Brakes warped at 14k miles?
05-26-2012, 11:35 PM
#22
05-26-2012, 11:37 PM
#23
EDIT: It seems obvious to me that some of the folks in this thread are mistaken and believe some common braking myths. It's late so I'm not going to post anything tonight, but if the races tomorrow get dull, I'll post up some braking facts that will explain whats going on and help everyone make more informed decisions when it comes to brakes.
Last edited by gt40mkii; 05-26-2012 at 11:45 PM.
05-27-2012, 05:10 PM
#24
I worked at a shop for a few years and can not tell you how many break jobs I have done. You are warping your rotors because you are pulse braking. No not pumping you are not applying even pressure during breaking. Thus you heat and then cool the rotors to fast creating them to warp like a samurai sword. Rotors do not warp just because they get to hot it is constant uneven heating that warps them.
05-27-2012, 05:16 PM
#25
hmm
get a plain white wrapper in your rear view... that'll solve all your braking and driving issues. lol
06-05-2012, 11:31 AM
#28
OK, it took some time to get back to this thread (I was at the race track all weekend.)
I thought I'd address some of the braking myths that have cropped up in this thread (and perhaps a few others as well.)
First though -- my background. I've been working on cars for 41 years. I got into open-track driving (driving on a road course non-competitively,) in 1995 and competitive racing in 2005. The entire time I've been researching and modifying brake systems for high-performance driving. My research has involved not only talking to brake engineers at companies like Stoptech, Brembo, and Alcon, but also with dozens of other racers who are trying to solve the same problems I am.
MYTH #1: My brakes are pulsing. They must be warped.
it turns out that a truly warped brake rotor is fairly rare. I have never spoken with a brake engineer who was worried about his rotor design warping, and I've asked them specifically about this. Not a single one I've talked to has spent myuch, if any, time worrying about warping.
The white paper I mentioned earlier stated that most times when there's a pulsing felt in the brake pedal, its due to an uneven layer of pad material being deposited on the rotor's surface. Even a few thousandths of an inch unevenness can be felt through the pedal.
It's fairly easy to end up with uneven deposits. Typically this happens either from improper bedding of the pads, (or not bedding them at all,) or from extreme overheating (to the point where the pad's material starts to deteriorate.)
Also, if you get the brakes really hot and then leave the pads in contact with the rotor immediately afterwards, you can actually see a pad-shaped deposit left on the rotor. This is why, at the track, we tell novice drivers not to use their parking brake after a session on track.
Shops like to diagnose warped rotors for several reasons:
Go back and read the Stoptech white paper. It was written by the late Carroll Smith. Smith was an accomplished driver, mechanic and engineer who has competed at all levels of motorsport from junior go-karts to Formula 1. Carroll knew pretty much everything there is to know about cars and racing and that extended to braking systems as well.
MYTH #2: Cross-drilled rotors make the brake work better. cooler, etc....
This is hands-down the most common braking myth. Whenever someone wants to increase their brake's performance, the first thing mentioned is usually drilled rotors.
Drilled rotors were developed to solve a SPECIFIC problem in racing. Back in the '60's and '70's, brake pad material technology was in its infancy. The compounds were awful. The chemistry used resulted in compounds that would produce gas when they got hot. The gas would get trapped between the pad and the rotor, and the brakes would stop working. Drilling holes in the rotor gave the gas a way to escape. Modern high-performance brake pads do not have this problem (normal street pads do, but not to the extent they once did.)
BUT there are downsides to this. First, a rotor's main job is to store energy as heat. the less material in the rotor, the less heat it can store. Drilling removes material, so a drilled rotor can hold less heat compared to an equivalent non-drilled rotor. The upshot of this is that if you stop two identical cars from 100 to 0, the car with drilled rotors will have hotter rotors. This is a Bad Thing.;
The second downside to this is that as heat stresses build up in the rotor, metal epands and contracts, stressing the material. It WILL eventually crack. It will crack quicker in a drilled rotor because the holes limit the areas where stresses can be dissipated. Cracks will form between the holes, running from one hole to its neighbors.
In this photo of a Corvette rear rotor, a radial crack has formed between every pair of holes:
"But-but-but FERRARIS and PORSCHES have cross-drilled rotors!"
Yep. They also have $700 carbon-fiber gearshift ***** and $3000 luggage that matches the car's upholstery. These guys want to sell cars, so they pander to what the customer wants and to the uneducated, cross-drilled rotors are racy and imply really fantastic brakes.
OK, ok. There are real race cars that use drilled rotors, but not for the reason you think. They use them mainly to save on weight. Cross drilling (and slotting,) can also increase the brake's initial "bite" making it more aggressive. If you still think you want to run drilled rotors because of this, remember race teams replace the rotors after every race. they're a disposable item for them.
"Cross-drilled rotors dissipate heat faster!"
Wrong. Rotors are cooled mainly by radiating heat. Vented rotors are also designed to pump air through the vanes which also cool the rotor. Not much air actually flows through the holes, since they are drilled perpendicularly to the direction of airflow. They do cool slightly more quickly, but not dramatically so.
MYTH #3: You have to buy rotors to match the performance of your pads.
There is no correlation between the performance of the pad and the rotor. You can run any pad with any rotor. Pads and rotors DO become matched sets when you bed the brakes in because the pads transfer a thin layer of pad material to the rotor's face. That's why when you install new pads or a new rotor, the pads must be re-bedded.
MYTH #4: This...
OK -- I've got to say this is a new one on me. I've NEVER heard anyone claim that a rotor was being heated unevenly. For this to happen, you'd have to time the application of the brakes such that the pads were quickly applied when a specific section of the rotor was beneath the pads on every rotation. and then just as quickly released to limit the pad contact to a small section of the rotor.
It's possible in theory, but I just don't see this happening in the real world.
MYTH #5: Big brakes make you stop faster.
False. Absolutely false. No brake myth can be more false than this.
Brakes do not slow your car down. Tires slow your car down (unless your car has a parachute.) Can you stop faster on ice or asphalt?
Brakes work by converting momentum into heat. The tires act to transfer the momentum of the car to the brakes by turning the rotor (or drum.) But once the tires reach their maximum, they start to slide, and sliding doesn't let as much momentum be transferred to the brakes. Once the tires lock up, NO momentum is transferred to the brakes any more, so they can't slow the car. All that's left is energy dissipated by heating the tire itself any by tearing it apart.
So the TIRES limit how quickly the car can slow down (Drag racers know this -- thy buy big, fat, sticky tires so their car can accelerate harder.)
Case in point. When I get started in open-track driving, I took part in a demonstration. My car weighed 3300# and had 10.8" front disc brakes and 9" rear DRUM brakes. (Hardly a performance setup!) We measured the 60-0 stopping distance of my car compared to a Camaro with 13" disc brakes in the front and 12" disc brakes in the rear. Both of us were on the same tire (Yokohama Intermediates.) And the same driver was in each car. The stopping distance was the same within a few inches of each other.
BUT, as we repeated the stops, both cars took longer and longer to stop. The difference was my car with the small brakes was taking longer each time compared to the Camaro. it was obvious my brakes were heat-soaking and becoming more ineffective compared to the Camaro's larger brakes, which could deal with the increased heat better.
So bigger brakes don't make you stop shorter -- tires do. But bigger brakes are more durable, capable of more high-speed stops in a row, compared to smaller brakes.
So driving around town, big brakes aren't likely to give you any benefit on their own. But if you are doing anything that puts a lot of heat into the brakes (raceing, towing down long grades, or dealing with heavy loads,) bigger brakes have a definite advantage, which is why trucks usually have them.
I thought I'd address some of the braking myths that have cropped up in this thread (and perhaps a few others as well.)
First though -- my background. I've been working on cars for 41 years. I got into open-track driving (driving on a road course non-competitively,) in 1995 and competitive racing in 2005. The entire time I've been researching and modifying brake systems for high-performance driving. My research has involved not only talking to brake engineers at companies like Stoptech, Brembo, and Alcon, but also with dozens of other racers who are trying to solve the same problems I am.
MYTH #1: My brakes are pulsing. They must be warped.
it turns out that a truly warped brake rotor is fairly rare. I have never spoken with a brake engineer who was worried about his rotor design warping, and I've asked them specifically about this. Not a single one I've talked to has spent myuch, if any, time worrying about warping.
The white paper I mentioned earlier stated that most times when there's a pulsing felt in the brake pedal, its due to an uneven layer of pad material being deposited on the rotor's surface. Even a few thousandths of an inch unevenness can be felt through the pedal.
It's fairly easy to end up with uneven deposits. Typically this happens either from improper bedding of the pads, (or not bedding them at all,) or from extreme overheating (to the point where the pad's material starts to deteriorate.)
Also, if you get the brakes really hot and then leave the pads in contact with the rotor immediately afterwards, you can actually see a pad-shaped deposit left on the rotor. This is why, at the track, we tell novice drivers not to use their parking brake after a session on track.
Shops like to diagnose warped rotors for several reasons:
- The mechanic probably does think they're warped. Mechanics aren't educated in materials technology and probably don't realize or understand that pad material gets transferred to the surface of a brake rotor, even under normal conditions. Something getting too hot and warping is easier to understand.
- Evidence supports their mistaken theory. They turn the rotor and the problem goes away. They think they're made the rotor "true" again. What's happened is that by turning the rotor, they've removed the pad material, too, leaving a smooth, virgin surface that will not pulse.
- Even if they know its probably pad material, "warped rotors" are easily to explain to an uneducated customer. "Pad deposits" sounds more like BS.
Go back and read the Stoptech white paper. It was written by the late Carroll Smith. Smith was an accomplished driver, mechanic and engineer who has competed at all levels of motorsport from junior go-karts to Formula 1. Carroll knew pretty much everything there is to know about cars and racing and that extended to braking systems as well.
MYTH #2: Cross-drilled rotors make the brake work better. cooler, etc....
This is hands-down the most common braking myth. Whenever someone wants to increase their brake's performance, the first thing mentioned is usually drilled rotors.
Drilled rotors were developed to solve a SPECIFIC problem in racing. Back in the '60's and '70's, brake pad material technology was in its infancy. The compounds were awful. The chemistry used resulted in compounds that would produce gas when they got hot. The gas would get trapped between the pad and the rotor, and the brakes would stop working. Drilling holes in the rotor gave the gas a way to escape. Modern high-performance brake pads do not have this problem (normal street pads do, but not to the extent they once did.)
BUT there are downsides to this. First, a rotor's main job is to store energy as heat. the less material in the rotor, the less heat it can store. Drilling removes material, so a drilled rotor can hold less heat compared to an equivalent non-drilled rotor. The upshot of this is that if you stop two identical cars from 100 to 0, the car with drilled rotors will have hotter rotors. This is a Bad Thing.;
The second downside to this is that as heat stresses build up in the rotor, metal epands and contracts, stressing the material. It WILL eventually crack. It will crack quicker in a drilled rotor because the holes limit the areas where stresses can be dissipated. Cracks will form between the holes, running from one hole to its neighbors.
In this photo of a Corvette rear rotor, a radial crack has formed between every pair of holes:
"But-but-but FERRARIS and PORSCHES have cross-drilled rotors!"
Yep. They also have $700 carbon-fiber gearshift ***** and $3000 luggage that matches the car's upholstery. These guys want to sell cars, so they pander to what the customer wants and to the uneducated, cross-drilled rotors are racy and imply really fantastic brakes.
OK, ok. There are real race cars that use drilled rotors, but not for the reason you think. They use them mainly to save on weight. Cross drilling (and slotting,) can also increase the brake's initial "bite" making it more aggressive. If you still think you want to run drilled rotors because of this, remember race teams replace the rotors after every race. they're a disposable item for them.
"Cross-drilled rotors dissipate heat faster!"
Wrong. Rotors are cooled mainly by radiating heat. Vented rotors are also designed to pump air through the vanes which also cool the rotor. Not much air actually flows through the holes, since they are drilled perpendicularly to the direction of airflow. They do cool slightly more quickly, but not dramatically so.
MYTH #3: You have to buy rotors to match the performance of your pads.
There is no correlation between the performance of the pad and the rotor. You can run any pad with any rotor. Pads and rotors DO become matched sets when you bed the brakes in because the pads transfer a thin layer of pad material to the rotor's face. That's why when you install new pads or a new rotor, the pads must be re-bedded.
MYTH #4: This...
I worked at a shop for a few years and can not tell you how many break jobs I have done. You are warping your rotors because you are pulse braking. No not pumping you are not applying even pressure during breaking. Thus you heat and then cool the rotors to fast creating them to warp like a samurai sword. Rotors do not warp just because they get to hot it is constant uneven heating that warps them.
It's possible in theory, but I just don't see this happening in the real world.
MYTH #5: Big brakes make you stop faster.
False. Absolutely false. No brake myth can be more false than this.
Brakes do not slow your car down. Tires slow your car down (unless your car has a parachute.) Can you stop faster on ice or asphalt?
Brakes work by converting momentum into heat. The tires act to transfer the momentum of the car to the brakes by turning the rotor (or drum.) But once the tires reach their maximum, they start to slide, and sliding doesn't let as much momentum be transferred to the brakes. Once the tires lock up, NO momentum is transferred to the brakes any more, so they can't slow the car. All that's left is energy dissipated by heating the tire itself any by tearing it apart.
So the TIRES limit how quickly the car can slow down (Drag racers know this -- thy buy big, fat, sticky tires so their car can accelerate harder.)
Case in point. When I get started in open-track driving, I took part in a demonstration. My car weighed 3300# and had 10.8" front disc brakes and 9" rear DRUM brakes. (Hardly a performance setup!) We measured the 60-0 stopping distance of my car compared to a Camaro with 13" disc brakes in the front and 12" disc brakes in the rear. Both of us were on the same tire (Yokohama Intermediates.) And the same driver was in each car. The stopping distance was the same within a few inches of each other.
BUT, as we repeated the stops, both cars took longer and longer to stop. The difference was my car with the small brakes was taking longer each time compared to the Camaro. it was obvious my brakes were heat-soaking and becoming more ineffective compared to the Camaro's larger brakes, which could deal with the increased heat better.
So bigger brakes don't make you stop shorter -- tires do. But bigger brakes are more durable, capable of more high-speed stops in a row, compared to smaller brakes.
So driving around town, big brakes aren't likely to give you any benefit on their own. But if you are doing anything that puts a lot of heat into the brakes (raceing, towing down long grades, or dealing with heavy loads,) bigger brakes have a definite advantage, which is why trucks usually have them.
Last edited by gt40mkii; 06-05-2012 at 11:41 AM.
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