Drilled Por. Vs Solid Alcon rotars brake bias issue
06-04-2004, 08:19 AM
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Drilled Por. Vs Solid Alcon rotars brake bias issue
HI,
Had an interesting thing happen at NER Mt Tremblant DE last weekend.
I run 2300 lb GT1 car with 14" cup front and 12.75 S4 brakes rear. I started out with drilled Alcons rotors on the front and drilled Porsche on the rear. Due to wing, large rear tires and so forth I have always run a lot of rear brake. After about 8 track days the rear rotors were cracked to the outside edge and junk. We replaced with solid Alcon. We experenced a huge increase in rear braking. So much that could not dial out rear lock up with bias. We were running Padgit orange and had a set of the yellow ceramics that are suppose to have higher friction so but them in the front and still had too much rear. Last gasp was to grind three finger width grooves in rear pads to reduce surface area. That worked. So we are now changing rear master cylinder to reduce pressure. I was really surprised how HUGE a difference the change from drilled to solid made. Be aware if you make a similar change. Also for stock classes I would imagine this would be a good way to make adjustments.
Had an interesting thing happen at NER Mt Tremblant DE last weekend.
I run 2300 lb GT1 car with 14" cup front and 12.75 S4 brakes rear. I started out with drilled Alcons rotors on the front and drilled Porsche on the rear. Due to wing, large rear tires and so forth I have always run a lot of rear brake. After about 8 track days the rear rotors were cracked to the outside edge and junk. We replaced with solid Alcon. We experenced a huge increase in rear braking. So much that could not dial out rear lock up with bias. We were running Padgit orange and had a set of the yellow ceramics that are suppose to have higher friction so but them in the front and still had too much rear. Last gasp was to grind three finger width grooves in rear pads to reduce surface area. That worked. So we are now changing rear master cylinder to reduce pressure. I was really surprised how HUGE a difference the change from drilled to solid made. Be aware if you make a similar change. Also for stock classes I would imagine this would be a good way to make adjustments.
06-04-2004, 08:41 AM
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Bill, you can also change bias with pad compound changes front and rear.
I run a GT1R GT2 (which has ABS) and I still had way too much front bias.
I was running Pagid Black front and rear. I now run Pagid Orange in the front (which has less grip than the black) and run black in the rear. Now the balance has a little more rear bias than it did before.
Interesting about the drilled vs solid. I wonder if it is the difference in more surface area, or is it that the solid generates more heat and the oranges grip even better with more heat ?
Norm
I run a GT1R GT2 (which has ABS) and I still had way too much front bias.
I was running Pagid Black front and rear. I now run Pagid Orange in the front (which has less grip than the black) and run black in the rear. Now the balance has a little more rear bias than it did before.
Interesting about the drilled vs solid. I wonder if it is the difference in more surface area, or is it that the solid generates more heat and the oranges grip even better with more heat ?
Norm
06-04-2004, 09:24 PM
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Solid is less heat, not more, due to far more thermal mass, and the difference is likely totally because of the difference in swept surface area. Thanks for posting your account, maybe some of the people in the 944 forums will believe me now when I say drilled rotors are solely an appearance mod!
Sam
Sam
06-05-2004, 08:39 AM
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Hi Sam and Norm,
Sam, I don't know if I agree with you RE solids running cooler due larger heat sink. I've always thought that the drilled holes were to due due 2 things one eliminate build up of gases between pad and rotor and distribute cooling air across more surface area to reduce heat.
Norm, I did try a higher friction compound (yellow) on the front but it was not enough to stop the rears from locking up first.
As an interesting note. The yellow's we switched to in the fronts showed signs of much higher heat sooner than the orange I was running (IE the whole edge of the pad to the backing plate white-ish and the backing plate yellow paint turned a muddy brown and we had some material transfer to the rotors. I useually don't see the backing plates on the orange pads turn color until I'm 50% through the pad.
As a general FYI for all; Below is the pitch from a commercial web site on the 3 Pagid compounds.
I don't know if I agree with them on the Orange as just a DE pad. They did a nice job for me when I was running a 400 lb heavier car with smaller brakes (993TT front and 89turbo frt on the rear of car shown below). They definitely do make rotors last.
Black (RS14): This is the most aggressive of the three compounds. It has the highest friction coefficient and fade resistance. These pads are best in sprint races where maximum stopping power is needed, and for cars that are very hard on brakes. They offer decent pad life, but are the hardest on rotors.
Yellow (RS19): This is the endurance compound. The friction coefficient is less than the black, but higher than Orange. They are ideal for endurance races where maximum braking is not needed, and for cars that are medium hard on brakes. These pads are relatively easy on rotors and have the longest pad life of the three. We use these pads on Grand-Am Rolex / Cup series cars.
Orange (RS4-4): This is primarily a Driver's Ed Pad. The friction coefficient and maximum temperature are less than the Yellow and well below Black. These pads offer good stopping power, but when overheated have a tendency to 'melt' and deposit pad material into the rotor. This causes the sensation of severely warped rotors. They are easy on rotors and have decent pad life within their operating range. Only cars that are easy on brakes should use these pads; otherwise we recommend Yellow or Black.
regards,
Sam, I don't know if I agree with you RE solids running cooler due larger heat sink. I've always thought that the drilled holes were to due due 2 things one eliminate build up of gases between pad and rotor and distribute cooling air across more surface area to reduce heat.
Norm, I did try a higher friction compound (yellow) on the front but it was not enough to stop the rears from locking up first.
As an interesting note. The yellow's we switched to in the fronts showed signs of much higher heat sooner than the orange I was running (IE the whole edge of the pad to the backing plate white-ish and the backing plate yellow paint turned a muddy brown and we had some material transfer to the rotors. I useually don't see the backing plates on the orange pads turn color until I'm 50% through the pad.
As a general FYI for all; Below is the pitch from a commercial web site on the 3 Pagid compounds.
I don't know if I agree with them on the Orange as just a DE pad. They did a nice job for me when I was running a 400 lb heavier car with smaller brakes (993TT front and 89turbo frt on the rear of car shown below). They definitely do make rotors last.
Black (RS14): This is the most aggressive of the three compounds. It has the highest friction coefficient and fade resistance. These pads are best in sprint races where maximum stopping power is needed, and for cars that are very hard on brakes. They offer decent pad life, but are the hardest on rotors.
Yellow (RS19): This is the endurance compound. The friction coefficient is less than the black, but higher than Orange. They are ideal for endurance races where maximum braking is not needed, and for cars that are medium hard on brakes. These pads are relatively easy on rotors and have the longest pad life of the three. We use these pads on Grand-Am Rolex / Cup series cars.
Orange (RS4-4): This is primarily a Driver's Ed Pad. The friction coefficient and maximum temperature are less than the Yellow and well below Black. These pads offer good stopping power, but when overheated have a tendency to 'melt' and deposit pad material into the rotor. This causes the sensation of severely warped rotors. They are easy on rotors and have decent pad life within their operating range. Only cars that are easy on brakes should use these pads; otherwise we recommend Yellow or Black.
regards,
06-05-2004, 05:10 PM
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Drilled holes used to be there to give pad outgassing a place to go. That's totally a thing of the past now, past the initial bedding in, modern pads don't outgas any more. They do zip/zero/nada/zilch for cooling, cooling air flows from center out in a rotor, it's not going to turn 90' and flow axially through the holes when all forces are radial. They're totally an appearance mod, they've got a negative effect on both performance and durability. The thermal mass lost from the drilled holes can amount to 10-20% mass and a small amount of lost swept area. ~10% more swept area combined with 20% lower temps is what threw off your bias.
Sam
Sam
06-07-2004, 03:23 AM
#7
Rather than using different front/rear pads (whose frictional characteristics might change according to existing temp. conditions and wear), how about an adjustable proportioning valve in the rear circuit or a proper balance bar in a dual master cylinder pedal assembly to provide the desired front/rear braking balance you're after?
RE: Better braking w/undrilled rear rotors. Maybe it's the swept area of an undrilled rotor - there's more surface area to absorb heat than a holy rotor. Here's an analogy:
When placing wire mesh or screens in front of an air inlet, you can determine the effective air opening by calculating the length and width of wires x the number of vertical/horizontal strands, then deduct this figure from the intake opening area. Smaller mesh size and thick wire pose the most restriction. That's the tradeoff for preventing things that shouldn't enter.
Whereas in a drilled rotor, you add the area of all drilled holes, then subtract it from the total braking area of a rotor. That's the effective braking surface area - always less with drilled holes.
Sherwood
http://members.rennlist.org/911pcars
RE: Better braking w/undrilled rear rotors. Maybe it's the swept area of an undrilled rotor - there's more surface area to absorb heat than a holy rotor. Here's an analogy:
When placing wire mesh or screens in front of an air inlet, you can determine the effective air opening by calculating the length and width of wires x the number of vertical/horizontal strands, then deduct this figure from the intake opening area. Smaller mesh size and thick wire pose the most restriction. That's the tradeoff for preventing things that shouldn't enter.
Whereas in a drilled rotor, you add the area of all drilled holes, then subtract it from the total braking area of a rotor. That's the effective braking surface area - always less with drilled holes.
Sherwood
http://members.rennlist.org/911pcars
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06-07-2004, 11:55 AM
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my stock rotors have developed a lip after many 1000's of miles of driving and track days, and now i'll need to get new rotors soon. where can i get solid (non x-drilled) or perhaps slotted rotors for OEM 996 brakes?
btw i heard slotted accomplishes the same goal of drilled rotors but without losing as much surface area or mass
btw i heard slotted accomplishes the same goal of drilled rotors but without losing as much surface area or mass
06-07-2004, 02:48 PM
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For what it's worth, I'll chime in on the Pagid brake pads. I have used the different compounds and for the short races we do in PCA, the RS-14 Blacks are the best. I understand they are tough on a rotor, but if they are better at stopping the car and you want to win, then isn't a rotor a dispensable item?
06-07-2004, 04:48 PM
#10
Bill935K3,
Sorry I must have totally blanked out reading your initial post. You already tried changing rear brake bias; you slotted the rear rotors to reduce surface area; you're going to change the rear master cylinder.
I think you've got it covered. The only thing I can add is to suggest additonal rear brake cooling, perhaps with inline blowers.
Sherwood
Sorry I must have totally blanked out reading your initial post. You already tried changing rear brake bias; you slotted the rear rotors to reduce surface area; you're going to change the rear master cylinder.
I think you've got it covered. The only thing I can add is to suggest additonal rear brake cooling, perhaps with inline blowers.
Sherwood
