re: "Google Wallet may be making a return" (and "Why is it so complex

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.

Intuition, for the most part, *develops* from experience.

You tell that to the warped rotors I have discarded. FWIW, when you machine rotor, you can actually *see* the warp right up until they clean up.

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.

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

That depends on the *actual cause*.

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.

Short answer - no.

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.

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.

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.

That sounds fair! ;-)

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.

If that's "judder", then what's "shudder"?

And then what's "shake" while braking?

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).

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?

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.

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

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?

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).

We all have intuition, which, you and I agree, is borne of experience.

The problem is that companies take advantage of that intuition, e.g., many people "might" intuit that a tire worn to flat rubber has "less dry traction" than a tire with treads.... because they "think" the treads themselves, somehow "grip" the pavement (like fingers grasping the sand).

You, I'm sure, realize that the tire tread doesn't "grip" the road, even as advertising would have you believe that it does (we're talking macadam).

Intuition is borne of experience. But intuition is often wrong as a result.

In fact, I'd wager that in these contentious "what oil" arguments about cars, intuition is almost always wrong... simply because _marketing_ has swayed people's intuition where they don't remember _where_ they got the "experience" that they believe they have.

Why else would an iKook think that an iPhone could do half of what they claim it can do, when it simply can't for obviously well known reasons?

Marketing tells people that their brand of API-whatever SAE-whatever oil is "better" than the other brand, and, for some reason, people believe the marketing because that brand costs more than the other brand (yes, I know, some _are_ better even with the same specs, but not because marketing told them they were).

Marketing preys on people's intuition.

Hell, you know as well as I do that I can find a billion web pages from brake outfits saying your rotors have "warped" and the solution is their brand of rotors... which is just marketing preying on people's intuition.

Intuition, even as it's borne of experience, is a terrible thing when it's wrong.

Me? I don't trust my intuition more than I trust facts to the contrary.

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".

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

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.

Again, you are confusing warp with deposition. Don't do that. Look at the *symptoms*, then measure.

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

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.

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

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.

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*

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.)

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.

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.

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 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.

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).

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.

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

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?

where the pads had to move parallel to the rotor axis to remain in

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.

"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."

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.

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.

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."

This author also says in the same article, "Brake rotors become warped over time from the heat generated from the friction produced when braking."

Yes, "If one or more of your brake rotors becomes 'warped,' you might experience that dreaded vibration when you brake."

You'll probably find this study interesting:

Longer answer, verbatim... *Brake Rotors Warp From Heat -- Myth Busted*

1. 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:

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

That's warp.

As is this:

Empiricism:

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

That's warp.

As is this:

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

What's that if it's not warp, Arlen?