Sneak Peak - New Race Rotors

[JasonSSG]

Sweet keep me posted. Im thinking of having those calipers painted snake skin green

 

[ViperGeorge]

What are the benefits of the 6 piston calipers over the stock 4 piston units? Are they engineered in a way so that pedal travel and effort are the same? Do they generate the same or better clamping pressure at the caliper? I've read on the Stop Tech site that the brake components need to be designed as a system as changes to one component may necessitate changes to others? For example changing piston area may require a different master cylinder or different fulcrum on the pedal assembly.

Some folks have been upgrading to the ACR-X rotors and pads but in reality this upgrade does nothing for braking although it may help with dissipation of heat (this directly from an SRT engineer and validated on the Stop Tech site). Only way to improve braking would be to increase rotor diameter as this increases brake torque.

 

[Bill Pemberton Woodhouse]

Good comments Mr. Batejan

 

[GTS-R 001]

I heard from a few racers that the larger Brembo rotors and the CTSV pads helped braking with some of the racers, it definitely would have helped if there was a piston behind the pad for the extra surface area, and I guess I would question why that was marketed as an upgrade if it didn't work??? I didn't try it myself so I can't give a first hand account either way.

As for 6 piston vs 4 piston,

This is how it was explained to me,

There are a number of ways to make your brakes perform better, but, adding a grain of salt here, all theory needs to be proven out on the road, but here is how it was explained.

*Bigger pistons -- The larger the pistons are, and the greater the area over which they come in contact with the brake pads, the more clamping force they have on the rotor.

*More pistons -- Low-end floating brake calipers have a single piston, on the inboard side like the Gen 2 rear. Low-end fixed calipers have a single pair of pistons, flanking the rotor disc. High-performance calipers can have multiple pistons or pairs of pistons, mounted on opposing sides of the rotor. Six-piston models are increasingly common and even 12-piston models are not unheard of. Increasing the number of pistons also serves to increase the clamping force of the caliper. More pistons with a greater clamping area will outperform fewer pistons of equal SQ CM area. i.e. a 6 piston caliper with a larger pad will out brake a 4 piston with a smaller pad even if teh total square CM of piston clamping force is equal.

*Less heat retention -- In a sense, your brakes can be thought of as a device for converting movement into heat. As the vehicle slows down, all of that kinetic energy has to go somewhere and most of it ends up as heat. If you want to look at it another way, all that friction between the brake pads and the rotor generates heat in much the same way that striking a match generates heat. If too much heat builds up, the brakes begin to fade, or become less effective. So, the better ventilated the brake calipers are, the better they perform. Also, the larger the surface of the brake rotor, the more the heat is spread out.

* Differential bore calipers -- As the surface of the rotor heats up, the clamping force of the pistons has to be increased to avoid brake fade. If the caliper has multiple pistons (or multiple pairs of pistons), the brake rotor surface is initially heated by the pistons pushing against the brake pad at the leading edge of the caliper, making the rotor surface hotter when it rotates back to the pistons closer to the trailing edge of the caliper. Therefore it helps if the pistons closer to the rear edge of the caliper are larger. Differential-bore calipers use smaller pistons up front, larger pistons toward the back. The Viper uses differential bore piston calipers on the front and the back, 44/40 on the front and 42/38 on the rear (since 2003 anyways)

Here is a few pics to illustrate,







And the corvette 6 piston front, 4 piston rear set up that seems to be having a few people think that the vettes have a braking edge.



Corvette caliper specs are as follows

09-11 C6 ZR1 Brembo 30/34/38mm 6 pistons TOTAL CALIPER PISTON SURFACE AREA (PER CALIPER) 8.52 sq. in. 5497.8 sq. mm

09-11 C6 ZR1 Brembo 30mm / 34mm 4 pistons TOTAL CALIPER PISTON SURFACE AREA (PER CALIPER) 3230 sq. mm

 

[Voodoo Rob]

Great job on your homework before releasing the products.

 

[ViperGeorge]

There are only three ways to increase brake torque as far as I know. 1) Increase the rotor diameter, 2) Increase line pressure, or 3) increase piston surface area (although pedal travel would increase). Of course friction material and tire type and construction also can materially impact braking force. Following is from a Stop Tech white paper freely availalbe on their website:

1) Line pressure can only be increased by either increasing the mechanical pedal ratio or by decreasing the master cylinder diameter. In either case the pedal travel will be increased.

2) Clamping force can only be increased either by increasing the line pressure or by increasing the diameter of the caliper piston(s). Increasing the size of the pads will not increase clamping force. Any increase in caliper piston area alone will be accompanied by an increase in pedal travel. The effectiveness of a caliper is also affected by the stiffness of the caliper body and its mountings. It is therefore possible to reduce piston size while increasing caliper stiffness and realize a net increase in clamping force applied. This would typically improve pedal feel.

3) Only increasing the effective radius of the disc, the caliper piston area, the line pressure, or the coefficient of friction can increase brake torque. Increasing the pad area will decrease pad wear and improve the fade characteristics of the pads but it will not increase the brake torque.

Is the total surface area of the pistons in the 6 piston setup greater than in the 4 piston OEM calipers?

 

[ViperGeorge]

Here's the link to the Stop Tech white paper. Worth the read.

http://stoptech.com/technical-support/technical-white-papers/brake-system-and-upgrade-selection

 

[GTS-R 001]

Well I don't want to derail a thread about rotors just over some new caliper options I am working on, but you do have to take into account that:

Larger pads provide a greater swept area which means a greater area over which heat is generated. Because the total heat for a given stopping force is always the same, greater swept area means better heat dissipation and less brake fade. Having multiple pistons per side helps apply more consistent pressure over the entire surface of the pad which not only allows the larger pads, but also reduces chatter and flex, both of which generate additional heat as well as reducing overall brake feel.

So, while a one-time emergency stop will not show much difference between a single piston sliding caliper or a 4 piston or a 6-piston fixed caliper, the multi-piston fixed-caliper design will be more resistant to fade over several hard stops in quick succession, such as during racing, the 4 piston cleans up over the single and the 6 piston exceeds the capability of the 4 piston and as we all know, you win the race at the end of the last lap, not after you brake at turn 1 lap 1.

 

[REDSLED]

gbatejan,
I'm not following the point you are trying to make with Steve? Are you questioning whether or not there is an increase in piston surface area with the 6 *** caliper vs. the 4 *** caliper that you are using? Agreed, that simply using a larger pad doesn't equate to better braking, but a larger pad with increased piston surface certaily would be, correct? There is a big differnce between the braking characterisitics needed for a 20-30 min DE event (which is what you do, correct) and the braking needed for a 40-50 sprint race. I do beleieve that the Brembo 6 *** calipers were the upgrade for the World Challenge Comp COupes for this very reason. I'd take a 6 piston over 4 any day for that reason.
-Jonathan

 

[REDSLED]

as we all know, you win the race at the end of the last lap, not after you brake at turn 1 lap 1.

Perfect! Great answer.

 

[GTS-R 001]

Here's the link to the Stop Tech white paper. Worth the read.

http://stoptech.com/technical-support/technical-white-papers/brake-system-and-upgrade-selection

George,

Lots of good info but I guess I am looking at the entire picture versus the freeze frame.

"3) Only increasing the effective radius of the disc, the caliper piston area, the line pressure, or the coefficient of friction can increase brake torque. Increasing the pad area will decrease pad wear and improve the fade characteristics of the pads but it will not increase the brake torque."

Now, what do you think happens to brake torque once the brakes begin to fade because there is less surface area on the 4 *** caliper's pad, I would hazard a guess that the torque decreases once fade sets in vs stays the same, I do not see how else you could equate it.

increase in fade = decrease in torque, if the torque stayed the same, there could not be fade, I think, LOL

no fade = torque stays the same , therefore better braking after fade sets in with the 6 *** vs the 4 ***.

 

[ViperGeorge]

George,

Lots of good info but I guess I am looking at the entire picture versus the freeze frame.

"3) Only increasing the effective radius of the disc, the caliper piston area, the line pressure, or the coefficient of friction can increase brake torque. Increasing the pad area will decrease pad wear and improve the fade characteristics of the pads but it will not increase the brake torque."

Now, what do you think happens to brake torque once the brakes begin to fade because there is less surface area on the 4 *** caliper's pad, I would hazard a guess that the torque decreases once fade sets in vs stays the same, I do not see how else you could equate it.

increase in fade = decrease in torque, if the torque stayed the same, there could not be fade, I think, LOL

no fade = torque stays the same , therefore better braking after fade sets in with the 6 *** vs the 4 ***.

That is entirely true. This is the reason that the ACR-X has more surface area for the pads and rotors. It is not because they increase braking; they reduce fade. As fade increases more brake pedal pressure is necessary to compensate. Now having said that, I've never experienced fade in my ACR on the track using the Stop Tech rotors and OEM calipers (I do use Raybestos race pads). I have run sessions as long as 45-55 minutes as well (fuel became the issue not brakes). Increasing the surface area of pads, rotors, and pistons will improve resistance to fade. By the way the non-ACR OEM rotors also have more mass and are therefore better at absorbing heat than the Stop Tech rotors on an ACR. They do however increase rotating mass which is not a good thing.

I'm only pointing these things out so that folks understand what they get when they upgrade a braking system in some way. More pistons and more piston surface area will reduce fade but increase pedal travel some. They will not by themselves improve braking torque.

By the way, your rotor hats are killer. Very nice job. Are they the same thickness at the hub as the standard Stop Tech hats? In other words are the wheels positioned at the same place or are they pushed out further?

 

[GTS-R 001]

By the way, your rotor hats are killer. Very nice job. Are they the same thickness at the hub as the standard Stop Tech hats? In other words are the wheels positioned at the same place or are they pushed out further?

Right now the hats will be very very very close in spec to what the Stoptech hatsmeasure so that they can be an upgrade to the Stoptech hats for appearance and for replacement (fatigue will set in on cars that are tracked regularly)

 

[ViperGeorge]

Right now the hats will be very very very close in spec to what the Stoptech hatsmeasure so that they can be an upgrade to the Stoptech hats for appearance and for replacement (fatigue will set in on cars that are tracked regularly)

When you say fatigue will set in on the hats when the car is tracked regularly, is this true for both the Stoptech hats and yours? or are your hats less suseptable to fatigue given they are made out of what appears to be billet?

 

[GTS-R 001]

When you say fatigue will set in on the hats when the car is tracked regularly, is this true for both the Stoptech hats and yours? or are your hats less suseptable to fatigue given they are made out of what appears to be billet?

I just think that with some high stress items there is a point where you have to look at them and determine if they need to be replaced, I could see aluminum rotor hats being one of those items, especially since you do not know what they are made out of, they could be 6061, they could be 7075 like mentioned above and then I would really look at replacing them as they would have been annealed to super soft state by the heat of the brakes or they could be cast units.

Mine are 6061 T6 and should last a long long time, just as long, if not longer than anything else out there.