Brake pads.. what do you run?

[Eric Parham]

I'm curious about the "cookie cutter" type of failures. Having never had or seen this one, it seems to me that it would only happen once the pad material was gone so that the metal backing plate hits the metal rotor and gets hotter than otherwise possible. In that case it only makes sense that the high points (piston outline) could get hot enough to melt steel. Was that the case with Russ' failure?

[dominojd]

Originally posted by Eric Parham:
I'm curious about the "cookie cutter" type of failures. Having never had or seen this one, it seems to me that it would only happen once the pad material was gone so that the metal backing plate hits the metal rotor and gets hotter than otherwise possible. In that case it only makes sense that the high points (piston outline) could get hot enough to melt steel. Was that the case with Russ' failure?

Not nessisarily. I have seen a set of pads do this where the pad stopped the car as if the brakes were fine. Later it was found out while changing pads that th e backing plate had got hot enough to indent the piston in it and actuaaly warp the backing plate. The only material still touching the rotor was where the piston was located. And there was still plenty of material on the pad.
This tells me that the pad material can hold much more heat than steal backing plate. Pretty crazy. Oh BTW these brakes where Carbotech XP8's. They have some good pad material.


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Crazy Joe
#7 ITS pilot

[SPiN Racing]

Originally posted by Knestis:
Hmmm. Seems to me that some of the thermal failure modes that have been described here - the cookie cutter piston trick (I've seen that kind of thing), boiling fluid, or flaming seals - don't have a darned thing to do with pad compounds.

K

Actually.. It does have a lot to do with the brakes. The 1st generation RX-7 mentioned in the previous post is now running Blues.. and on Sebring I can run harder.. and deeper with less braking effort, and heat.. and the calipers experience no problems like they did with the Hawk Blacks.
The CF of the brake pad material is what generates the braking force.. combined with the Squeeze of the Rotor itself.. The combination generates heat. If the CF of the pads is high enough you will experience greater stopping power with less pedal effort. (Squeeze of the pads)
Therefore you are going to generate less heat.
Take a tire and spin it when the car is on a jack stand.. try to stop it with a handkerchief.. and then after it stops feel the heat generated by the pressure/friction generated.... Now press a brick to the tire to stop it while spinning.. The brick has greater CF and therefore requires less pressure to effect the force to stop the tire spinning... YES this is way over simplifying things.. But the basic concept I believe is sound..
The more badass the compound.. the greater the stopping force with lower effort on the pedal.
If you have a pad that sucks.. you are going to have to press harder.. and it will be a LOT more inefficient in stopping.. Therefore generate more heat than stopping power.

[Knestis]

Sorry - Newtonian physics argues against your explanation. Brakes turn kinetic energy into heat energy, and the fundamentals of thrermodynamics allows that heat energy to be transfered to the air.

A car going from 120mph to 70mph sheds a specific amount of energy this way and the only variable is the time over which it does it - and the driver controls that by picking his or her shutdown point.

If the backing plate is getting hot enough that it reaches its thermal yeild point - goes soft - it is because the pad material has reached that same temperature. More friction will only produce more heat energy, more quickly. This assumes that there is no improvement in airflow (velocity or temperature differential) to deal with the increased heat.

I guess that my earlier statement is incomplete in that if the pad compound can't cope with what it's being asked to do, it will physically wear and/or simply come apart - leaving the backing plate alone to do the job the compound should have.

If the pad material is STILL SOUND and the backing plate has gotten hot enough to distort (I've seen this), then there are two choices, given no change in ambient temperature - (a) brake earlier to put the time quotient more in your favor in the heat-shedding rate, or ( get more air to the brakes. Boiled fluid and failed seals? Even more so. I completely fail to understand how different compounds will fix those problems.

K

[JohnW]

Originally posted by SPiN Racing:

The more badass the compound.. the greater the stopping force with lower effort on the pedal.

This is correct only to a degree. There are negative trade-off's with too aggressive a compound.

Take the Hawk blue. Good compound but everyone I have spoken to say they lock up and flat spot tires easily. Hoosiers at 187.00 each are too expensive for that short-coming in the formula for me.

Another concern, How can one formula (Hawk Blue) be optimal on "all cars" from a ITC Honda to a T1 Z06???? It isn't possible. Sorry.

The compound is important, but how the materials are combined, what percent(s) are added and when along the production line they are introduced are as important. Componding is a true "Black Art".

I run Carbotech because they spend countless track hours tesing new compounds prior to their introduction. Not every compond is right for every car. The new XP1110s were too strong for my H1 Civic. However, they kick ass for a T1 Chevy that is 1500lbs heavier.

John- who spent 3 days last week at the Carbotech factory and encourages his competitors to continue to buy the other brands. :-)

[Carbotechmatt]

Kirk is absolutely spot-on with his assesment. The only thing that affects the amount of heat generated while braking is the weight of the vehicle and the velocity. KE=1/2*mass*(velocity)^2. If you stop your car using balsa wood in the caliper, you will generate the exact same amount of heat as you would if you used a real brake pad.

Now with a *real* brake pad, you can generate that heat in a shorter time and therefore acquire a higher *temperature*. That's something too many people do: they confuse *heat* and *temperature*. They are not the same thing.

We're damned if we do, and damned if we don't. If we give you a pad that fades at 1000F, you get on our case that our pads suck and you'll never buy them again. If we provide you with a material that is so fade free that the next part of the system fails (backing plate, seals, etc) you tell us how much our pads suck and you'll never buy them again.

You guys ever wonder why PFC is quickly getting out of the OE caliper racing market? Think this might have anything to do with it???

[lateapex911]

Slightly off topic, but as we have arrived at the theory part, lets look at cooling.

Simply, as Matt alludes to, cooling is the largest variable that will affect the pad material, backing material, et al.

So,....what do the experts recomend as the best and most effective cooling method?

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Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[Carbotechmatt]

Ducting directly to the caliper, not the rotor. And hose 1 foot away blowing in the general direction of the caliper doesn't count.

I would also try to find a wheel that is as open as possible for the best airflow.

[grjones1]

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Brakes? What Brakes? We don't use no steenking brakes!

I couldn't resist.
GRJ

[Greg Gauper]

I finally got a chance to test the Carbotech XP1109 compound at Blackhawk this weekend in my Civic. The results are encouraging. What I found was the pad do seem to conduct a bit more heat to the caliper, which is understood from the above comments. The stock Honda calipers have a great deal of flex and this seemed to get worse as the brakes got hotter, resulting in a somewhat soft pedal, however if I tapped the brakes once to pump them up, they worked fine. I suspect the heat and caliper flex are causing the pads to get kicked back slightly. I do have ducting directed towards the rotor but will redirect it towards the caliper. I'm not blaming the pads, this is a problem with Honda calipers that I have always faced.

The pads did seem to be more rotor friendly than my Hawk Blues. My brake fluid was fine and I wasn't boiling them. I'm running Wilwood 575 but I am considering switching to Valvaline synthetic since it has only a few degrees lower boiling point, but looks like it might be a bit more friendly to the seals, and is about 1/3 the cost of Wilwood.

Note: this was on an ex-IT car now converted to production, so with the racing slicks the brakes are getting a much harder workout than they would with DOT tires, and the cantilever tire design tends to block the cooling air to the rotors more, so ducting is required. Also, the national races are longer than regionals. I don't expect any problems at any of the other Cen-Div tracks if they lived thru a longer National race.

I'm curious...are the backing plates painted with one of those temperature activate paints like they use for checking rotor or caliper temps? They turned the weirdest pink color after I bedded them per the instructions.

[Carbotechmatt]

<font face=\"Verdana, Arial\" size=\"2\">I'm curious...are the backing plates painted with one of those temperature activate paints like they use for checking rotor or caliper temps? They turned the weirdest pink color after I bedded them per the instructions.</font>

No, just plain brown paint. The pink-ish color is typical after a few good heat cycles.

[Scott Nutter]

Originally posted by Knestis:
If the pad material is STILL SOUND and the backing plate has gotten hot enough to distort (I've seen this), then there are two choices, given no change in ambient temperature - (a) brake earlier to put the time quotient more in your favor in the heat-shedding rate, or ( get more air to the brakes. Boiled fluid and failed seals? Even more so. I completely fail to understand how different compounds will fix those problems.

K

I think different compounds address these problems by their CF. If a pad bites like your 2 year old niece then you know you don't have get on the brakes till very late, however if they have bite more like a suckling babe then even though you know they are never going to give up you might have to get on them a bit sooner thus increasing the braking time.

Anyhow I ran Hawk Blues on a 1st Gen Rx7 and they ate rotors. I am currently trying Carbotech Panther XP front/Plus rear and after 100 miles of track time the pads and rotors were great. I was at the track on Sunday, got 200+ miles in and I did notice that I had to apply more pedal pressure than I did with the Blues but the Carbotech's never faded and I actually started to like the extra effort (more modulation). I have not however pulled the tires to check the rotors/pads since I unloaded the car @ 9:30PM and had to get up @ 5:00AM for a flight to NC.

If the thread is still recent Next week, I'll post my findings.