OEM or Drilled/Slotted Rotors?. (auto, engine, Ferrari, costs)
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Correct, though I have seen some poorly designed vents work more as an airfoil, where air is directly diverted onto the inside rotor face, but any engineered system works as you say.
Correct. My response was geared more towards the people who are saying that cross drilled rotors are just for looks and that OEM, solid discs perform the same or better. You and I know better. It boggles my mind that people think that McLaren (they run drilled rotors on their 650S, 12C, etc!), Porsche, Ferrari, etc... are putting drilled rotors on cars... simply because they LOOK GOOD? Dumbest thing I ever heard. They do it because there is a performance benefit.
Agree with all of this. It's just a bit of a pet peeve of mine to read responses of people saying that cross drilled rotors were a fad, or don't work, and any other rubbish that they've read while have no real experience regarding them. On a track vehicle, drilled rotors provide a tangible improvement in braking. They're most certainly not just for looks. With lap times being measured in hundredths of a second, even the reduced mass from drilled rotors may add up to quicker times over the course of an entire race.
Sorry, but this sounds really naive to think if Porsche and Ferrari does it on exotic cars sold to rich guys who keep their car in an air conditioned garage it must be due to strict engineering requirements.
You really think supercar designers don't slap some cross drilled rotors on there just for looks? If you're buying a $250k car, don't you expect to see some fancier looking brakes than a Honda Accord? Do you think 21" wheels are really necessary on a performance car? Why wouldn't all racecars use them? Is Porsche just not sharing their super secret braking technology?
So air is coming through the rotor hub, out through the internal vents, now why would you want your air to exit through a hole in the side before it gets to the outside of the rotor? Ever see those glowing rotors on a race car? That's heat radiating off the rotor surface which it cannot do if it's drilled full of holes. You're exchanging heat transfer from radiation to a very inefficient convection method.
Then again there's this theory... Customers want huge wheels to fill huge fenders wells. Huge wheel need huge brakes otherwise it looks stupid. Huge brakes weigh a lot so they drill holes in them and customers think it's to cool the brake down.
I'm not using OEM parts, been there already when car was new. Being almost 12 years old, should I simply replace the calipers as well?.
Thanks again to everyone, this has been a real help. I've poured $3,500 into this car over the past year replacing everything the now defunct Chevy messed up. So I'm keeping it until the brand new tires I hate fall off. I purchased Goodyear Comfort Tread Touring, good performance but too noisy.
I probably wouldn't replace the calipers. One of those items that could go on you tomorrow or they could all last another 10 years. If pad wear is fine, I'd leave it alone, and not get too upset if you have to do it in 6 months. Not to mention, I've had a couple of rebuilt calipers not work properly out of the box anyway, so I prefer not to mess with something working.
The holes are there to increase cooling ability and reduce weight. .
BWAHAHAHAHAH
O. M. G.
Tell me Mr. Metallurgst, how does reducing mass and surface area increase cooling ability? Here's a little hint: it doesn't.
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, 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 here. 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
Crossdrilled rotors are currently for looks only, with two glaring exceptions: Porsche still uses them on their top race cars for getting water out of the rotor/pad interface while racing in heavy rain. they cast the holes into the rotors in order to reduce the thermal effects that drilling them has, and to reduce the amount of strength lost in having holes in them. they STILL crack, but Porsche simply chooses to replace them regularly. And motorcycles use them to reduce mass.
Crossdrilling was originally done to allow the outgassing of the asbestos pads to have someplace to go. Pads haven't outgassed since at least the early '60s, if not earlier.
Drilling holes in the metal, reduces the total amount of metal in the rotors. This reduces the amount of surface area for generating braking friction PLUS reduces the amount of material to accept the dissapated heat generated by that friction.
From the Stoptech link (braking manufacturers and racers):
1) The brakes don't stop the vehicle - the tires do. The brakes slow the rotation of the wheels and tires. This means that braking distance measured on a single stop from a highway legal speed or higher is almost totally dependent upon the stopping ability of the tires in use - which, in the case of aftermarket advertising, may or may not be the ones originally fitted to the car by the OE manufacturer.
2) The brakes function by converting the kinetic energy of the car into thermal energy during deceleration - producing heat, lots of heat - which must then be transferred into the surroundings and into the air stream.
For many years most racing rotors were drilled. There were two reasons - the holes gave the "fireband" boundary layer of gasses and particulate matter someplace to go and the edges of the holes gave the pad a better "bite".
Unfortunately the drilled holes also reduced the thermal capacity of the discs and served as very effective "stress raisers" significantly decreasing disc life. Improvements in friction materials have pretty much made the drilled rotor a thing of the past in racing. Most racing rotors currently feature a series of tangential slots or channels that serve the same purpose without the attendant disadvantages.
powerstop sells drilled and slotted rotors for a variety of applications, and they have seen a REDUCTION in brakes temperatures, as much as 200 degrees in some cases.
powerstop sells drilled and slotted rotors for a variety of applications, and they have seen a REDUCTION in brakes temperatures, as much as 200 degrees in some cases.
Never trust a company testing their own product.
There are dozens of ways to show cooler brakes.
1) holes don't create friction, thus no temperature.
2) compare small solid rotors to huge drilled rotors then claim it's the holes that's cooling them down
3) test solids one on hot day. The drilled ones on cold day
4) stop harder after several runs with solid rotors, then once with no runs on drilled rotors
It's a small company selling products, not a research university with no skin in the game, so take it with a grain of salt.
Not that this proves anything. but just some anecdotal experience.
But, when I was setting up the brake setup on my weekend car, I was attempting to dial in the adjustable proportioning valve "on a closed course" which involved some aggressive braking, followed with shooting each rotor with a laser thermometer. I recorded these temps, and just so happened to do this with a set of solid rotors, followed by the drilled/slotted rotors. I was not attempting to compare the two, I just happened to swap rotors in the middle of this. Long story short, I did not observe any sort of difference in rotor temps I could attribute to the x-drilled rotors. They seemed to be about the same.
Again, I was not testing the differences of the rotors, so don't take this as conclusive testing at all.
A few years back, GM presented a white paper. SAE paper #2006-01-0691 circa 2006 titled "The Effect of Rotor Crossdrilling on Brake Performance". It specifically addressed the pros and cons of the X_drilled rotor option offered on the corvette. It's been years since I read it (and I can't seem to find a copy) but it did show improvements in performance with the x-drilled rotors, as well as some drawbacks. Was a pretty good read done by a company with the ability to do some actual performance testing...and not just some guy shooting his rotors with a laser thermometer in a parking lot somewhere.
I did find a pretty good synopsis that sums it up. Basically, under certain conditions the x-drilled rotor did perform better, and under certain conditions, the blank rotors did perform better. http://www.tazcobra.com/SAE_2006010691_Synopsis.pdf
Last edited by BostonMike7; 06-08-2017 at 07:11 PM..
I was going to get to that, but I'm still here banging my head on my desk over the notion that drilled rotors are just for looks.
That was the first thing I did, too. Fresh blinker fluid works better than changing the bulbs or the lens.
As for rotors, the most obnoxious thing about them is the "rub rub rub rub" noise that almost every car seems to get after a time. I should probably google exactly what causes that and what the permanent cure is before asking it on here. Seems like making a rotor that doesn't warp is an impossibility.
Sorry, but this sounds really naive to think if Porsche and Ferrari does it on exotic cars sold to rich guys who keep their car in an air conditioned garage it must be due to strict engineering requirements.
You really think supercar designers don't slap some cross drilled rotors on there just for looks? If you're buying a $250k car, don't you expect to see some fancier looking brakes than a Honda Accord? Do you think 21" wheels are really necessary on a performance car? Why wouldn't all racecars use them? Is Porsche just not sharing their super secret braking technology?
So air is coming through the rotor hub, out through the internal vents, now why would you want your air to exit through a hole in the side before it gets to the outside of the rotor? Ever see those glowing rotors on a race car? That's heat radiating off the rotor surface which it cannot do if it's drilled full of holes. You're exchanging heat transfer from radiation to a very inefficient convection method.
Then again there's this theory... Customers want huge wheels to fill huge fenders wells. Huge wheel need huge brakes otherwise it looks stupid. Huge brakes weigh a lot so they drill holes in them and customers think it's to cool the brake down.
Quote:
Originally Posted by Tiffer E38
BWAHAHAHAHAH
O. M. G.
Tell me Mr. Metallurgst, how does reducing mass and surface area increase cooling ability? Here's a little hint: it doesn't.
Crossdrilled rotors are currently for looks only, with two glaring exceptions: Porsche still uses them on their top race cars for getting water out of the rotor/pad interface while racing in heavy rain. they cast the holes into the rotors in order to reduce the thermal effects that drilling them has, and to reduce the amount of strength lost in having holes in them. they STILL crack, but Porsche simply chooses to replace them regularly. And motorcycles use them to reduce mass.
Crossdrilling was originally done to allow the outgassing of the asbestos pads to have someplace to go. Pads haven't outgassed since at least the early '60s, if not earlier.
I'm waiting for you to post something that is actually correct.
Literally everything you've said in this thread is WRONG. Here's one little example for you to wrap your head around... cross drilling INCREASES surface area of a rotor. Yep, that's right. Seriously, if you don't even know that just stop talking.
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