Article: How to Choose Street and Track Brake Pads

Very thorough grounding of the basics, facts and thought processes. Always good to revisit the state of the industry and your purposes/needs.

I've had to convince many people that simply by changing pads, they can get a huge increase in performance for the track and _probably_ do not need that $3000 pair of "big brakes" that someone is telling them they need.

When talking to people about their brake pad preferences (time to duck and watch the fanboy stories fly as J mentioned) and experiences, you should factor in two aspects:

1. Everyone has a different braking "style" or technique whether they know it or not. A pad for someone who brakes very slowly and over a longer period of time may well overheat a pad that someone who brakes very hard and over a short period of time may not. So when someone relates a story of brake fade, dig in a bit: what 's the pad, what's that pad's melting temps, can you see how the person brakes under speed?
2. Car weight, tires, suspension and other variables do not affect ho brakes work, they can cloud stories/experiences people tell.

Another suggestion is to try or go for a ride with a person with the pads you are interested in. Or better yet, a brief drive of their car under the conditions/purposes you are looking for as J detailed (careful though: break it and you buy it. You'll get to compare some of the factors at play in the tales/opinions related by other people.

So now you've got the right pad. Now what? Brake technique. Do not mash the brakes. Smooth inputs into any car control: acceleration, slowing (lifting, shifting, clutching, braking) and steering. The only think connecting you to the ground is the contact patch of the tires; upset them with abrupt inputs and they may let go. Think of it as your wife/girlfriend/partner. If you hit them, they'll hit back ;-). Apply the brake pedal smoothly and accelerate into the brake pedal (pressing faster and faster). Just before the corner, reverse with the last amount of lift off the brakes being as slow and smooth as possible (helps with the weight transfer into the corner). The lift off the brakes should be slower than the initial application. At first this "long" process will require you to brake longer. Over time you will get faster and faster until it seems to others that you are stamping the brakes. As you get faster at it, you can then shorten your braking distance without upsetting the car. If you do not have ABS, then as you reach the maximum braking effort shown in the diagram (can be maximum braking capacity), then approach that line smoothly as well. At that point you can module at the threshold to prevent lock-up, maintaining steering and maximum braking capacity.

Enjoy and keep the rubber side down!

Hagen
92 348 ts serie special #14

CV if that matters? 5 years racing touring cars (BMWs), 12 years instructing (in car) at performance schools/DEs (BMW CCA, BMW CC, FCA, PCA, Audi, Saab, Raven, FastLaps, MCO winter and summer, MCO race schools), 5 years selling BMW performance bits. But I'm still learning. I certainly have not tried even 1/4 of the ultra race pads out there let alone all the other combos: street, performance street, street/track, track/street, race, endurance etc.
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Looking forward to them!

 

Jeff,

Considering advances in technology what is the current thinking on bedding road race brake pads? Are there manufactuers who are specifically for it or against it or indifferent to it? Naming names is just fine too. Bedding modern race pads from carbotech and cobalt friction seem to do absolutely nothing for me but I race without data aqu so I don't know if there is some barely significant gains to be made bedding pads.

 

My opinion (and what I've done) is bed my race pads when on my street cars but not for racing. I find the bedding procedure as recommended by Hawk and Carbotech to be inadequate. I perhaps do overkill but have had pads last longer and usually my customers have too (disclosure - that is all anecdotal and I have not done any data comparison of longevity). I also did not spend a great deal of time figuring out the optimal bedding procedure.

On my street M3, I used Carbotech XP1110s. This car was also tracked 15-20 days per year at DEs. What worked for me was 15 stops from 70 km/h to 50km/h with gradual pedal pressure and gradually increasing the pressure over each stop. I'd then do 15 at 100 km/h to 50 km/h again never reaching "panic stop" pressure or coming to a full stop.

On the race car (BMW 325) I used Carbotech XP1108s to 1112s over the years (as the compounds evolved). I never bedded those.

On my 348 I have a local company (KVR) and on my BMW 325 (street not race car), Hawk Ceramic and have not bedded either of them. Both are street oriented performance pads.

One factor that we haven't discussed: I never changed my rotors when I changed my pads. As a result, pads need to conform to the rotor surface quickly otherwise your getting less contact surface. So, bedding for the harder pads.

I look forward to Jeff's response to see if I need to learn something new.

Hagen
92 348 ts ss #14

 

Brilliant. Thank you. Can't wait to read the remainder of the article (you said Tuesday right

 

Me too! Thanks for posting.

I have bed race pads and noticed no difference. So I don't do it anymore. I am notoriously easy on brakes. Perhaps the whole issue of not getting pads hot enough during bed-in was my problem.

Is there a guaranteed way to know for sure if you got your temps up say with tempilaq paint on the steel pad backing edge? Is there a general temp range to shoot for or are all pads too different to comment on bed-in temp? If tempilaq is a good idea and pad material absorbs heat well is there a differencial of how much heat is in the pad vs. what I would see on the tempilaq on the steel backing?

 

I have done the stinky thing but look forward to seeing your video. Watching a pro work always pays dividends. Keep us posted. Thanks!

 

I'll have to respectfully disagree with your recommendation of slow application of brake pressure and then accelerate into the brake pedal. Wet conditions aside, heavy braking corners almost always require instant maximum brake pressure. The first 10 meters of the braking zone is the difference between keeping your position or losing it.

 

Jeff:

Do you have any knowledge of PFC 01, 03, and 05 race compounds for sprint road course racing?

 

FBB:

For sure bedding in the pads makes a big difference in performance and longevity, especially when both pads and rotors are new. The smell, the slight ash color of the pad's contact edge, plus a nice even layer of slate grey transfer layer on the rotors are sure signs they are bedded in properly.

 

Jeff:

Thanks for your input. Yes, I also like PFC01 very much. I used them in the last 4 seasons of road course racing in Asia. Right now I'm thinking of switching to 03 or 05 compound with supposedly more initial bite. I have not been able to get details of the newer compounds in terms of rotor wear and trail braking modulation as compared to 01 compound. PFC has great products but it's not very responsive to customer inquiries.

 

I agree in that racing has much different braking requirements from the average joe or the guy on the track at a DE.

 

I'm not sure what I do because I don't think to much about what I do. I just drive. But I hear both of you and probably do both. Two points FWIW once I had a real pro guy on TV etc. drive me in "my" car. I thought for sure we were going gardening at my home track. He was 20mph over my top speed at the end of the straight. When I brake the car is all over the place so that caps my top speed out of fear. He put the brakes on at that huge speed and the car tracked like on rails! He was doing what BC posted earlier extremely smooth braking. He really changed the way I view brakes. Point two when racing what I think is pretty close to my 10/10ths, the battle between two of us always seem to slow us down and allow the guy behind us to catch up. If we are too focused on fighting each other sometimes we both loose position to the guy behind! We might be doing that heavy braking in the first 10 meters and that may help maintain position but I am not convinced that's the fast way around the track and maintaining the equipment and tires is critical to maintaining position at the finish. Sometimes if I kill myself to stay ahead of one guy and spend myself I end up getting passed by two guys instead of just one. I have found that my passes stick when I'm "calculating" and pick the perfect time to pass rather than force a pass only to give it back. The use of upstream traffic is critical as well as watching who is coming up on the rear. Racecraft is what makes the sport fun.

 

That is no how the physics of the problem works::

Lets say you are at full acceleration and going fast. Thus the engine power at the rear wheels is holding the front nose of the car a little above its normal stationary position. The rear is correspondingly lower due to the power and due to the aero drag acting at the center of pressure which is above road surface. Finally, aerodynamic pressure on the body is pushing the car from front towards the read accentuating both of the previous effects. Thus the car is nose high and tail low.

With the nose high and tail low, the front tires do not have as much weight on them as they will have after the application of the prake pedal. Correspondingly the tail has more weight on it and will have less after brakes are applied.

You cannot get full brakes into the car, until it has transfered weight from the rear to the front. If you do, the fronts will lock and ABS. Thus, you should progressively add brake pedal pressure as the nose goes down, reaching full pressure as the nose settles into its full brakes position.

Under full power at mid-160 MPH levels, the front tires will have about 100 pounds less weight on them than static, and after application of the brake pedal will have about 200 more pounds of weight than static. Static weight on an F355 front tire is about 740 pounds. Thus, around 40% more braking power is available after weight is transfered than before. This means the driver can go immediately to about 65%-70% brakes and add more pressure as the nose settles.

Ths springs and shocks ultimately determine how long this takes--not the driver applying the pressure. In any event the time constant is at least 0.5 seconds and probably just a hair over 1.0 seconds. Race cars have stiffer springs and shocks so that this time period can be as low as 0.2 seconds--but it is still finite and appreciable.

 

So basically you say instantly go for 70% brakes to get the weight transfer then ramp up the pedal when you are now able to apply more brake and that this occurs in about 0.5 second?

If so I don't buy it. The braking equation is not linear. I don't think you can do a physics solution to it with the ideal car, ideal suspension on the ideal road surface etc. The problem is not like calculating general gas law and the ideal gas. There are too many issues that make this become an argument of which is better big springs or big sway bars?

 

What I am saying is that the front tires have enough weight on them that they will not lock up instantly at 70% brakes from a full throttle situation. I did not mean to imply that this is the best course of events.

All of the articles on smoothness imply that a cosine curve from 0% brakes through 100% brakes corresponding to the time it takes for the nose to change from up to down. This will alow a smooth removal of power, a smooth drop of the nose and smooth rise of the rear; at the rates the springs and shocks can control.

The physics just says that you can go instantly to 70% and the tires won't lock up. The suspension will be all out of whack as the nose descends faster than the springs and shocks can control the front end. The physics does not say this is the best way to apply the brakes.

 

Jeff - Can you comment on the difference in bedding procedure (if any) that cryogenically-treated rotors would make. As they are supposed to be more wear resistant would that affect the buildup of the transfer layer? Thanks.

Gary

 

I apologize to Jeff in advance if he object to us sort of hi-jacking his thread on how to choose brake pads and side track it into braking technique discussion.

If Jeff will indulge us a bit, then I have the following observations from my personal racing experiences and tips learned from multiple world class pro drivers for both Formula and GT cars.

Pro drivers always make the car handle as if on rails even when they are at the limit.

Pro drivers always brake a bit later yet carry more corner speed than me, thus, shaving a tenth or two per corner. I envy their amazing ability, but I guess that's why they can make a living out of it, while I'm just a reasonably good gentleman driver.

In high speed straight line braking into slow corners, brake pressure traces from pro drivers' logger data that I have seen always have initial high pressure spike then maintain constant pressure then trail off without locking up the tires or unsettling the car. Their brake pressure traces never look like a half sinusoidal wave.

Braking later than optimal braking point to defend a position; therefore, over shoot the apex or over slow the car mid corner is not quite the same as braking at maximum pressure as late as possible yet still maintain highest possible corner speed and hit the apex.

Exact amount of initial braking pressure spike is dependent on initial bite characteristic of pad, car setup, grip available (ie. wet track), and corner shape, etc..

Exact amount of trail braking pressure is dependent on brake pad torque rise due to temperature, car setup, grip, corner shape, etc..