warping rotors

Read this..................


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

 

Cross drilling is supposed to help the disc stay cooler. Also makes it lighter.

According to some folks rotors don't warp at all, it's just uneven deposit of pad material on the disk. After reading this I used their bedding in procedure on a car of mine and never had any problems again.

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

 

You beat me to it!!

 

Err, no.

Cross drilling makes the rotor lighter, yes.
But;
A) friction between the pads and rotors is what removes energy from the car
B) the same amount of energy goes into the rotors whether they are drilled or not drilled
C) the rotors are made of the same materials drilled or not drilled
D) the specific heat of the rotors is not changed drilled or not drilled
E) Therefore, the lighter rotor HAS to end up hotter than the nondrilled rotor.
Now;
F) after the braking event ends, there is a small chance that the drilled rotor cools faster
G) but it does start out cooling from a higher temperature

If you were going to make one single panic stop from 180 MPH, you would be significantly better off with undrilled rotors that weight a bit more than with drilled rotors that weight a little less.

For a car like a Ferrari, there is rather plenty of airflow between the rotors to cool them adequately under anthing less than racing situations. For High Performance track driving situations, a change in pads (and fresh fluid) is all that is necessary for street tires.

 

Great analysis, Mitch.

 

the progression of brake rotor developemt was from solid to vented to vented cross drilled. The vented rotors added cooling surface by making the rotors hollow but without any air flow. Cross drilling allowed for air to flow through the rotor increasing the effectiveness of cooling. It was further enhanced by machining channels in the surface of the rotor which terminated at the holes. This resulted in a pump, effectively forcing air into the holes, then vented out through the core, as the brake pad swept across the rotor, further increasing ability to cool.

 

Joke, yes???

Maybe a bit more reading or a stay at a Holiday Inn Express

 

Without the pejorative jab, the above is definitely incorrect. The main reason for cross-drilling was reduced weight and arguably, for some pad compounds, relief for the pad outgassing as it heats. Ventilation for the rotor is readily achieved with internal vanes and preferably proper external air ducting to the hub to force air through the rotor and keep the hub cool for better bearing life.

Trust me, a rotor needs a certain thermal mass or it will get so hot that too much pad material is deposited and other overheating problems can occur, which can include rotor warping. I never, under any circumstances turn a race rotor as the loss of mass is not worth it. I am pretty sure that rotor minimum thickness specs are due to a need for suffucient material to dissipate the braking energy and due to structural problems that can result from too thin a rotor.

I toss rotors when the surface cracks radiate or seriously threaten to radiate to the outer edge. Otherwise, I beat them to submission.

 

Brake pads from teh 50s and 60 could outgass at racing temperatures (1200dF) and some kinds of holes in the disks or slots in the surface would allow the gas to escape. This ceased to be an issue in the middle 1970s. But by them motor heads had decided holes in rotors looked cool, and continue to advance all kinds of arguments to justify something that is no longer necessary.

Carbon-Carbon (F1) disks have holes but not for weight or airflow. The holes are present to allow the acreation of carbon to the carbon fiber backbone as the disk is cooked in an autoclave under high pressure for months with some kind of carbon depositing gasses involved.

Under some kinds of situations, holes and slots can be useful to minimize the time it takes to wipe water from the surface of the disks in a heavy stop in seriously heavy rain. But these are not for cooling, nor for weight reduction.

 

Hence the word "supposed".

 

"Under some kinds of situations, holes and slots can be useful to minimize the time it takes to wipe water from the surface of the disks in a heavy stop in seriously heavy rain. But these are not for cooling, nor for weight reduction."

nuff said

 

Iirc, the holes in the rotors should be cast in the rotor and not drilled into the rotor. Drilling causes the cracking around the holes. Maybe someone can expound on this. Bottom line is buy a high quality rotor.
Ed

 

Indeed in the days of the one and only DS11 pad, we would have to go through a very careful bed in/fade in process. The rule then was always never new pads with new rotors as the temps needed to process the pad material would warp rotors unless they were already used. Much of the procedures outlined in the Stoptech article were very much de rigeur in the 60s-70s.

 

Interesting you brought up 60s and 70s as below is an opinion someone provided after reading the link that also mentions being dated.

I read the article. The author is a spankster. Brake rotors warp. He’s just referring to it as “run-out” and “thickness variation”. Both are terms used to identify a non-parallel or a non-linear surface condition on the rotor friction surface, in layman’s term: warpage. He identifies other causes of a pulsating pedal correctly when he talks about material transfer, that is why some manufacturers have advised to try using sandpaper on the friction surfaces first, then if the problem persists, refinishing or replacement. And as for his “myths” section, maybe this article is a little out of date, but most real race cars now use carbon-ceramic rotors. The new Corvette ZR-1 comes from the factory with carbon-ceramic rotors. If you did a little research you would probably find some of the hotter Ferrari’s, Lamborghini’s and Porsche’s also are factory equipped as such.

 

hahahahaha

 

"If you did a little research you would probably find some of the hotter Ferrari’s, Lamborghini’s and Porsche’s also are factory equipped as such"
correct..slotted with holes, never had a problem with warping unless i was at the track...and that is expected..

 

My 02c;

I destroyed the factory (non-drilled) rotors returning from a track day when the car was almost new. Rifledriver had warned me when I took delivery that the 360 "likes to eat rotors", but I didn't have spares and thought I could get home OK. Lesson learnt.

The dealer replaced 'em with drilled rotors from, IIRC, Brembo. - They lasted better but RD noticed cracking in the fronts after a few more track days - I use 'em hard, but wasn't expecting 'em to crack "from" the holes.

He recommended (and I obviously accepted ) the slotted Girodiscs as replacements and they were great.

I don't think warping is an issue unless you put the handbrake on upon returning to the paddock after some "hot laps" - The theory being that the handbrake pads stop 'em cooling evenly and can cause warping - This may be an urban legend, but made sense to me.

So, IMO, in summary, drilled rotors suck!.....

Cheers,
Ian

 

I have a Corvette Grand Sport and it's factory equipped with big, 15" plus, thick drilled rotors. All I did was to use the Hawk pads in place of the dusty oem pads. The car has been tracked and I have never had a warped rotor. Now whether it's from the size / thickness or drilled is up for debate however all combined may help this.
Maybe the 6 piston calipers with individual pads help displace heat and offer more uniform braking surface combined with the drilled rotors.
As a side note, C5 corvettes would warp rotors just by leaving the garage. I have resurfaced many at my shop and replaced a few due to insufficent material after maching. And these are not tracked at all.

 

tirecrap.com sells rotors that are cryogenically treated to prevent warping.....tried em....immediately warped on a daily driver, what a load of crap.
ed

 

I get 30 track days on a set of F355 rotors while turning lap times within 2 seconds of the lap record!

{Lap record for 400 HP cars weighing 3200 pounds on street (not r-compound) tires.}

 

Pretty much sums it up in a nut shell. I can't believe two pages would be devoted to this subject.

Slotted/drilled rotors are for out gassing from the pads only, no other purpose.

 

OT Question. My son's RR went in for the 40K check up. Pads worn, they replaced the rotors also even though the pads were not were worn to the point the sensors activated. I called dealer, typical "RR is a high performance off road vehicle designed to uncompromising specifications and maintain this level ... yada yada yada..."
My R8 was in for an oil change. Pads were fine for now" but will need replacing in another 5K". Web search reveals that they will also want to replace rotors also as the Audi "does not recommend turning rotors."
Should I request pad replacement now to prevent the need for $1500 rotors?

 

No. In the days of excess and cheap gas rotors where made of high quality steel and moere than you needed. Sometines you could turn a rotor 3-4 times before you had to replace them. Now with efficient manufacture (code word for they are cheap as can be) development of new profit centers, and increasing level of difficulty for the DIY'er OEM now make "just what you need" rotors engineered so when the pads are worn the rotors would trun flat under the wear limit. That makes it harder for joe shade tree to just pull pads and swap while drinking his beer. Now shadetree needs to measure the rotors, pull caliper, maybe bleed calipers, maybe have more serious tools to remove rotors so they can be replaced and higher profit margins to suppliers because now you buy rotors and pads. The days of the pepboys 50 dollar brake job have given way to simple toyota requiring 800 dollar brake jobs. Also, oems like audo don't want the hassle or returns if say a rotor is turned badly and the new age technician is now a part replacer because few are trained to understand how the brakes work understanding things like runout, minimum thicknesses, rebuilding calipers, pad transfer, etc.