proxim2020 wrote:
OH48Lt wrote:
Rotors don't have to absorb heat before they dissipate it, they do have to get rid of the heat and one good way to do it is to not absorb it in the first place. Some heat leaves via the slots, it never gets absorbed by the rotor. Drilled rotors are OK IF the holes are chamfered correctly.
OEM rotors are not drilled or slotted because it costs more to do that. OEM's have engineers that do nothing but figure out what would be less expensive and still perform adequately. That's why they use cheap steel and as little machining as possible, instead of a quality steel like reputable high-end aftermarket manufacturers do. Ford's rotors are not high quality, they warp like the low-end aftermarket stuff. On my trucks, when those rotors warp at 20K-40K miles, they get replaced by decent parts. I usually use Brake Performance parts, and have had outstanding service from those parts.
Then there are the people who still use ceramic pads on trucks. OK for the wife's car, but not advisable on heavier vehicles. Use a quality semi-metallic pad. They'll dust a bit more, but they sure work better.
Go to brakeperformance dot com or one of the other quality manufacturers and read their FAQ concerning rotors and pads.
Absorbing heat is primarily one of the functions of the rotor. It's not possible for a rotor to not absorb heat. During braking, kinetic energy is transformed into thermal energy via friction. The massive amount of heat generated doesn't just magically dissipate into the air. That's just not possible. The heat is absorbed by the components that's doing the conversion of the energy (pads and rotors). Same as rubbing both of your hands back and forth. Each one of your hands gets warm.
The rotors not only serve as a braking surface, but also as a really large heatsink. The larger the heatsink the more heat it can absorb and thereby dissipate through convection. This is why HD trucks have nice thick rotors. If you were to fit the same diameter, but thinner rotors on a HD truck you would find that they are woefully inadequate for the job. They just can't accept the necessary amount of heat.
Every vehicle out there has a minimum rotor thickness for a reason. As the rotor gets thinner, its ability to absorb and thereby dissipate heat is reduced. If the rotor is no longer absorbing the correct amount of heat, then the friction surfaces begin to overheat as the heat is transferred elsewhere. Pads start to overheat, brake fluid boils, and brake fade sets in.
As Turtle n Peeps pointed out, in the racing world weight really matters. You're just wasting HP by having to constantly accelerate this useless weight. Drilling out a rotor is a creative way to reduce weight, but it also reduces braking ability. There's less material for the heat to be transferred into. At some tracks there are not many heavy braking areas so this is a non issue. At tracks with lots of tight corners you just alter your braking zone to get around it. There's no way that removing material from a rotor will increase its performance.
All of your high dollar racing teams are switching back to solid rotors, but doing it with carbon pads on carbon disc. Carbon weighs about half as much as iron so now there's no longer a need to drill out rotors. F1 cars, probably the toughest test for brakes, use pads, calipers, and solid carbon discs. No holes and no slots. These cars are capable of dropping from 200 mph to 0 in a matter of seconds.
Thank you Proxim2020. For a minute I thought I was living in the brake twilight zone where rotors don't get hot. :R :B
OP please read Proxim2020's post and then read it again. It's 100% accurate and correct.
Let me also add this to his post. Brake rotors are exactly like the radiator in your truck. It's a heat sink. It takes kinetic energy in and transforms it into thermal energy. As Proxim2020 said, if the rotors take in more heat than the designed temp, you will have over heating of the pad and fluid and rotor which causes brake fade. :E
When you make that radiator (rotor) smaller, you have less material to absorb the heat from the kinetic energy.
It always made me chuckle when people say: "when I changed to brand X pads and rotors on my truck it stops soooooooo much better!"
"Better" to me, means "a lot" quicker. And to that I say, no it doesn't. Why? Because "you" don't decide how fast the truck stops; a computer and your tires do. Your tire choice you have on your truck has a WAAAAAAAAAAY bigger decision on how fast your truck stops than ANY rotor or brake pad combo you pick.
The ABS system on your truck won't let your tires lock up. Now if you have a really hard tire on your truck the ABS is not going to be applying much continuing pressure to the calipers or slave cylinders because the tire is so hard it wants to continually lock up and skid. That equals a looooooooog stopping distance. Soft tires have a really high coefficient of friction so they grip the road a lot better and will stop your truck a lot faster because the ABS pressure will stay on a lot longer.
Let me close in saying this. It's very important to stay with OEM pads with some (most?) vehicles now days. Why? Because the ABS software matches the pad spec material. I know for a fact BMW is that way. When you put a different spec pad than what was matched with the software the two won't jive and you will have longer stopping distances.
Be safe out there; the brakes now days aren't your fathers 1947 Oldsmobile brakes. :B