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warming and cooling down rotors makes senseoutside of road racing does that apply to drag racing as there is no real or practical way to warm up rotors or as its just one stop the warm up is not really necessary.I know that brake pads are broken in by a series of controlled stops as i went to a brake seminar by Raybestos many years ago basically they wanted to see heat built up graduallyand a pulsating pedal in a hi performance application is oftentimes caused by pad material deposited on the rotor by holding brake pedal on when brakes are vey hot but for long rotor lif is the pad break in suffient for rotors or is some sort of repeated heat cycle necessary.....brakes can sometimes be very $$$ on a vette thanks for sharing this info ...can only reach people this knowledgeable on the forum
Wow, that blue color can't be too good for the wheel bearings and seal.
I toss my bearings each winter* as well. Just part of tracking your car.
I bleed my brakes before each track weekend, too.
When I do those HARD stops, they are almost like motorcycle stoppies.
On the brakes so hard the ABS kicks in and it feels like the nose is on the ground and rear wheels are up in the air. ( every one should practice this. Never know when you need your brakes like that in an emergency )
I have a very stiff T1 suspension and a front splitter with 2 1/2" of ground clearance. Those stops are so much fun
On a different note:
* Each winter I replace all four brake calipers, all four bearings, all four tie rod ends, Valve spring, check valve clearance and spring tension, replace belts, plugs, wires . New alignment, retune and dyno and anything else that is needed
When you beat the chit out of your car it takes maintenance to keep it up.
Now my wifes vette, I bleed the brakes each winter and that is about it
Gray iron has great thermal properties - high thermal capacity and high thermal conductivity.
It has poor thermal fatigue properties.
A rapid rise in heat or a large temperature gradient across any section will eventually cause problems. It is weak in tension and has high expansion/contraction rates. This is where the cracks around the holes stem from.
Those Porsche discs have a very elegant design to attempt to compensate for this. First off - they are generally pretty big for the vehicle in question. They also have many vanes - this increases mass and surface area for cooling.
Look even closer and you'll see 'half vanes' that dangle in the airstream.
And lastly - they take a lot of effort to keep the holes smooth and free from sharp edges. There is a relief in the vanesfor the hole to go through.
And still - they fail
Now remove all that design intended to minimize the effect of drilled rotors and go punch a few holes through that $30 chinese casting.
At the last company I worked at we used Link. The drilled rotors got the hottest and had the longest stopping distances. It was a weak test overall - the owner was a cheap dumbass but it was still a test.
Is the forum great or what everybody says their piece with candor and conviction,you get information from personal experience without an agenda i'm an old dog and this post has taught an old dog some new tricks..,.even though i'm a drag racer you still have to hit the brakes and turn at the end of the 1/4 mile
For those that might not know... Todd Cook (TCE) has been a race car driver and professional racing mechanic most of his adult life.
His shop in Tempe, AZ specializes in race car maintenance, gear box rebuilds and designing and producing big brake kits for both street cars and racers.
He probably has more experience with brakes and what happens to them, than anyone I know... and I'm no spring chicken! He's done lots of work on my cars over the years, both street and race.
interesting long debated topic.
As a vehicle design engineer my understanding is holes were old techonology for old pad chemistry. I have also seen them on track cracking badly, and filled with brake dust.
I also found an interesting conglomerate of info posted below.
I do a bit of track days myself and I have only noticed porsche with holes on their cars, and their serious track cars dont have them, and race cars dont have them. Corvettes have been massively underbraked for a long time so I wouldnt use them as a standard, especially if they have holes. I quickly outgrew my stock setup and went to a 6pot two piece setup from AP that is in another world compared to the stockers.
"===========
First, lets get some physics. Tell me how a heatsink with less mass will cool better? You do realize that a brake rotor acts as a large heatsink to transfer heat from the brake pads to the rotor. The heat generated from pads has to go somewhere and so it transfers to the rotor and caliper.
Porsche claims: "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."
They have said nothing about enhancing normal braking circumstances and the larger diameter rotors probably make up for the lack of material present in a smaller cross drilled rotor.
From Wilwood's website:
QUOTE
Q: Why are some rotors drilled or slotted?
A: 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. Wilwood has a large selection of drilled and slotted rotors for a wide range of applications.
As for the porsche rotors, a few notes from a forum I frequent:
QUOTE
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.
3) The holes are placed along the vanes, actually cutting into them giving the vane a "half moon" cut along its width. You can see that here:
This does a couple of things:
First, it greatly increases the surface area of the vanes which allows the entire rotors to run cooler which helps prevent cracks by itself.
Second, it effectively stops cracking on that side of the hole which makes it very difficult to get "hole to hole" cracks that go all the way through the face rotor (you'll get tiny surface "spider cracks" on any rotor, blank included if you look hard enough).
That's why Porsche rotors are the only "crossdrilled" rotors I would ever consider putting on my car.
BTW, many of the above features are not present in older Porsche brakes. The above is for "Big Reds" and newer.
This is quite different from the standard drilled rotors you get from brembo/kvr/powerslot/"insert random ricer parts brand name here" brake rotors.
Further proof of the uselessness of cross drilled rotors are found here:
Those Poor Rotors
QUOTE
Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the 40’s and 50’s, 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’. These gasses then formed a thin layer between the brake pad face and the rotor, acting as a lubricant and effectively lowering the coefficient of friction. The holes were implemented to give the gasses ‘somewhere to go’. It was an effective solution, but today’s friction materials do not exhibit the same gassing out phenomenon as the early pads.
For this reason, the holes have carried over more as a design feature than a performance feature. Contrary to popular belief they don’t lower temperatures (in fact, by removing weight from the rotor, the temperatures can actually increase a little), they create stress risers allowing 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.)
The one glaring exception here is in the rare situation where the rotors are so oversized (look at any performance motorcycle or lighter formula car) that the rotors are drilled like Swiss cheese. While the issues of stress risers and brake pad wear are still present, drilling is used to reduce the mass of the parts in spite of these concerns. Remember – nothing comes for free. If these teams switched to non-drilled rotors, they would see lower operating temperatures and longer brake pad life – at the expense of higher weight. It’s all about trade-offs.
From Stoptech:
QUOTE
Which is better, slotted or drilled rotors?
StopTech provides rotors slotted, drilled or plain. For most performance applications slotted is the preferred choice. Slotting helps wipe away debris from between the pad and rotor as well as increasing the "bite" characteristics of the pad. A drilled rotor provides the same type of benefit, but is more susceptible to cracking under severe usage. Many customers prefer the look of a drilled rotor and for street and occasional light duty track use they will work fine. For more severe applications, we recommend slotted rotors.
That almost sounds like an excuse to use cross drilled rotors, and for your street car which probably is never driven on the track, the drilled rotors are fine, but as Stoptech states, they will crack and are not good for severe applications.
From Baer:
QUOTE
"What are the benefits to Crossdrilling, Slotting, and Zinc-Washing my rotors?
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."
Then from Grassroots Motorsports:
QUOTE
"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...Slotting rotors, on the other hand, might be a consideration if your sanctioning body allows for it. Cutting thin slots across the face of the rotor can actually help to clean the face of the brake pads over time, helping to reduce the glazing often found during high-speed use which can lower the coefficient of friction. While there may still be a small concern over creating stress risers in the face of the rotor, if the slots are shallow and cut properly, the trade-off appears to be worth the risk. (Have you looked at a NASCAR rotor lately?)
And then, let's check out what was said on the aforementioned Altima thread [[[ Long thread at altimas.net that was deleted by that server. it is hosted here ]]]:
QUOTE
Here is how it works. The friction between the pad and rotor is what causes you to stop. This friction converts your forward energy into heat (remember Einstein: Energy is neither created nor destroyed, it is converted). Now that heat is a bad thing. Yes it is bad for the rotors but it is a lot worse for the pads. A warped rotor will still stop the car - it will just feel like ****. 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. Here is the list again. Memorize it because I will be using it a lot in this post:
#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? No? Too bad assclown we are doing it anyway.
#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 (negative acceleration if you want) you ideally want as much as possible right? 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. Does that make sense Ace? Good. Let's move on.
#2 DISSIPATE The Heat:
Let's assume for a second that the vehicle in question is running with Hawk Blue pads on it. The brand doesn't really matter but that is what I am using as my example. 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. As we all know glass is very smooth and very hard. It doesn't have a very high coefficient of friction. This is bad - especially when I am coming down the back straight at VIR at 125MPH. 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. Make sense? This isn't rocket science here d00d.
#3 REMOVE the heat from the brake system:
Now comes your favorite part of the process. This is what you thought DISSIPATION was. It is ok. I will allow you to be wrong. This is the step where the rotor takes the heat it DISSIPATED from the pads and gets rid of it for good. How does it do this? By radiating it to the surface - either the faces or inside the veins. It is here where cool air interacts with the hot metal to cool it off and remove the heat. Once again there is a reoccuring theme of "the bigger the better" here. The bigger the rotor, the more surface area it will have which means more contact with the cooling air surrounding it. Got it? Good.
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? Since you are obviously a man of great knowledge and experience surely 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 when pimpin' bling-bling drilled y0! Since you are also an expert on thermodynamics why not explain to the group what happens to a cast iron molecule when it is overheated. I will give you a little hint - the covalence bonds weaken. These bonds are what hold the molecules together boys and girls. You do the math - it adds up to fractures.
So why don't race teams use them if they are so much better? Consistency? Hmmmm . . . no. I am gonna go with the real reason her chodeboy. 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"
I've had a $500 bounty out for nearly ten years for anyone to prove this:
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.
It's great "internet lore" past down from forum to forum to the point it's become all but fully believable. Even the companies own literature runs counter to that as "cross drilled" (one would think that clearly if so cast you'd certainly be chest thumping the cast benefits vs other manufactures..)
I've had discussions with various reps from many companies far larger than my own...all of which either roll their eyes or laugh when asked.
I've had casting suppliers cringe at the notion of what would be involved with the tooling necessary to do so- even if they could.
I've had images from around the globe sent to me purporting to show this and it's being done only to clearly see flat plates (the walls) and tooling marks on the holes. (if cast you wouldn't touch them with a tool nor would it be necessary) One manufacture when pushed confessed that they cast the disc specific to the needs of the hole and its placement for it. Ok, I'm good with that seems a good idea. But admitted the actual "hole" is drilled, post casting. Doh!
I've picked up Porsche parts (broken rotors) off the race track when doing Race Official duties only to clearly note the tooling marks of the drilled holes.
For all that I remain open minded to the notion that it "could" be done (albeit at a ridiculous cost and process) and aside from some one-off or carbon deals etc, will gladly pay to see the proof of these on any basic production car, cast iron rotor and tooling to do so.
We've simply gotten to the point that we believe it because we've read it so much. Other say it's up to me to prove it's not done. No...I'm calling BS on all of it and thus far nobody has been able to refute that.
And no beef with the rest of the discussion here. I think they look great. And are fine on a street car or light race app. Hell, they're on my race car. Uh, all 1400lbs of it.
For anyone with hard use apps I'd suggest not tho. Unless you'd like to become a "good repeat customer" and that's cool too!
Corvettes have been "massively underbraked for years?" The stock brakes on a C5 are pretty damn good, I can activate ABS on Pirelli slicks at any point in a 30 minute session with Raybestos ST 47 pads.
Drive a 4th Gen Fbody on track to experience a car that is "massively underbraked."
Drilled rotors are for car shows, blank rotors are for track cars.
Corvettes have been "massively underbraked for years?" The stock brakes on a C5 are pretty damn good, I can activate ABS on Pirelli slicks at any point in a 30 minute session with Raybestos ST 47 pads.
Drive a 4th Gen Fbody on track to experience a car that is "massively underbraked."
Drilled rotors are for car shows, blank rotors are for track cars.
I agree drilled dont seem to be for track. Maybe Massively was the wrong word as a general statement. For me, in a track setting, at the tracks i frequent, with my abilities and pace i run, for the duration I run it just doesnt cut it.
I also dont want average braking at the end of the straight from 140+mph. I want great consistent braking. I dont need to drive a car that is **** poor at braking to appreciate the c5 brakes. for street use, autocross and spirited driving, and light track use they do great, but its my opinion/experience that they dont cut it. This is after several years of people telling me that they are just fine for my use all the while i was having serious issues after several 30 minute sessions. I also am skeptical that ABS is the best signifier that they work well, that just means the tire is losing grip, which yes could be because of clamping force but also other variables.
From my experience after a couple seasons of lapping days in my C5, they are inadequate FOR ME and the tracks i frequent. Many cars are marketed to have great brakes but i have constantly been let down accept by the porsches I have been in. Many of them are compromises between cost, weight, street driving, maintenance etc. That being said some of the new cars lately look like they might have nice stuff in their track packs but they are also typically much heavier than cars in the c5 time frame.
I think its fair to say they work for you. for me it seems they dont have the thermal mass needed, they arent rigid enough, they give uneven pad wear, and the end result is inconsistent braking and pad/rotor wear, that doesnt give me the results and confidence i need throughout the day. I tried several compounds from various brands, several brake fluids, brake ducting mounted to the hub and vented to the center of the rotor, different alignments, backing plates etc. I was tired of trying to eliminate and improve each variable in the stock system to get OK braking, so i begrudgingly dropped the cash to solve the issue. Trust me i didnt want to spend that kind of money and I am not one of the guys rolling in with a trailer to the track, im on a shoe string budget compared to most guys at the track. Given I am on R888's 295 square and not slicks i would expect better results given less grip. Either way if it works for you then sweet, you get cheaper running costs than me, lucky you
on another topic how do you like the Raybestos ST 47 pads? Im trying out Ferodos ds1.11's as i got a decent deal on them and heard good things. I have heard the raybestos are great too. Porsche guys i have spoken with seem to like the Pagids. I have found many of them are nice guys, but it seems they just do what their shop tells them to as they tend to have the money to not do their own work or research.
Raybestos pads are the best I have run, I have run a lot of different pads and I don't see me moving away from these. The Wilwood H is also a big fav, rumored to be the same as the ST43 from Raybestos. The life is incredible, can't kill them.
My home track is Nola Motorsports Park that has a 3300 ft front straight and a 90 degree right hander at the end of it. I step on the brakes at 140-143 MPH.
Last edited by FASTFATBOY; 07-27-2016 at 09:08 PM.
03-22-2010, 03:43 PM
