms, it makes sense.

But then real life happens and this faulty explanation doesn't
hold up to scientific scrutiny.

What is often described as "warping" is actually the presence of
two separate phenomena that can happen in isolation or in combination
with each other, and neither has anything to do with warping.
These phenomena are:
a. Brake torque variation (BTV), and
b. Disc thickness variation (DTV)

BTV is a variation of torque across the rotor's face which causes
the rotor to slip and catch as the brake caliper is engaged.
The differences in torque across the rotor may be caused by
inconsistencies in the rotor's finish or metallurgy.

BTV can be caused by uneven deposits of friction material.
This might not cause a pulsation in pedal feel, but it will cause
vehicle judder or vibration.

DTV, on the other hand, is the result of measuring the thickness
of the rotor surface in multiple spots around the rotor.
DTV measurement can be found simply by finding the difference
between the thickest part of the rotor from the thinnest.

As the rotor's variable thicknesses pass through the restricted
caliper, the piston moves in and out, causing pulsations in
the brake pedal while stopping."

On 2022-05-11 1:16 p.m., Andy Burnelli wrote:
> NY wrote:
>
>> I saw a demonstration in a TV program(me) about physics in the early
>> 1980s, in which a car was repeatedly braked from high speed (and then
>> accelerated back up to speed) over a very short time. A camera mounted
>> so it could see one of the front discs showed the disc was glowing
>> cherry red after n iterations (for unknown n!). They were
>> demonstrating the conversion of kinetic energy into heat.
>
> There's no doubt rotors get hot during braking.
> That's what friction is all about.
>
> Black body radiation is well studied, which is what you were seeing.
> Everything glows "red" (but usually in the infrared which our eyes can't
> easily see but interestingly, digital cameras generally see it better).

Only if you redefine "red" to mean "infrared"...

>
> Try this:
> a. Point a TV remote at your face and click the button.
> b. Point a TV remote at your phone and look at the screen.
>
> See any difference?
>
> BTW, FUN fact. Do you know _why_ friction works?
> HINT: Why don't we fall thru the earth when we stand on it?
> Doublehint: It's not what most people intuit it to be.
> Triplehint: Rutherford Model of the atom (it's almost all empty space).
>
>> I wonder what effect that high temperature had on the pads once they
>> were red hot. Would you want to ride in that car afterwards - would
>> the pads have been made less effective? How hot do discs get if you
>> descend a long hill (let's say a mile long, average 1:4 aka 25%) using
>> brakes only. My wife remembers a friend descending such a hill
>> (Porlock Hill in Devon, England) in a motor caravan which may have had
>> a mixture of discs and drums. By the end of the hill, there was smoke
>> coming from the wheels (brake pads, presumably) - the driver learned
>> an important lesson: to engage a low gear on a long steep hill so
>> there is a bit of transmission braking to supplement the normal
>> friction braking.
>
> *Six Brake Rotor Myths Debunked*
> <https://www.onallcylinders.com/2017/05/19/6-biggest-brake-rotor-myths-debunked/>
>
> Brake Rotors Warp - Rotors don't warp.
> Back in the 1970s, in what was probably a scene right out of the movie
> Dazed and Confused, someone came up with a theory about brake-rotor
> "warping," and it totally stuck. Why? Probably because, in layman's
> terms, it makes sense.

Brake rotors DO warp.

See all my previous posts with actual video of actual warped rotors.

On 2022-05-11 1:17 p.m., Andy Burnelli wrote:
> Vic Smith wrote:
>
>> After a period of severe braking I unintentionally drove
>> though a long, deep puddle.  Went from a smoothly braking car to a
>> shuddering
>> beast at the next stoplight.
>
> Nothing wrong with anecdotal evidence but here is what the pros say.
>
> *Nuts & Bolts: Warped Rotor Myth*
> <https://www.motortrend.com/how-to/1808-nuts-and-bolts-warped-rotor-myth/>
> "It's exceedingly rare to actually warp a rotor. Instead, the cause  of
> the shudder you feel through the pedal is an uneven buildup  of brake
> pad material on the rotor itself.  As little as 0.0004 inch  can be felt
> through the pedal & 0.001 inch can be downright annoying"
> *Warped Brake Rotors - Vibrating Reality or Internet Myth?*
> <https://blog.fcpeuro.com/warped-brake-rotors-vibrating-reality-or-internet-myth>

"Exceedingly rare" means that it DOES happen...

....contrary to your "I'm all about the facts" statements.