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Okay, so Dogzilla and I were discussing rotors and what not when I posed a question. Where do rotors really come from? What I mean is that most products come from a few sources and are just branded with different names. We know Nismo actually buys their stuff from someone else and puts their name on it. Food, gasoline, tools, they all come from a few select manufacturers or suppliers and then it gets distributed by another company with that name on it.
Are brakes and their components any different? People pay good money for great quality products such as Wilwood, Brembo, or Rotora. Do we know if those companies actually make their own products? Or do they have intelligent buyers who look for the best manufacturer with the highest stringent guidelines on producing a product? Well, we pretty much know off the bat that Brembo does make their own stuff.
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Brakes 101
Think of heat as a form of energy or power. A more familiar term is "horsepower." We all know what horsepower is, right? It is the stuff that spins the crankshaft when fuel is burned inside an engine. Combustion produces heat, and heat pushes the pistons that make the crankshaft go around. One horsepower is equal to 33,000 pounds-feet of torque per minute, or 550 pounds-feet per second.
We measure an engines horsepower output by hooking it up to a dyno and seeing how much force it can exert against the resistance created by the dyno. In effect, the dyno acts like a giant brake, so the engines power output is sometimes called its "brake" horsepower output.
By the same token, we can also measure how much horsepower a vehicles brakes must absorb when bringing the vehicle to a stop from a given speed. This is also called "brake" horsepower, but in this case it refers to the brake system, not the engine.
The brake systems on vehicles must be capable of absorbing a lot more horsepower than the engine typically produces because the heat (power) that is generated when braking occurs over a short period of time. Thus, a small car might only need 100 horsepower from the engine to accelerate from zero to a speed of 60 mph. If the driver slams on the brakes and comes to a screeching halt, the brakes have to absorb all the momentum in a much shorter period of time. This multiples the amount of horsepower that must be absorbed, as much as six times depending on the stopping distance. So a panic stop from 60 mph might require the brakes to absorb the equivalent of up to 600 horsepower!
Heat issues
The important point is the brakes often have to absorb a great deal of heat in a very short period of time.
How much heat, you ask? Using more math, units of horsepower can be converted into units of heat energy called BTUs (British Thermal Units). One BTU is the amount of heat it takes to raise one pound of water one degree Fahrenheit.
If you multiply horsepower by the proper conversion factor, you discover that one horsepower generates 42.4 BTUs of heat per minute. If stopping a 4,000 lb. vehicle from 60 mph in roughly 150 feet requires 600 horsepower of force, it is the equivalent of 25,440 BTUs of heat, which is enough heat to raise 15 gallons of water from zero degrees to boiling! No wonder the brakes get so hot.
One thing all brake manufacturers monitor very closely when testing and evaluating pads and rotors is the temperature of the brakes. Every time the brakes are applied, the pads and rotors generate heat that must be absorbed and dissipated. A quick stop from 60 mph can easily push the rotor temperature up 150 or more degrees. Several hard stops in quick succession can push brake temperatures into the 600, 700 or even 800 degree range. Remember, the heavier the vehicle, the more heat it creates when it brakes.
When brake temperatures get too high, the pads and rotors are no longer able to absorb any more heat and lose their ability to create any additional friction. As the driver presses harder and harder on the brake pedal, he feels less and less response from his overheated brakes. Eventually, he loses his brakes altogether.
All brakes will fade beyond a certain temperature. Semi-metallic linings can usually take more heat than nonasbestos organic or low-met linings. Vented rotors can dissipate heat more rapidly than nonvented solid rotors. Thus, high performance cars and heavier vehicles often have vented rotors and semi-metallic front brake pads to handle high brake temperatures. But if the brakes get hot enough, even the best ones will fade.
Rotors
Now that we have covered some of the physics of braking and the effects of friction and heat on the brake system, lets look at the rotors role in all of this. As we said earlier, the rotor's job is to provide a friction surface, and to absorb and dissipate heat.
Big rotors can obviously handle more heat than small rotors. But many cars today have downsized rotors to reduce weight. Consequently, the brakes run hotter and require better rotor cooling to keep brake temperatures within safe limits.
cross-drilled rotor
Anybody who works on brakes for a living knows that rotors can cause a lot of brake problems. Uneven rotor wear (which may be due to excessive rotor runout or rotor distortion) often produces variations in thickness that can be felt as pedal pulsations when the brakes are applied. The condition usually worsens as the rotors continue to wear, eventually requiring the rotors to be resurfaced or replaced.
Rotors can also develop hard spots that contribute to pedal pulsations and variations in thickness. Hard spots may be the result of poor quality castings or from excessive heat that causes changes in the metallurgy of the rotors. A sticky caliper or dragging brake may make the rotor run hot and increase the risk of hard spots forming. Hard spots can often be seen as discolored patches on the face of the rotor. Resurfacing the rotor is only a temporary fix because the hard spot usually extends well below the surface and usually returns as a pedal pulsation within a few thousand miles. That is why most brake experts replace rotors that have developed hard spots.
Cracks are another concern with rotors. Cracks can form as a result of poor metallurgy in the rotor (too hard and too brittle because the rotor was allowed to cool too quickly during the casting process), and from excessive heat. Some minor surface cracking is tolerable and can often be removed by resurfacing, but large cracks or deep cracks weaken the rotor and increase the risk of catastrophic failure. So cracked rotors should always be replaced.
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Okay, this is getting to be a long post and probably hard on the eyes. I'll pause here to let it sink in before I continue with the thread.
Are brakes and their components any different? People pay good money for great quality products such as Wilwood, Brembo, or Rotora. Do we know if those companies actually make their own products? Or do they have intelligent buyers who look for the best manufacturer with the highest stringent guidelines on producing a product? Well, we pretty much know off the bat that Brembo does make their own stuff.
So I asked if the standard rotors we see on most cars are quality parts that pass some kind of test? Yes they do. But what about the ebay stores that sell brands we've never heard or suspect are knockoffs? We're talking safety issues here, so I'm concerned about the fact that some people might buy the best deal and get something of a surprise when taking the fastest corner of a road course.
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Brakes 101
Brake horsepower defined or explained
Think of heat as a form of energy or power. A more familiar term is "horsepower." We all know what horsepower is, right? It is the stuff that spins the crankshaft when fuel is burned inside an engine. Combustion produces heat, and heat pushes the pistons that make the crankshaft go around. One horsepower is equal to 33,000 pounds-feet of torque per minute, or 550 pounds-feet per second.
We measure an engines horsepower output by hooking it up to a dyno and seeing how much force it can exert against the resistance created by the dyno. In effect, the dyno acts like a giant brake, so the engines power output is sometimes called its "brake" horsepower output.
By the same token, we can also measure how much horsepower a vehicles brakes must absorb when bringing the vehicle to a stop from a given speed. This is also called "brake" horsepower, but in this case it refers to the brake system, not the engine.
The brake systems on vehicles must be capable of absorbing a lot more horsepower than the engine typically produces because the heat (power) that is generated when braking occurs over a short period of time. Thus, a small car might only need 100 horsepower from the engine to accelerate from zero to a speed of 60 mph. If the driver slams on the brakes and comes to a screeching halt, the brakes have to absorb all the momentum in a much shorter period of time. This multiples the amount of horsepower that must be absorbed, as much as six times depending on the stopping distance. So a panic stop from 60 mph might require the brakes to absorb the equivalent of up to 600 horsepower!
Heat issues
The important point is the brakes often have to absorb a great deal of heat in a very short period of time.
How much heat, you ask? Using more math, units of horsepower can be converted into units of heat energy called BTUs (British Thermal Units). One BTU is the amount of heat it takes to raise one pound of water one degree Fahrenheit.
If you multiply horsepower by the proper conversion factor, you discover that one horsepower generates 42.4 BTUs of heat per minute. If stopping a 4,000 lb. vehicle from 60 mph in roughly 150 feet requires 600 horsepower of force, it is the equivalent of 25,440 BTUs of heat, which is enough heat to raise 15 gallons of water from zero degrees to boiling! No wonder the brakes get so hot.
One thing all brake manufacturers monitor very closely when testing and evaluating pads and rotors is the temperature of the brakes. Every time the brakes are applied, the pads and rotors generate heat that must be absorbed and dissipated. A quick stop from 60 mph can easily push the rotor temperature up 150 or more degrees. Several hard stops in quick succession can push brake temperatures into the 600, 700 or even 800 degree range. Remember, the heavier the vehicle, the more heat it creates when it brakes.
When brake temperatures get too high, the pads and rotors are no longer able to absorb any more heat and lose their ability to create any additional friction. As the driver presses harder and harder on the brake pedal, he feels less and less response from his overheated brakes. Eventually, he loses his brakes altogether.
All brakes will fade beyond a certain temperature. Semi-metallic linings can usually take more heat than nonasbestos organic or low-met linings. Vented rotors can dissipate heat more rapidly than nonvented solid rotors. Thus, high performance cars and heavier vehicles often have vented rotors and semi-metallic front brake pads to handle high brake temperatures. But if the brakes get hot enough, even the best ones will fade.
Rotors
Now that we have covered some of the physics of braking and the effects of friction and heat on the brake system, lets look at the rotors role in all of this. As we said earlier, the rotor's job is to provide a friction surface, and to absorb and dissipate heat.
Big rotors can obviously handle more heat than small rotors. But many cars today have downsized rotors to reduce weight. Consequently, the brakes run hotter and require better rotor cooling to keep brake temperatures within safe limits.
cross-drilled rotor
Anybody who works on brakes for a living knows that rotors can cause a lot of brake problems. Uneven rotor wear (which may be due to excessive rotor runout or rotor distortion) often produces variations in thickness that can be felt as pedal pulsations when the brakes are applied. The condition usually worsens as the rotors continue to wear, eventually requiring the rotors to be resurfaced or replaced.
Rotors can also develop hard spots that contribute to pedal pulsations and variations in thickness. Hard spots may be the result of poor quality castings or from excessive heat that causes changes in the metallurgy of the rotors. A sticky caliper or dragging brake may make the rotor run hot and increase the risk of hard spots forming. Hard spots can often be seen as discolored patches on the face of the rotor. Resurfacing the rotor is only a temporary fix because the hard spot usually extends well below the surface and usually returns as a pedal pulsation within a few thousand miles. That is why most brake experts replace rotors that have developed hard spots.
Cracks are another concern with rotors. Cracks can form as a result of poor metallurgy in the rotor (too hard and too brittle because the rotor was allowed to cool too quickly during the casting process), and from excessive heat. Some minor surface cracking is tolerable and can often be removed by resurfacing, but large cracks or deep cracks weaken the rotor and increase the risk of catastrophic failure. So cracked rotors should always be replaced.
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Okay, this is getting to be a long post and probably hard on the eyes. I'll pause here to let it sink in before I continue with the thread.
