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

We're having a conversation among friends when one casually mentions his wife's rotors "warped".
The other jumps on him and declares that street-use rotors don't warp (in
general). An Internet search bears him out, as MANY articles say rotor warp is a myth.
Googling, we find that brake torque variation is mostly from uneven pad deposition buildup (i.e., disc thickness variation) and axial runout. But then it gets confusing as the more enlightened sources begin to mention thermo elastic instability hotspots and breaking judder into low frequency cold judder and high frequency hot judder.
The heated discussion went on. And so did the confusion. For more than a few beers.
My question?
While we now know rotors rarely actually warp, does anyone know of a good scientific or engineering paper explaining the TRUE causes of brake related judder in street cars?
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Here's 8 pages of "words"... that conform to what I think I might have once known. http://www.powerbrake.co.za/downloads/tech_01_judder.pdf -----
- gpsman
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On 02/15/2013 10:52 AM, gpsman wrote:

words, but not a paper, just advertising.
their cited uneven disk thickness is relatively uncommon. distortion from the plane is very common indeed. it's the asymmetry of a caliper's component momenta that causes pulsing in the hydraulics. opposed pistons dynamically self-equilibrate - single sided calipers cannot.
--
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On Fri, 15 Feb 2013 16:51:20 -0800, jim beam wrote:

Yes, I'm looking for 'real' scientific engineering papers.
All these (which are decidedly NOT engineering papers!) say rotors aren't warping, but as you noted, it might just be advertising.
CENTRIC: Pad and Rotor Bed-In Theory, Definitions and Procedures http://www.centricparts.com/files/Centric%20White%20Paper%20C2-Bed-In%20Theory.pdf
AKEBONO: Brake Noise, Vibration, Harshness, causes http://www.akebonobrakes.com/company/media_center/white_papers/akebono_NVH.pdf
POWERBRAKE: The final word on brake judder and "warped" discs http://www.powerbrake.co.za/downloads/tech_01_judder.pdf
BREMBO: Judder caused by improper bedding procedure http://www.brembo.com/en/car/Racing/Street-products/Documents/USA%20CATALOGO.pdf
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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, all of which can probably be traced to some idiot mistorquing lugs. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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On 02/15/2013 06:35 PM, Scott Dorsey wrote:

did you mic them?

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.
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enches.

enty

I had a 1979 Plymouth Champ Twin-Stik I bought new. With about 5K miles on it, I took it on a hairball trip through the Sierras. By the end of the trip, the rotors were definitely warped. The dealer didn't have the special tool that car needed to remove the rotors, no one had needed it yet. So given the choice of waiting several weeks for one to be shipped from Japan, or machining their own tool, they made their own tool. At least, that's what they told me, and I can't imagine them making up stories to make more problems, work and expense for themselves.
Man, that was a little pocket rocket, before the term was invented. And I thought that coming from a '63 Vette.
Thanks for the judder links, Joe.
jg
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On Fri, 15 Feb 2013 16:48:16 -0800, jim beam wrote:

The proletariat be damned, I reach out to the literati to explain what "really" causes brake judder (because it's not rotor warp)!
Googling, I found these on the bimmer boards so far that I'm reading:
"Aspects of disc brake judder" Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering http://pid.sagepub.com/content/217/6/419.full.pdf
Analysis of the vehicle brake judder problem by employing a simplified source–path–receiver model Acoustics and Dynamics Laboratory, Department of Mechanical Engineering, The Ohio State University, Columbus, Ohio, USA http://www.researchgate.net/publication/233988829_Analysis_of_the_vehicle_brake_judder_problem_by_employing_a_simplified_sourcepathreceiver_model/file/79e4150e7d38711887.pdf
A Parametric Study of Brake Roughness Robert Bosch Corporation http://sem-proceedings.com/20i/sem.org-IMAC-XX-Conf-S17P04-A-Parametric-Study-Brake-Roughness.pdf
Judder, Diagnosis, & Prevention, Mohamed Khalid Abdelhamid, AlliedSignal Automotive, Europe http://sem-proceedings.com/14i/sem.org-IMAC-XIV-14th-Int-14-5-5-Judder-Diagnosis-Prevention.pdf
Improved mathematical models of vehicle brake judder and experimental observations Osman Taha Sen, Rajendra Singh Acoustics and Dynamics Laboratory, Department of Mechanical and Aerospace Engineering, The Ohio State University, http://www.mecheng.osu.edu/adl/files/adl/C12-1.pdf
Judder vibration in disc brakes excited by thermoelastic instability Oscar Altuzarra, Enrique Amezua, Rafael Avilés, Alfonso Hernández, (2002), Engineering Computations, Vol. 19 Iss: 4, pp.411 - 430 http://www.ehu.es/compmech/welcome/doc/Paper%20867%20Engineering%20Computations.pdf
Experimental Analysis of Disc Thickness Variation Development in Motor Vehicle Brakes School of Aerospace, Mechanical & Manufacturing Engineering (SAMME) http://researchbank.rmit.edu.au/eserv/rmit:6260/Rodriguez.pdf
Thermal Brake Judder Investigations Using a High Speed Dynamometer David Bryant, John Fieldhouse, Andrew Crampton and Chris Talbot, University of Huddersfield http://eprints.hud.ac.uk/3878/1/2008-01-0818.pdf
Braking Process in Automobiles: Investigation of the Thermoelastic Instability Phenomenon M. Eltoukhy and S. Asfour, Department of Industrial Engineering, College of Engineering, University of Miami http://cdn.intechweb.org/pdfs/5380.pdf
Brake Vibration and Noise - A Review and Discussion Dihua Guan, State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing, China http://www.acoustics.asn.au/conference_proceedings/ICA2010/cdrom-ICA2010/papers/p46.pdf
NVH Simulation Technology for Disc Brake Calipers Hitachi, Suzuki Yoichi Kumemura Hayuru Inoue Yuichi Takagi Shinji Suzuki http://www.hitachi.com/ICSFiles/afieldfile/2009/12/25/r2009_07_107.pdf
SURFACE TEMPERATURE DISTRIBUTION IN A COMPOSITE BRAKE ROTOR A.A. Adebisi1, M.A. Maleque1 and Q.H. Shah Department of Manufacturing and Materials Engineering http://ejum.fsktm.um.edu.my/article/1146.pdf
DISCUSSION OF THE CHARACTERISTICS OF BRAKE JUDDER AND THE NECESSARY DATA ACQUISITION SYSTEM FOR COMPLETE ANALYSIS D. Bryant, A. Crampton, J. Fieldhouse and C. Talbot University of Huddersfield, Queensgate, Huddersfield HD1 3DH, UK http://eprints.hud.ac.uk/3797/1/10_PAPER_Final_D_Bryant.pdf
Order domain analysis of speed-dependent friction-induced torque in a brake experiment Osman Taha Sen, Jason T. Dreyer, Rajendra Singh Acoustics and Dynamics Laboratory, Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA http://www.mecheng.osu.edu/adl/files/adl/J187.pdf
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On 02/15/2013 05:44 PM, Joe Mastroianni wrote:

quickly scanning, i see nothing on caliper asymmetry.

http://www.researchgate.net/publication/233988829_Analysis_of_the_vehicle_brake_judder_problem_by_employing_a_simplified_sourcepathreceiver_model/file/79e4150e7d38711887.pdf
that one presumes disk thickness variation, nothing on caliper dynamics.

http://sem-proceedings.com/20i/sem.org-IMAC-XX-Conf-S17P04-A-Parametric-Study-Brake-Roughness.pdf
etc.

http://sem-proceedings.com/14i/sem.org-IMAC-XIV-14th-Int-14-5-5-Judder-Diagnosis-Prevention.pdf

http://www.ehu.es/compmech/welcome/doc/Paper%20867%20Engineering%20Computations.pdf

http://www.acoustics.asn.au/conference_proceedings/ICA2010/cdrom-ICA2010/papers/p46.pdf

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.
so you're just going to have to keep sucking it up and coughing it up.
--
fact check required

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On Fri, 15 Feb 2013 18:34:14 -0800, jim beam 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).
It will also take me a while to read them all, but I don't see anything (yet) about the single piston caliper design.
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On 02/15/2013 07:06 PM, Joe Mastroianni wrote:

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.
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On 2/15/2013 5:06 PM, Joe Mastroianni wrote:

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.

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On 02/15/2013 10:53 PM, dsi1 wrote:

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.

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

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.

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.

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On 2/16/2013 5:29 AM, jim beam wrote:

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

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On 02/16/2013 08:40 AM, dsi1 wrote:

there's lots of ways, but that's not the point. the point is that runout only a few molecules thick has absolutely no effect - surface roughness alone of the disk is many orders of magnitude larger.

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On 2/17/2013 5:49 AM, jim beam wrote:

If there's lots of ways, please name one of those ways. Just one. My point is that I'm not talking about surface roughness. Just the mechanical plating of pad material onto the cast iron surface.
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On 02/17/2013 10:51 AM, dsi1 wrote:

are you serious? i hope not.

dude, seriously, how do you think adding a "molecular layer" to a disk surface makes the slightest difference? surface roughness is in the order of 10 microns. that's at least 10,000 times bigger than even a huge "molecular layer".
oh, and oem runout tolerance is ~10 times greater than that.
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On 2/17/2013 4:32 PM, jim beam wrote:

Oh yeah, "there's lots of ways" - none of them are serious. Nothing personal, but you're the dude that full of bs. You don't even know what the heck I'm talking about. Have a nice life dude.

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On 02/17/2013 11:54 PM, dsi1 wrote:

i'm glad i didn't bother! i spent years of my life measuring stuff to microns and below, so if you think i'm going to try to educate a guy who's clutching at "molecular layer" straws and being hostile about it because he can't be bothered to pay attention to fact or can't be bothered to google, you need to think again.

just as i suspected, the relevant stuff is way over your head.
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On Monday, February 18, 2013 5:29:50 AM UTC-10, jim beam wrote:

ut

Yeah, don't bother to respond to me if you can't even understand what the s ubject is. You're talking about brake runout but I'm not talking about that . What I'm talking about, dude, is the transference of pad material onto th e surface of the cast iron surface of the rotor. This layer is invisible to the naked eye and you can't measure it as runout because the whole idea of seating new pads is to get an even layer of this stuff onto the surface of the rotor. I'm not interested in getting sucked into your discussion about warped brakes and disk runout - dude.
P.S., If you think that machining a rotor results in a grooved surface... w ell that just explains everything.

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