The Myth of the "Warped" Brake Rotor

Lots of misinformation about brakes lately. Looks like its time to pull out the ol'Stoptech Technical FAQ. Enjoy.

 

http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

 

The term "warped brake disc" has been in common use in motor racing for decades. When a driver reports a vibration under hard braking, inexperienced crews, after checking for (and not finding) cracks often attribute the vibration to "warped discs". They then measure the disc thickness in various places, find significant variation and the diagnosis is cast in stone.

When disc brakes for high performance cars arrived on the scene we began to hear of "warped brake discs" on road going cars, with the same analyses and diagnoses. Typically, the discs are resurfaced to cure the problem and, equally typically, after a relatively short time the roughness or vibration comes back. Brake roughness has caused a significant number of cars to be bought back by their manufacturers under the "lemon laws". This has been going on for decades now - and, like most things that we have cast in stone, the diagnoses are wrong.

With one qualifier, presuming that the hub and wheel flange are flat and in good condition and that the wheel bolts or hat mounting hardware is in good condition, installed correctly and tightened uniformly and in the correct order to the recommended torque specification, in more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history - I have never seen a warped brake disc. I have seen lots of cracked discs, (FIGURE 1) discs that had turned into shallow cones at operating temperature because they were mounted rigidly to their attachment bells or top hats, (FIGURE 2) a few where the friction surface had collapsed in the area between straight radial interior vanes, (FIGURE 3) and an untold number of discs with pad material unevenly deposited on the friction surfaces - sometimes visible and more often not. (FIGURE 4)

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.

In order to understand what is happening here, we will briefly investigate the nature of the stopping power of the disc brake system...

 

UNEVEN PAD DEPOSIT REMOVAL FAQ

Max, ya can't post up this factoid and not include what to do about it.

 

http://stoptech.com/technical-support/technical-white-papers/uneven-pad-deposit-removal

I recently swapped pads and rotors in the front. While the braking surface had .001" runout measured a dial indicator, the edge of the rotor had corroded and was digging into the pads, unevenly, and causing vibration at speed. Just an FYI.

Thanks for finally posting this, ive been telling people this forever... no one seems to believe me!

I recently swapped pads and rotors in the front. While the braking surface had .001" runout measured a dial indicator, the edge of the rotor had corroded and was digging into the pads, unevenly, and causing vibration at speed. Just an FYI.

 

You could have just turned the edge down and kept the rotors.

 

Lots of rotors these days actually have a chamfer on the edge to prevent exactly this from happening.

I have been spouting this for years. Pad deposits, not warping.

I'm just doing my part to share the info that folks like you and stoptech have been drilling into me for years. Threads keep popping up and several regulars keep saying "warping".

 

While most technical data is way too much info to the casual user, this is the type of information that I think is particularly useful to EVERYONE and should be included as part of drivers training.

Yes, Yes, Yes. I actually had someone tell me they warped their rotors by applying their parking brake and letting the car sit overnight after a long session of highspeed driving/braking. I tried to convince him otherwise, but finally gave up.

You could have just turned the edge down and kept the rotors.

 

Lots of rotors these days actually have a chamfer on the edge to prevent exactly this from happening.

 

Yes, but couldn't have the downtime. Now I have spare set of rotors and it's not a problem.

Yes, but couldn't have the downtime. Now I have spare set of rotors and it's not a problem.

 

If you kept the old ones, turn down the edges and bead blast the hats and vanes. Spray them with some WD-40 and toss them in a trash bag or bigass zip lock, and keep them under your workbench in the garage. You never know when a spare set of good stock rotors will come in handy.

Max, ya can't post up this factoid and not include what to do about it.

 

http://stoptech.com/technical-support/technical-white-papers/uneven-pad-deposit-removal

You are totally right. Added to the first post. Thanks Drew. I was being REALLY lazy when I posted this. I did not even edit the cut and paste...