Brake system factor?

[wayner]

Over the years I have read multiple threads on brake system design.

I think I have captured the elements here in this drawing. Maybe this can help focus the discussion?

Let me know if you find it helpful and feel free to make suggestions for improvement such as missing elements.

[Flieger]

I don't really understand how the triangle and word placement factor in.

Steel brakes don't really need to worry too much about over-cooling like Carbon-Carbon brakes do. I think C-SiC brakes are also pretty good from cold. That is one boundary condition for time between braking events (better term than corners since what is a corner? and when they are on top of each other you are not braking in between them). There is some point in the middle where there is enough braking energy being put in and not enough time to cool at the current rate of cooling.

You want the maximum cooling so that you can drop weight. If you can't get anymore cooling and the brakes still fade, then go to wider rotors in order to delay the onset of fade.

In F1 they worry about drag from brake ducts and over-cooling, but on a 911 those factors are not really a concern.

[RWebb]

besides the above, I don't see Bling in that diagram

[wayner]

The diagram was meant to show that regardless of size or type of material or number of pistons or whatever... The factors are clamping force vs heat. Vs ability to cool. Carbon disks cool very quickly ( almost instant compared to steel)

Maybe I could have left out the outside variable of corner to corner meant to illustrate not the amount of cooling, but the the duration

So, if I dropped that bottom line does it make more sense?

Maybe I should have used a diamond to represent bling :-)

[James Brown]

i don't think stock turbo brakes are that much bling but work very well due to the mass of the rotor. Just about all porsche's can lock up the brakes so clamping power is there. it gets down to cooling as the main factor and brake pad longevity in racing applications. 322mm sloted rotors, aluminum hats, 6 piston calipers is bling!!

diamond=bling, nice!

[RWebb]

What about subjective feel to the driver?

I f you have two braking systems, with equal clamping force, heat absorption capacity (let's call it thermal mass), ability to cool quickly enough, etc. so that deceleration is the same, can there still be differences in feel to the driver?
- things like number pistons for example? can that change the way the brakes "feel"?

[wayner]

Hear capacity in my diagram was meant to address wider vs thinner rotors. ( more cooling "might" diminish this requirement. The line between cooling and capacity is meant as a sliding scale )

Have I captured that correctly?

[wayner]

I also just realized that clamping force should somhow factor in clamping duration

And, less force and duration would also reduce the need for heat capacity of the rotor. Each line is meant as a sliding scale with each point on the triangle being a constraint.

[Flieger]

I think this calls for a flowchart.

1. Can you lock up your wheels? If yes, good. Your brakes are strong enough. If no, then you need more clamping force and/or larger diameter rotors.

2. Now, are you experiencing fade? If no, then great. Your brakes are fine but try lighter calipers and rotors, then go back to #1. If no, then you need more cooling.

3. Are you still experiencing fade even with cooling? If yes, then try different pads and high temperature brake fluid. Lighten the car if possible.

4. Are you still experiencing brake fade? If yes, then get larger rotors.

5. Are you still experiencing fade? Then stop riding the brakes and learn to carry more speed through the turns you pansy!

[James Brown]

Flieger, your on to something. There IS a bunch of variables: car weight, CG, car suspension, driver experience/balls, type of brakes, break fluid, type of caliper, type of tires/wheels (ding, ding), type of cooling, type of rotor, race track, duration of race, ergonomics, ease of maintenance, cost, ect. Finding the "sweet spot" should not be that hard. Most will overkill (especially on street cars) for the bling factor.
ok, i think were up to a pentagon chart!!

[chrismorse]

Road and track used to publish a brake swept area/ton number for most cars, generally indicating the brake sytems ability to dissipate heat.

For sure, lightening the car, using more heat resistent pads and adding cooling will improve the braking performance.

As you approach the brakes ability to dissipate heat, you get very rapid pad and disc deterioration - sometimes using up pads/rotors in a single day of DE/track use.

Along with this brakes on fire experience, we get to experience soft/no brake pedal, long/uncertain braking into the corners, accompanied by wet seats, and or, seat material puckered up while sweating and praying for salvation...dear lord, just this once.....

Clearly, we need to be operating well under this temperature of perishing pads and cracked discs.

I have noticed on every ferrari car specific thread, (prior to the most recent cars), that the stock brakes are not up to the task, when tracking.

I have also put 356 C discs on an old 55 speedster, S calipers front and 914-6 calipers, rear, with vented discs on my 175 hp 914-4.

My most recent brake inferno and rebuild involved a 77 ferrari 308, a 3200 pound car with 240 hp and basically equipped with early vented 911 ATE brake discs and calipers.

One of my theories is that you can improve brake feel and performance by increasing the disc diameter as far as possible, ...simply, more leverage and greater heat sink capability. More heat sink/dissipation capability can be gained by increasing the thickness of the disc. Larger discs require less pressure, thus less pressure related problems, (brake line swelling & caliper deflection), which detract from "feel".

It is difficult to optimize a car that is used for routine street usage and track racing because the pad requirements are difficult to compromise: high temp friction/life vs cold friction, low noise and dusting. Good luck.

Ideally, the friction co-efficient of friction would be fairly flat cold to hot, so that you could adjust the brake bias for the shortest braking distance, that is optimal rear braking effort without locking the rears. Clearly, there are differences in tire capability, track grip and sensitivity of the driver, but we hope for the best :-)

Weight transfer, under deceleration necessitates either an educated approximation of braking force needed, given "normal" tire/road friction, (the stock set up for early cars), an adjustable Bias Bar for two master cylinders, or an adjustable proportioning valve, to more finely adjust the front to rear brake torque, given variable circumstances.

It would be nice if the heat generation and dissipation front and rear were close to the same so that any difference in coefficient fo friction front to rear would be minimized, so that the total of front and rear braking effort could more closely approach THE MAX.

If you increase the piston area to master cylinder area, you get more leverage, but at the expense of a longer softer pedal. So, bigger caliper piston area usually means a bigger master cylinder.

Here is a photo of my old green car brake upgrade.
F-50 brembo calipers, (40-44 pistons), 352x32 drilled discs, (that is the way i got them off of ebay.
New 332x28 rear discs with 36-40 brembo "lotus" calipers, all with floating aluminum hats and pagid R4s pads.
28 mm Wilwood tandem master cylinder with tilton adj prop valve. all tucked inside some 18 " BBS 360 wheels, rear narrowed to 9 inches.

Results: lower pedal effort, firm pedal, dead linear deceleration hot and cold, absolutely no fade running the car as hard as i was able.
The plastic suspension bushings, aluminum shocks, stiffer springs and bars don't hurt either.

Ciao from the dark side, (will never sell my dad's 74).

chris

[James Brown]

this might make everything moot:

Carbon Ceramic Road Car Brakes

• Home : SGL Group

Whilst HITCO leads the development of carbon racing brakes, the (CFC) business unit oversees the development of carbon/ceramic brakes for road car applications. Combining low weight with exceptional strength and hardness, carbon/ceramic is a ceramic composite material, composed of carbon fiber within a silicon carbide matrix (C/SiC).

C/SiC brake performance is revolutionary; the ceramic brake disc achieves not only very high, but also consistent frictional coefficients, maintaining them independent of temperature and weather conditions. Like carbon, C/SiC brakes offer a tremendous weight advantage over conventional steel brakes (about 65%) and this provides consequential improvements in vehicle handling, performance and fuel economy.

On the road, the SGL Group manufactures brakes for Audi, Porsche, Bentley, Bugatti and Lamborghini; equipping cars such as the Veyron, 911 Carrera, S8 and RS5 to name but a few.

[Flieger]

Cool, somebody supports my belief that C-SiC rotors do well from cold compared to C-C.

[James Brown]

more importanly when the get hot, almost no degradation.

[Flieger]

Originally Posted by James Brown

more importanly when the get hot, almost no degradation.

But on a street car (or a car that is used on the street sometimes) you need cold friction. And if you go for maximum cooling then on some tracks you can over-cool C-C. I thought it was kind of obvious that they work when hot.

[James Brown]

i'm not that quick

[1-ev.com]

Hey guys what about "Fade Stop Brake Coolers" link is here Pelican Parts.com - Fade Stop Brake Coolers

Are they any good?