The State of Braking
Thread Starter
Junior Member
Joined: Jul 2001
Posts: 274
Likes: 0
From: gone to the track or rally
The State of Braking
http://www.popsci.com/popsci/a....html
In serious driving, one car's big brakes can outmaneuver another car's bigger engine.
by Stephan Wilkinson
May 2003
I'm about to do a brake job on my daughter's fun-racer, the 1983 911SC Porsche coupe that I spent two years turning from somebody's sorry beater into her loud, slick, tautly sprung street-and-track machine.
This brake job is costing me $4,800 just for the parts. (My labor is free, which is about what it's worth.) No, that's not $4,800 for brake pads and turned rotors—your standard "brake job." Even Porsche parts aren't that overpriced. What I have waiting in my little cellar workshop is an entire new brake system: huge front and rear four-piston Brembo calipers, massive cross-drilled and vented rotors, a Turbo Porsche master cylinder, vacuum booster, brake lines, high-temp brake fluid…most of it originally designed for the 1,100-horsepower Porsche 917 Le Mans and Can-Am car.
The calipers and rotors were modified for mounting on an SC by my Porsche guru Steve Weiner, of Rennsport Systems in Portland, Oregon. The 1989 Turbo rotors that he rehabilitated were originally cast by Porsche with the myriad holes for gas venting and rapid water dissipation that also look so cool. (Here's how cool: I remember asking a Ferrari PR guy why the full-race 360 Modenas at a Ferrari Challenge race had channeled but solid rotors while the ordinary road 360s' rotors were cross-drilled. "Cosmetics," he said.)
Porsche measures and boasts about braking power by relating it to the horsepower of its cars. In the basic 911, for example, is "a braking system that is approximately four times as powerful as the engine." The set I'm installing can do almost 1,500 hp worth of work, in a car that probably weighs about 2,500 pounds and whose engine on a good day might motor along at about 270 hp. Newer Porsche Turbo Brembos, 30 percent more capable than my set, are sometimes referred to as 2,000-hp "hand-of-God brakes," and can do His deceleration work all day long.
The technical problem of mechanically assisting the deceleration of a machine obviously dates back at least to the invention of the wheel. Some of the earliest brakes were blocks of wood or metal that bore against a wheel rim and rubbed hard enough to gradually slow it. Not a lot of progress was made in said technology for a long time. I've seen some pretty primitive brakes, for example, on flying machines. I flew a Russian Antonov An-2 cargo biplane that was about the size and speed of a Winnebago. It had pneumatic brakes, activated by sausage-shaped bladders that inflated to press brake shoes against the inside of a brake drum. They wheezed and farted and eventually locked solid as I was taxiing back to the ramp. RAF Spitfires, believe it or not, had a similar system.
Indeed, the invention of disc brakes was sparked by aviation requirements: the need to stop heavy, fast-moving early jets by the application of braking power to just the main wheels. Airplane brakes face brief but stringent demands, and they can be a factor in a machine's overall performance. When I flew a Cessna Citation 500—an economy business jet slow enough we joked that we would be rear-ended in flight by Learjets—we were not allowed to take off for 30 minutes after landing on a runway that required major braking effort. Otherwise, if we had to reject the next takeoff, the brakes would be so hot the tires would catch fire.
Jaguar brought disc brakes to racing in the early 1950s, on the Le Mans C- and D-Types, at a time when even the Mercedes juggernaut was still relying on huge, finned, inboard drums. (The patent for automotive disc brakes was held by British Dunlop, which wouldn't sell the brakes to the Germans.) The Jags were slower than the big Ferraris and Benzes, but they'd drive deep past the Italians and Germans at every corner before they had to brake, and be long gone by the time the competition had managed to slow and go again.
And that's the key to the other way in which good brakes relate to horsepower: If a 270-hp racecar is going into a corner alongside a lesser-braked 370-hp machine, it can go deeper into the corner before braking and then start its acceleration out the other side sooner. On the right racecourse, that can negate the engine-power advantage. Out-braking a competitor becomes more meaningful than his ability to out-accelerate you. In other words, stop can be more important than go.
If you ask your average enthusiast driver which is the trickiest pedal to use, he'll probably answer "the clutch." This is wrong. Few of us, and I don't count myself among these select few, have the experience and talent to brake correctly. In a panic situation, we either brake too gently or, if the accident is truly imminent, so hard we lock up the wheels. In fact, that's why the Germans first developed ABS and then added "brake-assist" electronics to apply extra braking when the microchip senses a panic stop that is far too puny.
"You can teach somebody in a day or two how to read a corner, how to go around it, how to pick an apex, but learning to decelerate a car at its maximum is a feel, a matter of experience, and many people never develop that feel," Weiner says. "It's the toughest thing to teach a driver."
Here's another thing that's hard to teach: Good brakes are worth the money I'm paying for those Brembos. Weiner notes that "Americans who want high- performance cars have no qualms about spending $10,000 to make a car accelerate faster, but they recoil in horror if you suggest they spend half that amount to stop the car faster. Adding horsepower without paying any attention to the brakes is all part of our culture."
In serious driving, one car's big brakes can outmaneuver another car's bigger engine.
by Stephan Wilkinson
May 2003
I'm about to do a brake job on my daughter's fun-racer, the 1983 911SC Porsche coupe that I spent two years turning from somebody's sorry beater into her loud, slick, tautly sprung street-and-track machine.
This brake job is costing me $4,800 just for the parts. (My labor is free, which is about what it's worth.) No, that's not $4,800 for brake pads and turned rotors—your standard "brake job." Even Porsche parts aren't that overpriced. What I have waiting in my little cellar workshop is an entire new brake system: huge front and rear four-piston Brembo calipers, massive cross-drilled and vented rotors, a Turbo Porsche master cylinder, vacuum booster, brake lines, high-temp brake fluid…most of it originally designed for the 1,100-horsepower Porsche 917 Le Mans and Can-Am car.
The calipers and rotors were modified for mounting on an SC by my Porsche guru Steve Weiner, of Rennsport Systems in Portland, Oregon. The 1989 Turbo rotors that he rehabilitated were originally cast by Porsche with the myriad holes for gas venting and rapid water dissipation that also look so cool. (Here's how cool: I remember asking a Ferrari PR guy why the full-race 360 Modenas at a Ferrari Challenge race had channeled but solid rotors while the ordinary road 360s' rotors were cross-drilled. "Cosmetics," he said.)
Porsche measures and boasts about braking power by relating it to the horsepower of its cars. In the basic 911, for example, is "a braking system that is approximately four times as powerful as the engine." The set I'm installing can do almost 1,500 hp worth of work, in a car that probably weighs about 2,500 pounds and whose engine on a good day might motor along at about 270 hp. Newer Porsche Turbo Brembos, 30 percent more capable than my set, are sometimes referred to as 2,000-hp "hand-of-God brakes," and can do His deceleration work all day long.
The technical problem of mechanically assisting the deceleration of a machine obviously dates back at least to the invention of the wheel. Some of the earliest brakes were blocks of wood or metal that bore against a wheel rim and rubbed hard enough to gradually slow it. Not a lot of progress was made in said technology for a long time. I've seen some pretty primitive brakes, for example, on flying machines. I flew a Russian Antonov An-2 cargo biplane that was about the size and speed of a Winnebago. It had pneumatic brakes, activated by sausage-shaped bladders that inflated to press brake shoes against the inside of a brake drum. They wheezed and farted and eventually locked solid as I was taxiing back to the ramp. RAF Spitfires, believe it or not, had a similar system.
Indeed, the invention of disc brakes was sparked by aviation requirements: the need to stop heavy, fast-moving early jets by the application of braking power to just the main wheels. Airplane brakes face brief but stringent demands, and they can be a factor in a machine's overall performance. When I flew a Cessna Citation 500—an economy business jet slow enough we joked that we would be rear-ended in flight by Learjets—we were not allowed to take off for 30 minutes after landing on a runway that required major braking effort. Otherwise, if we had to reject the next takeoff, the brakes would be so hot the tires would catch fire.
Jaguar brought disc brakes to racing in the early 1950s, on the Le Mans C- and D-Types, at a time when even the Mercedes juggernaut was still relying on huge, finned, inboard drums. (The patent for automotive disc brakes was held by British Dunlop, which wouldn't sell the brakes to the Germans.) The Jags were slower than the big Ferraris and Benzes, but they'd drive deep past the Italians and Germans at every corner before they had to brake, and be long gone by the time the competition had managed to slow and go again.
And that's the key to the other way in which good brakes relate to horsepower: If a 270-hp racecar is going into a corner alongside a lesser-braked 370-hp machine, it can go deeper into the corner before braking and then start its acceleration out the other side sooner. On the right racecourse, that can negate the engine-power advantage. Out-braking a competitor becomes more meaningful than his ability to out-accelerate you. In other words, stop can be more important than go.
If you ask your average enthusiast driver which is the trickiest pedal to use, he'll probably answer "the clutch." This is wrong. Few of us, and I don't count myself among these select few, have the experience and talent to brake correctly. In a panic situation, we either brake too gently or, if the accident is truly imminent, so hard we lock up the wheels. In fact, that's why the Germans first developed ABS and then added "brake-assist" electronics to apply extra braking when the microchip senses a panic stop that is far too puny.
"You can teach somebody in a day or two how to read a corner, how to go around it, how to pick an apex, but learning to decelerate a car at its maximum is a feel, a matter of experience, and many people never develop that feel," Weiner says. "It's the toughest thing to teach a driver."
Here's another thing that's hard to teach: Good brakes are worth the money I'm paying for those Brembos. Weiner notes that "Americans who want high- performance cars have no qualms about spending $10,000 to make a car accelerate faster, but they recoil in horror if you suggest they spend half that amount to stop the car faster. Adding horsepower without paying any attention to the brakes is all part of our culture."
Junior Member
Joined: Nov 2002
Posts: 154
Likes: 0
From: Los Angeles, CA
Re: The State of Braking (4WDrift)
I disagree. The article misses the point. Big brakes don't stop you sooner, they simply reduce the effects of (or eliminate) fade.
Larry Webster of C&D fame wrote this in his big brake article:
"Assuming a brake system is properly balanced, strong enough to lock a wheel, and not yet hot enough to fade, the stopping distance is largely a function of tire traction, not brakes. Think of it this way: All brake systems, stock and aftermarket, are able to activate the ABS, so how could a stronger brake shorten a stop? Eric Dahl, a brake engineer from Brembo, put it this way: "Don't expect the brake kits to stop you sooner, but expect the 20th lap to feel like the first.""
Larry Webster of C&D fame wrote this in his big brake article:
"Assuming a brake system is properly balanced, strong enough to lock a wheel, and not yet hot enough to fade, the stopping distance is largely a function of tire traction, not brakes. Think of it this way: All brake systems, stock and aftermarket, are able to activate the ABS, so how could a stronger brake shorten a stop? Eric Dahl, a brake engineer from Brembo, put it this way: "Don't expect the brake kits to stop you sooner, but expect the 20th lap to feel like the first.""
Honda-Tech Member
Joined: Jan 2000
Posts: 1,288
Likes: 0
From: Fort Worth, TX
Re: The State of Braking (fidracer)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fidracer »</TD></TR><TR><TD CLASS="quote">I disagree. The article misses the point. Big brakes don't stop you sooner, they simply reduce the effects of (or eliminate) fade.
Larry Webster of C&D fame wrote this in his big brake article:
"Assuming a brake system is properly balanced, strong enough to lock a wheel, and not yet hot enough to fade, the stopping distance is largely a function of tire traction, not brakes. Think of it this way: All brake systems, stock and aftermarket, are able to activate the ABS, so how could a stronger brake shorten a stop? Eric Dahl, a brake engineer from Brembo, put it this way: "Don't expect the brake kits to stop you sooner, but expect the 20th lap to feel like the first.""
</TD></TR></TABLE>
Agreed. About the only other advantage I can think of with regards to huge multi-piston calipers and Honkin' big vented rotors is that it is easier to modulate them at the threshold of wheel lock. So they might help compensate very slightly for lack of skill with the middle pedal and allow you to threshold brake with ~1% more force. But if you're just going into ABS everytime you really need to stop, I doubt they'd stop you even 1 ft quicker.
Larry Webster of C&D fame wrote this in his big brake article:
"Assuming a brake system is properly balanced, strong enough to lock a wheel, and not yet hot enough to fade, the stopping distance is largely a function of tire traction, not brakes. Think of it this way: All brake systems, stock and aftermarket, are able to activate the ABS, so how could a stronger brake shorten a stop? Eric Dahl, a brake engineer from Brembo, put it this way: "Don't expect the brake kits to stop you sooner, but expect the 20th lap to feel like the first.""
</TD></TR></TABLE>
Agreed. About the only other advantage I can think of with regards to huge multi-piston calipers and Honkin' big vented rotors is that it is easier to modulate them at the threshold of wheel lock. So they might help compensate very slightly for lack of skill with the middle pedal and allow you to threshold brake with ~1% more force. But if you're just going into ABS everytime you really need to stop, I doubt they'd stop you even 1 ft quicker.
Trending Topics
Member
Joined: Dec 2000
Posts: 1,506
Likes: 0
From: Only those who dare to lose, win.
Re: The State of Braking (Geezer)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Geezer »</TD></TR><TR><TD CLASS="quote">On a Porsche, would it be "das bling"? </TD></TR></TABLE>
:snort, chuckle, snicker: LOL
:snort, chuckle, snicker: LOL
New User
Joined: Apr 2001
Posts: 1,720
Likes: 0
From: Portland, OR
Re: The State of Braking (4WDrift)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 4WDrift »</TD></TR><TR><TD CLASS="quote">
Adding horsepower without paying any attention to the brakes is all part of our culture."</TD></TR></TABLE>
So True!
Although a big brake kit will not improve stopping distance if current setup can lock-up,,, but a big brake kit will be working at a far less than its potential... say 50% of its capabilities rather than 90% of a factory system...which is the cause of longevity, or "fade resistant" characteristics of an upgraded kit.
Adding horsepower without paying any attention to the brakes is all part of our culture."</TD></TR></TABLE>
So True!
Although a big brake kit will not improve stopping distance if current setup can lock-up,,, but a big brake kit will be working at a far less than its potential... say 50% of its capabilities rather than 90% of a factory system...which is the cause of longevity, or "fade resistant" characteristics of an upgraded kit.
Honda-Tech Member
Joined: Feb 2002
Posts: 1,113
Likes: 0
From: Go Bears, CA
Re: The State of Braking (4WDrift)
Can brake systems be calibrated? The way I figure it, what makes brakes good and bad is how progressive they are. Ideally, I would like to "tune" how much stopping force I'm getting to how much pedal pressure I'm applying, looking for the most linear relationship (picture a graph with "distance traveled by break pedal" on the x axis, and "stopping force" on the y axis).
I would think that I'd like a brake with the most amount of travel between "no brake" and lockup.
I dont' know if this makes any sense...I guess what I'm trying to say that the less a brake pedal is an "on-off" situation, and the more progressive it is, the easier it would be to manipulate in a track situation.
For example. On a car with really cheap brakes, sure, you can lock up the wheel...if you stomp on it. Good brakes, however, will transition smoothly from no brake to brake.
Is this a totally useless/stupid concept, or is it already well known/played on?
I would think that I'd like a brake with the most amount of travel between "no brake" and lockup.
I dont' know if this makes any sense...I guess what I'm trying to say that the less a brake pedal is an "on-off" situation, and the more progressive it is, the easier it would be to manipulate in a track situation.
For example. On a car with really cheap brakes, sure, you can lock up the wheel...if you stomp on it. Good brakes, however, will transition smoothly from no brake to brake.
Is this a totally useless/stupid concept, or is it already well known/played on?
Honda-Tech Member
Joined: Sep 2000
Posts: 2,768
Likes: 2
From: Kings Mt., NC
Re: The State of Braking (JustChou)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote »</TD></TR><TR><TD CLASS="quote">I dont' know if this makes any sense...I guess what I'm trying to say that the less a brake pedal is an "on-off" situation, and the more progressive it is, the easier it would be to manipulate in a track situation.
</TD></TR></TABLE>
A gold star for this guy. He knows the secret.
Matt-maker of very progressive brake pads with outstanding modulation ability...
</TD></TR></TABLE>
A gold star for this guy. He knows the secret.
Matt-maker of very progressive brake pads with outstanding modulation ability...
Honda-Tech Member
Joined: Apr 2000
Posts: 3,846
Likes: 1
From: I started it
Re: The State of Braking (JustChou)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JustChou »</TD></TR><TR><TD CLASS="quote">I would think that I'd like a brake with the most amount of travel between "no brake" and lockup.</TD></TR></TABLE>
What JustChou said.
Modulation is king. Initial bite might "feel good" but I'll take an attenuator over an on/off switch any day.
What JustChou said.
Modulation is king. Initial bite might "feel good" but I'll take an attenuator over an on/off switch any day.
Junior Member
Joined: Nov 2002
Posts: 154
Likes: 0
From: Los Angeles, CA
Re: The State of Braking (JustChou)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JustChou »</TD></TR><TR><TD CLASS="quote">I would think that I'd like a brake with the most amount of travel between "no brake" and lockup.</TD></TR></TABLE>Again, I disagree. Your brain/foot relationship is not great at judging displacement. It is really good at judging pressure. Ideally you want a pedal with zero travel, but instead linearly applies braking force as pedal pressure increases.
If you don't believe me, try this. Prop a bathroom scale up against a wall and sit down facing it with your foot pressing on it like it would a brake pedal. Now apply pressure. You'll be amazed at how well you can fine tune how much force you apply. Try doing a similar thing with displacement, and you'll find that it is much harder to judge.
If you don't believe me, try this. Prop a bathroom scale up against a wall and sit down facing it with your foot pressing on it like it would a brake pedal. Now apply pressure. You'll be amazed at how well you can fine tune how much force you apply. Try doing a similar thing with displacement, and you'll find that it is much harder to judge.
Junior Member
Joined: Nov 2002
Posts: 154
Likes: 0
From: Los Angeles, CA
Re: The State of Braking (MaddMatt)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MaddMatt »</TD></TR><TR><TD CLASS="quote">Matt-maker of very progressive brake pads with outstanding modulation ability...</TD></TR></TABLE>
Matt knows the secret. Pad compound is key. Put different pads in the same caliper and the effects can be huge. In fact, Frank Markus in C&D wrote an article about brake feel in Aug '99 (yes, I trust C&D). He swapped out the standard pads in a test Bonneville for some PF street pads and recorded a 10% improvement in stopping distance.
Granted this somewhat goes against what I wrote earlier about traction, not brakes dictating stopping distance, but we're just getting more advanced so bear with me here. How well a pad releases from the rotor is what determines its ability to be modulated well. So pads that release faster are better. A modern ABS system does a great job of proving this. The whole point of ABS is to maximize vehicle deceleration by keeping each wheel at a rate of deceleration where it can achieve its maximum grip. Wheel speed should be about 10-20% (I think) less than vehicle speed for traction to be maximized under braking. So ABS just cycles between lockup/unlocked as fast as possible to get near this point. For that to be effective, you want a pad that can lock a wheel immediately and then unlock that wheel immediately.
Matt knows the secret. Pad compound is key. Put different pads in the same caliper and the effects can be huge. In fact, Frank Markus in C&D wrote an article about brake feel in Aug '99 (yes, I trust C&D). He swapped out the standard pads in a test Bonneville for some PF street pads and recorded a 10% improvement in stopping distance.
Granted this somewhat goes against what I wrote earlier about traction, not brakes dictating stopping distance, but we're just getting more advanced so bear with me here. How well a pad releases from the rotor is what determines its ability to be modulated well. So pads that release faster are better. A modern ABS system does a great job of proving this. The whole point of ABS is to maximize vehicle deceleration by keeping each wheel at a rate of deceleration where it can achieve its maximum grip. Wheel speed should be about 10-20% (I think) less than vehicle speed for traction to be maximized under braking. So ABS just cycles between lockup/unlocked as fast as possible to get near this point. For that to be effective, you want a pad that can lock a wheel immediately and then unlock that wheel immediately.
Honda-Tech Member
Joined: Sep 2000
Posts: 2,768
Likes: 2
From: Kings Mt., NC
Re: The State of Braking (fidracer)
Imagine an x-y axis, with pedal pressure (or line pressure) on the x axis, and brake torque on the y-axis....
The plot of every friction material starts out a straight line at some angle, and eventually turns parabollic upward. At some point the amout of pedal (or line) pressure generated produces enough brake torque to lock up the wheel. But where is that point on the graph? Is it on the straight line portion? Or is it on the parabollic portion? Which is better? If it's on the parabollic portion, what happens is a small change in line pressure produces a large change in brake torque. There's your on/off switch. If it's on the straight portion of the graph, there's a linear relationship between the amount of line pressure and brake torque, so a small change in pressure yields a small change in torque. This is the true definition of "linear" when describing friction materials. These graphs change with temperature and speed (radial velocity of the rotor).
As a good rule of thumb, a high initial bite brake material will not have very good progressive behavior (think Hawk Blue on/off switch). It's all about who can achieve threshold braking the quickest and maintain it for the longest period of time. THAT'S the guy who will out-brake everyone going into a turn.
Modified by MaddMatt at 7:54 PM 5/3/2003
The plot of every friction material starts out a straight line at some angle, and eventually turns parabollic upward. At some point the amout of pedal (or line) pressure generated produces enough brake torque to lock up the wheel. But where is that point on the graph? Is it on the straight line portion? Or is it on the parabollic portion? Which is better? If it's on the parabollic portion, what happens is a small change in line pressure produces a large change in brake torque. There's your on/off switch. If it's on the straight portion of the graph, there's a linear relationship between the amount of line pressure and brake torque, so a small change in pressure yields a small change in torque. This is the true definition of "linear" when describing friction materials. These graphs change with temperature and speed (radial velocity of the rotor).
As a good rule of thumb, a high initial bite brake material will not have very good progressive behavior (think Hawk Blue on/off switch). It's all about who can achieve threshold braking the quickest and maintain it for the longest period of time. THAT'S the guy who will out-brake everyone going into a turn.
Modified by MaddMatt at 7:54 PM 5/3/2003
Honda-Tech Member
Joined: Sep 2000
Posts: 2,768
Likes: 2
From: Kings Mt., NC
Re: The State of Braking (PupaScoopa)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote »</TD></TR><TR><TD CLASS="quote">Matt knows the secret. </TD></TR></TABLE>
Only partially true. A better statement would be "Carbotech knows the secret"
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote »</TD></TR><TR><TD CLASS="quote">Pad compound is key.</TD></TR></TABLE>
Yup.
Only partially true. A better statement would be "Carbotech knows the secret"
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote »</TD></TR><TR><TD CLASS="quote">Pad compound is key.</TD></TR></TABLE>
Yup.
Thread
Thread Starter
Forum
Replies
Last Post
JDMTEG98
Suspension & Brakes
4
Jul 10, 2009 09:20 PM
E_Bird
Honda CRX / EF Civic (1988 - 1991)
1
Aug 28, 2003 06:47 AM
