No such thing as warped rotors

[V6nside]

I know this is hard to hear, but your braking issues are not from warped rotors.

I always assumed warping was a common issue until someone educated me on braking 101.

So I thought I would share what was given to me since I see a lot of "Brake" threads being bounced around.

Here is just one of several pages on the topic, lots of good info in here, if any one has some thing different to add please share.

I feel the more we can dispel myths, the further we can advance our passion for road performance.

http://www.stoptech.com/tech_info/wp...rakedisk.shtml

[Magnum375 Jr]

Thats a decent report, but those deposits and spots do change the shape of the disc, making them warped in appearance. Thats a hard statement to prove, i think its wrong, because mine are warped, you can see where the rust forms after washing, and then go drive it and in the one spot the rust will still be there...thats warped.

[V6nside]

Thats a decent report, but those deposits and spots do change the shape of the disc, making them warped in appearance. Thats a hard statement to prove, i think its wrong, because mine are warped, you can see where the rust forms after washing, and then go drive it and in the one spot the rust will still be there...thats warped.

Could it be something else? Hub or control arm not being perfectly true? Just trying to think outside the box.

One way to eliminate everything else would be to remove the rotor, turn 180 degrees reinstall, see if the rust disappears then reappears in another spot on the face, if it does it would point to something else, if nothing changes and the rust spot does'nt move than you could be right.

I think people cry "warped rotors" to often without truly identifying the root cause.
There are professionals that say using an impact gun instead of a torque wrench can cause the rotor to appear/feel warped due to uneven torquing of each lug. Another theory is manufacturer run out tolerances are not equal across all brands.
Lots to consider.

[slvr bullet]

Interesting report however I have reservations about it's validity. In the first case most brake racing applications do not apply to the street. I have been around racing all my life and raced myself for 15 years. In racing trim most rotors are vented or drilled to aid in the dissipation of heat and are usually of an after market variety able to withstand much higher temperatures. If you have ever had rotors turned on a lath you will quickly notice that they have high and low spots which go well beyond deposit build up. In addition after turning you will probably notice smoother braking for a short time. I say for a short time because turning rotors reduces the volume of metal and thus makes them less capable to dissipate heat. I personally refuse to have rotors turned.

[Super T]

There IS such a thing as warped rotors, it's just not nearly as common as people assume it is.

[desquirrel]

So you can't turn rotors because reducing the metal reduces cooling but you can drill holes in them???. Cross drilling is a cosmetic touch stemming from the need 40 years ago to get rid of pad out-gassing which doesn't happen with modern pads. Drilled rotors are banned in many venues (Nascar brakes use massive solid rotors). High end cars (Porsche, Lambo, etc) use rotors with holes CAST in them for the bling.

Rotors are also not "ventilated". Those radial holes primarily reduce mass. In operation air does not circulate through them, it is stagnant.

[slvr bullet]

I will have to file a law suit for false advertising http://www.alamomotorsports.com/KVR/kvrrotors.html

[MattRobertson]

There IS such a thing as warped rotors, it's just not nearly as common as people assume it is.

Bingo. Bedding brakes as the proper measure to reduce/eliminate brake judder is well documented here in many threads. The fact that the problem often re-occurs doesn't mean that the rotors are really warped. Only that the condition that caused the problem still exists. The standard solution seems to be to walk away from Dodge/Chrysler rotors (which are made by Bosch, actually) and go aftermarket. Or totally replace your braking system with big and bad ones, assuming you have the need for it.

High end cars (Porsche, Lambo, etc) use rotors with holes CAST in them for the bling.

That is a common misconception repeated frequently on the internet. They really are drilled. I believe its Zeckhausen who goes into detail disproving this, but I could be wrong.

It seems you can get away with drilling rotors on a high performance car if you have massively overbuilt the system in the first place (so the loss in cooling mass isn't such an issue) and have extremely high quality standards. Porsche, for example, is well known for borderline unbelievable brake performance and I can tell you from personal experience those cars can and do repeatedly burn off speed on the track at an amazing rate, without trashing their rotors.

But otherwise drilling rotors is for street cruisers who don't need brake performance and think they look nice.

[Super T]

It seems you can get away with drilling rotors on a high performance car if you have massively overbuilt the system in the first place (so the loss in cooling mass isn't such an issue) and have extremely high quality standards. Porsche, for example, is well known for borderline unbelievable brake performance and I can tell you from personal experience those cars can and do repeatedly burn off speed on the track at an amazing rate, without trashing their rotors.

To Matt's point:
In order to prevent cracking (common on aftermarket and cheap drilled rotors), you must drill, then chamfer, then hone the holes... no sharp edges, no rough surfaces inside the holes... that's why they're so damn expensive, you have to actually finish the new edges and surfaces you create. ANY deviation in flatness is a stress concentration point... you ever notice things always break at bends, corners, etc? Also, the smaller the radius of the "corner," the higher the concentration of stress at that location. So small pits, chips, or grooves are a big no-no in brake applications.

[Rt's RT]

Slotted has replaced drilled in most cases these days. Also, racing rotors are a much higher percentage of ceramic vs. steel and therefore do not warp from the heat as street rotors do.
I totally believe the steel rotors warp. I have had quite a shimmy when braking after a very hard stop (or 5) and it went away after I cut the rotors, not to mention it the blades hitting imtermitently when starting to cut.

[desquirrel]

From Wildwood:
Rotors are drilled to reduce rotating weight, an issue near and dear to racers searching for ways to minimize unsprung weight. Drilling diminishes a rotor's durability and cooling capacity.
Slots or grooves in rotor faces are partly a carryover from the days of asbestos pads. Asbestos and other organic pads were prone to "glazing" and the slots tended to help "scrape or de-glaze" them. Drilling and slotting rotors has become popular in street applications for their pure aesthetic value.

From Porsche:
"Discs are cross-drilled to enhance braking in the wet. The brakes respond faster because the water vapour pressure that builds up during braking can be released more easily."
1) The holes are cast in giving a dense boundary layer-type crystalline grain structure around the hole at the microscopic level as opposed to drilling which cuts holes in the existing grain pattern leaving open endgrains, etc, just begging for cracks.

2) The holes are only 1/2 the diameter of the holes in most drilled rotors. This reduces the stress concentration factor due to hole interaction which is a function (not linear) of hole diameters and the distance between them.

3) Since the holes are only 1/2 as big they remove only 1/4 as much surface area and mass from the rotor faces as a larger hole. This does a couple of things:

It increases effective pad area compared with larger holes. The larger the pad area the cooler they will run, all else being equal. If the same amount of heat is generated over a larger surface area it will result in a lower temperature for both surfaces.

It increases the mass the rotor has to absorb heat with. If the same amount of heat is put into a rotor with a larger mass, it will result in a lower temperature.

From Baer:
In years past, crossdrilling and/or Slotting the rotor for racing purposes was beneficial by providing a way to expel the gasses created when the bonding agents employed to manufacture the pads...However, with today’s race pad technology, ‘outgassing’ is no longer much of a concern...Slotted surfaces are what Baer recommends for track only use. Slotted only rotors are offered as an option for any of Baer’s offerings."

From Grassroots Motorsports:
"Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the '40s and 50s, not a whole lot. Rotors were first drilled because early brake pad materials gave off gasses when heated to racing temperatures, a process known as "gassing out." ...It was an effective solution, but today's friction materials do not exhibit the some gassing out phenomenon as the early pads. Contrary to popular belief, they don't lower temperatures. (In fact, by removing weight from the rotor, they can actually cause temperatures to increase a little.) These holes create stress risers that allow the rotor to crack sooner, and make a mess of brake pads--sort of like a cheese grater rubbing against them at every stop. Want more evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it...

From a tech article in Car & Driver:

The friction between the pad and rotor is what causes you to stop.
This friction converts your forward energy into heat. Now that heat is a bad thing.
Yes it is bad for the rotors but it is a lot worse for the pads. Overheated pads however WILL NOT stop the car.
It is here where the rotors secondary responsibility comes in.
Its job now is to DISSIPATE the heat away from the pads and DISPERSE it through itself. Notice that DISSIPATE and DISPERSE are interchangeable? Once the heat is removed from the pad/surface area it is then removed.
Notice where the removal falls on the list of duties? That's right - number 3.

#1 Maintains a coefficient of friction with the pad to slow the forward inertia of the vehicle

#2 DISSIPATE the heat

#3 REMOVE the heat from the brake system

Let's look more in-depth at each step now shall we?

#1 Maintains a coefficient of friction with the pad to slow the forward inertia of the vehicle:
This one is pretty simple and self-explanatory. The rotor's surface is where the pads contact and generate friction to slow the vehicle down. Since it is this friction that causes the conversion of forward acceleration into deceleration you ideally want as much as possible. The more friction you have the better your stopping will be.
This is reason #1 why BIGGER brakes are the best way to improve a vehicle's stopping ability. More surface area on the pad and the rotor = more friction = better stopping.

#2 DISSIPATE The Heat:
Let's assume for a second that the vehicle in question is running with Hawk Blue pads on it. They have an operating range of 400 degrees to 1100 degrees. Once they exceed that 1100 degree mark they fade from overheating. The pad material gets too soft to work effectively - glazing occurs. This means that a layer of crude glass forms on the surface of the pad. Lucky for us the rotor has a job to do here as well.
The rotor, by way of thermal tranfer DISSIPATES the heat throughout itself. This DISSIPATION lessens the amount of heat at the contact area because it is diluted throughout the whole rotor. The bigger the rotor the better here as well. The more metal it has the more metal the heat can be diluted into.

#3 REMOVE the heat from the brake system:

Now let's look at why cross-drilling is a bad idea.

First - as we have already established, cross-drilling was never done to aid in cooling.
Its purpose was to remove the worn away pad material so that the surfaces remained clean. As we all know this doesn't have much of a purpose nowadays.

Next - In terms of cooling: Yes - x-drilling does create more areas for air to go through but remember - this is step 3 on the list of tasks.

Let's look at how this affects steps 1 and 2. The drilling of the rotor removes material from the unit. This removal means less surface area for generating surface friction as well as less material to accept the DISSIPATED heat that was generated by the friction. Now because of this I want to optimize step one and 2 since those are the immediate needs. If it takes longer for the rotor to get rid of the heat it is ok. You will have a straight at some point where you can rest the brakes and let your cooling ducts do their job. My PRIMARY concern is making sure that my car slows down at the end of the straight. This means that the rotor needs to have as much surface as possible to generate as much friction as possible and it needs to DISSIPATE the resulting heat AWAY from the pads as quick as possible so they continue to work.
In both cases x-drilling does nothing to help the cause.

Now let's talk about strength - and how x-drilled rotors lack it. This one is simple.
Explain again just how drilling away material/structure from a CAST product DOES NOT weaken it?
You have seen what can happen to a x-drilled rotor on track right?
Yes it can happen to a non-drilled rotor as well but the odds are in your favor.

Why not explain what happens to a cast iron molecule when it is overheated?
The covalence bonds weaken. These bonds are what hold the molecules together boys and girls. It adds up to fractures.

So why don't race teams use them if they are so much better? It is because of several factors actually. They are as follows but in no particular order:

- Less usable surface area for generating friction
- Less material to DISSIPATE the heat away from the pads
- Less reliable and they are a safety risk because of fatigue and stress resulting from the reduced material.

[stevesrt8]

So you can't turn rotors because reducing the metal reduces cooling but you can drill holes in them???. Cross drilling is a cosmetic touch stemming from the need 40 years ago to get rid of pad out-gassing which doesn't happen with modern pads. Drilled rotors are banned in many venues (Nascar brakes use massive solid rotors). High end cars (Porsche, Lambo, etc) use rotors with holes CAST in them for the bling.
Rotors are also not "ventilated". Those radial holes primarily reduce mass. In operation air does not circulate through them, it is stagnant.

I agree with you until you get to the end. Vaned rotors actually move air when spun on the car. They suck air into the center and vent it out the edge. Try it sometime, it is a surprisingly large amount of air on an SRT8 at only 10-15 mph or so. At high speed it would be a significant contributor to heat loss.

Might want to look at MattR's car and the fantastic powered ventilation setup he uses on the front. Also, every NASCAR setup I've seen DOES have vented discs. Solid discs are hardly used anymore except on the rear end of slow cars!

Any folks with serious brake questions will get unbiased and accurate info from Dave Z. at ZeckhausenRacing.Com.

[MattRobertson]

Steve I think what desquirrel means by the ventilation reference is with regard to the holes being an aid to ventilation, which they aren't. You are talking about the directional vanes and of course you are right on there.

Very surprised to read the Porsche comment regarding cast-in holes. Turns out it was ToddTCE who was the one offering the monetary reward for proof that the Porsche rotors were cast-in. From a well-known Porsche forum:

http://forums.pelicanparts.com/showt...t=214546&pp=20

You will find similar comments at Rennlist (*the* Porsche forum on the web) and over at PCA.

The Porsche guys themselves cast doubt on the cast-in story. One take is that they dimple in via casting and drill out the dimples. Another is that the holes are cast in, then the chamfers are drilled. A search of Porsche.com yields nothing of this sort. Where is your source on this? There is no shortage of opinion but I have yet to see an official source.

[Super T]

The Porsche guys themselves cast doubt on the cast-in story. One take is that they dimple in via casting and drill out the dimples. Another is that the holes are cast in, then the chamfers are drilled. A search of Porsche.com yields nothing of this sort. Where is your source on this? There is no shortage of opinion but I have yet to see an official source.

Either one would help immensely over just drilling, but I would imagine the first would be cheaper (easier to produce and release the molds).

[2005rtmag]

I have been doing brake jobs on my cars and my familys cars for decades and I have watched the rotors being resurfaced too many times to believe that they don't warp. The amount of metal and where the metal comes off will convince anybody who watches that rotors do indeed warp. Passenger cars typically have small and inexpensive brakes and they are not in the same category as race car brakes.

I have been reading comments about this article for years and in my opinion it is very misleading, if not bs.