Performance Brake question

[Ekliptix]

ok, I know that perf brakes(larger rotor/slotted whatever) prevent brake fade after a situation like hot lapping.
But when a magazine does a before and after test of say 120-0 how could there be any improvment over stock?

The reason I'm saying this is because the tire friction is the limiting factor to the deceleration. I know that it's a different story when the brakes are hot.

discuss?

[buh_buh]

bigger rotor + caliper (stock 1 piston vs. 2 or 4 piston caliper) better braking due to more friction between caliper and rotor.

[Ekliptix]

yea, but the tire to ground has the least friction. You can have stock brakes and get on them hard to the point where they're on the verge of locking up(tire sliding) and stop. If you did the same thing w/ bigger brakes, why would you stop in a shorter distance?

[buh_buh]

no, because if your locking them up, it doesn't matter. Tires matter in that case.

[Ekliptix]

right, so doing a brake test of stock vs. aftermarket while the calipers are cool isn't fair.?

[kenny]

Originally posted by Ekliptix
yea, but the tire to ground has the least friction. You can have stock brakes and get on them hard to the point where they're on the verge of locking up(tire sliding) and stop. If you did the same thing w/ bigger brakes, why would you stop in a shorter distance?

Because most stock brakes usually do not have the power to lock up the wheels at the higher speeds. Most of the braking distance that is cut, I would guess is at the higher speeds rather than the lower speeds where traction becomes a bigger issue.

High performance brake kits would also be able to repeat the results while the stock brakes would usually get worse and worse as heat builds up.

[buh_buh]

Originally posted by Ekliptix
right, so doing a brake test of stock vs. aftermarket while the calipers are cool isn't fair.?
it would still be fair.
There should still be better braking in the aftermarket brakes.

[Glowrider]

I've ordered Brembo's for my M3, who knows when they are going to get here, it's been a while.

But anyways, they do make a huge difference. Cross drilled or slotted rotors disperse heat generated by friction between the bad and the rotor ALOT faster. They also give the pads some rough surface to grab onto when stopping, as opposed to the rather smooth surface of most stock brake rotors. Plus, more/bigger brake pistons mean better grabbing power, making the car slow down even faster from high speeds.

[Ekliptix]

Except for Kenny's explination of not having enough force at high speeds to achieve max pad pressure, I still don't understand why a bigger caliper would be better when cool.
physics please

[RickDaTuner]

Originally posted by kenny


Because most stock brakes usually do not have the power to lock up the wheels at the higher speeds. Most of the braking distance that is cut, I would guess is at the higher speeds rather than the lower speeds where traction becomes a bigger issue.

High performance brake kits would also be able to repeat the results while the stock brakes would usually get worse and worse as heat builds up. Right...
its at High Rotor rev that make the difference stock brakes do a mediocre job at high wheel speed but will lock up at low wheel speed

The Slots and cross drilled holes are the to
1 dissipate heat and
2 expel excess gas created by a dirty pad or rotor

the older Pads used to create a gas barrier between the friction pad and the Rotor, greatly reducing stopping distances, and that’s primarily why we have Slotted rotors, this isn’t the case any more though, advance compounds have eliminated that and make the friction pad more effective against the rotor.
Also some brakes are designed to Work better at higher tempters, warming them up before a hard run is essential, so it’s not always ideal to get as much cooling to the rotors as Posible this could also result in craked rotors wich could brake off Mid Run Warped rotors is better than no rotors hehe

[Glowrider]

also some brakes are desinged to Work better at Higer tempetures

That reminds me, anyone whose into road course racing or auto cross, STAY AWAY FROM PORTERFIELD RACE PADS!

[RickDaTuner]

Originally posted by SE-r.net


Brake fade is the number one high performance driving braking problem that is encountered. Brake fade is a dangerous situation when after braking hard several times in a row such as when you are racing, you lose brake effectiveness. This usually occurs gradually so you can compensate in your brake point by braking sooner, but sometimes happens so suddenly you can end up going on a wild off-road excursion with sometimes fatal results.

There are three kinds of fade commonly encountered in fast driving; pad fade, green fade and fluid fade. Below are listed an explanation of each.


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Pad Fade
Pad fade occurs for several reasons. All friction material (brake pad stuff) has a coefficient of friction curve over temperature. Friction materials have an optimal working temperature where the coefficient of friction is the highest. Sometimes you can use the brakes so hard that you get the temperature over the point of maximum friction to where the coefficient of friction curve starts to decline.

The mechanics of this decline in the coefficient of friction are varied. At a certain temperature, certain elements of the pad can melt or smear causing a lubrication effect, this is the classic glazed pad. Usually the organic binder resin starts to go first, then even the metallic elements of the friction material can start to melt. At really high temperatures the friction material starts to vaporize and the pad can sort of hydroplane on a boundary layer of vaporized metal and friction material which acts like a lubricant. Pad fade is felt as a car that still has a decent, non mushy feeling brake pedal that won’t stop even if you are pushing as hard as you can. Usually it builds somewhat slowly giving you time to compensate for it ,but some friction materials have a sudden drop off of friction when the heat is put on them resulting in sudden dangerous fade.


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Green Fade
This is perhaps the most dangerous type of fade that has injured more race car drivers than any other type of brake incident.

Green fade is a type of fade that manifests itself on brand new brake pads. Brake pads are usually made of different types of heat resistant materials bound together with a phenolic resin binder. These are thermosetting plastic resins with a high heat resistance. On a new brake pad, these resins will out-gas or cure when used hard on their first few heat cycles. The new pad can hydroplane on this layer of excreted gas. Green fade is dangerous because many people assume that new brakes are perfect and can be used hard right off the bat. Green fade typically will occur much earlier than normal fade so it can catch a driver that is used to a certain car’s characteristics unaware. Typically the onset of green fade is rather sudden, further increasing the danger factor. I was a victim of green fade once. The crew forgot to tell me that new brake pads were installed on the car and when I went out on the track, I was flying down the escape road at about the third corner! Some teams have a new pads warning sign that they place on the steering wheel to inform the drive to be careful on his first few laps.

Green fade can occur if you change the pads and drive on the street for a few hundred or even thousand miles, never braking hard, then suddenly start using the brakes hard. I think that this is the fade that many list member complain about on their own cars.

Green fade can be prevented by bedding the pads. This is a simple procedure to boil off the resins and break in the pads under controlled conditions which I will explain later.
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Fluid fade
Fluid fade is caused by the boiling of the brake fluid in the calipers. This produces bubbles in the brake system. Since bubbles are compressible, this makes for a soft spongy pedal. In worse cases, the pedal can plunge to the floor with very little slowing! Fluid fade can be avoided by running a high grade racing type brake fluid and/or frequent changes of brake fluid. Also if you change the pads before they get super thin, the remaining friction material will help insulate the calipers from the heat. Some people have had some success with having swaintech spray thermal barrier coating on the backing plate of the pads to help isolate the heat but I have never tried this.

Fluid fade usually has a gradual onset.


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If you are having an exceptionally bad day your brakes can fade from all three of the above reasons at the same time! The reason why I am explaining them to you is so that you can identify what kind of fade that you are suffering from and do the proper thing to fix the type of fade that you have with the correct countermeasure. If you are experiencing pad fade, switching brands of brake fluid won’t help. If you are getting fluid fade, the trickiest carbon pads won’t stop you a bit sooner. If you have the finest brake parts available, you could still fall prey to green fade.

[4wheeldrift]

Originally posted by RickDaTuner
Right...
its at High Rotor rev that make the difference stock brakes do a mediocre job at high wheel speed but will lock up at low wheel speed

The Slots and cross drilled holes are the to
1 dissipate heat and
2 expel excess gas created by a dirty pad or rotor

the older Pads used to create a gas barrier between the friction pad and the Rotor, greatly reducing stopping distances, and that’s primarily why we have Slotted rotors, this isn’t the case any more though, advance compounds have eliminated that and make the friction pad more effective against the rotor.
Also some brakes are designed to Work better at higher tempters, warming them up before a hard run is essential, so it’s not always ideal to get as much cooling to the rotors as Posible this could also result in craked rotors wich could brake off Mid Run Warped rotors is better than no rotors hehe The slots and holes in a rotor are ONLY there to expel gas and clean the pad. In terms of dissipating heat, they do very little. The ventilation vanes in the center of the rotor and the material of the rotor itself are doing most of that work.

Getting as much cooling to the rotors as possible is ALWAYS a good idea on the track or in any racing application, even on vehicles where the rotors are glowing red hot. If the rotors become heat soaked (the material is so hot it can no longer effectively transfer heat) it will destroy a set of even the most hard core race pads in short order, and then you are well and truly fucked. Consistent cooling will not warp a rotor, nor will it crack it. A big, sudden change in temperature (ie driving into a swamp with hot rotors) will warp or crack a rotor. Pads need high temperatures, rotors do not.

Yes, a lot of pads require high temperatures to work effectively. This is true of most aftermarket pads, even ones labeled "street". A stock pad is designed to provide good braking at low temperatures, because most people don't drive hard enough to really get them hot. Switching to an aftermarket pad with a higher activation temperature will make high speed driving easier, since the brakes will get hotter and allow the pads to operate properly, but when the pads are cold they won't stop very well. This is something you have to be conscious of on the track, because in the same way your tires won't work properly when cold, neither will your brakes. Going out there and going maximum attack on the first lap is virtually guaranteeing an off-track excursion. One semi-hard warm up lap should be enough to get enough heat into the pads and tires to get them operating well, if not at peak efficiency.

To answer Ekliptix question: A bigger caliper works better in all conditions, because of a larger lever arm, meaning more force against the rotor and more stopping power for a given pad size. More force against the rotor = more friction = more stopping power. This equation works regardless of what pad material is being used, and even considering rotors and pads of the same size and only bigger calipers.

[RickDaTuner]

Thanks for Clearing that Up, i kinda Knew My post wasnt on the Ball after reading that Brake Write up , good to know we have Knolegable people here to Steer us all on the RIght Track!:thumbsup: