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

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"

See also: *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."

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

*Nuts & 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?* "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* "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."

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.

Verbatim...

*Six 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."

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

Brake rotors DO warp.

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

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

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

Your own sources disagree.

We've had this discussion many times, where I'm well aware that there is conflicting information even in any one given article on the subject.

What we have is a difference in terminology and measurement skills.

For example:

*The Mystery of Warped Brake Rotors* "Contrary to popular belief, brake rotors, and especially brake rotors supplied by a reputable manufacturer such as DBA don't warp, no matter how aggressively a vehicle is driven. Yet, as we know, brake pedal pulsation caused by out-of-true brake rotors is a fairly common problem that is almost invariably attributed to warped rotors, which is almost invariably confirmed by excessive amounts of rotor run out that is easy to "prove" with a dial gauge."

*Nuts & 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."

The conflicting information is why you heard me say a few times in the beginning that I wasn't saying it can't happen, but that it doesn't. [I'm well aware some reliable references say it can't happen also.]

Given of the 100% of people who _say_ their rotors warped, 0% of them actually measured it (and probably only 10% would know how), it's not warp.

Nice catch. Right down my line.

*The Effect of Residual Stress on the Distortion of Gray Iron Brake Disks*

From the first two sentences, it appears they studied: a. "thermal distortion" b. of "gray iron brake disks" c. due to "residual stress" d. on both a heat-treated & non-heat-treated gray iron disk (singular) e. measured by "neutron scattering" f. and by "dynamometer tests" to measure "disk runout" during braking g. and by "high temperature tensile tests" for "plastic deformation" h. all due to "residual stress" *_during_* "brake applications.

It's a bit confusing but they _also_ added a separate action of "heat treating in a vacuum furnace" to "simulate distortion at high temperatures", um, so, um, they purposefully distorted the discs, it appears... and _then_ they tested them for distortion under pressure. (I admit that's a bit confusing to swallow.)

Also notice they're talking _during_ the brake application, and that they're comparing residual stress between a single heat treated & a single non heat treated gray iron rotor.

Nothing wrong with a test of just one component, but let's keep that in mind (although I'm not saying anything was done wrong).

Presumably, if these numbers are meaningful, heat treating works: "The results showed that the average residual stress of the ' heat-treated disk (47.6 MPa) was lower than that of the non-heat-treated disk (99.6 MPa)."

"Dynamometer tests at high temperatures (up to 600°C/1112°F) indicated that the residual stress pronounced the runout: the increase in disk runout after the tests for the non-heat-treated sample was more than twice that for the heat-treated sample."

Notice this is testing at high heat _during_ braking only; not afterward. Their conclusion was that heat treating works, and that disks improperly manufactured (i.e., no "stress relaxation" performed on them during the manufacturing process) could be "deformed _during_ severe braking".

After first reading the abstract (which is how you read scientific peer-reviewed papers, and yes, I've been published myself), you jump to the conclusion next.

In the conclusion they state their goal was to study the difference between heat treated and non heat treated gray iron rotors on high heat distortion _during_ braking. At elevated temperatures, they found the heat treated rotor (singular) distorted less than the heat treated rotor (singular - as they only used two rotors for the test).

I found their conclusion interesting in that after they purposefully introduced runout, they found that the largest increase was found "along the circumference near the edge", which they opined "indicates the necessity for a more refined design of the casting process and the disk shape."

At that point I started to read how they ran their experiment, but let's not summarize that here as I don't see anything wrong with what they did (nor am I'm qualified to critique them).

Tell me, Mr. Well-educated:

Does "exceedingly rare" actually mean "impossible"?

This is your idea of only stating facts, is it?

Claiming things you cannot possibly know?

Did I call it?

:-)

I worked for a company where we made industrial test beds (I was the programmer). One of those was for testing brakes. During testing at the brake factory where this machine was installed, the chap there actually brought the disk to that hot. The testing procedures included braking from 40, 60, & 80 down to 0, several times in a row, while graphing disk temp, fluid pressure, torque...

He said a good pad material would not degrade or "fade" suddenly when too hot, but would lose the friction coefficient gradually as temperature increases, thus warning the driver of the danger.

<snip>

Decades ago I replace the brake pads on a VW Rabbit (Golf in other regions) with pads that I ordered online from JC Whitney, a mail-order parts house. Descending a steep hill, in San Francisco, the pads glazed over from the heat. The rotors were fine. Did another brake job immediately, using high-quality pads from an import car parts store.

Unfortunately, in the U.S., not a lot of vehicle owners still do their own car maintenance so the number of auto parts stores is greatly reduced. In my town of 60,000 people we've lost all three of our auto parts stores as well as a fourth that's just across the city boundary. I now buy my oil at Costco or Walmart and I order my oil filters from a dealer that sells OEM parts on eBay.

Two of our vehicles are hybrids and because of regenerative braking the brakes last a very long time, easily more than 100K miles. On my old VWs I had to do brake jobs every 25K-30K miles.

<snip>

"Back in the olden days" I kept a spare set of rotors so when I was doing a brake job I didn't have to stop and take the rotors to be machined in the middle of the work. I'd then take the rotors that I removed to be put on a lathe (for free since my relative had a repair shop) and they'd be ready for the next brake job in 25,000 miles or so.

But back then discs were thick and heavy and could be machined multiple times before they were too thin. Nowadays rotors are so thin they can usually not be machined even once, but they've also become less expensive (when adjusted for inflation).

My brother-in-law saw a lot of vehicles with warped rotors back in the mid-1990's to 2000's, when the manufacturers started making them very thin without the material science knowledge of how to prevent warping. Just one serious overheating and the rotors were warped beyond repair. There was one GM brand, that is now defunct, that was particularly susceptible to warped rotors. His shop was in San Francisco and there are lot of very steep hills (when San Francisco was first laid out the proposal was to not do a grid because of the hills, but to have roads winding up the hills; real estate people protested that this would be too complicated).

Is someone actually claiming that disc rotors don't warp? That would be very surprising since nearly every car mechanic in the world is well aware of this issue

, ,

Yes, in many cases "uneven" would be a better adjective than "warped" but there are still cases where the steel brake rotor is deformed from heat.

"Warped" is a perfectly fine descriptor and no one would argue that a

2x4 piece of lumber was "warped" simply because all it had was (say) a twist.

High quality? How did you know? By the advertising?

HINT: What's the cold/hot friction rating (coefficient) of those pads? DOUBLEHINT: It's printed on every passenger vehicle pad sold in the USA.

Is that true?

Do people do less of their maintenance now that it's easier than ever before to do typical maintenance on a car for a whole bunch of reasons: a. Cars require less maintenance nowadays (e.g., no points) b. Videos abound on YouTube for how to do all sorts of maintenance c. Cars are simpler now than they have ever been (IMHO) d. The Internet makes finding & buying the correct parts super easy etc.

Were auto parts stores more prevalent in the past than they are now?

Maybe that (and Internet shopping) is why you lost your auto parts stores? Why do you think that loss is only due to a presumed lack of home DIY?

I still have a RWD vehicle with drum brakes, whose shoes lasted, oh, about

180K miles (and which were still meaty when I replaced them), and, let's be clear, I live on the top of a mountain which is clearly tough on them.

The fronts go more frequently of course...

Some brake compounds aren't compatible with what came before and the new pads can do that.

Why would I have had to read the article then and there?

The article was posted (checking) at 11:35, and I replied to Vic at

12:53pm with my prediction.

Sorry, but I'm not into the game playing.

Brake rotor warping can be and has been demonstrated by me with actual video of warped rotors.

TRIPLEHINT: The cold/hot friction rating is not all that matters.

Probably, yes.

Vehicles have become far more complex.

I can do my own brake pads if I care to, and I do do so for my 1998 Van Diemen RF98-2 Formula F.

Easily, yes.

Let's be clearer:

You talk bullshit on a regular basis.

I wonder if _anyone_ here realizes _why_ there's a minimum thickness spec?

HINT: It's not what everyone intuits (e.g., it's not for heat dissipation).

It's amazing how you concoct your own imaginary belief systems, Steve.

If a rotor got hot enough to warp your rubber brake lines turned into marshmallows & your brake fluid boiled off & your pads disintegrated.

Again, you fabricate purely imaginary belief systems, and then you frantically strive to find the most insane reasons to bolster it up.

Yeah. Like the entire world. That's a lot more than "someone", Steve.

It's always amazing how you find all the bullshit on the Internet and yet you _miss_ all the reliable references, where you _aim_ for bullshit, Steve.

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

"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."

"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. " *Stop the "Warped" Rotors Myth and Service Brakes the Right Way* 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."

---

*The 'Warped' Brake Disc & Other Myths of the Braking System* "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."

---

"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."

---

"Calling it brake rotor warp demonstrates a complete misunderstanding of the metallurgy and the braking process"

---

"Brake rotors do not warp from heat, even when driven by the most aggressive traffic officer."

---

*The Mystery of Warped Brake Rotors* "Contrary to popular belief, brake rotors, and especially brake rotors supplied by a reputable manufacturer such as DBA don't warp, no matter how aggressively a vehicle is driven. Yet, as we know, brake pedal pulsation caused by out-of-true brake rotors is a fairly common problem that is almost invariably attributed to warped rotors, which is almost invariably confirmed by excessive amounts of rotor run out that is easy to "prove" with a dial gauge."

---

**Why Do Brake Rotors Warp?** "The thing is, rotors don¢t actually permanently warp. It may feel that way when braking, but what really happens is that they become irregular due to excessive lateral run out of the rotor face. You can feel through the brake pedal as little as .002" of run out. This amount of run out is far smaller than you can see. In other words, rotors always remain true, but they can wear out irregularly for several reasons."

1. Lug torque
2. Hub rust
3. Hub runout

---

*Brake Rotors Warp From Heat -- Myth Busted* "there's simply no way that a brake rotor can get hot enough to warp or deform on an ordinary passenger car."

---

*Nuts & 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"

---

**Everything You Need to Know About High-Tech Rotors** "The most persistent myth about rotors is that they warp. It takes a lot of heat, the kind of heat used in the casting process, to actually warp a rotor. The two common problems that cause pedal pulsation are lateral run-out and disc thickness variation. Lateral run-out is typically caused by run-out from the hub face, wheel bearing, uneven lug nut torque, or a buildup of rust and corrosion between wheel and hub. Disc thickness variation is most often caused by excess pad transfer, the very thin layer of pad material that bonds to the rotor surface, and uneven wear from an improperly mounted caliper. "

---

*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* "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."

---

*Six 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."

---

*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."

--- Classic case of bullshit on the Internet:

*What Causes Brake Rotors to Warp?* "So what causes brake rotors to warp? The main cause of brake rotors warping is excessive braking at high speeds, which causes the rotors the heat up. When the rotors become too hot, the metal they are comprised of becomes soft and begins to warp, causing the rotors to malfunction."

If you read his definition of warp and how to tell, you'll catch the bullshit immediately (and he's an automotive instructor!).

--- Two more, all from Steve:

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

"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."

"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. " *Stop the "Warped" Rotors Myth and Service Brakes the Right Way* 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."