Got a track related question? I'll try to answer.

[CSG Mike]

Originally Posted by 86league

Thanks Mike. Still lots of questions :

Just so I can recognize it in the future - what is the evidence that shows you pads were overheated? Mike at carbotech didn't mention these looking overheated, but I can't say if he looked at the photos I sent.

Are the pads still useable? Why do I not have the discoloration across the entire face of the rotor vs. the ring more or less centered?

I read somewhere else that longer duration mild braking will overheat things vs. shorter harder braking. The former is probably a better description of how I was braking until more recently -- as I gained confidence I've been shortening my braking zones and braking harder. Is there any reason to believe I won't just have the same problem with the stock setup with new rotors (and pads?) ? I'm still on the stock tires as well - stickier rubber is in my future and will allow me to carry more speed in the corners, but will also let me brake harder ...

Again - thanks for the thoughts...

The shiny spots on your pads, the uneven heat/wear patterns, and platform-specific knowledge that already tells me the stock braking system is inadequate for even an intermediate level driver.

I got the stock calipers overheated in pouring rain conditions at Laguna Seca last weekend. I'm talking downpour so heavy they're allowing cars to be driven windows up (extremely rare).

There's a lot of pad options that will continue to increase in capacity before you *HAVE* to get a BBK.

[OkieSnuffBox]

Originally Posted by 86league

I read somewhere else that longer duration mild braking will overheat things vs. shorter harder braking. The former is probably a better description of how I was braking until more recently -- as I gained confidence I've been shortening my braking zones and braking harder. Is there any reason to believe I won't just have the same problem with the stock setup with new rotors (and pads?) ? I'm still on the stock tires as well - stickier rubber is in my future and will allow me to carry more speed in the corners, but will also let me brake harder ...

Again - thanks for the thoughts...

This is true. Slowing down from say 100 to 40mph, you're putting the same amount of thermal energy into the brakes (converting kinetic energy into thermal energy is what brakes do).

But longer braking events, even with the same thermal energy, give the brakes less time to cool off between braking events.

Make sense?

[ysu]

Originally Posted by OkieSnuffBox

This is true. Slowing down from say 100 to 40mph, you're putting the same amount of thermal energy into the brakes (converting kinetic energy into thermal energy is what brakes do).

But longer braking events, even with the same thermal energy, give the brakes less time to cool off between braking events.

Make sense?

But...but...
If I'm not braking, the car will still slow down (engine braking + mechanical friction in multiple places ) The cooling factor is the same on the disc; the car's movement provides the cooling, regardless if you're generating more heat on the brakes or not.
My logic says it should be less heat in the brakes with gentler braking, all other things equal.

I'm genuinely interested how can the quick hard braking be better cooling wise! I've heard it a number of times, too, btw.

[Uplink]

Originally Posted by ysu

But...but...
If I'm not braking, the car will still slow down (engine braking + mechanical friction in multiple places ) The cooling factor is the same on the disc; the car's movement provides the cooling, regardless if you're generating more heat on the brakes or not.
My logic says it should be less heat in the brakes with gentler braking, all other things equal.

I'm genuinely interested how can the quick hard braking be better cooling wise! I've heard it a number of times, too, btw.

So there's a couple of things to consider. Start with performance and two important factors.


If you are spending too much time slowing down, that's lap time lost. If you are not accelerating or at the very least maintaining speed, you are going too slow. That said, the other important reason is the benefit of weight transfer. If you use the brakes to gradually slow the car, you are not forcing the weight onto the front tires which will give you more grip for turn-in. You can see this at home by doing a push-up with your hands on a bathroom scale. Slowly sink a little without going all the way down and watch the numbers. Now do a full drop/stop and see how high they go. You are increasing the pounds per square inch of your contact patch which equates to higher available grip thus higher corner speeds.



As far as the heat, try this experiment if you have a bench grinder. Take a piece of steel and press it to the grinder hard but quickly then remove it. See how many times you can do that before it becomes too warm to touch. Now let the metal fully cool and do the same experiment but hold the metal there for 5-10 seconds. See how many less cycles you get before it becomes too warm. That's effectively what you are doing to the brakes.


Hope this helps. The other guys are welcome to chime in too.

[DocWalt]

I laughed at the comment about overheating stock calipers in the rain. I did the same, albeit at a track that's likely tougher on brakes than Laguna Seca, and it wasn't bad enough we had to put our windows up

Originally Posted by CSG Mike

Sounds to me like you're becoming a faster and faster driver!

My personal preference is for pads with higher bite than XP10/12.

Something tells me G-loc will be releasing new compounds in the upcoming years.

Yeah, the bite of the XP12 was less than the stock Brembo pads on the RS, lol. I'd have preferred something better (I knew they weren't going to do well, but they'd at least last a weekend unlike the stock pads), but had no options as it was a kinda last minute thing.


Do you have experience with ST-43s, Mike? I'm debating having a set custom made for the RS, and probably running a set on my GTI once I kill the XP10s in it (It's awesome having a light weight slow car, consumables are CHEAPPPP!!!!)

[CSG Mike]

Originally Posted by ysu

But...but...
If I'm not braking, the car will still slow down (engine braking + mechanical friction in multiple places ) The cooling factor is the same on the disc; the car's movement provides the cooling, regardless if you're generating more heat on the brakes or not.
My logic says it should be less heat in the brakes with gentler braking, all other things equal.

I'm genuinely interested how can the quick hard braking be better cooling wise! I've heard it a number of times, too, btw.

Heat impulse, and friction characteristics of the pad.

The pad rubbing against the bedding layer creates friction, which adds to the kinetic energy being dissipated. Extend that time long enough, and the total energy dissipated is greater, than a shorter period of time.

[CSG Mike]

Originally Posted by DocWalt

I laughed at the comment about overheating stock calipers in the rain. I did the same, albeit at a track that's likely tougher on brakes than Laguna Seca, and it wasn't bad enough we had to put our windows up



Yeah, the bite of the XP12 was less than the stock Brembo pads on the RS, lol. I'd have preferred something better (I knew they weren't going to do well, but they'd at least last a weekend unlike the stock pads), but had no options as it was a kinda last minute thing.


Do you have experience with ST-43s, Mike? I'm debating having a set custom made for the RS, and probably running a set on my GTI once I kill the XP10s in it (It's awesome having a light weight slow car, consumables are CHEAPPPP!!!!)

I do. They're not my top choice in pad though; the modulation range is rather small.

How about trying a set of R18?

[OkieSnuffBox]

Originally Posted by ysu

I'm genuinely interested how can the quick hard braking be better cooling wise! I've heard it a number of times, too, btw.

I just told you. It's simple physics.

But you seem like the type that instead of looking for the right answer, you're looking for someone to agree with your incorrect understanding of the process.

[86league]

Originally Posted by 86league

HPDE this weekend and my brakes developed a moderate pulsation under light to moderate pedal pressure, but very light (or no) pulsation when braking very hard (near threshold).

Got some time to pull the rotors and get a good look.

The passenger side, inner rotor surface looked like this - obvious difference in color for about 90 deg. Thinking that was the source of the problem.

Any advice for avoiding this in the future or knowledge of what I did wrong to lead to this?

[CSG Mike]

Originally Posted by 86league

Got some time to pull the rotors and get a good look.

The passenger side, inner rotor surface looked like this - obvious difference in color for about 90 deg. Thinking that was the source of the problem.

Any advice for avoiding this in the future or knowledge of what I did wrong to lead to this?

Step up the brake pads to a higher capacity pad.

Or, big brake kit.

[86league]

Originally Posted by CSG Mike

Step up the brake pads to a higher capacity pad.

Or, big brake kit.

OK - afraid that might be the answer. Was holding out some hope that maybe they just were not bedded properly...

Given I'm on the stock tires - when I move to something stickier and a bit wider (225 R-S3 for instance), what are the odds that just pads are going to be sufficient?

Thanks.

[strat61caster]

Originally Posted by ysu

I'm genuinely interested how can the quick hard braking be better cooling wise! I've heard it a number of times, too, btw.

Disc brakes operate on the principle that the big heavy iron rotors can absorb a lot of heat, and then reject it fairly quickly and consistently.

Think of it like a medium sized lake, 40+ ft deep, a body of water will collect heat and hold it, but if you dive down even a few feet, the temperature drops significantly.

With short braking hard braking zones it's like a short burst of intense sunlight on the lake, the top layers will get hot, but ultimately all that heat will escape quickly as the sun disappears.

Compare that to exposing the same lake to a long exposure, maybe slightly less intense. That heat will soak in, it'll travel deeper into the water warming up the whole body, when the sunlight disappears it will take longer for that heat to escape from the surface of the water as it has to travel back up to the surface.

With long slow braking zones you're heating up the core of the discs, the depths of the lake, more than a shorter harder braking zone. Yes for one stop, maybe you've lowered temperatures, but over the course of a lap, over the course of a session you've brought up your disc temperature to a higher average than someone who brakes 'harder'. There's a time element to the equation of "Q=mc delta T" that's difficult to describe and works in conjunction with the heat transfer through the thickness of the disc.

This is why brake discs sucked in the '60s and '70s, they didn't size them appropriately to handle holding all the heat, the lake was not deep enough and the core temperatures would just build and build until failure. They had to absolutely baby cars back then to even get them through a moderately long race. Mark Donohue wrote in his book how much better and more reliable the brakes got when they made them thicker and heavier racing in Trans-Am, great read.

It's also why brake discs have a wear limit related to thickness, once they've lost enough material it's like the lake evaporated and the threshold for overheating has lowered to what the OE deems a dangerous level. The purpose of getting a BBK is to make the lake bigger, it's not going to decrease your stopping distances, it's there to increase how much heat you can dump into that lake before trouble hits.

[CSG Mike]

Originally Posted by 86league

OK - afraid that might be the answer. Was holding out some hope that maybe they just were not bedded properly...

Given I'm on the stock tires - when I move to something stickier and a bit wider (225 R-S3 for instance), what are the odds that just pads are going to be sufficient?

Thanks.

It'll depend on how experienced you are, and how clean your technique is.

Lets step you up to a higher grade pad first, before committing to a BBK.

[bigbcraig]

Ok Mike, got a bit of a curveball for you-

I've been autocrossing for about 6 years now, and currently run an AP1 S2000 in B street class (very nearly stock). I also daily drive a 2015 WRX.

I moved at the beginning of the year and now have poor access to autocross but much better access to HPDE/track days, so those are starting to take a bit of a priority for me.

I've run 2 days of HPDE in the WRX and other than brake pads (stoptech street performance) getting significantly glazed over, it took it like a champ. But, its my daily that I'd rather not modify much and otherwise don't want to ptlut it into a wall.

What are your thoughts about an early FRS/BRZ for a replacement to the S2000 and dual purpose autox/track car? I think Ive read in the thread you actually own a '15 WRX and have significant S2000 experience. Would the twins leave me wanting more? I'm very attracted to having a newish, stiff platform with such low weight.

I'd also be interested in hearing other ideas for track cars - but, to make things harder, I need quite a bit of headroom at my height which makes a miata or S2000 significantly comprimised comfort and streetability wise to meet 'broomstick rule'

Thanks!