What exactly does the brake temperature displayed on center pad mean when Tesla is in track mode?

[wzj998]

How does the car know the temperature of the brake? There shouldn't be a temperature sensor, right?
Even if I use the RA MQ200 brake pads(50C~800C), when the regen level is set to 5%, it will show a very deep yellow after a few corners; When set to 100%, after a lap and a half, it will also turn yellow.

 

[gearchruncher]

You are correct that there is no sensor. It's just a calculated estimate based on the mass of the car and how much deceleration you have used, and an assumption of the mass of the braking system.

 

[Mash]

You are correct that there is no sensor. It's just a calculated estimate based on the mass of the car and how much deceleration you have used, and an assumption of the mass of the braking system.

Its also obviosly takes into account calculated traction per wheel.

 

[JCtx]

And probably stock brake fluid and pads. So better brake fluid and pads should render that useless.

 

[gearchruncher]

And probably stock brake fluid and pads. So better brake fluid and pads should render that useless.

Fluid and pads don't impact rotor temperature. They just survive higher temps better.

Its also obviosly takes into account calculated traction per wheel.

How does this matter? I mentioned that it factors in the amount of deceleration, and you can't get that deceleration without the traction, and it doesn't matter how much traction you have if you aren't braking.

 

[JCtx]

Fluid and pads don't impact rotor temperature. They just survive higher temps better.

Exactly my point. Rotor temperature doesn't matter as long as car is braking fine. Better pads and fluid withstand fade much better.

 

[Mash]

Fluid and pads don't impact rotor temperature. They just survive higher temps better.


How does this matter? I mentioned that it factors in the amount of deceleration, and you can't get that deceleration without the traction, and it doesn't matter how much traction you have if you aren't braking.

Because it calculates different temperatures per caliper.

 

[Mash]

Exactly my point. Rotor temperature doesn't matter as long as car is braking fine. Better pads and fluid withstand fade much better.

It doesn't calculate rotor temperature as a result, it calculates brake fluid temperature and pads influence that since they are the heat conductor to the fluid and so they conduct and dissipate differently.

 

[gearchruncher]

Because it calculates different temperatures per caliper.

Ahh, OK. But this comes from different brake pressures per caliper, either from various control systems or different amounts of ABS. It doesn't directly come from calculations of friction at each tire.

it calculates brake fluid temperature

Where do you get this information? The temperature estimates I see are way beyond the boiling point of any fluid I have ever seen and seem much more to be rotor temps than fluid temps.

 

[Mash]

Ahh, OK. But this comes from different brake pressures per caliper, either from various control systems or different amounts of ABS. It doesn't directly come from calculations of friction at each tire.



Where do you get this information? The temperature estimates I see are way beyond the boiling point of any fluid I have ever seen and seem much more to be rotor temps than fluid temps.

Unless ABS engaged - pressure is the same. It doesnt calculate from tire friction, it calculates tire traction based on accelerometer and slip angles.

Rotor temperature is a very quickly changing number that has no practical use. I don't know what that number means exactly, but it doesnt move up and down as rotor temperature does and it wouldnt make sense to show rotor temperature anyway.

 

[gearchruncher]

Unless ABS engaged - pressure is the same.

Not true. The Model 3 uses electronic LSD, which is just braking different wheels, and it makes a huge difference in brake temps. Also the car uses front-rear brake bias, so the front rear pressure is not the same.

Rotor temperature is a very quickly changing number that has no practical use.

100% Agreed that this is just a gimmick.

 

[Dangerous Fish]

Track mode data is labelled "Brake Temperature Front Right (% est.)" and we don't even know what value in degrees 100% is supposed to be, so at best it's just an indication they're getting quite hot.
I've measured stock rotor temperatures up to 800 deg. C on a M3P and by that point you'd be getting the warning message on the display to say you're overheating them.
TBH you're better off using an IR laser thermometer and measuring them as soon as you get back to the pits. Even then, they will have cooled down a fair bit from the last time you used them on track, but it gives you a number that means something at least.
Temperature paint on the rotors or LCD temperature stickers on the calipers will give you more reliable data too.

 

[Mash]

Not true. The Model 3 uses electronic LSD, which is just braking different wheels, and it makes a huge difference in brake temps. Also the car uses front-rear brake bias, so the front rear pressure is not the same.


100% Agreed that this is just a gimmick.

I dont believe there is any pressure difference of front and rear. OEM always sets it by brake piston area, not by any proportional valve like in race cars. Also there is only one brake pressure sensor in the system. Also FL-RR and FR-RL are 2 fluid circuits and that would require 2 valves with potential of going out of sync. So, no, i dont believe thats the case.

LSD simulation on an open diff is done by ABS pump.

 

[Mash]

Track mode data is labelled "Brake Temperature Front Right (% est.)" and we don't even know what value in degrees 100% is supposed to be, so at best it's just an indication they're getting quite hot.
I've measured stock rotor temperatures up to 800 deg. C on a M3P and by that point you'd be getting the warning message on the display to say you're overheating them.
TBH you're better off using an IR laser thermometer and measuring them as soon as you get back to the pits. Even then, they will have cooled down a fair bit from the last time you used them on track, but it gives you a number that means something at least.
Temperature paint on the rotors or LCD temperature stickers on the calipers will give you more reliable data too.

Yes. Rotor temperatures are only relevant as a maximum temperature to make sure its not going out of pad range. I only measure it in the pit to check that its cold enough to not voil the fluid while its parked. If not, im using a battery powered leaf blower. For other cases (except r&d) rotor temp paint is enough.

Fluid temperature is what really matters. There are relatively cheap sensors for that to install instead of bleeding valves.

 

[gearchruncher]

OEM always sets it by brake piston area, not by any proportional valve like in race cars.

Mechanical porportional valves are common on road cars, and these have been replaced by Electronic Brake Force Distribution as a function in the ABS pump. I mean, Tesla's page on braking in the Model 3 is huge:

https://www.tesla.com/ownersmanual/model3/en_au/GUID-3DFFB071-C0F6-474D-8A45-17BE1A006365.html

This is a car that can make up for brake pad fade or master cylinder failure with the ABS pump, and you think that it doesn't do EBD?

LSD simulation on an open diff is done by ABS pump.

Yes, by putting different pressure in each caliper, causing each brake at each corner to do different work, leading to different temperatures, which was my exact point.

 

[JCtx]

Even my 2020 BMW R1250R motorcycle does automatic F/R brake-force distribution with the front brake lever only (a great feature, since the rear brake pedal only activates the rear brake). ALL cars have done that for a long time now. And yes, the ABS module with 4 independent channels does that, as well as to prevent any wheel lock-up. My bike has cornering ABS/TC too, so also deals with complex computing (depending on riding mode).