Let's talk brakes...
04-17-2015, 02:54 PM
#1
Burning Brakes
Thread Starter
Let's talk brakes...
It has come to my attention recently that a lot of people don't think bigger rotors and calipers make a difference in stopping distance, only that they help with heat soak. They claim they only help on a race track.
I totally disagree with that belief and those statements. It seems like a no brainer to me, however a lot of people want to tell you their opinion (IMHO) or that they "think" it works a certain way. Since I work in Engineering, I believe in letting the facts decide the truth. So feel free to contribute. I will start with a few facts that I think help prove my case that a larger brake rotor does make a difference even in one stop.
To go further it is necessary to understand some of the physics involved, and that requires some definitions.
1) Mechanical pedal ratio: Because no one can push directly on the brake master cylinder(s) hard enough to stop the car, the brake pedal is designed to multiply the driver's effort. The mechanical pedal ratio is the distance from the pedal pivot point to the effective center of the footpad divided by the distance from the pivot point to the master cylinder push rod. Typical ratios range from 4:1 to 9:1. The larger the ratio, the greater the force multiplication (and the longer the pedal travel).
2) Brake line pressure: Brake line pressure is the hydraulic force that actuates the braking system when the pedal is pushed. Measured in English units as pounds per square inch (psi), it is the force applied to the brake pedal in pounds multiplied by the pedal ratio divided by the area of the master cylinder in square inches. For the same amount of force, the smaller the master cylinder, the greater the brake line pressure. Typical brake line pressures during a stop range from less than 800psi under "normal" conditions, to as much as 2000psi in a maximum effort.
3) Clamping force: The clamping force of a caliper is the force exerted on the disc by the caliper pistons. Measured in pounds clamping force, it is the product of brake line pressure, in psi, multiplied by the total piston area of the caliper in square inches. This is true whether the caliper is of fixed or floating design. Increasing the pad area will not increase the clamping force.
4) Braking torque: When we are talking about results in the braking department we are actually talking about braking torque - not line pressure, not clamping force and certainly not fluid displacement or fluid displacement ratio. Braking torque in pounds-feet on a single wheel is the effective disc radius in inches times clamping force times the coefficient of friction of the pad against the disc all divided by 12. The maximum braking torque on a single front wheel normally exceeds the entire torque output of a typical engine.
So you see that the equation for "braking torque" includes the "effective disc radius". Thus proving my point that the larger rotor is effectively a multiplier in the braking torque.
I totally disagree with that belief and those statements. It seems like a no brainer to me, however a lot of people want to tell you their opinion (IMHO) or that they "think" it works a certain way. Since I work in Engineering, I believe in letting the facts decide the truth. So feel free to contribute. I will start with a few facts that I think help prove my case that a larger brake rotor does make a difference even in one stop.
To go further it is necessary to understand some of the physics involved, and that requires some definitions.
1) Mechanical pedal ratio: Because no one can push directly on the brake master cylinder(s) hard enough to stop the car, the brake pedal is designed to multiply the driver's effort. The mechanical pedal ratio is the distance from the pedal pivot point to the effective center of the footpad divided by the distance from the pivot point to the master cylinder push rod. Typical ratios range from 4:1 to 9:1. The larger the ratio, the greater the force multiplication (and the longer the pedal travel).
2) Brake line pressure: Brake line pressure is the hydraulic force that actuates the braking system when the pedal is pushed. Measured in English units as pounds per square inch (psi), it is the force applied to the brake pedal in pounds multiplied by the pedal ratio divided by the area of the master cylinder in square inches. For the same amount of force, the smaller the master cylinder, the greater the brake line pressure. Typical brake line pressures during a stop range from less than 800psi under "normal" conditions, to as much as 2000psi in a maximum effort.
3) Clamping force: The clamping force of a caliper is the force exerted on the disc by the caliper pistons. Measured in pounds clamping force, it is the product of brake line pressure, in psi, multiplied by the total piston area of the caliper in square inches. This is true whether the caliper is of fixed or floating design. Increasing the pad area will not increase the clamping force.
4) Braking torque: When we are talking about results in the braking department we are actually talking about braking torque - not line pressure, not clamping force and certainly not fluid displacement or fluid displacement ratio. Braking torque in pounds-feet on a single wheel is the effective disc radius in inches times clamping force times the coefficient of friction of the pad against the disc all divided by 12. The maximum braking torque on a single front wheel normally exceeds the entire torque output of a typical engine.
So you see that the equation for "braking torque" includes the "effective disc radius". Thus proving my point that the larger rotor is effectively a multiplier in the braking torque.
04-17-2015, 03:09 PM
#3
I've always been under the impression that while without a doubt larger rotors and calipers will physically produce more stopping power than their smaller counterparts in any situation, the tires and amount of traction ends up being the limiting factor on your stopping distance.
For example if you have two exact same cars, using your formulas one with the absolutely smallest rotor and caliper combination physically needed to lock up the wheels, and the other with absolutely massive rotors and calipers, and have them going the same speed, same temperature, etc. and slam on the brakes they are both going to stop in the same distance because once you lock up the wheels increasing the amount of stopping power you have won't make you stop any faster.
But once you try to do that multiple times in a row the smaller setup's temperature will have more trouble dissipating all the heat and this is where the larger brake setup will begin to outperform the smaller one
That's just what I've always thought. What do I know
For example if you have two exact same cars, using your formulas one with the absolutely smallest rotor and caliper combination physically needed to lock up the wheels, and the other with absolutely massive rotors and calipers, and have them going the same speed, same temperature, etc. and slam on the brakes they are both going to stop in the same distance because once you lock up the wheels increasing the amount of stopping power you have won't make you stop any faster.
But once you try to do that multiple times in a row the smaller setup's temperature will have more trouble dissipating all the heat and this is where the larger brake setup will begin to outperform the smaller one
That's just what I've always thought. What do I know
04-17-2015, 03:14 PM
#4
Burning Brakes
Thread Starter
As far as the big brakes thing goes it is not a question of power levels that determine your need (IMHO). Big brakes are not needed unless you need the surface area to control heat due to tracking the car at speed for periods of time. What is important is the ability of your brakes to lock up. Once you lock your brakes up they have done their job. (you can't lock them up more) Standard brakes accomplish this just fine. What is vastly more important than your brake system is your tires. Stickier the tire better the braking. Just my 2 cents.
Big brakes are overkill on any street driving car unless you road course the car.
04-17-2015, 03:17 PM
#5
Team Owner
Any argument about this probably comes from the idea that once the brakes generate enough force to stop the wheel from turning (meaning that the tire starts skidding on the pavement), any more braking force is wasted. At that point, the stopped rotor is just being squeezed harder, but since it is stopped, it doesn't matter.
04-17-2015, 03:24 PM
#7
Burning Brakes
Thread Starter
I've always been under the impression that while without a doubt larger rotors and calipers will physically produce more stopping power than their smaller counterparts in any situation, the tires and amount of traction ends up being the limiting factor on your stopping distance.
For example if you have two exact same cars, using your formulas one with the absolutely smallest rotor and caliper combination physically needed to lock up the wheels, and the other with absolutely massive rotors and calipers, and have them going the same speed, same temperature, etc. and slam on the brakes they are both going to stop in the same distance because once you lock up the wheels increasing the amount of stopping power you have won't make you stop any faster.
But once you try to do that multiple times in a row the smaller setup's temperature will have more trouble dissipating all the heat and this is where the larger brake setup will begin to outperform the smaller one
That's just what I've always thought. What do I know
For example if you have two exact same cars, using your formulas one with the absolutely smallest rotor and caliper combination physically needed to lock up the wheels, and the other with absolutely massive rotors and calipers, and have them going the same speed, same temperature, etc. and slam on the brakes they are both going to stop in the same distance because once you lock up the wheels increasing the amount of stopping power you have won't make you stop any faster.
But once you try to do that multiple times in a row the smaller setup's temperature will have more trouble dissipating all the heat and this is where the larger brake setup will begin to outperform the smaller one
That's just what I've always thought. What do I know
The objective of the braking system is to utilize the tractive capacity of all of the tires to the maximum practical extent without locking a tire. In order to achieve this, the braking force between the front and rear tires must be nearly optimally proportioned even with ABS equipped vehicles.
In addition:
Braking performance is about more than just brakes. In order for even the best braking systems to function effectively, tires, suspension and driving techniques must be optimized.
And finally:
For maximum brake potential, vehicles benefit from proper corner weight balance, a lower CG, a longer wheelbase, more rear weight bias and increased aerodynamic down force at the rear.
04-17-2015, 03:32 PM
#8
I understand that logic, however I am assuming the cars have equal tires, thus:
The objective of the braking system is to utilize the tractive capacity of all of the tires to the maximum practical extent without locking a tire. In order to achieve this, the braking force between the front and rear tires must be nearly optimally proportioned even with ABS equipped vehicles.
In addition:
Braking performance is about more than just brakes. In order for even the best braking systems to function effectively, tires, suspension and driving techniques must be optimized.
And finally:
For maximum brake potential, vehicles benefit from proper corner weight balance, a lower CG, a longer wheelbase, more rear weight bias and increased aerodynamic down force at the rear.
The objective of the braking system is to utilize the tractive capacity of all of the tires to the maximum practical extent without locking a tire. In order to achieve this, the braking force between the front and rear tires must be nearly optimally proportioned even with ABS equipped vehicles.
In addition:
Braking performance is about more than just brakes. In order for even the best braking systems to function effectively, tires, suspension and driving techniques must be optimized.
And finally:
For maximum brake potential, vehicles benefit from proper corner weight balance, a lower CG, a longer wheelbase, more rear weight bias and increased aerodynamic down force at the rear.
Is the point that you are making that if you have two completely identical cars, one with a smaller brake setup and one with a larger one, both being pushed to the absolute maximum braking potential possible without locking up the wheels, that the car with the larger brake setup will stop in a shorter distance than the car with the smaller brake setup?
04-17-2015, 03:35 PM
#9
Burning Brakes
Thread Starter
Any argument about this probably comes from the idea that once the brakes generate enough force to stop the wheel from turning (meaning that the tire starts skidding on the pavement), any more braking force is wasted. At that point, the stopped rotor is just being squeezed harder, but since it is stopped, it doesn't matter.
So I say again:
The objective of the braking system is to utilize the tractive capacity of all of the tires to the maximum practical extent "without" locking a tire.
And again:
Braking torque in pounds-feet on a single wheel = the effective disc radius in inches X clamping force X the coefficient of friction of the pad against the disc / 12.
04-17-2015, 03:41 PM
#10
Burning Brakes
Thread Starter
All of those points make sense, but I still don't fully understand.
Is the point that you are making that if you have two completely identical cars, one with a smaller brake setup and one with a larger one, both being pushed to the absolute maximum braking potential possible without locking up the wheels, that the car with the larger brake setup will stop in a shorter distance than the car with the smaller brake setup?
Is the point that you are making that if you have two completely identical cars, one with a smaller brake setup and one with a larger one, both being pushed to the absolute maximum braking potential possible without locking up the wheels, that the car with the larger brake setup will stop in a shorter distance than the car with the smaller brake setup?
All things being equal except rotor dia and caliper piston area (big brake setup), the larger setup will stop in a shorter distance because the only variables would be the "effective disc radius" and the "clamping force". Two key elements in the equation for braking torque:
Braking torque in lb/ft = effective disc radius in inches X clamping force X the coefficient of friction of the pad against the disc / 12.
04-17-2015, 03:51 PM
#11
Your argument on the maximum braking force in optimal conditions makes sense to me, in the sense that if you are not locking up your tires but braking at maximum potential a big brake setup is going to have more stopping power than a small brake setup.
But wouldn't you agree that during 99% of street driving you are not going to be pushing your brakes to their absolute potential?
Even if you are making a relatively quick stop during street driving, you may be using say 80% of your smaller brakes capabilities to stop in the same distance that it would take 60% of your bigger brakes capabilities to equal, because since you aren't pushing either of them to the max there won't be a difference in stopping distance.
And in the 1% of the time that you need to stop as quickly as possible to avoid an emergency you are most likely going to hit the brakes so hard that you engage ABS in which case regardless of you are driving with big or small brakes you will stop in the same distance because they are locked up
So while technically you are right, that larger brakes are more aggressive and have more stopping power than their smaller counterparts, there is an incredibly slim chance that you are going to be utilizing the extra stopping power at the maximum capability without locking the wheels that you get from a larger brake setup, unless you are an exceptional driver that is able to properly brake in an emergency situation to your car's maximum potential without engaging ABS
Right?
But wouldn't you agree that during 99% of street driving you are not going to be pushing your brakes to their absolute potential?
Even if you are making a relatively quick stop during street driving, you may be using say 80% of your smaller brakes capabilities to stop in the same distance that it would take 60% of your bigger brakes capabilities to equal, because since you aren't pushing either of them to the max there won't be a difference in stopping distance.
And in the 1% of the time that you need to stop as quickly as possible to avoid an emergency you are most likely going to hit the brakes so hard that you engage ABS in which case regardless of you are driving with big or small brakes you will stop in the same distance because they are locked up
So while technically you are right, that larger brakes are more aggressive and have more stopping power than their smaller counterparts, there is an incredibly slim chance that you are going to be utilizing the extra stopping power at the maximum capability without locking the wheels that you get from a larger brake setup, unless you are an exceptional driver that is able to properly brake in an emergency situation to your car's maximum potential without engaging ABS
Right?
Last edited by corvette-kyle; 04-17-2015 at 03:53 PM.
04-17-2015, 03:59 PM
#12
Team Owner
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St. Jude Donor '15
"In honor of jpee"
While I respect your background, opinion and questions, you may want to read an 8-page thread (even tho it's titled fuel starvation and braking problems) in C7 Z06. The two problem items are related, but most importantly, a real "expert" in braking chimes in with his opinions on carbon ceramic brakes, brake force, longevity of rotors and pads, etc. under the extreme conditions of putting it on a track--see/note especially posts 101 and 118. I'd say there are more factors than rotor/caliper/pad size.
It is a long thread and you will see other experts comment both positively and negatively, but it is a good read and, at least for me, a good education. You can decide for yourself who are the real experts, and who are not.
https://www.corvetteforum.com/forums...rake-fade.html
It is a long thread and you will see other experts comment both positively and negatively, but it is a good read and, at least for me, a good education. You can decide for yourself who are the real experts, and who are not.
https://www.corvetteforum.com/forums...rake-fade.html
04-17-2015, 04:04 PM
#13
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All of those points make sense, but I still don't fully understand.
Is the point that you are making that if you have two completely identical cars, one with a smaller brake setup and one with a larger one, both being pushed to the absolute maximum braking potential possible without locking up the wheels, that the car with the larger brake setup will stop in a shorter distance than the car with the smaller brake setup?
Is the point that you are making that if you have two completely identical cars, one with a smaller brake setup and one with a larger one, both being pushed to the absolute maximum braking potential possible without locking up the wheels, that the car with the larger brake setup will stop in a shorter distance than the car with the smaller brake setup?
04-17-2015, 04:05 PM
#14
Burning Brakes
Thread Starter
Your argument on the maximum braking force in optimal conditions makes sense to me, in the sense that if you are not locking up your tires but braking at maximum potential a big brake setup is going to have more stopping power than a small brake setup.
But wouldn't you agree that during 99% of street driving you are not going to be pushing your brakes to their absolute potential?
Even if you are making a relatively quick stop during street driving, you may be using say 80% of your smaller brakes capabilities to stop in the same distance that it would take 60% of your bigger brakes capabilities to equal, because since you aren't pushing either of them to the max there won't be a difference in stopping distance.
And in the 1% of the time that you need to stop as quickly as possible to avoid an emergency you are most likely going to hit the brakes so hard that you engage ABS in which case regardless of you are driving with big or small brakes you will stop in the same distance because they are locked up
So while technically you are right, that larger brakes are more aggressive and have more stopping power than their smaller counterparts, there is an incredibly slim chance that you are going to be utilizing the extra stopping power at the maximum capability without locking the wheels that you get from a larger brake setup, unless you are an exceptional driver that is able to properly brake in an emergency situation to your car's maximum potential without engaging ABS
Right?
But wouldn't you agree that during 99% of street driving you are not going to be pushing your brakes to their absolute potential?
Even if you are making a relatively quick stop during street driving, you may be using say 80% of your smaller brakes capabilities to stop in the same distance that it would take 60% of your bigger brakes capabilities to equal, because since you aren't pushing either of them to the max there won't be a difference in stopping distance.
And in the 1% of the time that you need to stop as quickly as possible to avoid an emergency you are most likely going to hit the brakes so hard that you engage ABS in which case regardless of you are driving with big or small brakes you will stop in the same distance because they are locked up
So while technically you are right, that larger brakes are more aggressive and have more stopping power than their smaller counterparts, there is an incredibly slim chance that you are going to be utilizing the extra stopping power at the maximum capability without locking the wheels that you get from a larger brake setup, unless you are an exceptional driver that is able to properly brake in an emergency situation to your car's maximum potential without engaging ABS
Right?
Motortrend
2008 Corvette(z-51) 60-0 110 ft
2007 Z06 Corvette 60-0 108 ft
Car and Drive
2008 Corvette(z51) 70-0 172ft
2007 Z06 Corvette 70-0 149ft
The faster the speed you are going the more the bigger brakes will factor in.
04-17-2015, 04:08 PM
#15
Le Mans Master
Oh boy how much time did you waste typing this up just for me!!! 
I feel so special.
I'll contribute...
Brakes stop the tires. Tires stop the car.
I feel so special.
I'll contribute...
Brakes stop the tires. Tires stop the car.
04-17-2015, 04:10 PM
#16
Burning Brakes
Thread Starter
While I respect your background, opinion and questions, you may want to read an 8-page thread (even tho it's titled fuel starvation and braking problems) in C7 Z06. The two problem items are related, but most importantly, a real "expert" in braking chimes in with his opinions on carbon ceramic brakes, brake force, longevity of rotors and pads, etc. under the extreme conditions of putting it on a track--see/note especially posts 101 and 118. I'd say there are more factors than rotor/caliper/pad size.
It is a long thread and you will see other experts comment both positively and negatively, but it is a good read and, at least for me, a good education. You can decide for yourself who are the real experts, and who are not.
https://www.corvetteforum.com/forums...rake-fade.html
It is a long thread and you will see other experts comment both positively and negatively, but it is a good read and, at least for me, a good education. You can decide for yourself who are the real experts, and who are not.
https://www.corvetteforum.com/forums...rake-fade.html
04-17-2015, 04:14 PM
#17
Burning Brakes
Thread Starter
And hopefully we can all learn something in the process. So this is for everyone's benefit.
Once again I am open to pertinent facts on the subject!
Since you agree brakes stop the tires, then how can you deny the fact that bigger brakes do a better job of that, even on the street?
Last edited by db2012gs; 04-17-2015 at 04:19 PM.
04-17-2015, 04:22 PM
#18
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C6 of Year Finalist (appearance mods) 2019
These are some test results comparing stopping distances between a base model and Z06:
Motortrend
2008 Corvette(z-51) 60-0 110 ft
2007 Z06 Corvette 60-0 108 ft
Car and Drive
2008 Corvette(z51) 70-0 172ft
2007 Z06 Corvette 70-0 149ft
The faster the speed you are going the more the bigger brakes will factor in.
Motortrend
2008 Corvette(z-51) 60-0 110 ft
2007 Z06 Corvette 60-0 108 ft
Car and Drive
2008 Corvette(z51) 70-0 172ft
2007 Z06 Corvette 70-0 149ft
The faster the speed you are going the more the bigger brakes will factor in.
Bigger brakes and rotors will perform better given a fixed brake claiming pressure (foot pressure I am talking about). Once you reach max pressure and the tires lock up then the big benefit is heat disapation.
04-17-2015, 04:27 PM
#19
Team Owner
A lot of the difference is from bigger and stickier tires, along with bigger brakes.
Bigger brakes and rotors will perform better given a fixed brake claiming pressure (foot pressure I am talking about). Once you reach max pressure and the tires lock up then the big benefit is heat disapation.
Bigger brakes and rotors will perform better given a fixed brake claiming pressure (foot pressure I am talking about). Once you reach max pressure and the tires lock up then the big benefit is heat disapation.
04-17-2015, 04:31 PM
#20
Le Mans Master
This is my point also. Unless the smaller brake system does not have enough force to stop the wheel to begin with, then adding more force after the wheel has been stopped does no good. It would seem to me that the advantage of a bigger setup would be the ability to absorb heat and continue to exert that required force after multiple stops...combating brake fade.
