Dr Chill

Just curious what you guys thought. Assuming use on a high speed track, with the same car and the ideal tire/pad/duct setup.

4 piston Brand X caliper with 14" rotor or
6 piston caliper same brand with 13" rotor

Which is more important to stopping power and to fade resistance-number of pistons or rotor size?

My thoughts are the larger rotor will allow for more heat dissipation and less fade, but the 6 piston with the larger friction area would stop better. But the larger rotor should theoretically provide better brake torque. Who really knows?

AU N EGL

4 and 6 postion units are more for endurance racing and fade reistance, not neccessarely better stopping.

I have driven lots of 6 pots with big 14" rotors (with Padget race pads ) on avererage size 265-285 front tires, and the car stopped like chit

Keeping the 13" rotor keeps the rotation wt down and going to a 305 or 315 front tire will helps stopping dramticly.
So one needs to look at more then pistion numbers, pistion size and rotor size.

Look also at your front tire width and age of the rubber.

bobmoore2

Even the basic stock Corvette brakes can make the tires skid or engage the ABS, so you already have more braking torque than the tires can handle. If you want to stop quicker, then you need to increase the grip by putting bigger/stickier tires up front.

A bigger problem for our cars (especially on the track) is brake fade. If you want to prevent/reduce brake fade, then your brake system needs to dissipate heat as quickly as possible. Larger rotors will slightly improve heat dissipation, because their larger surface area transfers heat to the air better. Larger calipers also dissipate heat better for the same reason. However, if you really want to improve heat dissipation you need to get more air flow through your rotors. Therefore, the first thing you should do to your brake system is installing a good set of brake ducts. I know this from personal experience on the track.

DRM makes an excellent brake duct kit for Corvettes. Be sure you also get some good spindle ducts, to ensure the air goes directly into the rotors.

Bob

Dr Chill

Tom and Bob,

Thanks for your replies and I agree wholeheartedly with both of you. However, I am asking the question assuming the car has both full ducting and large good tires. I want to take this out of the equation. That being the case, what is your answer to the question?

AU N EGL

Stoptech BBKs with 14" slotted rotors. Hawk DTC70 front and 60 rear pads. Double master cylinders.
Then a Wilwood 6 pot front on 14" rotors

I have not driven AP Racing or Alcons. I have driven lots and lots of Brembos and I choose Stoptech and Wilwood over Brembo

John Shiels

you have to many variables to ever make a clear decision like master size, rotor design, caliper design. 2 or 4 pistons will not matter that much it will matter how it applies the froce to the rotor. Grand Am is all 4 piston calipers. People in WC are not running 14" and 15" for no reason. 14 is the way to go for the best braking in a general statement. I have the 13" and Wilwood from LGM. Let me run two piece rotors or NAPA. I also can use my 17" wheels.

Dr Chill

So, for stopping power and fade resistance in general, not relating to any particular brand, if you had to choose a larger rotor or more pistons, you'd choose more rotor?

gkmccready

More pistons covering the same surface area with the same M/C can't generate any more force than fewer pistons of the same surface area being displaced by the same amount of fluid, right?

A larger rotor gives you more leverage as well as more mass to dissipate the heat.

If you were willing to change the M/C and go to more, larger, pistons to increase the clamping force that may be a different story...

(This is theory from reading; somebody can likely explain it based on experience.)

davidfarmer

pistons have NO effect on performance, only used for reducing the size of the caliper and helping pad taper.

PROPER piston sizing (for bias) and thermal mass (ie larger rotors and good cooling) are what give you performance stop after stop.

Independent1

From everything I have read stopping power is not the issue with any of the braking systems out there, including the stock brakes. Every single one of them can lock the tires up. The limit to stopping power is tire traction. I would imagine even with race tires all the braking systems could lock up the tires.

The bigger issue is the ability of the brakes to repeatedly work at their maximum (i.e., no fade). As other posters have already stated there are a lot of factors that affect how hot the brakes get. Theoritically, all other factors the same, the bigger rotors should have less fade because they can handle more heat. This assumes the amount of heat produced is too great for the smaller rotors, which may not be the case.

I assume there is a reason you asked this question. If you have had brake fade problems there could be a lot of other reasons besides the size of the rotors or number of pistons that led to the fade such as not enough cooling air, bad choice of brake pads, wrong or contaminated brake fluid, etc.

Dr Chill

I need to choose between allocating my $$ toward 4 piston/370mm rotor setup or 6 piston/342mm rotor setup. Both cost the same. The recurring costs will be higher with the 6 piston setup. I'm leaning toward the larger rotors and 4 pistons at the moment.

ghoffman

You need more catagories.

John Shiels

what is the pad shape and thickness of each set up?

Dr Chill

4 piston caliper-18mm thick, 75.5 sq cm area


6 piston caliper-18mm thick, 106 sq cm area

Dr Chill

Gary, I think if you pick one of the four choices in the poll, the attribute for the other is determined too (ie if you say the 4 piston stops better, the 6 piston must stop worse).

Did you see the DPI Recirculator system I posted in the other thread? It looks very easy to do. I did a little reseaech on how ABS actually works, and I don't think a recirculator system will have any effect on it.

I'd love to go with the PFC ZR33 calipers with the thick pads, but they are just too expensive and lack the bling factor for the street. I'd be lying if I didn't confess this was important to me too.

Notice the wider friction surface than most of the other companies.
6 piston monobloc/370mm x 35mm rotor with 4mm cast holes under 18" Z06 rims

4 piston monobloc/342mm x 32mm rotor with 4mm cast holes

AU N EGL

If you really want to stop your car, screw the bling factor

as Farmer said. Pistion size has nothing to do with stopping power.

It is funny when I watch the Speed World challange GT race at Lowes motorspeed way from the Pits, all the calipers had fade excpt one.

Now granted these cars were doing 160 down to 40 mph twice per lap every 1:12 ( I will post that video of blazing brakes tomorrow)

The only caliper that DID NOT HAVE fade was the one you dont want, the PFC caliper on the porshces. Of course the porshces braked 10 feet sooner and weight less then all the other cars.

Dr Chill

It's not that I don't want them, I can't afford them.

Calipers $1350 each, rotors $400 each, brackets $200 each, pads $300/axle= Front brake kit $4200 plus shipping.

My car is not a WC car racing for money. It's a street car that does 10 track days a year. No need for bling, unless it's functional bling.

J Ritt

The size of the pad isn't going to do anything to affect "stopping power." That term is actually meaningless.

1. A bigger rotor will give you increased thermal capacity, the primary benefit of a big brake system. So, all other things held equal, a bigger rotor will always be more resistant to fade from repeated stops as you would see on a racetrack (assuming the metallurgy, internal vane design, etc. are the same between the two rotors under comparison). So, if you were looking at a 14" or 15" rotor of the same width, same design, same ducting, same caliper, etc., the 15" would always have more thermal mass and resistance to fade.
Thermal mass can be had by thickness as well however. In our systems, we sometimes use a smaller diameter and a thicker width to accomplish similar tasks. Overall though, because of the way the heat is stored and flows, a larger diameter is more effective at removing heat from the system.

2. The number of pistons doesn't really tell you anything by itself. Force output should be your main concern. The total piston area of all pistons combined, rotor diameter, and coeffiicient of friction of the pad are the three determinants of torque output. All else held equal, changing any one of those factors will change the force output on that axle, and change the brake balance of the car.
On our systems, it works like this:
A. Figure out what the stock torque output is on a given axle of the car by looking at the piston bores, rotor diameter, and pad compound.
B. Since we're looking to increase thermal mass with the brake system, we go to a larger diameter (and many cases thicker) rotor as described above in point 1. That's where you get the bulk of your heat capacity in the system.
C. Since the rotor diameter is going up, we need to put a caliper on that rotor that has a smaller overall total piston area than the stock setup to offset the larger rotor diameter (let's assume in this case that we use a four piston on a 14" rotor). If we used the stock total piston area, the torque output on that axle would be overamplified (since the rotor diameter went up, creating a longer lever arm on which the caliper operates). The brakes on that axle would be doing more of their intended share of the total work they were designed to do when combined with the stock brakes on the other axle of the car, the stock master cylinder, and pedal assembly. As a side benefit...when the pistons are properly sized (smaller), you get less brake fluid displacement into the caliper, which gives better pedal feel.
D. Now, let's say we have the same setup, but we go to a 15" rotor. What happens? We have to go down on piston sizing to counteract the rotor diameter increase.
E. What if we go to a six piston caliper? Piston area is the concern, not pad surface area. I'll bold this so it's clear, total pad area does not affect the brake torque on the axle, or what people generically refer to as stopping power. On our corvette systems, assuming the same rotor diameter, the torque output of our four and six piston calipers would be the same. So, you have six smaller pistons, rather than four larger ones...torque output/clamping force is the same...despite the pad surface area. So what is the benefit then of a six piston caliper?
F. Pad volume. A six piston caliper typically can hold a larger pad with a total overall volume/mass. The mass of the pad impacts its ability to hold heat, just like the mass of the rotor. So, a greater pad volume would be beneficial in a situation where you are saturating the pad with heat...as in endurance racing. If you're doing 20 minute sprint sessions on the track (typical HPDE style), you probably aren't going to see a big difference between a four and six piston caliper with remotely similar pad volumes.

So, if you see a competitive brake system that uses the same piston sizing on a variety of rotor diameters, chances are it's just plain wrong in terms of being properly balanced. There is an acceptable range, but going up an inch on rotor diameter makes a big difference, and would typically take it outside that acceptable range.

Again, pad volume in no way affects torque output (stopping power). Proper piston sizing is of critical importance. On the six piston system you posted pics of, our calculations tell us that the front system is dramatically over-amplified...which leads to your rear brakes not working efficiently, longer pedal travel, touchiness when trying to modulate the pedal / threshold brake, etc.

I still think you should go with our four piston system and call it a day (per our discussion)...but that's just my humble opinion. Keep in mind replacment part costs, pad availability, replacement rotor lead times, technical service from domestic people like myself, not to mention proper piston sizing and engineering know-how. Good luck with whatever you choose.

AU N EGL

In short it is not an either or question and too many factors involved; Piston size, piston number, rotor size, rotor thickness, tire width, tire brand, tire heat cycles, MC size.

and yes a good front brake system, any system will run $4-5K.

and partily why so many ppl still run the Stock PBR brakes with far better pads, and disposable rotors and biz arz front tires.

Dr Chill

Jeff, thanks for your well-written informative post.