.
02-20-2012, 06:09 PM
#31
Rennlist Member
all interesting thoughts, but remembrer, two things are happening here. you are gettnig more braking force , with less presssure. so, first instict woudl be to increase rear bias, to match. however, in threshold braking, you get better modulation, so you are in effect able to put more pressure for longer. PLUS, as you go deep in a turn, get the fronts hotter than the rears, you can use more than double the predal pressure, while the rears are still realtively cool. suddenly, you are 2x the rear pressure on the rear discs, having 2x the rear braking force. start to trail brake and walla, in experienced racers will loop it and ask evderyone what the hell happened. 
so, as a rule, go very very weak for the rear brakes until you get real good at braking and really understand the forces.
anderson with 4 x 330 real slicks is not really relavant, but what im running kind of approaches the topic with performance that better matches the goals here. by the way, ive been racing 9.5 and 11" rims and now 10s and 11". 275s and 305s and now 305s on all 4s in a DOT racing slick
so, as a rule, go very very weak for the rear brakes until you get real good at braking and really understand the forces.
anderson with 4 x 330 real slicks is not really relavant, but what im running kind of approaches the topic with performance that better matches the goals here. by the way, ive been racing 9.5 and 11" rims and now 10s and 11". 275s and 305s and now 305s on all 4s in a DOT racing slick
02-20-2012, 06:17 PM
#32
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they look great. so the pad sits down in the caliper further, but are you or brembo worried about the off center pressure of the pistons on the pad. or uneven wear?? nice idea though. now, im rethinking using the 355mm cayanne rotors again. the caliper raidus issue was killing the idea for me.
Best about this setup is weight: about 1lb difference than the stock S4 rotor. I imagine the full 355mm iron Cayenne rotor is quite heavy.
Mark
02-20-2012, 06:19 PM
#33
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For reference, here's the 355mm setup I came up with using a Big Black(red) caliper vs the 996TT stock front rotor.
Last edited by MarkRobinson; 02-27-2012 at 03:27 PM.
02-20-2012, 06:21 PM
#34
Rennlist Member
true dat!
i ran the first 2 races in speedGT with s brakes and racing pads. im sure they could stop the car as well as ANYTHING discussed here. however, to your point, dive down into turn 2 at laguna at 135 and try and slow to 40mph, and you are going to have some big fade. from 120, not so much.
the other thing that big brakes buys , is control and modulation.
no substitute for running the brakes correctly. ill never forget a guy that really started to shine after his first year of racing but had a beast of a car (evo with 400rwhp). he was running 4 seconds slower, but complainng of brake fade. so much that he was pulling the entire sytem off the car and changing out pads and rotors. his system was almost 2x the mass of mine. any brake system will fail if you dont use it right.
i ran the first 2 races in speedGT with s brakes and racing pads. im sure they could stop the car as well as ANYTHING discussed here. however, to your point, dive down into turn 2 at laguna at 135 and try and slow to 40mph, and you are going to have some big fade. from 120, not so much.
the other thing that big brakes buys , is control and modulation.
no substitute for running the brakes correctly. ill never forget a guy that really started to shine after his first year of racing but had a beast of a car (evo with 400rwhp). he was running 4 seconds slower, but complainng of brake fade. so much that he was pulling the entire sytem off the car and changing out pads and rotors. his system was almost 2x the mass of mine.
any brake system will fail if you dont use it right.Many differences between 928 race cars and street cars. While stock 928s are 50/50 weight the stripped out racers are closer to 60% front 40% rear. True race tires what ever size have so much more stick and fronts are usually much wider.
The bigger brakes are not going to stop Sterlings car any quicker the limiting factor is his tires. Huge brakes are only needed for repeated high speed "panic stops" . Bottom line on brakes is if you have enough clamp from the caliper to rotor to lock up tires that determines how much energy the brake system can absorb. Much like if you have enough horsepower to spin the tires more horsepower does not make you accelerate faster. You have exceeded the available traction of the tires.
But big brakes and rotors look good and that is often all that matters on a street car.
The bigger brakes are not going to stop Sterlings car any quicker the limiting factor is his tires. Huge brakes are only needed for repeated high speed "panic stops" . Bottom line on brakes is if you have enough clamp from the caliper to rotor to lock up tires that determines how much energy the brake system can absorb. Much like if you have enough horsepower to spin the tires more horsepower does not make you accelerate faster. You have exceeded the available traction of the tires.
But big brakes and rotors look good and that is often all that matters on a street car.
02-20-2012, 06:25 PM
#35
Rennlist Member
Pro-am (Brembo's hat mfr) has seen it mutiple times, though best advice was to try it & see about odd wear. with 1k break-in miles on soft pads, couldn't see any visible oddities but still, was only 1k miles.
Best about this setup is weight: about 1lb difference than the stock S4 rotor. I imagine the full 355mm iron Cayenne rotor is quite heavy.
Mark
Best about this setup is weight: about 1lb difference than the stock S4 rotor. I imagine the full 355mm iron Cayenne rotor is quite heavy.
Mark
caynanne rotors are about 23lbs and i think the S4 are 18lbs, right?
your next picture is the GTS diameter rotor, which are 330mm with the big blacks, for those playing at home.
however, ill take on 5 lbs of rotor weight any day of the week, that small in diameter, to save 200 bucks a rotor change. i get the cayanne rotors for about 95 bucks each. what are those outer rings costing each??
(and you have to buy hats too. ) but, i would be more inclided to use them for their ability to resist warping vs the solid rotors
02-21-2012, 10:14 AM
#36
Developer
I think the standard F50 setup uses 355x32, which is what I used as well.
Details here: http://www.928motorsports.com/parts/gt1_brake_kit.php
However - I am a kit builder and I have to keep an eye for the broadest range of installation applications. The 355 with a 4-piston caliper will fit under virtually all 18" wheels, and with a 6-piston caliper it will fit under some (not all) 18" wheels.
But Sterling is running 19's or 20's (guessing by looking at the picture) so he could do a one-of application on his car that is even bigger.
We are using 322mm on the rear - but there is room for more there too.
02-21-2012, 10:16 AM
#37
Developer
I thought this dictionary from our GT1 brake kit page may help some of the readers:
TERMS:
ROTOR DIAMETER: the easiest part of the upgrade to see. Larger diameter rotors Increase the thermal mass (decreasing brake fade) and improves stopping power by increasing the effective radius (see below). And they look AWESOME through aftermarket 18" wheels!
EFFECTIVE RADIUS: the benefit received when using a longer wrench to turn a tough bolt. In this case, using a longer wrench to stop the rotor from spinning. The longer the effective radius of the caliper/rotor combination, the more powerful the brakes. Not the same as the radius of the rotor, but the distance from the center of the rotor to the center of the caliper piston.
ROTOR WEIGHT: although increased thermal mass helps decrease brake temps, increased weight means more unsprung weight and higher rotational inertia - both which hurt performance. The answer is a two-piece rotor/hat combination that gives the rotor the thermal mass it needs, but lightens the assembly for less unsprung weight and inertia.
A WORD ABOUT 4-PISTON vs. 6-PISTON CALIPERS
We selected 4-piston calipers for our GT1 kit, and this is why:
There is a common misconception that 6-piston calipers have better stopping power than 4-piston calipers. That isn't true. The increase in stopping power comes from the increase in rotor diameter, effective radius, and the hydraulic gain of the system. Brake pad size and the number of pistons in the caliper have nothing to do with braking effectiveness.
Most 6-piston calipers flex more, cost more, and fit inside fewer wheels - making wheel fitment a challenge. Brake pads for a 6-piston caliper also cost more, and are offered in only a few materials. The only merit they have is that the brake pad on a 6-piston caliper is larger, so they last longer between pad changes - which is a valuable feature if you are endurance racing. But, it also means they cost more at each pad change.
On the other hand, our Brembo 4-piston caliper is stiffer, and requires 10mm less of clearance than the 6-piston model, so it will fit inside virtually all 18" wheels. It has a broad selection of brake pads available for it, and they cost less. Additionally, the 4-piston caliper features the quick release pad design, which is a nice feature for customers tracking their cars.
TERMS:
ROTOR DIAMETER: the easiest part of the upgrade to see. Larger diameter rotors Increase the thermal mass (decreasing brake fade) and improves stopping power by increasing the effective radius (see below). And they look AWESOME through aftermarket 18" wheels!
EFFECTIVE RADIUS: the benefit received when using a longer wrench to turn a tough bolt. In this case, using a longer wrench to stop the rotor from spinning. The longer the effective radius of the caliper/rotor combination, the more powerful the brakes. Not the same as the radius of the rotor, but the distance from the center of the rotor to the center of the caliper piston.
ROTOR WEIGHT: although increased thermal mass helps decrease brake temps, increased weight means more unsprung weight and higher rotational inertia - both which hurt performance. The answer is a two-piece rotor/hat combination that gives the rotor the thermal mass it needs, but lightens the assembly for less unsprung weight and inertia.
A WORD ABOUT 4-PISTON vs. 6-PISTON CALIPERS
We selected 4-piston calipers for our GT1 kit, and this is why:
There is a common misconception that 6-piston calipers have better stopping power than 4-piston calipers. That isn't true. The increase in stopping power comes from the increase in rotor diameter, effective radius, and the hydraulic gain of the system. Brake pad size and the number of pistons in the caliper have nothing to do with braking effectiveness.
Most 6-piston calipers flex more, cost more, and fit inside fewer wheels - making wheel fitment a challenge. Brake pads for a 6-piston caliper also cost more, and are offered in only a few materials. The only merit they have is that the brake pad on a 6-piston caliper is larger, so they last longer between pad changes - which is a valuable feature if you are endurance racing. But, it also means they cost more at each pad change.
On the other hand, our Brembo 4-piston caliper is stiffer, and requires 10mm less of clearance than the 6-piston model, so it will fit inside virtually all 18" wheels. It has a broad selection of brake pads available for it, and they cost less. Additionally, the 4-piston caliper features the quick release pad design, which is a nice feature for customers tracking their cars.
02-21-2012, 10:27 AM
#38
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The $95 Cheyenne rotors are OE? I'd rather run on a slotted rotor designed for racing, at $200 ea they're not too bad: cheaper than OE Brembo's and designed for racing (RacingBrake.com). I wanted to retain my recently painted calipers (as I figured others would too) so I chose that route for my car.
I certainly understand the inexpensiveness of that rotor & don't question your experience at all, though the 2pc sure is light & looks pretty pro as well.
I certainly understand the inexpensiveness of that rotor & don't question your experience at all, though the 2pc sure is light & looks pretty pro as well.
