braking technique
03-09-2005 | 10:46 AM
#26
Yeah this is just stupid.... Watch ANY type of racing and what do you ALWAYS see the guy who locks up his brake doing......Going right off the end of the track...The fastest way to stop, lock up the brakes and hit another car or a wall. :p
03-09-2005 | 11:01 AM
#27
RX8 and a Truk....
Joined: Nov 2004
Posts: 4,658
Likes: 7
From: OKC
Originally Posted by SoloII///M
"Consider the source."
This guy has no idea what he's talking about.
Had to look back and check, but I never said ABS gives the shortest stopping distances. I said it gives the most CONSISTENT braking and is very close to the shortest distance in practice. Theory is just that - theory.
Of course, you can verify this for yourself. Find an abandoned section of road and do some tests with and without ABS. It'll become obvious which is the faster way to stop pretty quickly.
This guy has no idea what he's talking about.
Had to look back and check, but I never said ABS gives the shortest stopping distances. I said it gives the most CONSISTENT braking and is very close to the shortest distance in practice. Theory is just that - theory.
Of course, you can verify this for yourself. Find an abandoned section of road and do some tests with and without ABS. It'll become obvious which is the faster way to stop pretty quickly.
Follow me here:
I didn't indicate you indicated ABS gives the shortest stoping distance...
I'm saying "ABS won't make your car stop quicker". Then I stated "If you want your car to stop in the shortest distance, lock up all four wheels." I still think I believe that last statement, but I'm having trouble proving it.
:D
03-09-2005 | 11:02 AM
#28
RX8 and a Truk....
Joined: Nov 2004
Posts: 4,658
Likes: 7
From: OKC
Originally Posted by ULLLOSE
Yeah this is just stupid.... Watch ANY type of racing and what do you ALWAYS see the guy who locks up his brake doing......Going right off the end of the track...The fastest way to stop, lock up the brakes and hit another car or a wall. :p
Nobody slides off the end of the track on a straight....
We're discussing straight-line stopping.
03-09-2005 | 11:13 AM
#29
Originally Posted by dmp
Nobody slides off the end of the track on a straight.... We're discussing straight-line stopping.
We're discussing straight-line stopping.Study the physics of static / sliding friction enough and you'll prove to yourself that the sliding tire has less friction.
03-09-2005 | 11:19 AM
#30
RX8 and a Truk....
Joined: Nov 2004
Posts: 4,658
Likes: 7
From: OKC
Originally Posted by SoloII///M
LOL. What is the reason you apply the brakes? For a turn, of course. :D
Study the physics of static / sliding friction enough and you'll prove to yourself that the sliding tire has less friction.
Study the physics of static / sliding friction enough and you'll prove to yourself that the sliding tire has less friction.
Maybe YOU have to apply brakes before turning....I drive an RX8!
:p
I'll research more...I still believe i'm right. :D
03-09-2005 | 03:27 PM
#34
What's next?
Joined: Feb 2004
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From: SE Mass
What aould it take for us to convince you that you may have been incorrect in your belief that a skidding tire will stop faster/in a shorter distance than a non-skidding one?
Here's two quick articles I have found.... I can find many more... just tell me what source you would beleive if I found it, or could get a hold of it... if you don't believe these two....
Exhibit A:
http://www.canadiandirect.com/Renderer.jhtml.88.html
Exhibit B:
http://www.waltersforensic.com/artic...n/vol2-no1.htm
Trust us when we say, and we have racing expereince... a skidding tire on pavement does not stop faster than a tire that's being threshold braked.
On snow, gravel, where you might be thinking you read this... you CAN stop faster by skidding. What happens is the locked tires form a wedge of snow/dirt and break through the loose surface to the substrate where it's not as slippery... and the wedge adds a coefficient of friction to the stopping tire by it's increasing base size. So... the choice is yours. This isn't a pissing contest. We're not going to hold you accoutable for a misunderstanding. We've all been there at one point in time.
--kC
Here's two quick articles I have found.... I can find many more... just tell me what source you would beleive if I found it, or could get a hold of it... if you don't believe these two....
Exhibit A:
http://www.canadiandirect.com/Renderer.jhtml.88.html
Then, squeeze the pedal down to the point just before the tires begin to skid - right at the limit of the tires's traction or grip. Never forget that if you lock-up the brakes and begin to skid, you have lost all directional control of the car. No matter what you do with the steering wheel, the car will continue straight ahead. Plus, a skidding car takes more distance to stop.
http://www.waltersforensic.com/artic...n/vol2-no1.htm
Wheel Slip-Threshold Braking
Wheel slip (skidding) occurs when the tire breaks traction with the road surface. When this occurs, friction is reduced between the tires and the road.
Skidding results in longer stopping distances. For the shortest possible stopping distance, the friction must be kept at a maximum. This is accomplished by "threshold braking", when the tire develops maximum friction without wheel slip.
A tire that is skidding has exceeded the maximum available friction and cannot provide maximum braking or effective steering.
Wheel slip (skidding) occurs when the tire breaks traction with the road surface. When this occurs, friction is reduced between the tires and the road.
Skidding results in longer stopping distances. For the shortest possible stopping distance, the friction must be kept at a maximum. This is accomplished by "threshold braking", when the tire develops maximum friction without wheel slip.
A tire that is skidding has exceeded the maximum available friction and cannot provide maximum braking or effective steering.
On snow, gravel, where you might be thinking you read this... you CAN stop faster by skidding. What happens is the locked tires form a wedge of snow/dirt and break through the loose surface to the substrate where it's not as slippery... and the wedge adds a coefficient of friction to the stopping tire by it's increasing base size. So... the choice is yours. This isn't a pissing contest. We're not going to hold you accoutable for a misunderstanding. We've all been there at one point in time.
--kC
Last edited by Imp; 03-09-2005 at 03:31 PM.
03-09-2005 | 03:32 PM
#35
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Posts: 7,966
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From: Boulder County, Colorado
That's enough of the pissing-contest folks. I've cleaned up the posts, but if it continues after this point I'll have to close this otherwise good thread and start handing out warnings. Let it go, please.
03-09-2005 | 03:45 PM
#36
RX8 and a Truk....
Joined: Nov 2004
Posts: 4,658
Likes: 7
From: OKC
Originally Posted by Imp
What aould it take for us to convince you that you may have been incorrect in your belief that a skidding tire will stop faster/in a shorter distance than a non-skidding one?
Here's two quick articles I have found.... I can find many more... just tell me what source you would beleive if I found it, or could get a hold of it... if you don't believe these two....
Exhibit A:
http://www.canadiandirect.com/Renderer.jhtml.88.html
Exhibit B:
http://www.waltersforensic.com/artic...n/vol2-no1.htm
Trust us when we say, and we have racing expereince... a skidding tire on pavement does not stop faster than a tire that's being threshold braked.
Here's two quick articles I have found.... I can find many more... just tell me what source you would beleive if I found it, or could get a hold of it... if you don't believe these two....
Exhibit A:
http://www.canadiandirect.com/Renderer.jhtml.88.html
Exhibit B:
http://www.waltersforensic.com/artic...n/vol2-no1.htm
Trust us when we say, and we have racing expereince... a skidding tire on pavement does not stop faster than a tire that's being threshold braked.
I've never claimed it'd be impossible to be 'proven wrong' - I'm saying I'm not convinced I just made it up - I know I heard/read it from a reputable source...still looking
On snow, gravel, where you might be thinking you read this... you CAN stop faster by skidding. What happens is the locked tires form a wedge of snow/dirt and break through the loose surface to the substrate where it's not as slippery... and the wedge adds a coefficient of friction to the stopping tire by it's increasing base size. So... the choice is yours. This isn't a pissing contest. We're not going to hold you accoutable for a misunderstanding. We've all been there at one point in time.
--kC
--kC
03-09-2005 | 05:24 PM
#37
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One of the reasons I posted this question was that in my mind, it seemed like using the ABS was a good idea, since its easy to use and be consistent. However, watching other drivers in cars that were ABS equipped, it did not seem like they were getting into the ABS.
Obviously in an autox you aren't trying to stop the car, just get it slower as quickly as possible. This is why I brought up the smoothness of not hitting ABS as opposed to using it. Is there a significant advantage to keeping the car's motion smooth? I would think so, but I would think that then the ideal technique would be to go hard into ABS, and then taper out of it and trail brake into the turn.
BTW, the 8's brakes / suspension-under-braking are outstanding. I was very impressed with the stopping distances I was able to achieve.
Obviously in an autox you aren't trying to stop the car, just get it slower as quickly as possible. This is why I brought up the smoothness of not hitting ABS as opposed to using it. Is there a significant advantage to keeping the car's motion smooth? I would think so, but I would think that then the ideal technique would be to go hard into ABS, and then taper out of it and trail brake into the turn.
BTW, the 8's brakes / suspension-under-braking are outstanding. I was very impressed with the stopping distances I was able to achieve.
03-09-2005 | 05:33 PM
#38
RX8 and a Truk....
Joined: Nov 2004
Posts: 4,658
Likes: 7
From: OKC
Information I found:
http://bimmer.roadfly.org/3series/me...w35/26310.html
http://bimmer.roadfly.org/3series/me...w35/26310.html
Your message says: "ABS puts the tires on the edge of lockup. That's as fast as your car will stop.".
Both parts of that sentance are flat out wrong.
First, ABS does not put the tires on the edge of lockup. ABS actually locks up the tires in small bursts. "Lock - off - lock -off" over and over again. It's not the edge of lockup, it's lockup and release, lockup and release, many times a second and much faster than a human driver.
The fastest way to stop a car is to lock up the wheels and skid to a stop. The only problem with doing so is you loose control of your car. Not a Good Thing. So ABS is one possible compromise: lock up your tires part of the time, but unlock them part of the time, so that you are able to steer your car in a full-braking situation. Another compromise is threshold braking - brake to the point that your wheels would lock, and not beyond.
Bigger rotors, nicer calipers, and etc will stop your car faster. If you've never experienced a brake conversion on a car, I guess I can't say anything to convince you otherwise. But nicer brakes will stop your car faster. Slotted rotors will allow for better disappation of heat, steam, and etc, which will allow for more consistent braking. Better gripping calipers or greater surface area on the rotors can cause the wheels to lock faster, and thus decrease braking distance. Better brakes can also allow you to threshold brake to a much higher degree, thus allowing for better braking.
Re-reading your message once again, I see that you could have been saying "ABS puts the car at the edge of lockup. And lockup is the fastest you can stop". If that's what you were trying to say, you didn't express yourself well
But to rebuke that, bigger brakes and better calipers will allow you to lockup your brakes faster than regular, which decreases brake time. Also, the better brakes allow for increased braking without lockup, good in real-world situations (outside of a 0-60-0 test that is).
Both parts of that sentance are flat out wrong.
First, ABS does not put the tires on the edge of lockup. ABS actually locks up the tires in small bursts. "Lock - off - lock -off" over and over again. It's not the edge of lockup, it's lockup and release, lockup and release, many times a second and much faster than a human driver.
The fastest way to stop a car is to lock up the wheels and skid to a stop. The only problem with doing so is you loose control of your car. Not a Good Thing. So ABS is one possible compromise: lock up your tires part of the time, but unlock them part of the time, so that you are able to steer your car in a full-braking situation. Another compromise is threshold braking - brake to the point that your wheels would lock, and not beyond.
Bigger rotors, nicer calipers, and etc will stop your car faster. If you've never experienced a brake conversion on a car, I guess I can't say anything to convince you otherwise. But nicer brakes will stop your car faster. Slotted rotors will allow for better disappation of heat, steam, and etc, which will allow for more consistent braking. Better gripping calipers or greater surface area on the rotors can cause the wheels to lock faster, and thus decrease braking distance. Better brakes can also allow you to threshold brake to a much higher degree, thus allowing for better braking.
Re-reading your message once again, I see that you could have been saying "ABS puts the car at the edge of lockup. And lockup is the fastest you can stop". If that's what you were trying to say, you didn't express yourself well
But to rebuke that, bigger brakes and better calipers will allow you to lockup your brakes faster than regular, which decreases brake time. Also, the better brakes allow for increased braking without lockup, good in real-world situations (outside of a 0-60-0 test that is).
03-09-2005 | 07:53 PM
#39
What's next?
Joined: Feb 2004
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From: SE Mass
Yeah, something like that posted in 2000 with no other "Googleable" sources... from an relative unknown... leads me to say one thing...
"I read it on a message board on the internet... it's got to be true." (Then again, same thing could be said for this thread too... but I posted links to a couple reputable sources that weren't message forums.)
By the way... if you do want to believe that link... look at the big text on the top of the page.. that part that says "Actually, lockup isn't the fastest way to stop (m)" ..which was a one line answer to that comment. (All the italics on that page are quoting the message before it.)
If lockup was the answer, tire companies would be even more rich from everyone flatspotting their tires from the skidding.
--kC
"I read it on a message board on the internet... it's got to be true."
(Then again, same thing could be said for this thread too... but I posted links to a couple reputable sources that weren't message forums.)By the way... if you do want to believe that link... look at the big text on the top of the page.. that part that says "Actually, lockup isn't the fastest way to stop (m)" ..which was a one line answer to that comment. (All the italics on that page are quoting the message before it.)
If lockup was the answer, tire companies would be even more rich from everyone flatspotting their tires from the skidding.
--kC
Last edited by Imp; 03-09-2005 at 07:55 PM.
03-09-2005 | 08:37 PM
#40
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From: PNW
I'm no expert, but, for autocross, I'm happy to engage ABS when I know that I'm going to be off the brakes before I turn the wheel, or expect to let up and do a bit of trail braking. It may be that an expert driver can slow down faster without ABS, but I can't, and one of the few things I've learned about autocross is that you want to be accelerating as much as possible in anything like a straight, so you will need to brake as you approach the sharp turns; you don't want to be braking hard in the turn, however. 
Also, it's easier for me to heel/toe effectively if I'm braking hard than if I'm trying to carefully modulate my braking.
Also, it's easier for me to heel/toe effectively if I'm braking hard than if I'm trying to carefully modulate my braking.
03-10-2005 | 07:10 AM
#41
Originally Posted by dmp
There are many fallacies in that post. First of all, "Bigger rotors, nicer calipers, and etc will stop your car faster" is a big lie. Rotors, pads, calipers, the brake pedal, the master cylinder, the braided lines - NONE of this stuff stops the car. The TIRE stops the car, specifically the friction that exists between the tire and the road.
If your car is like most cars, then it has sufficient braking power from the factory to lock the tires if ABS is disengaged. Well if that's the case, how will bigger rotors, stiffer calipers, etc. stop the car faster? They can't. Not for one stop, at least. The exceptions are that they have decreased fade resistance so multiple stops in rapid succession may be shorter. They may have better modulation or bias.
Let's go back to the tire. The key point to debate in this scenario is whether a tire has the ability to generate more grip if it's sliding or static relative to the road. The answer is the tire should be static or nearly static relative to the road. i.e. at the threshold of lockup. ABS does not acheive this, but it's the best thing we've got.
JV
03-10-2005 | 12:30 PM
#44
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I totally agree with what Solo II said:
Ideally you have to brake within a slip ratio of 2% to 20% (depending on the tire and surface conditions). The picture below shows a tire that reaches maximum braking performance (maximum friction coefficient) at about 18% slip ratio for a given surface:
The problem with ABS systems is that some of them reduce the brake pressure on the rear axle on purpose (so that the rear wheels won't lock at all), which makes the car more stable but also increases braking distance.
The DTM race cars use ABS and they wouldn't use it, if it wouldn't make the cars any faster.
http://www.dtm.de/
Ideally you have to brake within a slip ratio of 2% to 20% (depending on the tire and surface conditions). The picture below shows a tire that reaches maximum braking performance (maximum friction coefficient) at about 18% slip ratio for a given surface:
The problem with ABS systems is that some of them reduce the brake pressure on the rear axle on purpose (so that the rear wheels won't lock at all), which makes the car more stable but also increases braking distance.
The DTM race cars use ABS and they wouldn't use it, if it wouldn't make the cars any faster.
http://www.dtm.de/
03-16-2005 | 12:01 AM
#45
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From: Lake Forest, IL
I've only done 4 autocrosses (so take my advice with a grain of salt) but I've had some great training from a very good autocross driver.
I don't think there is a simple answer to your question. I think it depends on the course layout, the line you are taking, your driving skill, track conditions, etc... You'll have to judge each layout and probably experiment with both methods on any giving weekend to see what is the fastest way for you around the cones that day.
From my own experience, I was autoxing a newer BMW with ABS and recieving instruction from a guy with an older BMW without ABS. He had me going into full ABS lockup in some corners and trail braking through others. I would say that if you are going into a full braking situation that would otherwise lock up the tires, then you are better to use ABS as it will probably be smoother for you and you will lose less traction due to skidding tires. (think friction circle diagram)
Depending on the course layout, you might not do that really heavy braking very often. It would have to be a really tight hairpin for you to want to stop that completely. For sure use full ABS braking at the end of a run if you have a stopbox that you have to stop in.
I've never autoxed the RX8, but I would think brake less to carry speed through corners to compensate for lack of low end grunt. Torque shouldn't be a problem anyway as long as you keep the revs high. I'll be doing a ton of autocrosses in the 8 and a 2 day SCCA autocross shool next month. I'll let you know what I learn there.
I don't think there is a simple answer to your question. I think it depends on the course layout, the line you are taking, your driving skill, track conditions, etc... You'll have to judge each layout and probably experiment with both methods on any giving weekend to see what is the fastest way for you around the cones that day.
From my own experience, I was autoxing a newer BMW with ABS and recieving instruction from a guy with an older BMW without ABS. He had me going into full ABS lockup in some corners and trail braking through others. I would say that if you are going into a full braking situation that would otherwise lock up the tires, then you are better to use ABS as it will probably be smoother for you and you will lose less traction due to skidding tires. (think friction circle diagram)
Depending on the course layout, you might not do that really heavy braking very often. It would have to be a really tight hairpin for you to want to stop that completely. For sure use full ABS braking at the end of a run if you have a stopbox that you have to stop in.
I've never autoxed the RX8, but I would think brake less to carry speed through corners to compensate for lack of low end grunt. Torque shouldn't be a problem anyway as long as you keep the revs high. I'll be doing a ton of autocrosses in the 8 and a 2 day SCCA autocross shool next month. I'll let you know what I learn there.
Originally Posted by tuj
One of the reasons I posted this question was that in my mind, it seemed like using the ABS was a good idea, since its easy to use and be consistent. However, watching other drivers in cars that were ABS equipped, it did not seem like they were getting into the ABS.
Obviously in an autox you aren't trying to stop the car, just get it slower as quickly as possible. This is why I brought up the smoothness of not hitting ABS as opposed to using it. Is there a significant advantage to keeping the car's motion smooth? I would think so, but I would think that then the ideal technique would be to go hard into ABS, and then taper out of it and trail brake into the turn.
BTW, the 8's brakes / suspension-under-braking are outstanding. I was very impressed with the stopping distances I was able to achieve.
Obviously in an autox you aren't trying to stop the car, just get it slower as quickly as possible. This is why I brought up the smoothness of not hitting ABS as opposed to using it. Is there a significant advantage to keeping the car's motion smooth? I would think so, but I would think that then the ideal technique would be to go hard into ABS, and then taper out of it and trail brake into the turn.
BTW, the 8's brakes / suspension-under-braking are outstanding. I was very impressed with the stopping distances I was able to achieve.
03-20-2005 | 04:20 AM
#46
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From: Seattle, WA
I just read this thread for the first time, and now regret doing so -- I feel stupider for having done so. Hint: static versus dynamic coefficient of friction.
"It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt." - Mark Twain
"It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt." - Mark Twain
03-20-2005 | 09:23 PM
#47
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Originally Posted by Machan
I've only done 4 autocrosses (so take my advice with a grain of salt) but I've had some great training from a very good autocross driver.
I don't think there is a simple answer to your question. I think it depends on the course layout, the line you are taking, your driving skill, track conditions, etc... You'll have to judge each layout and probably experiment with both methods on any giving weekend to see what is the fastest way for you around the cones that day.
From my own experience, I was autoxing a newer BMW with ABS and recieving instruction from a guy with an older BMW without ABS. He had me going into full ABS lockup in some corners and trail braking through others. I would say that if you are going into a full braking situation that would otherwise lock up the tires, then you are better to use ABS as it will probably be smoother for you and you will lose less traction due to skidding tires. (think friction circle diagram)
Depending on the course layout, you might not do that really heavy braking very often. It would have to be a really tight hairpin for you to want to stop that completely. For sure use full ABS braking at the end of a run if you have a stopbox that you have to stop in.
I've never autoxed the RX8, but I would think brake less to carry speed through corners to compensate for lack of low end grunt. Torque shouldn't be a problem anyway as long as you keep the revs high. I'll be doing a ton of autocrosses in the 8 and a 2 day SCCA autocross shool next month. I'll let you know what I learn there.
I don't think there is a simple answer to your question. I think it depends on the course layout, the line you are taking, your driving skill, track conditions, etc... You'll have to judge each layout and probably experiment with both methods on any giving weekend to see what is the fastest way for you around the cones that day.
From my own experience, I was autoxing a newer BMW with ABS and recieving instruction from a guy with an older BMW without ABS. He had me going into full ABS lockup in some corners and trail braking through others. I would say that if you are going into a full braking situation that would otherwise lock up the tires, then you are better to use ABS as it will probably be smoother for you and you will lose less traction due to skidding tires. (think friction circle diagram)
Depending on the course layout, you might not do that really heavy braking very often. It would have to be a really tight hairpin for you to want to stop that completely. For sure use full ABS braking at the end of a run if you have a stopbox that you have to stop in.
I've never autoxed the RX8, but I would think brake less to carry speed through corners to compensate for lack of low end grunt. Torque shouldn't be a problem anyway as long as you keep the revs high. I'll be doing a ton of autocrosses in the 8 and a 2 day SCCA autocross shool next month. I'll let you know what I learn there.
Which brings up another interesting question: how many people are left-foot braking? It seems like this would be an ideal car for that technique, just like the older rally cars with the laggy turbos. Guess I'll have to start learning.
03-21-2005 | 06:14 AM
#48
Originally Posted by tuj
Which brings up another interesting question: how many people are left-foot braking? It seems like this would be an ideal car for that technique, just like the older rally cars with the laggy turbos. Guess I'll have to start learning.
JV
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