Braking - More then Big Rotors and Lots of Pistons

[JMortensen]

To be fair to AZC, there is an ADJUSTABLE proportioning valve in there which can supply more pressure to the rears. It's still blingy overkill at the expense of rotating weight in my opinion.

[primadonna z]

Well, maybe I was being too subtle. You were stating how well engineered and matched the AZC set up was. If it is so well balanced with the 4 pistion, 12.2 inch front brakes, how can it possibly be balanced with the larger stuff up front and the same rear brakes? Unless, of course, the bigger front brakes have no more stopping power than the smaller ones. So either one of those two systems is an unbalanced, mixed bag of catalog parts or "the option" just adds $650 of bling.

In my mind.

Earlier in this thread we discussed that the same size brake pads are used in both AZC systems. Thus the pad surface area remains the same. Yes the rotors are larger in the upgrade allowing a larger durable surface area, and ability to disapate heat. As far as the calipers, Wilwood's site says it best;

Staggered piston sizes distribute pressure to compensate for the natural variances in temperature, load, and wear rate that occur over the length of the pad. Pad life is extended and performance is measurably improved.

 

Frankly in my mind again. I see the extra money buying me extended life, heat dissipation, increased feel/control, and predictability. Sorry, I don't understand your point. But you have a right to your opinion.

 

Oh Yea, I like the looks too. That's my opinion.

[Dtsnlvrs]

260DET, do you mean something like this.

 

I want one of those

[jt1]

About a year ago I was buying new calipers for the front of my car, and whatever the piston sizes in the 6 piston caliper were at that time, the 4 piston calipers had a good bit more piston area than the 6's. I don't recall the actual numbers, but it was by a pretty good amount.

 

John

[johnc]

Ultimately, everything else being equal, doesn't it come down to the brakes being able to bring the rubber/road interface to maximum static friction, and keeping it there long enough to bring the vehicle to a halt?

 

The "...everything else being equal" caveat is a cop out. Everything else is never equal in the real world and that was the point of Mark Ortiz's reply. Controllability, repeatability, balance, and feedback are critical aspects of braking. In a racing situation they are pretty much equal with ultimate braking force.

 

The ideal situation is a braking system with a lot of braking force AND controllability, repeatability, balance, and feedback. If I had to trade one for the other, I would have to think long and hard before I chose ultimate braking. Its pretty scary going hard into a corner knowing you have enough force to instantly lock up all 4 wheels and no clue when that might actually happen.

[Supra510]

The ideal situation is a braking system with a lot of braking force AND controllability, repeatability, balance, and feedback. If I had to trade one for the other, I would have to think long and hard before I chose ultimate braking. Its pretty scary going hard into a corner knowing you have enough force to instantly lock up all 4 wheels and no clue when that might actually happen.

 

I couldn't agree more. Here's what my big brakes gave me.

 

Braking force--Yes, plenty

 

Controllability--Yes, I can actually modulate the brakes on the edge of lockup from 130+, not so with my previous 280zx set up. The window of controllability is much better. It doesn't go from braking hard to blam! lockup. You can tell when it's about to happen.

 

Repeatability--Yes, less fade=repeatable results

 

Balance--Yes, now. With my first rear brake set up the caliper pistons were too small, so even with the bias all the way to the rear I couldn't lock them. Now with bigger pistons I have all the adjustability I want and good balance as well.

 

Feedback--Yes, hand in hand with controllability. I can feel when they are on the verge of lockup, not so with the previous setup.

 

You won't get any argument here that handling/weight wise you should go with a system as small as you can that meets the above criteria. That being said when I'm stopping from 130+ at the end of PIR's front straight I'd rather have brakes a little too big than a little too small.

[dimsum]

A few questions in reference to the original post:

 

Brake release is more important than many people realize. If the brakes continue to drag after the pedal is released, not only does that heat the brakes unnecessarily, it saps cornering power from the tires. That lowers cornering speed, again requiring earlier braking.

 

How do you improve or ensure good brake release? Is it as simple as keeping your calipers clean?

 

 

The highlighted section above is why I keep harping about how a properly setup stock 240Z braking system can work better then a slapped together 13", 6 piston caliper setup. Its all about balance and control.

 

I've read in multiple places on this forum, including this thread, that stock 240Z brakes are sufficient to stop the car in both street and track situations. Does this theory apply to the stock 240Z rear drum brakes? I always thought that a disc setup was a significant improvement over drum brakes based on the mechanics of disc vs. drums. Or, does this theory only apply to the front brakes?

[260pos]

I keep harping about how a properly setup stock 240Z braking system can work better then a slapped together 13", 6 piston caliper setup. Its all about balance and control.

 

So John, how do we properly setup the stock system?

[260DET]

260DET, do you mean something like this.

 

Yeh, except that one looks like it attaches via a single bolt each end. Which loses some rigidity.

[jeromio]

More questions. Most discussions of brake balance are in regards to front/rear. I currently have a problem with side to side. I am experiencing some braking issues and I need to tear things apart. So it may turn out that something is just broken - braking performance used to be much better than it currently is. But during a panic stop, my left wheel locks up. Obviously not a good situation. I guess my question is, if you're really trying to optimize a braking system, the braking force needs to be very well balanced both front to back and side to side. So, are there ways of measuring this left/right balance and tweaking things?

[buZy]

FWIW Nothing new here, you have heard it from many before.

Street car.

I did the azc four piston hd front and rear upgrade with the zx master. Repeated stops from 120 plus are straight, comfortable and very predictable threshold approaching lock up. For me at least, it would take ALOT of braking instance to actually overheat these parts. Safety was greatly improved keeping up with todays abs cars. Also the rear end ran much smoother above 100 from just swapping to discs with no other changes. It must be from not having the drums pulsing the adjusted brake shoes. Must also add I took the time to face the the stub axels and adjusted all the rotors to runount under .004.

[tube80z]

I guess my question is, if you're really trying to optimize a braking system, the braking force needs to be very well balanced both front to back and side to side. So, are there ways of measuring this left/right balance and tweaking things?

 

Yes, you can get a pressure gauge that screws into the bleeder. Then you have someone press on the brake and you get a reading. Before you go down this path take a look at everything on the right side of the car. It sounds like you have something sticking and when that happens all the pressure goes to the other side.

 

Eliminate the obvious then go from there. I'd guess a sticking caliper or some obstruction of the line. Severe cross weights can cause this but I've never seen or heard of both tires on one side locking first.

 

Have you flushed all the fluid and done a decent bleed? That and inspecting the brakes to make sure they are actually working is probably step one.

 

Cary

[jeromio]

I definitely need to tear everything apart, bleed, change pads, etc. - but it did make me start thinking about optimizing side-to-side.

 

It sounds obvious now, but had you not mentioned it I never would've conceived of a gauge that screws into the bleeder valve:

Doesn't look like SAE threaded - I would need metric.

[lbhsbZ]

From Mark Ortiz's latest chassis newsletter:

 

 

 

The highlighted section above is why I keep harping about how a properly setup stock 240Z braking system can work better then a slapped together 13", 6 piston caliper setup. Its all about balance and control.

 

I'm not sure if you are referring to brakes for a street car or brakes for a racecar, but I'm going to assume the later, because you're a racer...in which case....(and since I like to argue)....

 

 

I usually agree (after much questioning) with most of your thoughts...but not this one.

 

What I agree with: The stock brakes, in good working order can stop (or slow) your car just as good as big boy brakes.

 

What I disagree with: The stock brakes, in good working order, can stop your car just as good as big boy brakes.

 

I know, that might be confusing, but here's what I've got:

 

Any brake system that allows you to lock up the wheels is adequate, but not ideal. Like your article said, locking up the wheels is not the fastest way to slow a car. Your article also mentioned release, which is a function of pad characteristics and has not much at all to do with the actual brake system design, so I'm not going to get into that. If you can lock up the wheels, you have enough braking power to stop the car as fast as it can possibly be stopped (short of running into a wall)...period. If you can lock up the wheels, larger brakes are not going to make your car stop faster....BUT, read on....

 

Larger rotors have several advantages....with a larger rotor, you have more leverage about the spindle to slow the wheel (like trying to loosen a lug nut with a 3/8" ratchet versus a 3 foot long breaker bar), so with the same sized master cylinder, and the same size and number of caliper pistons, a larger rotor will require less pedal pressure for the same degree of stopping power.

The job of the brake rotor, aside from providing a friction surface, is to absorb and dissipate heat. Rumor has it that objects of greater mass and having more surface area can absorb more heat and dissipate it faster than objects having less mass.

Larger calipers, aside from having the ability to more evenly distribute the clamping force over the pad, have no benefit at all. If you use a caliper with larger pistons, you will need less pedal pressure to accomplish the same level of braking than you did before, but at the expence of pedal feel. If you have smaller pistons, you will have to use more pedal pressure to accomplish the same level of braking you had before, but now you will have a firmer pedal, and consequently, better modulation.

Running big brakes on the street is stupid IMO. All it does is add weight. If small brakes will stop the car and don't overheat, why bother upgrading. For an autocross car, I don't see why the stock brakes wouldn't be more than adequate.....but there will come a point, where the rotors cannot dissipate the same amount of heat that they are being forced to absorb....ducting can only go so far on a solid brake rotor.

For a Road Race or Endurance car, the stock brakes are nowhere near adequate. On my old VW, I had 10" vented rotors in the front and 9.4" solid rotors in the rear, with high dollar race pads....and ducting, and at the end of a 1 hour enduro race, the brakes were gone. When I pulled into the pits, the rotors had 2 large cracks through each one of them....that was on a 1800lb car.

 

 

In conclusion....I agree with John's perspective for applications that do not see extreme temperature use....which the article did not discuss, but I disagree with John's perspective for applications that DO see extreme use, where lots of heat is generated. Big brakes are not to make you stop better, they simply allow you to stop more.

 

I have 13" front rotors on my car and 11" rear disks, and I would be willing to bet a cold beer that in a series of threshold stops from 100-0, I could carry out 20 in a row, with less than a 20% increase in stopping distance from the first one. I would also be willing to bet another cold beer that a car (the same weight as mine) with stock brakes (using comparable pads)could not perform the same back to back series of stops and keep the distance within 50%.

[Mikelly]

Couple of things I want to contribute first hand that could shed some more light...

 

My 99C5 Chevy corvette had upgraded fluid, upgraded pads, upgraded brake lines, and factory 13inch front rotors, and 12.2 rear rotors, both solid, both vented. The braking on that car was ALWAYS responsive, always dependable, and always easy to modulate. Speed bleeders made it easy to maintain, and Hawk HT08 pads were always used to stop the 3250# beast consistantly on high speed road courses, making 382#ft. torque and 386HP.

 

My 2001 996 Twin Turbo Porsche has "world renound" brakes. They are 13 inches front and rear, vented and crossdrilled, have the best fluid (Castrol SRF) and pads (Pagid Yellow RS29s) along with some major brake duct cooling at all four wheels... The brakes, when properly heated are again very responsive, very predictable, and very easy to modulate. This in a 3600# AWD package that puts out 532#ft. torque and 510AWHP.

 

These two platforms are "World renound" and considered benchmarks to shoot for. The corvette brake sysem is well documented for spreading calipers and eating rotors with aggressive pads. The Porsche NON-6 piston, non-14inch two piece caliper system is known to be underpowered, due in no small amount to the weight/power potential. Heat and weight are serious issues, especially when the platform is modified.

 

The Zcar is well documented as having a WIDE RANGE of power and weight ranges... These ranges truly make each build different, requiring different braking needs. Regardless of the rotor or caliper size, Pad compound, brake bias and fluid wet and dry boiling points are of utmost importance. Heat buildup, inability to shed that heat, and fluid boiling will cause you to lose total confidence in your vehicle. I've suffered this first hand... It isn't pretty. Know your requirements for your platform. Know what you need to do to stop your platform repeatedly and consistantly, for 30 minutes at a time, 4 sessions per day.

 

Rotor size, caliper size, piston size, number of pistons, ventilaton of hub/rotor, all these items play into the overall chassis dynamics and power/weight ratio. Add larger wheel/tire combos to the "lever" effect, and it gets more complicated... Heavier mass rotation, larger levers, less deflection of tire types, all play into the equation.

 

My Corvette was hitting 145MPH on the front straight at VIR. My 911 Twin Turbo will easily top 170mph at the brake markers on that same front straight. I'll be praying to god that they function properly. POwer to weight is a huge factor. Build your braking system to accomodate the platform, calculating power to weight.

 

Mike