Help Needed!!! Rear brakes overheating on track

[tlrid3r]

Pfc 11 does better on rear

[VictorH]

I'm at the track now and I'm willing to bet there's nothing wrong with your rear brakes.
Here are my measurement with IR gun. All sessions DSC off.


Session 1 (cold out upper 30s)
Front Caliper (PFC Z-54) 245F. Front Rotor 260F
Rear Caliper (stock) 360F. Rear rotor 315

Session 2 (temp in upper 50s) and running a lot faster
Front caliper 355. Front Rotor 271
Rear Caliper 468. Rear rotor 430

Evidently though they are not doing as much work there must not be much air flow so they run really hot. That's just they way they are.

[dparm]

I'd suggest using the temperature stickers + paint, too. IR gun on a rotor face isn't hugely useful, as I understand it, due to the high reflectivity.

[pbonsalb]

Still well within the stock pad heat range, right? But since they do run hotter, maybe a different pad choice that would not be as near the end of its heat range and titanium shims to reduce fluid boiling and fresh high boiling temp brake fluid would help.

[VictorH]

Latest data outside temp 61F
DSC off, just off track didn't stop to check anything else.
More traffic this session so average speeds will be a bit slower

Right front caliper 280F. right front rotor 420F
Left front caliper 242F, left front rotor 425F

Rear (there's no doubt it runs hotter than front)
Right rear caliper 449F. right rear rotor 475F
Left rear caliper 430F, left rear rotor 474F

It's not just the IR gun temps (yes paint might be more accurate) but they are hotter, more clicking, popping (hear nothing from the fronts) and just holding you hand up to the rim, there's no question it's oven hot.

[VictorH]

I don't think stock rear pads would be happy at these temps, keep in mind this is after cool-down and driving in the paddock.
I'm on track pads all around.

[dparm]

Originally Posted by VictorH

I don't think stock rear pads would be happy at these temps, keep in mind this is after cool-down and driving in the paddock.
I'm on track pads all around.

Definitely not, plus, having a huge bias in pad performance like that front-to-rear is not going to help car control. Rear pad fade is not a scenario that will end well.

I would also be concerned about caliper longevity at temps like that.

[VictorH]

Originally Posted by dparm

Definitely not, plus, having a huge bias in pad performance like that front-to-rear is not going to help car control. Rear pad fade is not a scenario that will end well.

I would also be concerned about caliper longevity at temps like that.

True, but these temps are not through-and-through, it's a surface temp only. I changed my rear pads this afternoon and if the entire caliper was at 470F then my dust boots should be completely melted, but they are not, they still look okay.

There still is a question of what the overall mean temp is of the caliper and rotor is, however, there is no question the rears run hotter than the fronts, even with the electronic nannies off.

[SYT_Shadow]

Originally Posted by VictorH

True, but these temps are not through-and-through, it's a surface temp only. I changed my rear pads this afternoon and if the entire caliper was at 470F then my dust boots should be completely melted, but they are not, they still look okay.

There still is a question of what the overall mean temp is of the caliper and rotor is, however, there is no question the rears run hotter than the fronts, even with the electronic nannies off.

If you have the front pfc bbk and stock rear rotor then for sure your rear runs hotter than your front

On my e90 with the full bbk the rear is cooler. It is less efficient and singing the hair straight off my legs

[roastbeef]

By any chance, are your rear brakes starting to keep a rust ring around the inner diameter of the rotor?
I recently upgraded to a rear bbk to complete my ap kit.
My rears were starting to stick. I knew the dust boots had failed, but now the pistons were not releasing correctly and wouldn't allow the caliper to function properly. Obviously, I was getting some uneven pad wear.
My rear rotors were starting to take a dump with very small cracks extending from the center drilled holes.

[FMLYSDN]

Originally Posted by dparm

I'd suggest using the temperature stickers + paint, too. IR gun on a rotor face isn't hugely useful, as I understand it, due to the high reflectivity.

Thank you!

IR Guns work under the same principle as IR Cameras. Measuring the temp of a rotor's surface is inaccurate as the emissitivity (an objects ability to emit radiant energy" is so low that the temperature your reading is the reflected temperature from the surrounding environment. You're better off reading temperature from the caliper or the rotor hat as it will provide a much more accurate reading. So many people use these so inaccurately.

[VictorH]

Originally Posted by FMLYSDN

Thank you!

IR Guns work under the same principle as IR Cameras. Measuring the temp of a rotor's surface is inaccurate as the emissitivity (an objects ability to emit radiant energy" is so low that the temperature your reading is the reflected temperature from the surrounding environment. You're better off reading temperature from the caliper or the rotor hat as it will provide a much more accurate reading. So many people use these so inaccurately.

That's true but the issue at question here is, "do the rear calipers and rotors run hotter than the fronts ( on the track)?" Based on my experience and the OP the answer is "yes." There's no question. You guys can argue the magnitude and accuracy but they do run hotter.

[FMLYSDN]

Originally Posted by VictorH

That's true but the issue at question here is, "do the rear calipers and rotors run hotter than the fronts ( on the track)?" Based on my experience and the OP the answer is "yes." There's no question. You guys can argue the magnitude and accuracy but they do run hotter.

I don't dispute your statement. I was merely commenting on a technical aspect of this discussion.

Carry on!

[dparm]

Originally Posted by FMLYSDN

Thank you!

IR Guns work under the same principle as IR Cameras. Measuring the temp of a rotor's surface is inaccurate as the emissitivity (an objects ability to emit radiant energy" is so low that the temperature your reading is the reflected temperature from the surrounding environment. You're better off reading temperature from the caliper or the rotor hat as it will provide a much more accurate reading. So many people use these so inaccurately.

The guns aren't worthless, but you'll want to take readings from various points on the rotor and hub. The rotor isn't going to be uniformly heated, and the hub will be a different temperature. Just randomly pointing it at the rotor face doesn't tell you a lot. Same thing applies to using heat probes on tires.

The reason I like the caliper stickers is that it shows me what the peak temp was even after I've pulled off and cooled things down. Same thing for the rotor paint.

[VictorH]

What I'm wondering is what would be the fix to get more air in there?

I'm doing open track session early April and though I'm not inclined to run an hour, I might run 35-40 minutes and I suspect that the rears might be really cooking by then.

[FMLYSDN]

Originally Posted by dparm

The guns aren't worthless, but you'll want to take readings from various points on the rotor and hub. The rotor isn't going to be uniformly heated, and the hub will be a different temperature. Just randomly pointing it at the rotor face doesn't tell you a lot. Same thing applies to using heat probes on tires.

The reason I like the caliper stickers is that it shows me what the peak temp was even after I've pulled off and cooled things down. Same thing for the rotor paint.

I'd recommend taking readings from the outside edge of the rotor. The face will give you inconsistent readings due to the polished face whereas the edge does not have the same type surface finish. Regardless of camera or gun, there is still value in using these items for temperature readings. It's the method in which it is done that is important. The two work in the same principle.

The video link is cool to see the different things going on. In the early part of the video, you can see that the rotor is reflecting the radiant energy of the environment, especially when the person walks past (acts like a mirror) As the rotor gets up to temperature, you can see that the edge is giving off a higher temperature through the camera. How can this be? Wouldn't the rotor face and the edge be the same temperature? Certainly they are, however the properties for giving off that radiant energy are different due to the finish and therefore the accuracy is going to vary greatly.

At any rate, I don't mean to take this thread off topic! Just trying to provide some additional input that some may find helpful.

[SYT_Shadow]

Originally Posted by VictorH

What I'm wondering is what would be the fix to get more air in there?

I'm doing open track session early April and though I'm not inclined to run an hour, I might run 35-40 minutes and I suspect that the rears might be really cooking by then.

you know what the fix is... PFC z45....

[VictorH]

Originally Posted by SYT_Shadow

you know what the fix is... PFC z45....

Yes, that's true and I'm sure it would be amazing, but I was hoping maybe something less than a 4-figure fix!
(I'm still tempted though).

[SYT_Shadow]

Originally Posted by VictorH

Yes, that's true and I'm sure it would be amazing, but I was hoping maybe something less than a 4-figure fix!
(I'm still tempted though).

the problem is the damn rotor... the OEM rotor doesn't flow any air through it so it reaches the temperature of the sun!

With the full PFC BBK, front rotors/pads last 1/3 of the rears

[Ximian]

Step up to Formula 1 level technology and bring a leaf blower to cool your rotors between sessions.

[Move Over]

To echo FMLYSDN - FWIW - The IR guns are worthless on a rotor as the emissivity of a shiny metal surface is very low. They are not giving off accurate readings and are just giving the gun a reflection of surrounding temperatures. If you look into one of the drilled holes to use it as a thermal cavity, it should give you a better reading. I started working for Fluke developing thermal imagers not long ago and man have i learned a lot about how to read temps.

The only accurate way to get a temp reading from a rotor is a surface touch method (no not your fingers lol). You could potentially paint the outer rim of a rotor to get a reading, as the emissivity of a painted surface will give you an accurate reading. I would get yourself a nice thermocouple thermometer if you are doing off track temp readings.