SL/R230: Rotors
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Originally Posted by ricky.agrawal
Front brake rotors are drilled, the rear ones aren't.
Front brakes usually have more work to do. Most cars have brake bias in the front, therefore they do more work.
Front brakes usually have more work to do. Most cars have brake bias in the front, therefore they do more work.
You forgot the question. "the holes"
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With age comes maturity.. and the ability to answer questions.. 
The holes are there to help dissipate heat. Air passes through the holes better than if there were no holes.
Heat is the biggest enemy to brakes. Heat is usually the biggest enemy to anything. When your brakes get too hot, you lose braking power and it gets harder to brake. That's why most sports cars have huge brake rotors.. not because it gives more braking force, but because it dissipates heat better.
My X5 has enough braking force to lock the wheels, the trick is to get it to slow down the car repeatedly over and over and over again, that's why a big brake upgrade is a MUST if you're going to track the car. Most stock setups aren't designed to be pushed to the limits.
I think I've answered the question then combined with my previous post.
Since there is a front brake bias in your car (as well as most other cars) they are cross drilled to dissipate heat. The rear brakes don't have to go through a lot of stress therfore they don't generate enough heat (or Mercedes though they didn't generate enough heat) to warrent them being cross drilled.
The holes are there to help dissipate heat. Air passes through the holes better than if there were no holes.
Heat is the biggest enemy to brakes. Heat is usually the biggest enemy to anything. When your brakes get too hot, you lose braking power and it gets harder to brake. That's why most sports cars have huge brake rotors.. not because it gives more braking force, but because it dissipates heat better.
My X5 has enough braking force to lock the wheels, the trick is to get it to slow down the car repeatedly over and over and over again, that's why a big brake upgrade is a MUST if you're going to track the car. Most stock setups aren't designed to be pushed to the limits.
I think I've answered the question then combined with my previous post.
Since there is a front brake bias in your car (as well as most other cars) they are cross drilled to dissipate heat. The rear brakes don't have to go through a lot of stress therfore they don't generate enough heat (or Mercedes though they didn't generate enough heat) to warrent them being cross drilled.
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2023 BMW 760i and 2025 MAYBACH EQS680V4
Originally Posted by ricky.agrawal
With age comes maturity.. and the ability to answer questions..
The holes are there to help dissipate heat. Air passes through the holes better than if there were no holes.
Heat is the biggest enemy to brakes. Heat is usually the biggest enemy to anything. When your brakes get too hot, you lose braking power and it gets harder to brake. That's why most sports cars have huge brake rotors.. not because it gives more braking force, but because it dissipates heat better.
My X5 has enough braking force to lock the wheels, the trick is to get it to slow down the car repeatedly over and over and over again, that's why a big brake upgrade is a MUST if you're going to track the car. Most stock setups aren't designed to be pushed to the limits.
I think I've answered the question then combined with my previous post.
Since there is a front brake bias in your car (as well as most other cars) they are cross drilled to dissipate heat. The rear brakes don't have to go through a lot of stress therfore they don't generate enough heat (or Mercedes though they didn't generate enough heat) to warrent them being cross drilled.
The holes are there to help dissipate heat. Air passes through the holes better than if there were no holes.
Heat is the biggest enemy to brakes. Heat is usually the biggest enemy to anything. When your brakes get too hot, you lose braking power and it gets harder to brake. That's why most sports cars have huge brake rotors.. not because it gives more braking force, but because it dissipates heat better.
My X5 has enough braking force to lock the wheels, the trick is to get it to slow down the car repeatedly over and over and over again, that's why a big brake upgrade is a MUST if you're going to track the car. Most stock setups aren't designed to be pushed to the limits.
I think I've answered the question then combined with my previous post.
Since there is a front brake bias in your car (as well as most other cars) they are cross drilled to dissipate heat. The rear brakes don't have to go through a lot of stress therfore they don't generate enough heat (or Mercedes though they didn't generate enough heat) to warrent them being cross drilled.
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I'll add further clarification-
Modern car braking systems utilize heat transference to the brake rotors to expend the energy from braking - with a metal rotor friction is used to generate/transfer the heat and with ceramic rotors it is some combination of friction and contact-transferance.
Vented or ventilated brake rotors provide for additional cooling by passing air through the center of the rotor to disipate more heat.
Drilled rotors also add additional help in cooling/dissipating heat.
Slotted rotors help in allowing gasses, built up chemically from the friction of pad and rotor contact, to escape more quickly and thus enable more contact between the pad and rotor, and thus arguably further enhance braking. Some argue that the loss of surface area due to the slotting reduces friction/contact enough to negate the advantage of the gas-escape. AMG does not utilize slotted rotors....
When braking/decelerating weight is transferred forwards (through the laws of physics) puting more load or 'work' on the front brake system/rotors.
And larger diameter brake rotors do have both a mechanical advantage in generating more friction/heat, and an advantage in dissipating more of the energy/heat from the braking. (a performance car usually has rotors in an 11" or larger diameter, a racecar usually in a 14" or larger diameter).
Modern car braking systems utilize heat transference to the brake rotors to expend the energy from braking - with a metal rotor friction is used to generate/transfer the heat and with ceramic rotors it is some combination of friction and contact-transferance.
Vented or ventilated brake rotors provide for additional cooling by passing air through the center of the rotor to disipate more heat.
Drilled rotors also add additional help in cooling/dissipating heat.
Slotted rotors help in allowing gasses, built up chemically from the friction of pad and rotor contact, to escape more quickly and thus enable more contact between the pad and rotor, and thus arguably further enhance braking. Some argue that the loss of surface area due to the slotting reduces friction/contact enough to negate the advantage of the gas-escape. AMG does not utilize slotted rotors....
When braking/decelerating weight is transferred forwards (through the laws of physics) puting more load or 'work' on the front brake system/rotors.
And larger diameter brake rotors do have both a mechanical advantage in generating more friction/heat, and an advantage in dissipating more of the energy/heat from the braking. (a performance car usually has rotors in an 11" or larger diameter, a racecar usually in a 14" or larger diameter).
Last edited by ClayJ; Jan 16, 2006 at 11:34 AM.
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Originally Posted by ClayJ
I'll add further clarification-
Modern car braking systems utilize heat transference to the brake rotors to expend the energy from braking - with a metal rotor friction is used to generate/transfer the heat and with ceramic rotors it is some combination of friction and contact-transferance.
Vented or ventilated brake rotors provide for additional cooling by passing air through the center of the rotor to disipate more heat.
Drilled rotors also add additional help in cooling/dissipating heat.
Slotted rotors help in allowing gasses, built up chemically from the friction of pad and rotor contact, to escape more quickly and thus enable more contact between the pad and rotor, and thus arguably further enhance braking. Some argue that the loss of surface area due to the slotting reduces friction/contact enough to negate the advantage of the gas-escape. AMG does not utilize slotted rotors....
When braking/decelerating weight is transferred forwards (through the laws of physics) puting more 'work' on the front brake system/rotors.
And larger diameter brake rotors do have both a mechanical advantage in generating more friction/heat, and an advantage in dissipating more of the energy/heat from the braking.
Modern car braking systems utilize heat transference to the brake rotors to expend the energy from braking - with a metal rotor friction is used to generate/transfer the heat and with ceramic rotors it is some combination of friction and contact-transferance.
Vented or ventilated brake rotors provide for additional cooling by passing air through the center of the rotor to disipate more heat.
Drilled rotors also add additional help in cooling/dissipating heat.
Slotted rotors help in allowing gasses, built up chemically from the friction of pad and rotor contact, to escape more quickly and thus enable more contact between the pad and rotor, and thus arguably further enhance braking. Some argue that the loss of surface area due to the slotting reduces friction/contact enough to negate the advantage of the gas-escape. AMG does not utilize slotted rotors....
When braking/decelerating weight is transferred forwards (through the laws of physics) puting more 'work' on the front brake system/rotors.
And larger diameter brake rotors do have both a mechanical advantage in generating more friction/heat, and an advantage in dissipating more of the energy/heat from the braking.
You are right there, but you left out a few things.
First, bigger rotors means more mass, they can accumulate more heat, means braking down to zero from higher speeds, without trouble / overheating (fading).
When you brake, the energy is first absorbed by the mass of the rotor, and when the temp. diff. between air and rotor starts to rise, the air will slowly start to transport the heat away. This takes time, mainly because air has a poor specific heat, witch means that a lot of air is nessesary to transport away the heat. That is why you need bigger brakes when going on the track, because you brake harder and more offen, so the brakes have to be bigger to be able to accumulate more heat, they need a bigger surface to get in contact with the cooling air, and they need to flow more air to transport away the heat.
The holes have one more function, the do help relive the stress being built up in the rotor, when the surface gets rapidly heated up and the rotor tends to crack. The pattern and the hole diameter are established in Finite Element Programs (FE software ), where all driving conditions can be simulated.
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Originally Posted by SLcharger
First, bigger rotors means more mass
Er, it just hit me, it might have been the same size rotor.. but the argument still stands. A lightweight rotor can be the same mass yet still be larger. That's one of the selling points of a properly balanced big brake kit.
Brakes are so complicated...
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Originally Posted by ricky.agrawal
Nice write up guys, but I just want to clarify on this thing. Bigger rotors doesn't mean more mass all the time. Take for example lightweight multi-piece rotors from Evosport for the E55 compared to the stock E55 rotors. I believe it was a 5lb (or 20, I can't remember) weight savings per corner.
Er, it just hit me, it might have been the same size rotor.. but the argument still stands. A lightweight rotor can be the same mass yet still be larger. That's one of the selling points of a properly balanced big brake kit.
Brakes are so complicated...
Er, it just hit me, it might have been the same size rotor.. but the argument still stands. A lightweight rotor can be the same mass yet still be larger. That's one of the selling points of a properly balanced big brake kit.
Brakes are so complicated...
isn´t it so that those bigger rotors have more mass where it counts, ( brake pad surface area ), compared with OEM rotors ?
Anyway, you cant fool physics, so when heat is generated by friction, it has to either be accumulated, or cooled away. If you want to get rid of the heat, instantly when braking, you will need a huge blower and a lot more cooling area than even the biggest rotors provide.
A another thing is mass distribution. If you have a small but very thick rotor, it will get hot very quick, because the heat generated cant disapear that fast into the thick casting. On the other hand, large rotors with thin casting will distribute the heat very fast, and therefore run cooler.
Right, there is a lot more to brakes than one thinks.
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Originally Posted by SLcharger
Please explain ?
And of course, Americans' usage of the english language is particularly bad or inexact in this manner....
Last edited by ClayJ; Jan 17, 2006 at 02:40 PM.
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Originally Posted by ClayJ
Mass is more a measure of weight, such as how much mass does that thing have? Or, it takes alot of power to move that much mass. Technically it is size times density equals mass, or volume times density equals mass (?). Whereas size is more a measure of physical dimension(s) , and not of weight or density -- and in referring to rotors we're usually talking diameter, vs. diameter and thickness, or "mass"....
And of course, Americans' usage of the english language is particularly bad or inexact in this manner....
And of course, Americans' usage of the english language is particularly bad or inexact in this manner....
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Originally Posted by SLcharger
You are right, I appologize that my english is not as good as needed to express my exact message.
