Brake rotor temperature right/left and front/rear comparison questions

[Gforce]

Originally Posted by Lynxis

For a 3rd party source, I am one. I have Winmax W5 pads. They are a proper track/race pad and I have daily driven them for about a month. Dead cold, they bite harder than my OEM pads did. The reason they are considered a dedicated track pad is because they make too much noise, dust like mad, and wear too quickly while cold to be feasible on the street and that is why I stopped daily driving on them. As a bonus, they are also really difficult to modulate with low pedal effort although this isn't nearly the issue the other ones I mentioned are.

How do you know the track pads bite harder? Have you measured the difference in stopping distances? I think you may be surprised. Your other remarks about the issues harder pads can cause are important considerations for anyone thinking of upgrading pads.

[churchx]

With all that misinformation/false theories/lies that gforce/suberman/ubersuber spreads .. result happens to be rather funny & rising mood, like watching some comedy channel. I'd say .. this forum needs such troll, to liven things up .. just that one should post informational notice for all new members, to not try to take by mistake seriously whatever he posts

[WRBrzRX]

this guy

[Lynxis]

Originally Posted by Gforce

How do you know the track pads bite harder? Have you measured the difference in stopping distances? I think you may be surprised. Your other remarks about the issues harder pads can cause are important considerations for anyone thinking of upgrading pads.

You'll never get measured shorter stopping distances when both the OEM pads and dead cold W5 race pads are perfectly capable of engaging ABS which means the limiting factor in both cases are not the brakes but the tires. I have documentation to back this up, the brake torque curve for various Winmax brake pads:



The W1 and the W5 both have similar cold bite friction levels and the W1 is their "OEM-like" street pad and the W5 is their entry level full race pad. Even the W6/7 which are intended for top level racing in heavy/powerful cars will have no issues engaging ABS dead cold on a regular street tire.

I think I know where you get your ideas, I've also seen lots of scary talk on here about cold race brakes having practically no bite and "do not run these on the street because cold bite is dangerous" but those guys are referring to pads like the WE1 which are purpose built for endurance racing, not your average race pad. Compromises are made so these kinds of pads will last the 3 hours of hard racing conditions and one of those compromises is to cold bite. The reality is that no one is going to run a street car in events where a pad like this would be desired so there is simply no usage case to find a pad like this on the street. And, even if you did, .28 might not be enough to engage ABS on a good street tire but I'm certain I can find you some shitty all-season tire that someone is driving around on that will. Now that's what's really scary.

[wparsons]

Originally Posted by Gforce

Braking system cannot be sealed.

When the cap is on, it's sealed. The reservoir isn't open to the atmosphere.

Originally Posted by Gforce

You'll need to explain the heat impulse idea. The capacity remark is also incomplete.

Are you talking about making a hot brake system suddenly hotter when you first apply the brakes hard or a cold system suddenly hot?

What he means by heat impulse is that the amount of braking force required to stop a given car at a given speed on a flat surface is constant. If you don't change tires, traction is also constant. Since the main force stopping the car (ignoring air and rolling resistance) is the brakes, the amount of work they do is also constant. Adding pads that can take more heat, or rotors with thermal mass don't change how much work the braking system has to do. It just changes how much heat it'll tolerate before fading, or how fast it can shed heat.

There's nothing incomplete about the capacity remark, he's just talking about thermal capacity... not fluid capacity like you're assuming.

Originally Posted by Gforce

Are you suggesting the BRZ needs larger brake caliper cylinder volume?

Again, no.

Originally Posted by Gforce

My point is that any road car needs brake pads that deliver maximum performance from cold. The very first stop of the day might be your last. Using track pads on the street is just plain dangerous.

You're assuming that track pads are worse than stock when cold, which just isn't the case for all of them. I wouldn't run an endurance pad on the street, but they have narrow operating temp ranges and are a different beast. There are TONS of track pads with huge operating temp ranges that are significantly better than OEM on the street, and get even better when hotter. Sure they make noise and dust, but they have more bite/torque.

Originally Posted by Gforce

You'll need to explain this one. You must mean the car needs bigger caliper pistons. There's not much fluid circulation in a brake hydraulic system unless ABS is working hard.

No, he means thermal capacity. There's not enough thermal mass in the rotors to absorb/dissipate heat fast enough.

Originally Posted by Gforce

How do you know the track pads bite harder? Have you measured the difference in stopping distances? I think you may be surprised. Your other remarks about the issues harder pads can cause are important considerations for anyone thinking of upgrading pads.

1) the co-efficient of friction, which isn't open to interpretation, it's a physical property and hard fact. You might want to go back and revisit how co-efficients of friction work to see how your earlier comment about higher line pressures is also incorrect.
2) Because unlike you, we've actually driven it back to back vs stock pads and immediately felt it. If I let anyone drive my car their first stop, from cold, they always brake WAY too hard when they're just trying to give a tiny bit of brake. Like stopping 10m before where they intended to, even from 50km/h and not a panic stop.

[Gforce]

If the cap were to be sealed the master cylinder could not work. The air space above the fluid needs to be at atmospheric pressure.

Heat capacity of the braking system isn't an issue unless you get to fluid boiling temperatures. For that to happen the heat has to get into the caliper cylinders. Brake rotor temperature will be much higher than the fluid boiling point. Bolting heavier rotors onto your car may or may not improve that. For street use the fluid isn't going to boil, ever.

Brake pad material certainly does not experience a constant coefficient of friction. Street pads have a higher coefficient of friction when cold. Track pads have a higher coefficient if friction when hot. All known pad materials exhibit a coefficient curve dependent on temperature.

[Gforce]

Originally Posted by Lynxis

You'll never get measured shorter stopping distances when both the OEM pads and dead cold W5 race pads are perfectly capable of engaging ABS which means the limiting factor in both cases are not the brakes but the tires. ...

...

I think I know where you get your ideas, I've also seen lots of scary talk on here about cold race brakes having practically no bite and "do not run these on the street because cold bite is dangerous" but those guys are referring to pads like the WE1 which are purpose built for endurance racing, not your average race pad. Compromises are made so these kinds of pads will last the 3 hours of hard racing conditions and one of those compromises is to cold bite. The reality is that no one is going to run a street car in events where a pad like this would be desired so there is simply no usage case to find a pad like this on the street. And, even if you did, .28 might not be enough to engage ABS on a good street tire but I'm certain I can find you some shitty all-season tire that someone is driving around on that will. Now that's what's really scary.

Agreed braking distance is limited by tires. It is axiomatic therefore that track pads should not be used for the street. Begs the question of why anyone would try to use track pads for the street. I know there are harder street pads available that are capable of withstanding track heat. That doesn't make them track pads.

Disc brakes do not fade unless the pad temperature exceeds the design range. Even street pads keep working at very high temperatures.

Ceramic brakes are a marketing boondoggle for a road car. The only objective evidence I have seen was published by evo magazine when they tested identical F Type R models equipped with iron brakes and ceramics. They tested by measuring stopping distances after consecutive full stops from 100 mph. The iron brakes outperformed the ceramic brakes for the first four stops and equalled the performance for the first 11 stops before the stock pads began to catch fire.

My original post in this thread is correct. Until you are running slicks the stock BRZ brakes are fine.

Answering the op question: no, brake temperature is not any indication of brake performance. Tire temperature will help in that higher tire temperature means the tire is working harder. In consecutive straight stops higher front tire temperatures would confirm more weight transfer indicating better brake performance.

[Gforce]

This thread is worth a recap. I've noticed over the years I've lurked on the fringes of this site there is a strong bias in favour of track performance and relatively little information about improvements to this car as a pure sportscar, a level of intolerance to that side of things even.

This thread is a good illustration of this bias.

The op asks whether his carefully thought out and modest brake modifications can be tested for objective measurement of any improvements.

The responses include the obvious: it's the tires. I am firmly in that camp. Unless the tires can develop grip to exploit the additional brake performance then you cannot tell if the brakes have been improved. The stock tire is a very good tire in its category, one of the best in fact. Michelin builds the HP version of its grand touring tire and this version of the Primacy has many virtues, light weight being first among those. Wet grip is also very good. But, no grand touring tire can match a high or ultra high performance tire.

The responses also include some conundrums. The op fitted drilled brakes which reduce the heat sink capability while lowering unsprung weight and improving cooling. Net benefit? Apparently not since the stock brakes are heat limited. More disc mass is deemed preferable to lower pad temperatures.

Reference is made to heat impulse which I now understand to be a shorthand reference to heat saturation. If braking heat cannot be fully dissipated between braking events then brake temperature inevitably rises and keeps rising. This never happens on the street but can happen if you track your car. If you persist in heating up your brakes they will cease to perform to their optimum. Fitting harder pads with a higher optimal temperature range will delay this but eventually the fluid will boil and there is no solution to that problem. That only works if the tires can use the higher braking forces at elevated temperatures. Tires also suffer from heat "fade"

At that point I recommend adherence to the advice given by the late great Fangio to his team mate, who may have been Gonzales at the time. When asked how he (Fangio) could get faster lap times in the exact same car he replied "less brakes, more accelerator ".

Fangio was driving for Maserati at the time and he knew all about brake fade, real brake fade not the fluid boil or pad overheating we now call fade (which it isn't, just btw). His race car was fitted with massive drum brakes and they really did fade, pedal to the floor fade. Experience that just once in your lifetime and you'll never claim again that disc brakes fade, they just don't.

[venturaII]

Originally Posted by Gforce

If the cap were to be sealed the master cylinder could not work. The air space above the fluid needs to be at atmospheric pressure.

.

Wow...you really don't know how ANY of this works...lol. A brake fluid reservoir is such a fundamentally simple part and yet you have it all wrong. Quelle surprise.

[stevesnj]

anyway, to the OP, we have EBD, rotor temps will vary.

[wparsons]

Originally Posted by Gforce

If the cap were to be sealed the master cylinder could not work. The air space above the fluid needs to be at atmospheric pressure.

Go take the cap off and have a closer look...

Originally Posted by Gforce

Heat capacity of the braking system isn't an issue unless you get to fluid boiling temperatures. For that to happen the heat has to get into the caliper cylinders. Brake rotor temperature will be much higher than the fluid boiling point. Bolting heavier rotors onto your car may or may not improve that.

Thank you captain obvious? You said boiling the fluid wasn't possible unless the fluid was old. Mike and I said you can easily boil stock fluid because there isn't enough thermal capacity in the stock system for the OEM fluid. The implication there is that you're putting a lot of heat into the system.

Originally Posted by Gforce

For street use the fluid isn't going to boil, ever.

Who said it would? Again, you're not actually reading properly. All anyone has said is that you can easily boil the stock fluid. Easily doesn't mean driving to the grocery store.

Originally Posted by Gforce

Brake pad material certainly does not experience a constant coefficient of friction. Street pads have a higher coefficient of friction when cold. Track pads have a higher coefficient if friction when hot. All known pad materials exhibit a coefficient curve dependent on temperature.

No one said the coefficient was constant. You're half right in that a stock pad will have a higher co-efficient of friction at street temperatures than when at track temps and that a race pad will have a higher coefficient of friction when hotter, but what you're missing is that it's possible (and common) for the track pad to have a higher coefficient of friction than stock pads when cold.

Lets say (totally fictitious since I can't find actual specs on our OEM pads) the stock pads have a coefficient of friction curve that is like this:

0*C - 0.20
50*C - 0.25
100*C - 0.30
150*C - 0.15

And a race pad is like this:

50*C - 0.40
100*C - 0.45
400*C - 0.50
800*C - 0.40

So yes, the OEM pad is better at lower temps, and the race pad is better at higher temps, BUT the race pad is better than OEM across the board.

It's already been posted, but look at this chart again:


The WE1 is their endurance pad, and not what anyone has been talking about. The W1 is a street pad, the W7 is their highest heat capable non endurance pad. Notice the W7 starts at a higher coefficient of friction even at ambient temperatures? Are you going to argue with the Winmax published specs? You better have some data (ideally brake dynos) to back that up.

Higher coefficient of friction typically means more noise and dust, more rotor wear, and they're harder to modulate. That's why OEM pads tend to be lower.

Also keep in mind that OEM pads have to deal with extreme freezing temperatures too, I would be they're rated down to -40C. If you go back, you'll find that I have said that running track pads in our winters doesn't work, but in summer tire weather it's totally fine.

Like it's been said many times in this thread, you can easily engage ABS on track pads when cold, which means your claims of it being unsafe are completely unfounded and false.

Until you've actually driven a car back to back with good modern track pads and OEM pads, just give up arguing what you don't know about.

[wparsons]

Originally Posted by Gforce

Fangio was driving for Maserati at the time and he knew all about brake fade, real brake fade not the fluid boil or pad overheating we now call fade (which it isn't, just btw). His race car was fitted with massive drum brakes and they really did fade, pedal to the floor fade. Experience that just once in your lifetime and you'll never claim again that disc brakes fade, they just don't.

Ummmmmm... you do realize what causes the pedal to go to the floor, right? Boiled fluid is what causes a soft (up to zero pressure) pedal.

You've just proven once again you don't actually know what you're talking about.

Just BTW, EBC and Alcon brakes don't agree with your statement about fade:

https://alconkits.com/drmassets/Brake-Fade-Solved.pdf
https://ebcbrakes.com/articles/what-is-brake-fade/
https://ebcbrakes.com/articles/brake-fluid-vapour-lock/

[CSG Mike]

Originally Posted by Gforce

Braking system cannot be sealed.

You'll need to explain the heat impulse idea. The capacity remark is also incomplete.

Are you talking about making a hot brake system suddenly hotter when you first apply the brakes hard or a cold system suddenly hot?


Are you suggesting the BRZ needs larger brake caliper cylinder volume?

My point is that any road car needs brake pads that deliver maximum performance from cold. The very first stop of the day might be your last. Using track pads on the street is just plain dangerous.

That brake cap? It seals your system. That's why... it has a rubber seal on top!

https://en.wikipedia.org/wiki/Impulse_(physics)

A racing pad's minimum performance exceeds that of a street pad's maximum performance.

[Gforce]

Originally Posted by CSG Mike

That brake cap? It seals your system. That's why... it has a rubber seal on top!

https://en.wikipedia.org/wiki/Impulse_(physics)

A racing pad's minimum performance exceeds that of a street pad's maximum performance.

Actually the mc needs a diaphragm type seal under the cap otherwise the piston would create a partial vacuum every time you tried to apply the brakes. Make no mistake, water contamination of brake fluid remains a problem. Car makers and brake system makers all recommend routine and regular flushing of brake fluid for this reason.

As for the performance of "race pads" equalling that of street pads under all conditions I will defer to your racing experience. Whether race pads are better for a road car then street pads is the issue I am discussing. On that metric race or track pads are dangerous, in my opinion. Brake pad makers agree. The first time you rear end someone would prove my point. However, most drivers will be unaware that they do so because of their track biased brake setup.

Thanks for the link but an understanding of high school physics is sufficiently sophisticated to understand braking systems. "Impulse" is not a helpful concept. The cause of brake overheating is simply the delta between heat creation and dissipation. The resulting net quantity is absorbed by the rotors. Conduction eventually raises the temperature of the brake fluid above its boiling point. The pads will continue to brake the car as long as the driver is able to apply sufficient line pressure. Unlike a drum brake which fades to nothing regardless of mc piston stroke, lining material or driver strength. That is the fundamental difference between real brake fade, as is still experienced by heavy truck drivers, and disc brake "fade" which rarely occurs in reality. Just recently I observed a Red Bull F1 car with a dragging left front brake resulting from overheating of the brakes, the mechanic was using a dry ice cooled blower to free up the caliper. Thermal expansion assists the driver using disc brakes.