Actual Brake Improvement

[onemoremile]

I guess one way this could be tested would be with a G-Tech Pro RR that could show negative acceleration (deceleration) as a function of g loading. Of course people would comment on accuracy and whatnot but it is the best available for the money and time involved. Accuracy isn't nearly as important as repeatability in this case anyway. If multiple laps showed consistent numbers or a consistent drift due to heat then it is good enough for an informal conversation on a web forum. It isn't like any of us are professionals anyway.

[onemoremile]

well how about i do this... and using equipment from the physics department take measurements, with both setups. then we can have some experimental to go with the theorys.
Then we can yell at my experimental setup :O

I'd love to see the results.

[ModifiedA4]

and this people, is why you go to school.

[onemoremile]

Still haven't read the Stoptech info?

What textbooks cover isn't application specific and the 3' stroke on a front end loader is significantly different than the couple millimeters of a brake caliper. I guess if your book is better than Stoptech's research then more power to you.

What that book is saying is that power isn't magnified since more travel is required. That should be obvious. How it works in the real world isn't. If we follow you and your book then there is no way any calipers will be stronger than any others as long as the rest of the system stays the same. We all know that just isn't true. Boxster calipers over A8 rotors develop more force than the stock calipers. The difference is that they use slightly more fluid to do it. If that wasn't true then Alcon and Stoptech would be out of business.

[onemoremile]

as long as the pads and tires can handle it, and all other things being equal, larger rotors will always decrease braking distance.

Get that one from a textbook too?
http://www.stoptech.com/tech_info/wp...formance.shtml

Long, long ago in a magazine far, far away, a few renegade brake engineers rallied together to bring forward the following message:

“You can take this one to the bank. Regardless of your huge rotor diameter, brake pedal ratio, magic brake pad material, or number of pistons in your calipers, your maximum deceleration is limited every time by the tire to road interface. That is the point of this whole article. Your brakes do not stop your car. Your tires do stop the car. So while changes to different parts of the brake system may affect certain characteristics or traits of the system behavior, using stickier tires is ultimately the only sure-fire method of decreasing stopping distances.”

[ModifiedA4]

I just read the stoptech info to placate you.

Everything written there agrees with the physics equations i derived on my own earlier in this thread. wow. if you read into their equations they make a big deal over bias in order to not overload the tires.

from them

Calculating Optimum Brake Balance
In order to achieve optimum brake balance, or to achieve 100% base
ratio of the front and rear braking forces will be equal to the ratio
vertical forces (axle weights). Under static conditions, this leads

(equations)

However, as the brakes are applied the effects of weight transfer
the ratio of front and rear vertical forces will change as follows:

(equations)

From this relationship it becomes apparent that while the ratio
braking forces is a fixed parameter based on the mechanical sizing
components, the ratio of the front and rear vertical forces
deceleration and vehicle geometry. This dictates that relationship
only one vehicle deceleration level and loading condition
deceleration with the highest percentage of static front weight).

They are talking about tire forces (see the pdf with equations)...why? to prevent skidding. this is the reason why stopping distances increase if bias shifts too far forward. no friggin revelation there.

as i stated this from my first post: as long as the pads and tires can handle it, and all other things being equal, larger rotors will always decrease braking distance.

the physics dont lie, and stoptech uses the same physics to design their braking systems that anyone with a technical background knows. go ahead email them this thread...i have no fear of being wrong with anything ive posted.

you dont understand the mechanics behind braking. instead you brag about patents (i have one too whoopeedeedoo), discount wikipedia (surprising that they have the same info as my 15year old physics book, huh?) and blindly rely external links.

[onemoremile]

Well, if you go back and read through page one you'll find that you've just supported everything I said there and in every other post I've made on the subject. Thanks.

Those statements were based on physics. Did you think I just made this stuff up?
I'm not bragging about patents. They are pretty much worthless. All they do is show that a degree isn't necessary for engineering experience. My experience with the subject began in 1993 when I fitted larger brakes to a Corvette and performance got worse. A few of us swapped parts and experimented until we saw improvement. No professors were injured in the process...

I think you should go watch Good Will Hunting again. And for what its worth, my first college engineering course was 21 years ago when I was TWELVE years old. And yes, I'm bragging about that one. And the 1380 SAT that got me there. And the Mensa letters. And on and on and on...

[ModifiedA4]

Well, if you go back and read through page one you'll find that you've just supported everything I said there. Thanks.

how could i have done that?

all quotes by you:

i have poor judgment, nothing i said makes any sense, i should Stop making things up and shouldnt extrapolate strange ideas. dont forget you know i am an engineer because (i) cling to false concepts and close (my) mind to real knowledge

uh, huh.

when you spew gems like this:

We're going to make up numbers to illustrate the point. Assume that it takes 100psi of line pressure to get the job done with stock brakes. Also assume that the fronts do 80% of the work and the rears do the other 20%. The 4 piston calipers will get more work done with that 100 psi. That proportionally lowers the amount of work the rears do. If it now takes 75 psi line pressure to generate the same amount of brake torque (as the stock fronts at 100 psi) then the rears are now limited to 75% of their potential.

which is sooooo friggin wrong its laughable.

have a nice day.

[onemoremile]

which is sooooo friggin wrong its laughable.

have a nice day.

If a caliper generates more clamping force from the same line pressure then it throws off the balance. That statement is still correct. It could have been said differently but it is still correct.

Run it by your prof. Maybe if you're proven correct he'll let you come up for air.

[ModifiedA4]

If a caliper generates more clamping force from the same line pressure then it throws off the balance. That statement is still correct. It could have been said differently but it is still correct.

Run it by your prof. Maybe if you're proven correct he'll let you come up for air.

stay classy audizine.

and you're still wrong. really wrong. so wrong you cant even comprehend it. thats the worst, not knowing what you dont know.

not once have you debated the facts, or even the equations posted, its because you dont understand them.

im sorry this thread got out of control. i figured a good technical discussion helps the a4 crowd. unfortunately it became a dork-off.

[Joey T]

We're going to make up numbers to illustrate the point. Assume that it takes 100psi of line pressure to get the job done with stock brakes. Also assume that the fronts do 80% of the work and the rears do the other 20%. The 4 piston calipers will get more work done with that 100 psi. That proportionally lowers the amount of work the rears do. If it now takes 75 psi line pressure to generate the same amount of brake torque (as the stock fronts at 100 psi) then the rears are now limited to 75% of their potential.

In a short stroke hydraulic system the piston area determines how much work gets done. Psi is pressure per square inch and larger pistons have more square inches. The fronts will grab harder with less pressure and that is what makes them feel so good. They feel tight and powerful and most of the time that is just fine but when you really need to stop now the rears are down on power.

I *almost* don't know where to start with this... well, anyway.

You most certainly should not be designing brake systems. A few short points..

The front and rear brakes use two, separate, unlinked, non unified, different hydraulic systems. The master cylinder has two brake lines, one front, and one rear. So there is *no way* larger front brakes take away any line pressure from the rear.

And torque is not how far you push the wall. That is inertia. If you put your car up against the wall and hit the gas, then torque would be how far you pushed the wall.

[Joey T]

If you limit brake dive this weight transfer is limited and the rears can do more work. How much of a difference is some labor intensive math best left to computer modeling.

You cannot transfer weight on your vehicle by braking, turning or accelerating. As long as you don't count your ego on the passenger seat sliding around.

Load, on the other hand, can most certainly be transfered.

[audinutt]

So Joey, are you saying i was correct that on the a4 you CAN upgrade the front brakes and it WILL decrease stopping distances.

Thanks,
-Richard

[Joey T]

So Joey, are you saying i was correct that on the a4 you CAN upgrade the front brakes and it WILL decrease stopping distances.

Thanks,
-Richard

Yes. Any arguments against this being the case presented here had large, factual, real world errors. Which is great, considering the person who posted them made fun of engineers who he claimed did the same thing.

[Squarrl]

Where in Scotia are you?

[djwimbo]

You cannot transfer weight on your vehicle by braking, turning or accelerating. As long as you don't count your ego on the passenger seat sliding around.

You're talking about one of the most intelligent guys I know.
And YES, weight transfers. Whether you call it "load" or not, your suspension, tires, etc. all "see" it as weight.

As far as making fun of other engineers, they've all made grave mistakes. You know who ends up fixing the problems engineers make? People in the field, that have real world experience. Not everything works like it does in a lab.
Don't get me started on how TECHNICIANS have to fix what ENGINEERS have fuct up over the years.

As far as the original question, topic, whatever...
If you want a usable brake upgrade, go with the A8/TT rotors up front, a quality set of stainless steel lines and a high end brake fluid. At this point tires will be the limiting factor.
Upgrading the brakes correctly will improve stopping distances.

Personally I have A8 front rotors (slotted) and Slotted rears, both with matching brake pads. Always make sure the front and rear friction material is the same. This is one of the reasons you want to do both sets of brakes at the same time.
My first A4 had a stickier brake pad in the rear, and on a panic stop(or AutoX stop box), the rears would lock up and walk the ass over about a foot.
I am very happy with my braking performance. Side by side comparison between my car and my roommate's built Turbo Miata(1000lb advantage) was damn close. His advantage was in the tires he was using. 60-0 was within a car length w/ me on all seasons.

[biketsai]

i hate physics, hard shit

[hoganalley]

I've read all of this and I've read the Stoptech stuff too. I'm not an engineer, but I do have some design sense. Here's what I understand. The ABS system is pre-programmed to react to a specific response time. If the tires are too good, the system acts up and thinks the car is skidding. That's basic, but essentially, true. Flame if you want.

Here's what I've done. A8 fronts, A8 (269mm) rears, Stasis SS, new stock lines, +1 brake fluid, Axxis Ceramics and Falken 912's.

Based from Stock Sport suspension, A8 fronts (Hawk HPS), stock rears (Axxis Ceramics) and Khumo 712's, with the current setup the brake dive now is almost gone. I have A LOT more level and consistent braking. I would personnally reccomend the full A8 upgrade to anyone. And yes, if you measure stock brake size vs A8 brake size, it's almost a perfect upgrade......depending on your needs of course!

[djwimbo]

A8 rear brakes does sound like a good idea. I'd be willing to give it a try.

Why run a different pad f/r though?

as far as the ABS system and tire relation, as long as the tire isn't drastically larger or smaller than stock, the system will function normally.

[Squarrl]

Based from Stock Sport suspension, A8 fronts (Hawk HPS), stock rears (Axxis Ceramics) and Khumo 712's, with the current setup the brake dive now is almost gone. I have A LOT more level and consistent braking. I would personnally reccomend the full A8 upgrade to anyone. And yes, if you measure stock brake size vs A8 brake size, it's almost a perfect upgrade......depending on your needs of course!

How is brake dive changed by A8 brake size... wouldn't that make it worse if we say they work better then stock?
I would have though brake dive was more a suspension related issue

[hoganalley]

Why run a different pad f/r though?

Before I switched the rears, I had stock sport suspension and stock rear brakes. The pads had to be switched and it was a package deal when I got the A8 fronts. I wouldn't do it normally.

How is brake dive changed by A8 brake size... wouldn't that make it worse if we say they work better then stock?
I would have though brake dive was more a suspension related issue

Sorry....I wrote it late last night.....probably not clear. Stock sport suspension and A8 fronts I swear the front of my car would touch the ground under hard braking. Once I upgraded the suspension, all of that is gone. It is a suspension issue for sure, but since the shocks and the A8 rears were done at the same time, I can't give a specific feeling from adding the bigger rears. It's just mathematically proportioned from our stock sizes.

The only drawback for me is the pedal is a bit mushy which should happen without upgrading the Master Cylinder.....although, the only part number that's different between the A8 system and ours is the hydraulic pump. I have stock rubber lines, but that's only because if you run SS lines, technically, they should be swapped every 2 years or so. I'm sure SS lines would help with the mushy pedal.

[onemoremile]

You cannot transfer weight on your vehicle by braking, turning or accelerating. As long as you don't count your ego on the passenger seat sliding around.

Load, on the other hand, can most certainly be transfered.

It may not seem like it after reading through this thread but I really don't have any ego. I'm a student of everything and love nothing more than gaining a deeper understanding of any given subject. In this case I've chosen what I believe to be an excellent teacher. A few friends that do what he does have also shed some light on the subject. These guys aren't professors of physics they are engineers and scientists running countless real world tests and virtual simulations. A prof can tell you what he would do but these guys show you what they've done. Would you rather read a book on track driving or ride shotgun with Randy Pobst? We're talking about the real world here as viewed from behind a helmet visor not from a lecture hall.

Load is the correct term but it is often referred to as weight, weight transfer, weight jacking, etc.. The terminology is definitely different in the paddock. I've never heard a driver or chief use the term load transfer. Lots of things are misnamed like the proportioning valve. Such is life.

-----------------------
You guys aren't arguing with me but James Walker Jr.. Take a little look at his bio. Maybe he doesn't have the experience or knowledge that you guys possess but I know he's a hell of a lot smarter than I am. Although qualifications are not always indicative of talent, I'm going to go out on a limb here and say that he probably knows a little something or two.

James Walker, Jr.
StopTech Consultant


James Walker, Jr. is currently the supervisor of vehicle performance development for brake control systems at Delphi Energy & Chassis. His prior professional experience includes brake control system development, design, release, and application engineering at Kelsey-Hayes, Saturn Corporation, General Motors, Bosch, and the Ford Motor Company. Mr. Walker created scR motorsports consulting in 1997, and subsequently competed in seven years of SCCA Club Racing in the Showroom Stock and Improved Touring categories.

Through scR motorsports, he has served actively as an industry advisor to Kettering University in the fields of brake system design and brake control systems. In addition, Mr. Walker contributes regularly to several automotive publications focusing on brake system analysis, design, and modification for racing and other high-performance applications. He is a recipient of the SAE Forest R. McFarland Award for distinction in professional development/education. Mr. Walker has a B.S. in mechanical engineering from GMI Engineering & Management Institute.

To find out more about Mr. Walker and scR Motorsports, visit their website at www.teamscR.com.
-----------------------


The ever-present weight transfer phenomenon

Let’s assume we have a 2500 pound car with a 50/50 static weight distribution. If we are only concerned with the vehicle at rest, it’s easy to determine the weight on each wheel. We just need to find some scales and weigh it. The sum of the front corner weights is equal to the front axle weight (1250 pounds), and the sum of the rear corner weights is equal to the rear axle weight (also 1250 pounds). The weight of the vehicle is of course equal to the sum of the two axle weights (our original 2500 pounds), and this weight can be thought of as acting through the vehicle’s center of gravity, or CG. Figure 1 sums it up nicely.


Note that when at rest, there are no horizontal (left or right) forces acting on the vehicle. All of the forces are acting in a vertical (up and down) direction. But what happens to the vehicle when we start to apply forces at the tire contact patch to try to stop it? Let’s find out.

During braking, weight is transferred from the rear axle to the front axle. As in cornering where weight is transferred from the inside tires to the outside tires, we can feel this effect on our bodies as we are thrown against the seat belts. Consequently, we now need to add several more arrows to our illustration, but the most important factor is that our CG now has an deceleration acting on it.

Because the deceleration force acts at the CG of the vehicle, and because the CG of the vehicle is located somewhere above the ground, weight will transfer from the rear axle to the front axle in direct proportion to the rate of deceleration. In so many words, this is the effect of weight transfer under braking in living color.

This deceleration force is a function of a mechanical engineer’s most revered equation, F=ma, where F represents the forces acting at the contact patches, m represents the mass of the vehicle, and a represents the acceleration (or in our case, deceleration) of the vehicle. But enough of the engineering mumbo-jumbo – just have a look at these additional factors in Figure 2.


n Figure 3 (the beginning of what we call a “fishbone diagram” – more on this later), we see how our 2500 pound vehicle with 50/50 weight distribution at rest transfers weight based upon deceleration. Under 1.0g of deceleration (and using some typical values for our vehicle geometry) we have removed 600 pounds from the rear axle and added it to the front axle. That means we have transferred almost 50% of the vehicle’s initial rear axle weight to the front axle!

FIGURE 3.



At this point, the brake system we so carefully designed to stop the vehicle with a 50/50 weight distribution is going to apply too much force to the rear brakes, causing them to lock before we’re getting as much work as we could out of the front brakes. Consequently, our hero is going to get that white-knuckled ride we talked about earlier because he creates more tire slip in the rear than the front, and it’s going to take longer for him to stop because the front tires are not applying as much force as they could be.
So what influences brake bias?

If we look at the equations we have developed, we see that all of the following factors will affect the weight on an axle for any given moment in time:

· Weight distribution of the vehicle at rest
· CG height – the higher it is, the more weight gets transferred during a stop
· Wheelbase – the shorter it is, the more weight gets transferred during a stop

We also know from fundamental brake design that the following factors will affect how much brake torque is developed at each corner of the vehicle, and how much of that torque is transferred to the tire contact patch and reacted against the ground:

· Rotor effective diameter
· Caliper piston diameter
· Lining friction coefficients
· Tire traction coefficient properties

It is the combination of these two functions – braking force at the tire versus weight on that tire – that determine our braking bias. Changing the CG height, wheelbase, or deceleration level will dictate a different force distribution, or bias, requirement for our brake system. Conversely, changing the effectiveness of the front brake components without changing the rear brake effectiveness can also cause our brake bias to change. The following table summarizes how common modifications will swing bias all over the map.

[onemoremile]

Before I switched the rears, I had stock sport suspension and stock rear brakes. The pads had to be switched and it was a package deal when I got the A8 fronts. I wouldn't do it normally.



Sorry....I wrote it late last night.....probably not clear. Stock sport suspension and A8 fronts I swear the front of my car would touch the ground under hard braking. Once I upgraded the suspension, all of that is gone. It is a suspension issue for sure, but since the shocks and the A8 rears were done at the same time, I can't give a specific feeling from adding the bigger rears. It's just mathematically proportioned from our stock sizes.

The only drawback for me is the pedal is a bit mushy which should happen without upgrading the Master Cylinder.....although, the only part number that's different between the A8 system and ours is the hydraulic pump. I have stock rubber lines, but that's only because if you run SS lines, technically, they should be swapped every 2 years or so. I'm sure SS lines would help with the mushy pedal.

I agree 110% Your configuration is well chosen. I've been considering the Big Reds and contemplating which rears (A8, B7 S4, S8, Stasis) would match and which master cylinder would feed them best.

The dive shown on the last page is stock stuff with the A8 kit and grippy street tires. It was manageable on street tires but could have been a real handful on r-comps. A couple days ago I pulled the stock front suspension off and installed Shine Racing's 500 pound springs with custom valved Bilsteins and the dive is gone. The car just throws out the anchor.

The later A4s and the S4 have a slightly larger master cylinder. I've read of an S8 that had problems with master cylinder or firewall flex. Can't remember the name but the guy always had a pic of the big beast on the track in his AW sig. If I remember it right he would stomp the pedal and the MC would hit the false firewall and he had to do some bracing.

Stainless lines and the Tyrol bushings both helped with the pedal. It still isn't hard or touchy like the S4 pedal. It is still relatively soft and very progressive for the first half inch (estimating) but then firms up and can't be pushed much farther. With the street pads there is plenty of clamping power and with the track pads warmed up it is unreal.

The Superformance mkIII has Wilwoods all around and no ABS. The 50/50 balance helps but the 88" wheelbase, 275/40-17 fronts, and 315/35-17 make things interesting. It got a full brake overhaul over the weekend and stops on a dime now.

[onemoremile]

Another great article that covers more of the braking system in plain english. I love GRM.
http://www.teamscr.com/grmbrakes.html



This one details how ABS treats brakes both stock and upgraded.
http://www.teamscr.com/bigbrakekits.html

Here is a little snippet of the last one. For those that believe the ABS system will magically sort things out and compensate for big fronts that do more work with the same pressure then this article is for you.

Pressure-Torque And Pressure-Volume Relationships

When a braking system is designed and installed, the components are chosen to provide a certain deceleration level for a certain amount of force applied by the driver to the brake pedal. While the overall relationship is critical, there are many ways to achieve the same end…but fundamentally the parts are chosen to work together as a system.

One of the most important relationships for the ABS engineer is the pressure-torque (P-T) relationship of the caliper/pad/rotor assembly. In so many words, for a given brake fluid pressure, X, the caliper/pad/rotor assembly will build up a certain amount of torque, Y. For the sake of argument, let's assume that adding 100 PSI of brake pressure to the stock caliper in our example vehicle generates 100 ft-lb. of torque.

Another important relationship is the pressure-volume (P-V) characteristic of the system. This relationship defines the swelling or expansion of the brake system for a given increase in pressure. Let’s also say that our stock vehicle brake system ‘swells’ 1cc for every 100 PSI.

Unfortunately, there are several big-brake systems available today which pay no regard to the original P-T or P-V relationships of the original vehicle…and in fact many make it a point to affect drastic changes in these relationships in order to give the consumer that feeling of ‘increased bite.’ While the upside is certainly a firmer pedal and higher partial-braking deceleration for the same pedal force, the trade-off can be ABS confusion.

[onemoremile]

Rotors anyone? I don't think I mentioned it in this thread but have a few dozens other times. Rotors are thermal management devices. Yeah, they've got more leverage and whatnot but the real deal is that they keep the surface temps of the pads down. Those lower temps transfer less heat to the fluid which is a good thing on the track but completely irrelevant on the street.

http://www.teamscr.com/rotors.html

Let’s look at some common rotor ‘modification’ and ‘performance’ upgrades that you may have been exposed to and try to separate the marketing from the engineering…

Super Sizing

Bigger rotors will make your friends think you are cool, bigger rotors look sexy, but bigger rotors do not stop the car. What a bigger rotor will do is lower the overall operating temperature of the brakes – which is a GREAT idea IF your temperatures are causing problems with other parts of the braking system. Take for example a F500 racecar – a small 800 pound single seat formula car. While the brakes are certainly much smaller than those found on a 3,000 pound GT1 Camaro, that does not necessarily mean that they need to be made larger. In fact, swapping on a GT1 brake package would probably do more harm than good – that’s a lot of steel hanging on the wheel that needs to accelerate each time the ‘go’ pedal is pushed. So, the motto of this story is bigger is better until your temperatures are under control. After that point, you are doing more harm than good…unless you really like the look (and hey – some of us do!).

Crossdrilling

Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the 40’s and 50’s, not a whole lot. Rotors were first ‘drilled’ because early brake pad materials gave off gasses when heated to racing temperatures – a process known as ‘gassing out’. These gasses then formed a thin layer between the brake pad face and the rotor, acting as a lubricant and effectively lowering the coefficient of friction. The holes were implemented to give the gasses ‘somewhere to go’. It was an effective solution, but today’s friction materials do not exhibit the same gassing out phenomenon as the early pads.

For this reason, the holes have carried over more as a design feature than a performance feature. Contrary to popular belief they don’t lower temperatures (in fact, by removing weight from the rotor, the temperatures can actually increase a little), they create stress risers allowing the rotor to crack sooner, and make a mess of brake pads – sort of like a cheese grater rubbing against them at every stop. (Want more evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it.)

The one glaring exception here is in the rare situation where the rotors are so oversized (look at any performance motorcycle or lighter formula car) that the rotors are drilled like Swiss cheese. While the issues of stress risers and brake pad wear are still present, drilling is used to reduce the mass of the parts in spite of these concerns. Remember – nothing comes for free. If these teams switched to non-drilled rotors, they would see lower operating temperatures and longer brake pad life – at the expense of higher weight. It’s all about trade-offs.

Slotting

Slotting rotors, on the other hand, might be a consideration if your sanctioning body allows for it. Cutting thin slots across the face of the rotor can actually help to clean the face of the brake pads over time, helping to reduce the ‘glazing’ often found during high-speed use which can lower the coefficient of friction. While there may still be a small concern over creating stress risers in the face of the rotor, if the slots are shallow and cut properly, the trade-off appears to be worth the risk. (Have you looked at a NASCAR rotor lately?)

Too cool!

Last year we bought 4 rotors. Two were bone stock, and two were subjected to a process know as Cryogenically Treating – one of the high-tech buzzwords floating around the paddock. The rotors were run back-to-back on the same track on the same car on the same day with temperatures taken to make sure that they saw the same level of heat. Following the track session, the parts were removed and we had them literally dissected by a materials lab.

The testing conducted included surface hardness, grain structure analysis, density, and surface scanning with an electron microscope. Guess what – after seeing the heat of use, the rotors looked identical in every regard. This is not to say that there is not a benefit from treating other parts which see lower temperatures and/or have different material properties, but treating our rotors on our car showed no tangible benefits (note that it didn’t seem to hurt anything either). Come to your own conclusions, but in our case, we’ll pass.

Summary

So, what’s the secret recipe? Again, there is no absolute right or wrong answer, but like most modifications, there are those which appear to be well-founded and those that ‘look cool.’ If ultimate thermal performance is your goal, look to what the top teams are running (relatively large, slotted rotors). However, if ‘image’ is your thing, break out the drillpress – and be prepared to replace your brake pads on a regular basis.

[onemoremile]

I want to thank James Walker Jr., Stoptech, and Grassroots Motorsports Magazine for putting such great articles out there where us amateurs can learn from them. This is a fine service and they should be commended for it. I also don't want anyone to think that I've made any of this stuff up. I made a couple analogies or anecdotal comments that may have been a little off-center but only because the material can be hard to relate without a full understanding of the subject.

[pinky]

# of rotor revolutions = # tire revolutions. This is why stopping distance reduction is related to rotor size. The more linear distance the pads act over per revolution (larger rotor), the more work is done converting energy per revolution.

The 'lever arm' people like to talk about is a red herring. All that does is change the braking 'feel' or onset of force to the rotor. As long as the brakes are not locking or the tires skidding, the lever arm has no impact on braking.

these two comments contradict each other.

as you increase the lever arm you are increasing the "linear distance" the pad is acting on.

[pinky]

And YES, weight transfers. Whether you call it "load" or not, your suspension, tires, etc. all "see" it as weight.

*technically* weight is the force resulting from gravity's effect on a mass...

so unless gravity or mass change weight doesnt change...

semantics, i know..

[rogerius]

any article regarding ABS+EBD(Electronic Brake force Distribution) and how this enables us or not to do Rear Big Brakes to get the most braking force out of them and to transfer the rest to the Big Ass Front Brakes?
Becouse this is what I believe will reduce the stopping distance one one hand and will increase the fade resistance on the other.
Please comment!

[Squarrl]

I would have thought the way to do these measurements would be A to use force (i would use newtons) B to setup vectors of forces at the center of each wheels simulated vs time as well as have a vector of forces at center of mass vs time... Then you could see the forces at all corners an direction of forces in realtime.

[hoganalley]

Stainless lines and the Tyrol bushings both helped with the pedal. It still isn't hard or touchy like the S4 pedal. It is still relatively soft and very progressive for the first half inch (estimating) but then firms up and can't be pushed much farther. With the street pads there is plenty of clamping power and with the track pads warmed up it is unreal.

That's it exactly! Perfect description. It's a little dis-heartening when you first press the pedal, I love the feel of the S4 pedal. However, once the pads warm up, it grabs like an angry SOB! Sometimes I wonder if it's too much and people behind me won't be able to compensate. I would love to try Bobcats and see what it's really like!

For the street, this setup is great. It's cheap and effective. If I was tracking my car, I would consider drilled rotors but it's not necessary on a street car. Just looks cool!

To go back to the original idea behind this post, bigger rotors will stop the car faster, but it's only 1 part of the equation. Everything else must be looked at and upgraded accordingly. That's why a lot of people do pads, fluid and tires because it's really all you need. You can upgrade all you like but it must be done in proportion.

[speedydragon]

i hate physics, hard shit

agreed lol.

I think after reading this thread, I realized that I learned more from this than in my physics class :P

[Mawhitey]

My head hurts !!!
Decent pads and stainless lines it is then

[onemoremile]

any article regarding ABS+EBD(Electronic Brake force Distribution) and how this enables us or not to do Rear Big Brakes to get the most braking force out of them and to transfer the rest to the Big Ass Front Brakes?
Becouse this is what I believe will reduce the stopping distance one one hand and will increase the fade resistance on the other.
Please comment!

Scroll on up to post #64.

The cliff note version is that the electronic systems are designed around a certain amount of brake torque. If that is changed the computers get confused and over or under correct. Since they are modulating more powerful brakes things get even stranger.

[onemoremile]

That's it exactly! Perfect description. It's a little dis-heartening when you first press the pedal, I love the feel of the S4 pedal. However, once the pads warm up, it grabs like an angry SOB! Sometimes I wonder if it's too much and people behind me won't be able to compensate. I would love to try Bobcats and see what it's really like!

For the street, this setup is great. It's cheap and effective. If I was tracking my car, I would consider drilled rotors but it's not necessary on a street car. Just looks cool!

To go back to the original idea behind this post, bigger rotors will stop the car faster, but it's only 1 part of the equation. Everything else must be looked at and upgraded accordingly. That's why a lot of people do pads, fluid and tires because it's really all you need. You can upgrade all you like but it must be done in proportion.

Don't bother with the Carbotech Bobcats. I had them and they are so not worth the 160 bucks. For about $60 the Axxis Ultimate Ceramics are a crazy value and outperformed the Bobcats in every way. The AUC are silent where the CB would occasionally squeal like a garbage truck. The CB would slip when cold just like when driving on the freeway in the rain whereas the AUC have a grip that feels consistent and predictable regardless of temperature. If the prices were reversed it would reflect the actual real world performance of the pads.

The Panthers on the other hand are sick. I ran the Bobcats one track day with street tires (the brake dive photo) and shaved otherwise new pads down to the backing pads. I ordered new pads the day after the track day and barely survived the few days of delivery time. The Panthers have no cold bite and sound much more aggressive - almost like they are filing or grinding down the rotors - until warmed up. I ran them as hard as I could trying to cook them (with r-comp tires too) and had a blast. They never failed (the Bobcats cooked and led to several drive-offs) and endured an enormous amount of heat. I didn't have the pyrometer with me but it hurt to check tire pressure with a gloved hand. Bare handed it singed the little hairs on the backs of my fingers before I got to the wheel itself. The pad wear was negligible and the rotors look fine. Other than the rubber boogers all over the car there were no signs of the track day. The Panthers are amazing.

[hoganalley]

Don't you just love asking a simple question and have it analyzed until the cows come home?!!!! LOL!!!

[onemoremile]

I would have thought the way to do these measurements would be A to use force (i would use newtons) B to setup vectors of forces at the center of each wheels simulated vs time as well as have a vector of forces at center of mass vs time... Then you could see the forces at all corners an direction of forces in realtime.

The hardest part is getting it all to make sense. I think 3D waterfall plots would be the way to go but a lot of people can't read those. Even those that can get confused often.

This is the kind of plot used to depict spectral decay for audio designs.
http://www.accuton.com/img/products/...-6_ATB_WTF.gif

[Squarrl]

well depending on the equipment and when I can do this it will probably be a custom written graphical program, since its all done in linux and the interface is custom. I might not be able too since my buddy will be going to Berkley for post doc in late July.

[onemoremile]

I still think a G-Tech Pro RR would be plenty usable. They can export info to a laptop for plotting or analysis. Repeatability is more important here than accuracy. If one setup repeatedly hit higher G under deceleration it wins. If everything else is the same the acceleration G can be used as a control or at least a guideline to let you know if things are matching up or not.

[Joey T]

You know, I jumped in this because the argument that bigger front brakes made less pressure available to the rears got me all riled up, and since everyone was arguing hydraulics, I hung my hat on the fact that the B5 has separate systems.

I would now like to rescind my statement that bigger and better front brakes has no effect on rear brake pressure. It does, but not for the reasons stated.

The whole idea of better brakes is to make the car stop better with less effort. More rotational energy is converted to heat quicker. So how do front brakes effect rears?

The more efficient front brakes require less pedal travel to perform the same energy conversion, and this shorter pedal travel results in less effort being performed by the rear brakes.

Does this *increase* stopping distance? My empirical testing on B5 chassis cars say no, no way. I would be interested in real data, but to be honest, I won't be doing any BBK installs for a while. Not that I know of.


I thought of this today while driving an S4 around that had a BBK. Stopping distance with the front BBK only was far less than the stock S4 I drove later in the day, but the first car had better tires. More testing proved difficult, as the next two cars I worked on were a 1977 VW Bus and a 1969 Mercedes 280. Neither of which stopped for shit.