pauldana

My son has the big C4 Brimbo brakes.. I think the front are a slight bit bigger, like 14.5" as compared to my 14" ,,,, as far as on the track, nether has faded yet... his stock C4 brakes we would burn through in 30 minutes of track time to full vapor lock.

And we upgrades the C5 427 Guldstrand to I think it was C6 Zr1 brakes... I think,,, been a while//

jb78L-82

No paul...a single large piston will not have the same piston area as multiply pistons like a 4 or 6 piston caliper...physically impossible for the large single piston to fit in a caliper that would fit the wheel and the bulkiness which is the reason every ultra high performance car with outstanding brakes has not only multiple piston calipers but Large rotors. The C4 brakes SUCKED versus the C3 system because the earlier ones used (4) single piston calipers at each wheel on small rotors

The technical articles I provided indisputably put an end to some of the myths repeated over and over about brake systems ( I understand more clearly the principles now but I was on the right track, just using the wrong terms).

There are multiple factors that contribute to brake torque and the ability to stop a vehicle quickly. As long as the tires do not lock, the rate of wheel deceleration is determined by brake torque. Just to review:

1) Mechanical pedal ratio: Because no one can push directly on the brake master cylinder(s) hard enough to stop the car, the brake pedal is designed to multiply the driver's effort. The mechanical pedal ratio is the distance from the pedal pivot point to the effective center of the footpad divided by the distance from the pivot point to the master cylinder push rod. Typical ratios range from 4:1 to 9:1. The larger the ratio, the greater the force multiplication (and the longer the pedal travel).

2) Brake line pressure: Brake line pressure is the hydraulic force that actuates the braking system when the pedal is pushed. Measured in English units as pounds per square inch (psi), it is the force applied to the brake pedal in pounds multiplied by the pedal ratio divided by the area of the master cylinder in square inches. For the same amount of force, the smaller the master cylinder, the greater the brake line pressure. Typical brake line pressures during a stop range from less than 800psi under "normal" conditions, to as much as 2000psi in a maximum effort.

3) Clamping force: The clamping force of a caliper is the force exerted on the disc by the caliper pistons. Measured in pounds clamping force, it is the product of brake line pressure, in psi, multiplied by the total piston area of the caliper in square inches. This is true whether the caliper is of fixed or floating design. Increasing the pad area will not increase the clamping force.

4) Braking torque: When we are talking about results in the braking department we are actually talking about braking torque - not line pressure, not clamping force and certainly not fluid displacement or fluid displacement ratio. Braking torque in pounds-feet on a single wheel is the effective disc radius in inches times clamping force times the coefficient of friction of the pad against the disc all divided by 12. The maximum braking torque on a single front wheel normally exceeds the entire torque output of a typical engine.

Clamping force is brake line pressure X total piston area of caliper in square inches

Brake Torque (The Holy Grail)= DISC RADIUS (half the diameter of the rotor) x Clamping force X the coefficient of friction of the brake pad.


The master cylinder design is important as well as the multiple piston caliper (fixed is much more rigid than floating and does distribute the greater clamping force more evenly on the pad)

Using a larger rotor in and of itself will INCREASE the brake torque...no question..it is not just about heat dispersion with a larger rotor...math does not lie...refer to the brake torque formula above^

When previously I shared my experience with my GP going to a 12 inch front rotor versus the OEM 11 inch rotor, multiple folks said that it just feels better...NO..the formula proves that the brake torque increases and substantially which was the logic for changing to the larger rotors.

The reason my 300 with the hemi brake upgrade braked so much better was twofold: MUCH BIGGER dual piston caliper versus the single piston caliper (Total caliper piston area-clamping force) AND going from a 12 to 14 inch rotor (Brake torque increase) . Put those numbers in the brake torque formula...gigantic increase in brake torque...yes they feel better and stay cooler but I was NOT imaging the difference in braking..it was real!

My Mustang Cobra conversion was even more dramatic:

A cobra Master cylinder (brake line pressure increase,#2 above), going from a 11 to 13 inch rotor (clamping force and brake torque formula) AND a higher coefficient of friction brake pad. The easiest way to increase brake torque is to use a pad with a higher coefficient of friction which is why everybody and their uncle sells brake pads

I always knew that the wilwood 4 piston calipers using the same OEM 12 inch rotors would have zero effect on the braking of C3 versus the stock brake system...all the above confirms that fact.

We also know now that using stock 4 piston calipers either wilwood or cast iron with a 13/14 inch rotor will increase brake torque and reduce stopping distances with greater deceleration to near lock up.

Using a 6 piston caliper on C3 with a 12 inch rotor will increase clamping force with additional gains from a 13/14 inch rotor.

Hopefully, those that understand will no longer say that a single or dual piston floating caliper offers as much clamping force as a 4/6 piston fixed caliper...not true.

My personal favorite, the false narrative about using a larger rotor only offers heat dispersion benefits..NOT TRUE. More clamping force and more brake torque. Clearly the technical articles state that more clamping force and more brake torque is all about reducing stopping distances so hopefully some will not attempt to refute this fact...some chose to ignore the statements earlier.

There is a lot of misinformation that gets floated around on some of these posts and this time I wanted to set the record straight..hopefully the technical articles provided will put some of this stuff to rest. Don't listen to me, read the articles..................take the time to absorb the formulas and math

pauldana

it just boils down to piston area covered, not number of pistons... if 2 pistons cover 1 sq" and a single piston covers 2 sq" then the single piston will have more clamping force.

and yes, obviously if you have a larger rotor you would need less clamping force due to leverage of the larger rotor, but that is NOT the reason we use larger rotors, the reason is heat.. pure and simple... if you can lock up the brakes with with a 1" rotor or a 20" rotor, locked is locked,, and if you have the pressure to lock em.. that is all you need in pressure,,, now how many times can you do it before the heat sets in????

AND larger rotors have more centrifugal weight/force, thus the reason I may go smaller rotors on the back,,, i think i have MORE than what I need..


And increasing clamping force has nothing to do with stopping distance or amount of times before overheat... Clamping force is only good for peddle modulation and ease o braking.. I use a hydroboost to do that job, and it does it quite well..



My personal favorite, the false narrative about using a larger rotor only offers heat dispersion benefits..NOT TRUE. More clamping force and more brake torque. Clearly the technical articles state that more clamping force and more brake torque is all about reducing stopping distances so hopefully some will not attempt to refute this fact...some chose to ignore the statements earlier.


100% not true.

ignatz

jb: Thanks for all you are doing to provide accurate technical information. I want to add one thing to what you've said about taking the time to absorb the formulas and do the math. So far no one has mentioned that the 14" Wilwood system has a smaller piston area than stock system. At least as I took down the data from their web site. F/R is 4.04/1.98 square inches vs. 5.51/3 square inches for the stock replacement kits. It still works out to be a 20% improvement and I would assume that the trade was done to reduce pedal pressure. It really is important when modifying GM's engineering to do a little of your own.

69427

NO! For the sixteenth time, NO!

The only thing that stops the car is the tires. That is what stops the car. Period! To make the tires/rims stop rotating requires a retarding torque be applied to the wheel. The wheel doesn't give one damn crap if the retarding torque is produced from a small rotor and a lot of line pressure or a lot of piston area, or if the retarding torque is produced from a large diameter rotor, a lot of piston area, and a 115 pound gal pressing the brake pedal in her fragile high heels. All the wheel knows is that there's a retarding torque being applied to it. It has no damn idea, nor does it care, what combination of parts and pressures produced that retarding torque.

69427

I've asked Paul multiple times what size pistons are in his calipers, but I've yet to get an answer.

Been a long day. but hopefully my math is still correct. The stock C3 brakes (F/R caliper piston area ratio/percentage) are 65/35. My Wilwood calipers give me 62/38. Using your Wilwood catalog numbers above give a ratio of 67/33, which as I believe you stated, is less rear brake bias than the stock C3 system.

69427

I agree that bigger brakes handle heavy braking better, but only if there's no cooling air available. All that extra cast iron makes for a good heat sink. However, with decent quantities of cooling air to the brakes, lighter weight rotors work just fine. I have lightweight Wilwood rotors on my car, and brake fade is not an issue for me on track days.

Regarding improved modulation, from personal experience I've been able to correctly modulate the brakes on a wide variety of vehicles, from motorcycles on track days, to crappy front wheel drive cars, to my Corvettes, and to reasonably large trucks I've driven in my life. Proper modulation seems to be more of a case of proper foot/brain interaction than anything inherently superior about different sizes of brake components.

pauldana

This^^^^^ This is correct

Sorry I just do not know thoes numbers off hand... I am sure they're on the willwood site somewhere I just haven't had the time to go there

jb78L-82

You keep saying the same thing...NO ONE is arguing that ultimate braking is determined by the tires! BUT you are ignoring the reduction in time to that lockup point which is what more brake torque gets you:

Another source: http://www.mgf.ultimatemg.com/group2...ake_myth_1.htm #1 below Clearly states this fact

"The most surprising things about deceleration under braking is that it hardly matters how much force the brakes are able to apply, the maximum rate of retardation (deceleration) is dictated pure and simple by coefficient of friction between the tyre and the road surface (see Background 2). Standard brakes are capable of inducing front tyre lock under extremis - and thus are capable of generating sufficient force for much of the braking cycle. If this is the case, fitting larger brakes that generate more force than standard will be wasted, as the amax will be constant - and the adhesion limit simply exceeded earlier. All that extra effort will be wasted in tyre smoke from locked wheels.

So why bother with bigger brakes?
1.More leverage means you can apply brakes harder faster: this can mean that the reaction time to maximum retardation is more rapid - and it probably makes it feel as though you are slowing faster. In fact, this can mean shorter braking distances if the brakes are applied quickly enough - and is usually more noticeable under those circumstances where the rate of brake application is at its most significant - i.e. from high speeds.
2.Better heat dissipation - there is more material for the heat to be soaked up into, and a greater area for that heat to be transferred into the surrounding air."

This fact is exactly what I have experienced with all 3 of my brake upgrades. Little to no difference at low speeds in brake deceleration but VERY Noticeable from high speeds-80-90 MPH!

jb78L-82

jb78L-82

While on the subject of brakes, you know what is all the rage in braking on supercars in 2017 that I have noticed on at least 3 models: McLaren, Acura NSX, and Alfa Romeo? 2 separate/individual calipers on the same REAR wheel: (1) massive 4 piston fixed caliper AND a smaller single 2 piston caliper on the same rotor. This concept is not new and comes from F1 racing cars of the late 90's/early 2000's. Now, why would these cars do that if brake torque does not matter in reducing stopping distances? Hmmmmm..........

REELAV8R

It wasn't stated as an "only" statement, it was a primarily statement.

Multiple heavy applications of standard sized/duty brakes will overheat them. When this happens friction is reduced and braking distance is increased. Ultimately if the heat dissipation continues to be grossly inadequate for the load being applied, all braking will be lost, the rotors will overheat and the brake pad gasses will burn. In addition the fluid will boil then no or very little pressure will get to the pistons. Heat management is of great importance when taxing brakes to limit.
I assume at times road racing does just this.
When I raced motorcycles you only had two modes of operation throttle or brake, no coasting. Very hard on the brakes.

Different types of pads can alter the friction quotient as well as rotor diameter and thickness, but heat still has to be managed.

jb78L-82

Again, no one said that larger rotors primary purpose are not to dissipate heat, agree. No one disputes that tires ultimately determine the absolute value for stopping distance of a particular car.

What has been stated repeatedly falsely on multiple posts are the following:

1. Clamping force has no effect in reducing stopping distances-FALSE

2. That larger rotors in and of themselves have no effect on stopping distnaces-FALSE- Refer to Brake Torque formula mentioned previous posted and the the clear statement that high brake force allows Quicker Faster application of the brakes, reducing stopping distances

3. That a single piston caliper has the same total piston area in sq inches as multiple piston calipers such as a 4 or 6 piston caliper which is directly related to brake torque. FALSE

4. That a floating caliper versus a multi piston fixed racing style caliper have the same effect on brake pressure pad distribution and brake torque application-FALSE. Floating single and dual piston calipers will warp under extreme load and apply the brake torque unevenly to the pads.

All of the factors that effect brake torque allow the maximum adhesion of the tires to be realized in the least amount of time, reducing the stopping distance for the said tire's adhesion.

The facts are the facts despite people's perception of their reality.

69427

Without seeing any pictures of these "super" cars I suspect that the second, small caliper is the parking brake. Give me a picture or some technical details and we can discuss the concept further.

Regarding dual calipers on the occasional F1 car (I believe I've seen dual front calipers on an Indy car once), I suspect that's due to several key issues: damn small rotors (11") due to F1 rims being 13" and Indycar are 15" rims, no power brakes, high speed/high kinetic energy, and damn sticky tires. To get to threshold braking under these circumstances requires either a ton of line pressure at the caliper (lots of effort by the driver), or the multiplication of the clamping force by additional piston area (ie: a second caliper if a single bigger piston area caliper is not available).

Simple physics.

jb78L-82

I observed the one on the Acura NSX and Alfa recently personally..might be a parking park but I do know also that the Maybach's use (2) 4 piston fixed calipers on the front rotors and they were definitely not parking brakes...same for the F1 cars on the rear.

TheSkunkWorks

Something which shouldn't get lost in the discussion is modulation characteristics. An overly sensitive system which has too little margin within which a driver can modulate the slow pedal near the point of locking doesn't lend itself to consistently achieving minimum braking distance. This applies to the initial hit as well, given a properly designed system should have the ability to lock all fours whenever desired (better than having ABS decide where you're headed once you've lost it). And, FWIW a car with a lot of aero downforce can require substantially more of a stomp braking from high speeds (I've actually bruised my foot), followed by easing off as speed drops. In any event, how precisely one can manage all of this while operating on the limits depends on this important quality.

As far as the speed at which one begins braking, the amount of energy being converted over to heat (that's what brakes do) increases at the square of velocity*. So, assuming the system in question can otherwise perform its job adequately, as speeds climb heat dissipation quickly becomes a first order problem. And trust me, glazed pads are about the last thing you want to discover at the end of a long straight! Anyway, hope my $.02 is worth something to the discussion...



* I'll post the formula for converting a car's speed into BTUs upon request.

69427

Given the size and blackout treatment of that caliper, I'm betting that's the parking brake.

The Mayback is a 5000+ pound car with 150 mph capability. That's a lot of kinetic energy to control. IIRC there's also some independence in the control of those dual calipers, but I'm not any kind of expert on porculent luxury cars.

I haven't had any luck finding any info on dual rear calipers on F1 cars.

Metalhead140

Thank you.
No one said that, what was said is that if the existing brakes are capable enough (i.e. can comfortably reach the limits of the tyre for the braking situation required), then increasing this will have no effect. No one is arguing that you don't need clamping force - that's what you modulate with the brake pedal after all.
Again, no one said that. But again, if the brake can already achieve the limits of the tyre at the speed required, no change in rotor size will reduce stopping distance.
No one said that. They said if they have the same area then they (theoretically, with an ideal caliper) have the same clamping ability. Obviously single piston calipers in reality do tend to have more issues with flex and pressure distribution - but this varies between calipers of the same design as well.
You can only reduce the stopping distance to the maximum ability of the tyres... No one has disagreed with you about what factors are important in increasing braking ability/torque. Whether these make a difference to stopping distance is dependent on the abilities of the brakes before the change relative to the tyres. This is all anyone was saying.

jb78L-82

If you go back through 6 pages of this post and other posts, there are examples throughout of the misinformation in post #113, not everyone mind you, but examples. The point of the discussion is not who said what but to help others understand in a little more depth about the factors effecting brake distances and how to improve/reduce brake distances, not withstanding that tires are the ultimate determinent of this variable.

As I stated earlier, All of the factors that effect brake torque allow the maximum adhesion of the tires to be realized in the least amount of time, reducing the stopping distance for the said tire's adhesion...this pretty much summarizes what I have been trying to share