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      10-21-2007, 05:41 PM   #111
devo
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Originally Posted by GregW / Oregon View Post
Brake System Basic Facts
1) Line pressure can only be increased by either increasing the mechanical pedal ratio or by decreasing the master cylinder diameter. In either case the pedal travel will be increased.

2) Clamping force can only be increased either by increasing the line pressure or by increasing the diameter of the caliper piston(s). Increasing the size of the pads will not increase clamping force. Any increase in caliper piston area alone will be accompanied by an increase in pedal travel. The effectiveness of a caliper is also affected by the stiffness of the caliper body and its mountings. It is therefore possible to reduce piston size while increasing caliper stiffness and realize a net increase in clamping force applied. This would typically improve pedal feel.

3) Only increasing the effective radius of the disc, the caliper piston area, the line pressure, or the coefficient of friction can increase brake torque. Increasing the pad area will decrease pad wear and improve the fade characteristics of the pads but it will not increase the brake torque.
--StopTech

It is true that multiple piston calipers do not necessarily offer more clamping force than single pistons, but might offer more piston area making this possible.
Swamp, obviously, the previous post regarding the color of the brakes was directed at Porsche, so I have to chime in. Feel free to lambaste me at will. I am accustomed to it. However, facts are facts.

+1 to the aforementioned post. More force over more of a swept area, making multi-piston brakes more effective than single piston ones. Everything else being equal, of course.

So, whether the rigid four and six piston "red" brakes on a Porsche offer "more" clamping force is moot. It is that they offer more clamping force over a broader area. Which is why BMW's brakes -in their current configuation- will not compete with Posche's over repeated hot stops. No matter how much road test data someone finds where the M3 bests the 911 in a single contest.

Whether or not better brakes are needed for the street has yet to be determined, however.

Great info, by the way!
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      10-21-2007, 06:15 PM   #112
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Originally Posted by m_bazeepaymon View Post
Mostly when you press power on the car or Sport on the E46 M3, ETC. Throttle response just makes the car "feel more sporty"
Even though it will feel a lot faster and have a higher kick off... The car is performing just the same
Not sure how to interpret this post. What do you mean by having a higher kick and performing the same?

If the response time between the driver input and the flow input to the engine is shortened, the driver would naturally have more control over what the engine is doing, and can use that to his/her advantage--depending on the driving scenario I guess.
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      10-21-2007, 06:44 PM   #113
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Originally Posted by lucid View Post
Not sure how to interpret this post. What do you mean by having a higher kick and performing the same?

If the response time between the driver input and the flow input to the engine is shortened, the driver would naturally have more control over what the engine is doing, and can use that to his/her advantage--depending on the driving scenario I guess.
A quicker throttle ratio, which is what we're essentially talking about, gives faster responses at the potential expense of precision. I drive in Sport mode in my E46 all the time on the street. However, many prefer Normal mode on the track, as it lets you make more subtle power adjsutments.
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      10-21-2007, 07:04 PM   #114
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Quote:
Originally Posted by devo View Post
+1 to the aforementioned post. More force over more of a swept area, making multi-piston brakes more effective than single piston ones. Everything else being equal, of course.

So, whether the rigid four and six piston "red" brakes on a Porsche offer "more" clamping force is moot. It is that they offer more clamping force over a broader area. Which is why BMW's brakes -in their current configuation- will not compete with Posche's over repeated hot stops. No matter how much road test data someone finds where the M3 bests the 911 in a single contest.

Whether or not better brakes are needed for the street has yet to be determined, however.

Great info, by the way!
I don't read that the way you do. The first most important "area" is the total piston area--A large single piston may have more area than dual pistons. This inceases potential clamping force and therfore stopping power.

"Increasing the size of the pads will not increase clamping force." The area over which the clamping force is applied is moot in terms of stopping power; larger "swept area" will only increas pad life, as each sq. cm. of pad is doing less work.

The second most improtant area is the rotor size; larger rotors offer a greater heat sink and area with which to dissapate heat, and greater moment arm for reverse torque application.
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Last edited by GregW / Oregon; 10-21-2007 at 10:45 PM.
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      10-21-2007, 07:36 PM   #115
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Quote:
Originally Posted by GregW / Oregon View Post
I don't read that the way you do. The first most important "area" is the total piston area--A large single piston may have more area than dual pistons. This inceases potential clamping force and therfore stopping power.

"Increasing the size of the pads will not increase clamping force." The area over which the clamping force is applied is moot in terms of stopping power; larger "swept area" will only increas pad life, as each sq. cm. of pad is doing less work.

The second most improtant area is the rotor size; larger rotors offer a greater heat sink and area with which to dissapate heat.

Sure, I would agree, however, I am not so sure that the M3's large single piston has more stopping "area" than Porsche's multi-piston caliper.

Without going back and checking the rotor sizes on each car, I'd have to guess -from memory- that the rotors are very close in size.

Larger rotors do increase heat sink as does the type of material used, the method by which they are made and the ventilated efficiency.

The part about an increase in pad size only increasing pad life applies to enlarging a pad without equally enlarging the forces behind it; i.e. more pistons and/or larger ones, which would create more pressure per sq. cm.
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      10-21-2007, 08:17 PM   #116
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Obviosuly, you are wrong

Quote:
Originally Posted by devo View Post
Swamp, obviously, the previous post regarding the color of the brakes was directed at Porsche, so I have to chime in. Feel free to lambaste me at will. I am accustomed to it. However, facts are facts.

+1 to the aforementioned post. More force over more of a swept area, making multi-piston brakes more effective than single piston ones. Everything else being equal, of course.

So, whether the rigid four and six piston "red" brakes on a Porsche offer "more" clamping force is moot. It is that they offer more clamping force over a broader area. Which is why BMW's brakes -in their current configuation- will not compete with Posche's over repeated hot stops. No matter how much road test data someone finds where the M3 bests the 911 in a single contest.

Whether or not better brakes are needed for the street has yet to be determined, however.

Great info, by the way!
You are completely incorrect in your assumption that my comments about caliper color was directed at Porsche. Since I have not spent enough time on this BMW forum complimenting Porsche (sarcasm…) I will make the record clear here. Porsche makes (buys actually) absolutely top notch brake systems including performance, fade and looks. I would be thrilled if BMW chose brakes as nice at Porsche for its M cars. Just FYI my color comment was directed at folks that believe multi-piston set ups (which just most often happen to be red and pretty) means definitively that the brakes are better. As I stated, rotor diameter, caliper size, rotor design and brake cooling are all more important than the number of pistons.

Your “conclusion” about Porsche brakes besting the E92 M3 brakes in fade performance is highly speculative. Until a test has been done that is all it is - speculation. I do agree that it is likely that the 997S will best the M3 by a bit in extreme fade performance given the negatives we have heard thus far about the M3 brakes and what we know about the reputation of Porsche brakes. However, a test is a test and data is data. All you have now is pride, prejudice and speculation.

Last the average pad diameter is more important to brake torque than pad or piston area, you need brake torque to decelerate, torque = force x radius and the radius is not the rotor radius but the average radius of the pad contact patch. Of course typically the average pad radius scales exactly linearly with rotor radius. Although it is certain that larger radius gives more torque it is not certain that more pistons = more force.

Sizes:
997S Front Rear (dia x width) (inches)
13.0 x 1.34 12.0 x 1.10
E92 M3
14.2 x 1.18 13.8 x .94

No big surprises here, the M3 is heavier and needs larger brakes to bring equivalent performance.
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      10-21-2007, 08:42 PM   #117
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Quote:
Originally Posted by swamp2 View Post
You are completely incorrect in your assumption that my comments about caliper color was directed at Porsche. Since I have not spent enough time on this BMW forum complimenting Porsche (sarcasm…) I will make the record clear here. Porsche makes (buys actually) absolutely top notch brake systems including performance, fade and looks. I would be thrilled if BMW chose brakes as nice at Porsche for its M cars. Just FYI my color comment was directed at folks that believe multi-piston set ups (which just most often happen to be red and pretty) means definitively that the brakes are better. As I stated, rotor diameter, caliper size, rotor design and brake cooling are all more important than the number of pistons.

Your “conclusion” about Porsche brakes besting the E92 M3 brakes in fade performance is highly speculative. Until a test has been done that is all it is - speculation. I do agree that it is likely that the 997S will best the M3 by a bit in extreme fade performance given the negatives we have heard thus far about the M3 brakes and what we know about the reputation of Porsche brakes. However, a test is a test and data is data. All you have now is pride, prejudice and speculation.

Last the average pad diameter is more important to brake torque than pad or piston area, you need brake torque to decelerate, torque = force x radius and the radius is not the rotor radius but the average radius of the pad contact patch. Of course typically the average pad radius scales exactly linearly with rotor radius. Although it is certain that larger radius gives more torque it is not certain that more pistons = more force.

Sizes:
997S Front Rear (dia x width) (inches)
13.0 x 1.34 12.0 x 1.10
E92 M3
14.2 x 1.18 13.8 x .94

No big surprises here, the M3 is heavier and needs larger brakes to bring equivalent performance.

Very informative, but do you find it necessary to accuse me of prejudice?

Speculation, sure. Pride, maybe, we're all guilty of that time to time. As much as it's expected of Porsche to have stellar brakes, it's equally expected of BMW to have less than stellar brakes.
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      10-21-2007, 10:14 PM   #118
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Prejudice

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Originally Posted by devo View Post
Very informative, but do you find it necessary to accuse me of prejudice?

Speculation, sure. Pride, maybe, we're all guilty of that time to time. As much as it's expected of Porsche to have stellar brakes, it's equally expected of BMW to have less than stellar brakes.
Well a literal meaning of the word was probably appropriate but my connotation also left a bit to be desired. And, yes, absolutely most of us are guilty of a bit of pride and speculation now and again.
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