Subaru Enthusiasts Car Club of the Sierras - View Single Post

Dean · 2004-02-22, 06:25 PM

I appreciate your further description of brake operation, especially the tire dynamics.

I'm sorry you don't want to discuss theory, torque curves etc., but that is your choice.

Unless I am mistaken , the single 45mm stock piston has less surface area than 2x36mm and 2 x40mm Stoptech pistons. Unless my math is wrong, that is 222mm^2 vs. 2 x 177.6 + 2 x 197.4 = 750mm^2. You didn't provide piston ring diameter, but it is undoubtedly larger for the larger rotors which only going to make it worse. How does this shift bias 10% to the rear?

You may want to discuss leading edge temperatures and pressures a little more with your “brake manufacturers, brake designers and brake engineers” to better understand the "facts" behind leading piston size.

I quote from http://www.stoptech.com/whitepapers/glossary/t.htm

“Uneven wear of brake pads caused by geometry, by the difference in temperature between leading and trailing edges and/or by lack of stiffness in the caliper.”

In another article, they mention debris etc., but it only effects the system to “some extent” . Leading edge temperature is the primary issue.
From: http://www.stoptech.com/whitepapers/...ons_122701.htm

“The trailing area (portion) of the pad, to some extent "floats" on the entrapped gasses and particulate matter generated from the leading portion of the pad. The leading portion of the pad will always be hotter than the trailing portion and so will correspondingly, wear faster - resulting in a pad that is tapered when viewed from the edge. This phenomenon is termed "longitudinal taper".

The differential in heat generated across the pad surface, leading to trailing, is characteristic regardless of caliper and pad design. This is why all racing calipers and most high performance street calipers have differential piston bores. Most high performance pads also feature a tapered leading edge”

A good analogy I found in another technical paper on brakes might help explain it: http://www.dietersmotorsports.com/tech/2000/1-00.html

“The relationship between the pistons, brake pads, and rotors is not as simple as it seems. The caliper must load the brake on the trailing edge of the pad. This is done so the pad bites into the rotor evenly for more stopping power. Think of it as if you were moving a 100-pound bag of sand across a dirt lot. If you pull it behind you, the front of the bag will be up and skim across the top of the sand (greatest load to the rear), leaving an even trail behind you. If you get behind the bag and try to push it (greatest load to the front), you will cause the front of the bag to dig into the dirt and create a hole. In the case of the brakes, the leading edge of the pad would then see greatly increased uneven wear.”

Enough of that.

I can't believe you said this:

”Standing a car on it’s nose every time you hit the brakes IS the best, fastest way to get around the track. Regardless of being at maximum braking with ABS or maximum braking on your own, you should always be braking at your maximum in the braking zones (except while trailbraking).”

Perhaps you consider every corner entry where you want to set the front end of the car, or need to scrub a small amount of speed trail braking.

Can you honestly tell me that every time you press the brake pedal, you are trying to reach maximum braking potential, ABS or not for however short of a time?

2004-02-22, 06:25 PM	#135
Dean Señor Cheap Bastarde Real Name: Dean Join Date: May 2003 Location: $99 Tire Store Posts: 9,294 Car: $.04 STI Class: Fast,Cheap & Reliable=STI Deal, did somebody say Deal? Oh, Dean, yeah that's me.	I appreciate your further description of brake operation, especially the tire dynamics. I'm sorry you don't want to discuss theory, torque curves etc., but that is your choice. Unless I am mistaken , the single 45mm stock piston has less surface area than 2x36mm and 2 x40mm Stoptech pistons. Unless my math is wrong, that is 222mm^2 vs. 2 x 177.6 + 2 x 197.4 = 750mm^2. You didn't provide piston ring diameter, but it is undoubtedly larger for the larger rotors which only going to make it worse. How does this shift bias 10% to the rear? You may want to discuss leading edge temperatures and pressures a little more with your “brake manufacturers, brake designers and brake engineers” to better understand the "facts" behind leading piston size. I quote from http://www.stoptech.com/whitepapers/glossary/t.htm “Uneven wear of brake pads caused by geometry, by the difference in temperature between leading and trailing edges and/or by lack of stiffness in the caliper.” In another article, they mention debris etc., but it only effects the system to “some extent” . Leading edge temperature is the primary issue. From: http://www.stoptech.com/whitepapers/...ons_122701.htm “The trailing area (portion) of the pad, to some extent "floats" on the entrapped gasses and particulate matter generated from the leading portion of the pad. The leading portion of the pad will always be hotter than the trailing portion and so will correspondingly, wear faster - resulting in a pad that is tapered when viewed from the edge. This phenomenon is termed "longitudinal taper". The differential in heat generated across the pad surface, leading to trailing, is characteristic regardless of caliper and pad design. This is why all racing calipers and most high performance street calipers have differential piston bores. Most high performance pads also feature a tapered leading edge” A good analogy I found in another technical paper on brakes might help explain it: http://www.dietersmotorsports.com/tech/2000/1-00.html “The relationship between the pistons, brake pads, and rotors is not as simple as it seems. The caliper must load the brake on the trailing edge of the pad. This is done so the pad bites into the rotor evenly for more stopping power. Think of it as if you were moving a 100-pound bag of sand across a dirt lot. If you pull it behind you, the front of the bag will be up and skim across the top of the sand (greatest load to the rear), leaving an even trail behind you. If you get behind the bag and try to push it (greatest load to the front), you will cause the front of the bag to dig into the dirt and create a hole. In the case of the brakes, the leading edge of the pad would then see greatly increased uneven wear.” Enough of that. I can't believe you said this: ”Standing a car on it’s nose every time you hit the brakes IS the best, fastest way to get around the track. Regardless of being at maximum braking with ABS or maximum braking on your own, you should always be braking at your maximum in the braking zones (except while trailbraking).” Perhaps you consider every corner entry where you want to set the front end of the car, or need to scrub a small amount of speed trail braking. Can you honestly tell me that every time you press the brake pedal, you are trying to reach maximum braking potential, ABS or not for however short of a time? __________________ I am a Commodore PET --- Now get off my lawn you kids...