princess peach
Member
- :
- '92 Miata, '06 MS6
^ hahahahahaha
MS3: turtle
3: Miakela
MSM: Tatiana
MSP: Gina
F-150: Bubba J
Cruze: Ethel
MS3: turtle
3: Miakela
MSM: Tatiana
MSP: Gina
F-150: Bubba J
Cruze: Ethel
The Ohio Random Thread... aka We Should Probably Be Working
- Thread starter THE Phen
- Start date
Perro del Sol
Member
- :
- 2003 MSP, Spicy Orange, 2004 Mazda 6 Hatch, 2004 Mazda 6 Wagon
Like Dr. Suess's Cat in the Hat......Thing 1 and Thing 2.....MSP 1 & MSP 2......not bad, not bad at all
Just to continue beating the dead horse...Big Brakes! Found this on 6 Club and thought it was nicely written. (removed the quote to make it easier to read)
QUOTE=CanyonRider = THE BIG BRAKE MYTH!
Having read many threads on many forums debating this very subject, I thought Id share my thoughts based on engineering principles and the laws of physics.
Before you run out and buy 6-piston calipers, two-piece carbon fiber rotors and 50 feet of stainless steel braided brake line, it would be wise to take a closer look at what brakes do (and dont do). Write this down 100 times: Brakes do not stop the car. Brakes convert kinetic energy (motion) into thermal energy (heat). What stops the car? TIRES! The coefficient of friction between the tires and the road. Why does it take more distance to stop when the road is wet or icy? It doesnt have anything to do with rotors, calipers, pad compounds or brake fluids. It has everything to do with the coefficient of friction between the tires and the road.
So, to decrease stopping distances you really have only 2 options:
Press the brake pedal harder. This only works until just before the tires lock up (max deceleration). Beyond that you just get a sore leg.
Increase the coefficient of friction between the tire and road.
There are four ways to increase the tires grip on the road. All of these not only help braking, but also accelerating and cornering.
1. Use stickier tires.
2. Use wider tires.
3. Drive on a stickier road (ie stay in the racing groove).
Increase the vertical load on the tires.
Vertical load on the tire increases traction. To prove it, hold a pencil with it's eraser on the table while you slide it across the table. Now, lean on the pencil and try to push it across the table. The eraser has a better grip on the table when you are pushing down on it, right? Vertical load is also why your front brakes do 80% of the work. Most of the car's weight is transferred to the front.
How do we increase vertical load? Obviously, we don't add weight to the car. That is counter to everything we know about going fast. Aerodynamic downforce! Unfortunately, effective aerodynamic downforce is tough to achieve at city speeds and it is not a proportional relationship. Doubling the downforce does not double the grip. There are practical limits.
So, why would anyone upgrade to larger brakes?
1. If your car is heavy, with wide, sticky tires and small rotors, you may not be able to achieve maximum deceleration or lock up the brakes, therefore you need bigger rotors. (this is rarely the case)
2. If you are converting too much kinetic energy into thermal energy and it is warping your rotors, causing your pads to fade, boiling your brake fluid or causing a fire. You need cooling ducts, larger rotors and/or other upgrades.
3. You just wanna look cool (and who doesnt?).
Bottom line: Dont expect shorter stopping distances thru brake upgrades. The practical reason for doing it is for thermal management.
But CR, what about brake fade??
For all but serious track duty (or descending Mt. Washington), brake fade is not an issue. But lets say you take your stock Mazda with OEM pads to the track. Generalizations are always dangerous, but typically the coefficient of friction (Cf) of OEM pads varies from 0.3 to 0.1 with temperature. Meaning as temperature increases, Cf decreases. And lets say after several laps the Cf drops to 0.1 and the brakes can no longer achieve max deceleration no matter how much clamping pressure is applied, then yes, you need to address the brakes. Now what to do? We are good engineers so we only change one thing at a time, so what are our options?
1. Bigger rotors? Larger rotors will take longer to heat up, but the problem will come back in a few laps.
2. Narrower, less sticky tires? This will help, but its counter to our goal of quick lap times.
Cooling ducts? These will work if they can provide enough air to keep the temps down and the Cf up.
Race Pads? Quality race pads have a very stable Cf over a wide temperature range - ie no fade. The result is the rotor temp will climb past where it leveled out with the OEM pad as you work them hard lap after lap. This only becomes a problem if the temp causes the fluid to boil or the rubber brake hoses to melt, etc.
The temperature of the rotors has no impact on braking distance. Youve seen red-hot rotors in night races, right? This doesnt mean the brakes arent working. As long as that temperature can be managed and it doesnt harm the brake components, the brakes will do their job.
But CR, bigger rotors and larger calipers provide a larger surface area. Wont that provide a larger friction force?
Yes, larger rotor, more pad surface area, high friction pads will all make the wheel stop sooner. Where you went off track is assuming the car stops when the wheel's rotational speed reaches zero. This assumes the tires don't skid. Unfortunately, this is not the case.
Let's look at this from a different angle. Some of you guys do the 1/4 mile thing and have figured out that the most important parts to low ETs is the launch and hooking up. Obviously, easing into the throttle doesn't yeild fast ETs, nor does smoking the tires off the line. Maximum grip occurs at 10% slip, ie when the tires are rotating 10% faster than they would if they were rolling freely. For a given tire, the fastest theoretical 1/4 mile time would occur if you could maintain 10% slip (max grip) over the entire 1/4 mile, right? Unfortunately, you would need a gazzillion hp. Most cars can only maintain that 10% slip for a short distance. Thats why you look at 60ft times. Assuming you weren't caught sleeping at the line, the 60ft time is a measure of how well the tires are hooking up. Beyond 60ft, the engine is responsible for the speed of the car and the tires are just along for the ride. So wouldn't you agree that if your engine were able to keep the tires at 10% slip for the entire run, any increase in hp would not yeild faster times? Any additional power would cause the wheels to spin and slow the car. If you wanted lower ETs you would have to use bigger tires, stickier tires or increase down force.
Fortunately, the rubber molecules in your tires are dumb, they don't know if you are braking or accelerating. Max grip during braking also occurs at 10% slip (wheel rotating 10% SLOWER than if it were rolling free - sounds alot like ABS). If your current brakes can maintain 10% slip for the entire braking distance, any additional braking would cause the wheels to skid and increase the braking distance. If you want to decrease the distance you would have to use bigger tires, stickier tires or increase down force.
All the magic happens where the rubber meets the road.
But CR, what about all those magazines with reviews of big brake kits with shorter stopping distances?
Have you ever seen one where they dont change the tires? They always include a wider, stickier tire that show off or compliment their brake kit. Is it possible the after-market is motivated to over-state the performance of their products just to make money? Say it isn't so!
You have to understand the basis of comparison in order to evaluate a product. Which generally means - change one thing at a time for a controlled comparison. If you increase the rotor size, number of pistons, width of tire and pad Cf all at once, how do you know what is responsible for the change in performance?
Think of brake upgrades as adding braking HP (or capability) to your car. It is alot like adding engine HP. The difference is your stock brakes are perfectly capable of providing that max deceleration so more braking HP doesnt stop sooner. Conversely, your stock engine cant provide max grip over a 1/4 mile so more HP makes a difference.
People often report a sensation of improved brake performance after a brake upgrade. They notice improved pedal feel, a sense that the brakes are more willing or capable of stopping the car, etc. All this is true, but unless there are changes at the contact patch, braking distances will be unchanged.
I'm not condemning anyone's decision to go really big. I'm just saying, understand what you're getting for your money.
QUOTE=CanyonRider = THE BIG BRAKE MYTH!
Having read many threads on many forums debating this very subject, I thought Id share my thoughts based on engineering principles and the laws of physics.
Before you run out and buy 6-piston calipers, two-piece carbon fiber rotors and 50 feet of stainless steel braided brake line, it would be wise to take a closer look at what brakes do (and dont do). Write this down 100 times: Brakes do not stop the car. Brakes convert kinetic energy (motion) into thermal energy (heat). What stops the car? TIRES! The coefficient of friction between the tires and the road. Why does it take more distance to stop when the road is wet or icy? It doesnt have anything to do with rotors, calipers, pad compounds or brake fluids. It has everything to do with the coefficient of friction between the tires and the road.
So, to decrease stopping distances you really have only 2 options:
Press the brake pedal harder. This only works until just before the tires lock up (max deceleration). Beyond that you just get a sore leg.
Increase the coefficient of friction between the tire and road.
There are four ways to increase the tires grip on the road. All of these not only help braking, but also accelerating and cornering.
1. Use stickier tires.
2. Use wider tires.
3. Drive on a stickier road (ie stay in the racing groove).
Increase the vertical load on the tires.
Vertical load on the tire increases traction. To prove it, hold a pencil with it's eraser on the table while you slide it across the table. Now, lean on the pencil and try to push it across the table. The eraser has a better grip on the table when you are pushing down on it, right? Vertical load is also why your front brakes do 80% of the work. Most of the car's weight is transferred to the front.
How do we increase vertical load? Obviously, we don't add weight to the car. That is counter to everything we know about going fast. Aerodynamic downforce! Unfortunately, effective aerodynamic downforce is tough to achieve at city speeds and it is not a proportional relationship. Doubling the downforce does not double the grip. There are practical limits.
So, why would anyone upgrade to larger brakes?
1. If your car is heavy, with wide, sticky tires and small rotors, you may not be able to achieve maximum deceleration or lock up the brakes, therefore you need bigger rotors. (this is rarely the case)
2. If you are converting too much kinetic energy into thermal energy and it is warping your rotors, causing your pads to fade, boiling your brake fluid or causing a fire. You need cooling ducts, larger rotors and/or other upgrades.
3. You just wanna look cool (and who doesnt?).
Bottom line: Dont expect shorter stopping distances thru brake upgrades. The practical reason for doing it is for thermal management.
But CR, what about brake fade??
For all but serious track duty (or descending Mt. Washington), brake fade is not an issue. But lets say you take your stock Mazda with OEM pads to the track. Generalizations are always dangerous, but typically the coefficient of friction (Cf) of OEM pads varies from 0.3 to 0.1 with temperature. Meaning as temperature increases, Cf decreases. And lets say after several laps the Cf drops to 0.1 and the brakes can no longer achieve max deceleration no matter how much clamping pressure is applied, then yes, you need to address the brakes. Now what to do? We are good engineers so we only change one thing at a time, so what are our options?
1. Bigger rotors? Larger rotors will take longer to heat up, but the problem will come back in a few laps.
2. Narrower, less sticky tires? This will help, but its counter to our goal of quick lap times.
Cooling ducts? These will work if they can provide enough air to keep the temps down and the Cf up.
Race Pads? Quality race pads have a very stable Cf over a wide temperature range - ie no fade. The result is the rotor temp will climb past where it leveled out with the OEM pad as you work them hard lap after lap. This only becomes a problem if the temp causes the fluid to boil or the rubber brake hoses to melt, etc.
The temperature of the rotors has no impact on braking distance. Youve seen red-hot rotors in night races, right? This doesnt mean the brakes arent working. As long as that temperature can be managed and it doesnt harm the brake components, the brakes will do their job.
But CR, bigger rotors and larger calipers provide a larger surface area. Wont that provide a larger friction force?
Yes, larger rotor, more pad surface area, high friction pads will all make the wheel stop sooner. Where you went off track is assuming the car stops when the wheel's rotational speed reaches zero. This assumes the tires don't skid. Unfortunately, this is not the case.
Let's look at this from a different angle. Some of you guys do the 1/4 mile thing and have figured out that the most important parts to low ETs is the launch and hooking up. Obviously, easing into the throttle doesn't yeild fast ETs, nor does smoking the tires off the line. Maximum grip occurs at 10% slip, ie when the tires are rotating 10% faster than they would if they were rolling freely. For a given tire, the fastest theoretical 1/4 mile time would occur if you could maintain 10% slip (max grip) over the entire 1/4 mile, right? Unfortunately, you would need a gazzillion hp. Most cars can only maintain that 10% slip for a short distance. Thats why you look at 60ft times. Assuming you weren't caught sleeping at the line, the 60ft time is a measure of how well the tires are hooking up. Beyond 60ft, the engine is responsible for the speed of the car and the tires are just along for the ride. So wouldn't you agree that if your engine were able to keep the tires at 10% slip for the entire run, any increase in hp would not yeild faster times? Any additional power would cause the wheels to spin and slow the car. If you wanted lower ETs you would have to use bigger tires, stickier tires or increase down force.
Fortunately, the rubber molecules in your tires are dumb, they don't know if you are braking or accelerating. Max grip during braking also occurs at 10% slip (wheel rotating 10% SLOWER than if it were rolling free - sounds alot like ABS). If your current brakes can maintain 10% slip for the entire braking distance, any additional braking would cause the wheels to skid and increase the braking distance. If you want to decrease the distance you would have to use bigger tires, stickier tires or increase down force.
All the magic happens where the rubber meets the road.
But CR, what about all those magazines with reviews of big brake kits with shorter stopping distances?
Have you ever seen one where they dont change the tires? They always include a wider, stickier tire that show off or compliment their brake kit. Is it possible the after-market is motivated to over-state the performance of their products just to make money? Say it isn't so!
You have to understand the basis of comparison in order to evaluate a product. Which generally means - change one thing at a time for a controlled comparison. If you increase the rotor size, number of pistons, width of tire and pad Cf all at once, how do you know what is responsible for the change in performance?
Think of brake upgrades as adding braking HP (or capability) to your car. It is alot like adding engine HP. The difference is your stock brakes are perfectly capable of providing that max deceleration so more braking HP doesnt stop sooner. Conversely, your stock engine cant provide max grip over a 1/4 mile so more HP makes a difference.
People often report a sensation of improved brake performance after a brake upgrade. They notice improved pedal feel, a sense that the brakes are more willing or capable of stopping the car, etc. All this is true, but unless there are changes at the contact patch, braking distances will be unchanged.
I'm not condemning anyone's decision to go really big. I'm just saying, understand what you're getting for your money.
Perro del Sol
Member
- :
- 2003 MSP, Spicy Orange, 2004 Mazda 6 Hatch, 2004 Mazda 6 Wagon
One of the best articles I have read to date, simple and precise.......
While i can't comment on our current situation here, we had a similar situation. Things will work out eventually. Think of it as a challenge!
I'm not worried about it, just means job security and some extra cash for me.
Hope everyone is doing well. Wish I weren't getting kicked in the balls by life so much and could A bs with you all on here more often B come hang with you
Also looks like I'm gonna get to tear apart a car in the near future. If anyone wants to come wrench on her to help me, I'd greatly appreciate it
Also looks like I'm gonna get to tear apart a car in the near future. If anyone wants to come wrench on her to help me, I'd greatly appreciate it
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Yes! Fiat is Angelo, Smart was Maxwell, Green Miata is Lee.... but I haven't named ALL of my cars, lol.
Thank you. Everyone rails on me for not putting a BBK on the V8 Miata. I said give it time. I don't need it right this second, I'll see where the sport rotors and HP+ put me. Besides, I'm not anywhere near driving the damn car 10/10's to need crazy brakes.
