[img]carbon/carbon brakes[/img]

I don't think I've ever mention 'drool' in any my posts EVER, but this sure does deserve it. DAMNNNNNNNN.

 

Hahaha...I'm glad you enjoyed that Daniel I actually had Frank price me a similar set, and managed to get it for a bit under hyperion's guessimate, but after talking to Chuck Mallett, I couldn't justify the cost on a car that wasn't being professionally raced, esp. when it wouldn't be streetable at all - and I'm adamant about having a full trackworthy FD in *full* street trim I don't want going to the post office in the FD to become an impossible task...

~Ramy

 

So are we ok to use Stoptech front big brake kit and Rs/RZ for the rear? I have complete RS/RZ set up for the rear but I have not decide which front brake kit that is the best way to go to balance the rear. Any suggestion?

 

Yes, order the custom Stoptech kit from Dave at Zeckhausen Racing...he knows the custom caliper sizing to match the 99 rears. This will result in a very balanced setup. Hyperion's only concern is running non-matching track pads.

 

I think you could also use the 99 RZ's w/ the regular front StopTechs. The ST's are "ballanced" with the stock rears with the assumption that you'll use the same pad compound F/R, but many use a milder rear like Crispy's 01/99 combo, or Hawl Blue/black etc... that ought be enough to offset the torque difference.

 

p.s., no arguement on pad selection, but I picked up a universal brake "tool" for like 5 bucks that goes on the end of a 3/8" ratchet... I just slap on a long extention, and screw in those pistons post haste. It actually takes less time that the StopTech fronts now.

 

Another setup that works GREAT with the RZ rears is...

... the RZ fronts! Of course, I have no idea what the pad selection for the RZ fronts is. Might be limited to stock or require custom made.

 

RE: the carbon-carbon setup--RUF had a 911 that ran some Carbone Industrie rotors (same people that make the F1 rotors) and they swore it was streetable but I never believed it. However, I thought the Ezno has some kind of hybrid that is C/C but matrixed to give better cold bite. But they are $5K a piece, so it's not very valuable to us.

-ch

 

Well keep in mind that the 911s are 600some lbs heavier than our FDs, easy.

 

RZ fronts run the same pads as our 93-95 OEM calipers

 

READ: limited pad selection

Crispy

 

They only "had a disaster" when guys started tracking their cars and revealing the lack of complete R&D that Porsche had put into the brakes. Ceramic composite brakes in and of themselves are not "crap"-- only when they're not designed and applied properly.
The reason there was "no modulation" was because they were never up to proper operating temps, which is impossible to achieve on the street. Once up to proper temps, properly designed carbon/carbon brakes have plenty of feel and modulation.

The other major disadvantage with carbon/carbon brakes is just that: in order to generate the proper friction coefficients, carbon must be used against carbon. The carbon weaves used are actually pretty soft on a general hardness scale. That's one of the reasons why carbon discs are so thick: carbon discs wear very quickly, and are typically junk after one race.

 

Hi Kento! haha. Haven't seen you in a minute. Always glad to have you chime in Nice updated avatar btw

That's good to know. Have any other manufacturers employed a carbon-ceramic blend successfully? Or was Porsche the first to take the jump?

Yep, that's what I was told.

I asked about this specific point, as I had heard the F1 cars junk their brake system every race. I don't recall the exact answer, but I believe it was something to the effect of that's not b/c they have no further use for 'em, but b/c they have the budget to do so, as they tear down and rebuild motors quite regularly - again not b/c they're blown or worn, but simply b/c they can afford to have everything running in tip-top brand-new condition each and every time. And also, the level of wear an F1 car will put on its brakes is considerably different than the wear a tracked FD would put on it's brakes.

~Ramy

 

Basically, "junk" can also be interpreted as "cannot be used any more with safety". Yes, you could "reuse" a set of carbon discs that have had a race on them, but I seriously doubt that they would last that second race. Plus, you run the risk of brake problems due to the excessive piston travel. Carbon brakes' wear rate is very high, far higher than any organic compound.
It's basically all relative. Would you want to be replacing your outrageously expensive brake pads/discs five times as often as conventional steel brakes that are probably five times less expensive?

 

N-Tech can get you the 99 RZ rear brakes and Stoptech front kit with matched pistons. Nick's price was good on the Stoptech kit, $1750. It was $200 extra for matching pistons (Stoptech recently raised the price for this option) and $100 extra for springs to prevent the pistons from sticking. Not sure about N-Tech's price for the rears since I already had the rotors from a Precision group buy and got the calipers/backing plates from Jason at the Rx7 Store.

Nick/N-Tech was very helpful and full of good information concerning brakes for the FD.

Jack

 

Ramy--sent you a PM. Curious what your plans are for your brake kit. I sent email to Frank but haven't heard back yet. If you want to chat brake ideas, send me an email to hyperion@obscure.org.

-ch

 

Jack--the springs in the race version of the Stoptech kit are 'anti-knockback' springs. They keep the pistons from being pushed back into their bores by the rotor and pads (which move around more on floating hats and with slots/drill holes). This makes the brake pedal more consistent and eliminates dead spots at the beginning of pedal travel. The drag about this setup is...well, pad drag. The pads are slightly pressed into the rotors which causes things like a LOT of dust, reduced life, squeaking, and in the case of race pads, greatly accelerated rotor wear during street/highway use.

-ch

 

On C/C rotors for F1 cars--like iron rotors, the spec for a C/C rotor is about 1-2mm of wear. Typically, the F1 cars will see this much wear during the course of a 200km race, so they throw out the rotors when they are done. (Race teams do this with iron rotors, too.)

The other big advantage to the C/C rotors is weight. But they do require carefully managed termperatures to be effective. Too much or too little cooling can push them way outside their effective range of operation. Generally speaking, iron rotors are more tolerant of temperature variations (although they operate at much lower surface temps than C/C rotors.)

-ch

 

hyperion, I PMed ya back

 

Okay, I'm TTT on this thread because I want to share some ideas and get some feedback. Here's my thesis:

I like the Stoptech philosophy of "don't change the factory brake bias". You keep the ABS system happy, and you leverage all the testing the factory guys did on the system dynamics.

HOWEVER, I'm suggesting that this may not be the most valuable thing in the world. Here's an example where this may not have as much value as you think.

Let's say that your FD was tuned for high-performance all season tires. At the limit they offer 0.9G of deceleration. The factory sets it up so the front tires lock slightly before the rears.

Now, you fit some DOT approved road race tires. Your adhesion limit goes up to 1.1G. What happens to the brake bias? Well, assuming that your center of gravity is above the road (it is, prob 18-24") then the effect of the increase in deceleration is to put MORE weight on the front tires. This means the rear tires will lock SOONER than before because there is less weight over the axle. In order to fix this you would need to push the braking bias forward slightly.

Okay, now another thought experiment. Let's say you buy that set of swanky coil overs. You lower the car 1" in the front and 2" in the rear. Looks cool! Lowers the CG, too. That's a good thing...but it changes the braking bias at the limit. This time, the lower CG actually reduces the weight over the front axle during braking, meaning that the fronts will lock even sooner than before. In order to fix it, you have to push the bias rearward.

These problems are compounded by the fact that brakes work best when you keep them at an optimum temperature. So a simple in-line bias valve doesn't do the trick--you have to size the rotors (dia and thickness) appropriately.

Race teams address this by having:

1) A balance bar
2) Multiple rotor thicknesses (with corresponding pad depths)
3) Variable ducting sizes
4) Lots of temperature strips
5) Lots of track testing

Like I said before, I really appreciate the fact that Stoptech actually performance tests their kits, and I think this helps matters quite a bit. But if you significantly alter the ride height or tire compound on your car, you can push the car outside the operating envelope that Stoptech designed (and tested) their system to.

The funny thing about the brake discussion is that it's a lot like the suspension discussion. 99% of the public think that a stiff car is a fast car. This is almost never the case, and certainly untrue about street cars. Having giant swaybars and 1000lb springs FEELS quick because of the steering response, but as soon as you try to go through a corner on a public road *at the limit* you instantly can see (and feel) that you've made a big mistake.

My point is that most people don't corner at the limit, especially on the street. (Thank god.) By the same token, most people don't operate their braking system at the limit, either.

Based on my crude calculations and assuming a pretty sticky tire, one possible setup would be 14" front rotors and 13" rears. The rear calipers should have 50-55% of the piston area as the front calipers. Ducts for the front rotors with block off plates of several sizes at the inlet (for different driving conditions). The rear calipers will do about 25% of the braking work and rotors thickness should be sized appropriately. To be safe, over-provision the piston size on the rears and install a bias valve just after the master cyliner to fine-tune the balance. And hope the ABS system will still work!

This setup would result in wheel lock at about 50-60% of the pressure needed by the stock brake design. However, the volume displacement of the system goes up by 50% in the front and 75% in the rear. In order to restore pedal feel and travel, you'll need a master cylinder that moves more fluid per inch of stroke. The 929 master cyliner increases the flow by only about 14% over the stock cylinder. So the pedal will be longer with less effort at lock unless you get a fully aftermarket MC setup...which will make things a LOT more complicated. (Unfortunately, most people prefer pressure modulation as opposed to position modulation to manage threshold braking.)

Of course, this is all theory. Gotta test to be sure!

Thoughts? (I know someone will say 'shut up and buy the Stoptech/RZ combo'... )

-ch

 

Can I be first? "shut up and buy the Stoptech/RZ combo"

J/K

Most if not all your comments are pertinent. However, there is one thing you failed to consider. Some of us are NOT installing BBK's to simply reduce stopping distances although there may be some reduction. The stock system is VERY good at doing that already. And if the ABS is operating all 4 tires at the limits of adhesion you will not be able to stop any sooner anyways. You are tire limited NOT brake limited. But to my point, some of us have gone with a BBK for durability and consistency of braking.

I drove for several years with the stock brakes and Hawk Blue pads and it worked VERY well, even with 255 series Yoko A032 R tires on 17" rims. Problem was I was overheating everything in the area of the brakes and trashing rotors on very short order, not to mention the issues with braking inconsistency. Now with the BBK's I can stand on the brakes every time and not worry if they are too hot or too cold or how long my rotors will last (sorta - I need some front brake ducts) even if my stopping distances are a tad longer than what they *may have been* with the stock brake setup. Granted it is VERY hard to make any corollary between my stock brakes on street tires with track brake pads and a stock suspension and what I run with now -275 series Hoosiers on 17" rims, front and rear BBk's, PF track pads, and a full worked suspension. With this I would STILL consider myself *TIRE* limited as I can still feel the ABS pumping either front OR rear depending on the dynamics of the corner or how I place the car.

So ask yourself the question, what is my purpose for the BBK, because there is more than one answer.

Food for thought,
Crispy
- runs shocks near full soft on the track but has a monster front sway bar

 

Another misconception that people have when talking about brakes is that going to larger diameter discs will automatically guarantee you more braking power. It's basically the same as the six/eight/two hundred twenty-five piston caliper myth; if the discs and calipers are capable of handling the heat transfer, a properly designed 310mm disc/pad combination will offer just as much braking power as a 332-350mm (or whatever) size disc. It's the brake pad/disc interface that determines the actual braking power, not the size of the disc or the amount of pistons in the caliper. This is why there are so many brake pads on the market; the science (and art) of formulating brake pad compounds is a very complicated and varying task that requires even more testing than any racetrack testing with varying bias, track bars, ducting, yadda yadda yadda...

 

Agree with both previous posts. Some additional thoughts:

One of the indisputable advantages of an 8-pot caliper over a 6 or 4-pot is that you get much less pad taper with two smaller pads than one large one. There is also arguably an advantage in having two leading edges, better pressure distribution, and more efficient scavenging of pad material.

There IS a mechanical advantage to the larger diameter rotors--in fact, racing brakes tend to run a much smaller radial section (annulus) than production brakes in order to maximize the mechanical advantage of the system and reduce unsprung weight. (This is another advantage of calipers with a large number of small pistons--you can run a more narrow annulus.) But I totally agree that the overall stopping power is a function of CF * effective radius which could be the same for many different rotor diameters.

Here's an interesting question: what F/R bias do manufacturers target in order to account for the variety of tire compounds that are likely to be used on their cars? My guess is that they are substantially forward-biased to account for the potential of sticky tires being used. If they weren't, you'd see a lot more rear lockup on street cars with R-compound tires at the track.

I just realized how primitive this conversation is. Even my lowly STi has electronic brake distribution to address this issue in real-time. I feel like a guy who is discussing which jets to use in his carburetor.

New phrase that someone should be saying to me: "just shut up and buy a C6 Z06 or GT3."

-ch

 

That's if the six-pot caliper even comes with four separate pads. Many of the ones I've seen use just one large pad, just like a four-pot. And boasting less pad taper is really the main reason six/eight pot calipers came into existence: The six-piston caliper was developed from endurance racing, where an inordinate amount of time used to be spent in the pits changing brake pads.
Those arguments are all very weak when the four-piston caliper and pad material is properly designed.
I figured that point was obvious enough to omit, and even then, that mechanical advantage goes out the window if the caliper and pad/disc interface is poorly designed.
That's only if you can keep the longer and thinner caliper from flexing, which is a lot more difficult than it appears.

 

I'm digging this thread back up for a comparison. I was doing some analysis of kits based on the AP CP5200. What I'm seeing is that with the larger pistons of the AP caliper (about 21% larger than stock) and the different rotor geometry, the effective moment for that setup is 1.38 times that of the stock brakes.

By comparison, the RZ rears offer a boost of 1.08 over the stock rears, all due to the larger effective radius.

So my sense is that the AP system will be extremely stable under braking because of a strong forward bias in the kit. Of course, the APs can handle much more heat than the stock brakes (and have a great selection of pads) but better balance and shorter braking distances should be possible from a front kit with smaller piston bores...like the Stoptechs.

Please let me know if you agree or not.

-ch