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A good brake pad will generally have a coefficient of friction which is approximately constant over some range of temperature. This range is typically a few hundred degrees. The friction coefficient usually drops very quickly outside of that range. Too cold can be as bad as too hot, at least from the pad's point of view (If things really get hot, the brake fluid will boil. Then your system won't be able to maintain any significant pressure.). In any case, the actual value of the friction coefficient in the pad's operating range isn't very important. All cars are designed such that within the appropriate temperature range, braking performance is limited by the tires rather than the amount of force a driver can apply to the pedal. The friction coefficient also doesn't affect heat generation directly. The driver has in mind a certain amount of deceleration every time he presses the brake pedal. If a particular pad doesn't grip as well, a driver would just press the pedal harder until he got the desired effect. Given that, I'm not sure what you want to optimize, or how exactly you want to define "braking efficiency." I think you want to calculate the worst-case temperature of the disks as a function of some parameters. The simplest thing to think of would be the change in temperature after a single stop. But that's something that can be understood with a few lines of calculation on a piece of paper (given the approximations we're using). In the real world, single stops are not difficult for any decent braking system. Problems come up when you try to brake hard over and over. This is something that might be good to use a computer for. The problem is that you have to come up with some model of how a car is driven. You also need to figure out how heat is taken out of the brakes. Otherwise the simulated temperature will keep rising without limit. Say that the heat Q in the braking system obeys d Q / d t = M a v − f ( T , v ) , d Q d t M a v f T v where M is the car's mass, a is its acceleration, v is its velocity, and f is the cooling function. The temperature of the brakes could then be T = T 0 + Q / m c , T T 0 Q m c where T0 is ambient temperature, m is the mass of the braking system, and c is its specific heat (you could look this up for iron). The problem here is f. Some googling seems to show that it's reasonable to take f ( T , v ) = k 1 ( T − T 0 ) ( 1 + k 2 v n ) . f T v k 1 T T 0 1 k 2 v n k1, k2, and n are constants. n should apparently be between 0.5 and 0.8. k1 can be reasonably estimated, but k2 can't. That depends on the details of the airflow around the brake components.
A good brake pad will generally have a coefficient of friction which is approximately constant over some range of temperature. This range is typically a few hundred degrees. The friction coefficient usually drops very quickly outside of that range. Too cold can be as bad as too hot, at least from the pad's point of view (If things really get hot, the brake fluid will boil. Then your system won't be able to maintain any significant pressure.). In any case, the actual value of the friction coefficient in the pad's operating range isn't very important. All cars are designed such that within the appropriate temperature range, braking performance is limited by the tires rather than the amount of force a driver can apply to the pedal. The friction coefficient also doesn't affect heat generation directly. The driver has in mind a certain amount of deceleration every time he presses the brake pedal. If a particular pad doesn't grip as well, a driver would just press the pedal harder until he got the desired effect. Given that, I'm not sure what you want to optimize, or how exactly you want to define "braking efficiency." I think you want to calculate the worst-case temperature of the disks as a function of some parameters. The simplest thing to think of would be the change in temperature after a single stop. But that's something that can be understood with a few lines of calculation on a piece of paper (given the approximations we're using). In the real world, single stops are not difficult for any decent braking system. Problems come up when you try to brake hard over and over. This is something that might be good to use a computer for. The problem is that you have to come up with some model of how a car is driven. You also need to figure out how heat is taken out of the brakes. Otherwise the simulated temperature will keep rising without limit. Say that the heat Q in the braking system obeys d Q / d t = M a v − f ( T , v ) , d Q d t M a v f T v where M is the car's mass, a is its acceleration, v is its velocity, and f is the cooling function. The temperature of the brakes could then be T = T 0 + Q / m c , T T 0 Q m c where T0 is ambient temperature, m is the mass of the braking system, and c is its specific heat (you could look this up for iron). The problem here is f. Some googling seems to show that it's reasonable to take f ( T , v ) = k 1 ( T − T 0 ) ( 1 + k 2 v n ) . f T v k 1 T T 0 1 k 2 v n k1, k2, and n are constants. n should apparently be between 0.5 and 0.8. k1 can be reasonably estimated, but k2 can't. That depends on the details of the airflow around the brake components.
We are definitely off topic here,but that is an outstanding explanation. I never understood why people claim one pad stops the car faster than another. Modern brakes are so good that the tire/road surface friction is more likely to be the determining factor than pad/rotor friction. Especially with ABS. If you want to stop faster with a low coefficient pad, press harder on the pedal. Our cars even have brake assist for hard stops. Again, outstanding explanation. It brought back memories of physics courses in college.
So you want to stop well . Buy quality rotors and brake pads. Get stickier tires, Lighter wheels, lighten the car, new dampers. These things make a difference in stopping distance for street driven cars. When buying rotors. Metallurgy matters. Type and number of cooling fins. Actual thickness of the rotor faces, not total rotor thickness ( yes they are two different things). Cheap rotors with a thinner rotor face is much more likely to warp because they can't dissipate as much heat. Under a single panic stop when abs is involved stopping distance is going to be basically the same ( with in margin of uncontrollable variables) with metallic, semi metallic, ceramic, carbon metallic pads. The difference is in feel, heat fade under repeated hard braking in a short time, dust, speed of pad or rotor wear.
We are definitely off topic here,but that is an outstanding explanation. I never understood why people claim one pad stops the car faster than another. Modern brakes are so good that the tire/road surface friction is more likely to be the determining factor than pad/rotor friction. Especially with ABS. If you want to stop faster with a low coefficient pad, press harder on the pedal. Our cars even have brake assist for hard stops. Again, outstanding explanation. It brought back memories of physics courses in college.
I have driven it probably 25 30 miles so far. I have to say, they are more responsive than the stock brakes. It's funny, but when I brake moderately hard I feel like they "suck in" and I have to relax the pedal a bit so I don't stop too soon. That's the only way I know to describe it. It's like the pedal feels very progressive now. Definitely better braking than before.
Originally Posted by Bgw70
Looking good Helo!
Have you had a chance to go out and really enjoy the new brakes?
Very nice description!
You make me want to order a new set right now!
When I do it, I am going to paint the calipers a nice blue to match the car and add a white Lexus decal to the caliper.
Here is a pic of my T/A caliper
I did the BBK (Big Brake Kit) upgrade to 4 piston Supra Twin Turbo Calipers in the front, StopTech stainless steel lines all around, new StopTech Drilled and Slotted Rotors all around, new official Toyota/Lexus ceramic pads all around, and new hardware. Painted all the calipers in Fire Engine Red and slapped on some Lexus decals. Had a few small problems due to installation error on the pads (forgot the antisqeual shims). Added them and the stopping power is unbelievable! So quiet now. StopTech makes some great stuff!
Hi everyone. Time for new brakes. I am checking sites like tirerack and see so many options. Centric, Powerstop, Brembo. What pads and rotors do you all recommend? Was hoping I'd find something that simply said "OEM" but no such luck.
I just installed a complete set of powerstop pads and rotors on my LS and they work just fine. This is the website, www.stylintrucks.com
I paid about $450 for everything. One piece of advice I found on the web. Push in your pistons before you remove the pads or caliper, it's a lot easier. I changed my brakes before and removed the caliper before pushing in the pistons and I hard a hard time getting them all pushed in. As I pushed one side in the other side came out. Oh and take pictures of everything with your phone before you remover any thing so you know exactly how to put it all back together. Some of those little springs it brackets can be tricky to replace if you forget how they came off.
I just installed a complete set of powerstop pads and rotors on my LS and they work just fine. This is the website, www.stylintrucks.com
I paid about $450 for everything. One piece of advice I found on the web. Push in your pistons before you remove the pads or caliper, it's a lot easier. I changed my brakes before and removed the caliper before pushing in the pistons and I hard a hard time getting them all pushed in. As I pushed one side in the other side came out. Oh and take pictures of everything with your phone before you remover any thing so you know exactly how to put it all back together. Some of those little springs it brackets can be tricky to replace if you forget how they came off.
Good tips, here is another, do one side at a time because you can look at the other side if you need a reference. It will also keep the other piston from coming out.
There should be no springs, only clips and the anti squeal plates attached to the pads.
BTW, Rockauto.com has the SC430 kit for $275
The kit for the 2009 LS600 is $363.
03-05-16, 07:45 AM
