Racing Brake XT910 vs XT970

[Dangerous Fish]

I had no idea SMT could do that, that is awesome. Ordered the adapter and the dongle, thank you!

It's great and updates are happening regularly. I just need a better tool to manipulate the data so I can view sections of it more easily, edit it, change scale etc. just like with an external data logger. If anyone looks into that side of it and has any suggestions, please post.

 

[Dangerous Fish]

Here are my front discs and XT970 pads after a couple of track days and 2000 road miles. They've lasted very well I'd say and are at 9mm of pad thickness now so I don't think they are wearing particularly fast. I can't say I've been on any very hard braking tracks yet though. There's some glazing there, but the feel and cold stopping power is still very good.

I've now put in Carbotech XP10 front and rear to see how they do. First track outing with those is this week so we will see.
I'll be using Scanmytesla to record the reported brake temperatures as before. It's still a mystery how these numbers are being generated as I don't see any evidence of temperature sensors anywhere near the brakes. If anyone has any information, please share.

 

[destructure00]

It's still a mystery how these numbers are being generated as I don't see any evidence of temperature sensors anywhere near the brakes. If anyone has any information, please share.

My uneducated guess is that there's a temp sensor built into the ABS/wheel speed sensor. I have nothing to base that on other than a WAG though, and I'm not even sure that makes sense since they are on the opposite side of the hub from the caliper.

 

[Dangerous Fish]

My uneducated guess is that there's a temp sensor built into the ABS/wheel speed sensor. I have nothing to base that on other than a WAG though, and I'm not even sure that makes sense since they are on the opposite side of the hub from the caliper.

I wondered about that, but they are only 2-wire sensors so unless they are detecting a change in resistance I can't see how that would work.

 

[beastmode13]

I wondered about that, but they are only 2-wire sensors so unless they are detecting a change in resistance I can't see how that would work.

An interesting experiment. Use a hair dryer to heat all the wheel speed sensor a bit to see if ScanMyTesla register any change.

 

[MasterC17]

My uneducated guess is that there's a temp sensor built into the ABS/wheel speed sensor. I have nothing to base that on other than a WAG though, and I'm not even sure that makes sense since they are on the opposite side of the hub from the caliper.

I would also make that uneducated assumption. I never saw a warning for brake over-temp when I was using the Model S brakes, and I can tell they got quite hot!

 

[destructure00]

Only other thing that comes to mind is maybe it's calculated off of wheel speed change over time, with some consideration for pedal or brake fluid pressure.

 

[Dangerous Fish]

I just tried heating up the area around the speed sensor with a heat gun. No change in reported temperature in SMT. I then went all around the front wheel arch with the heatgun trying different areas and also heating up the disc, hub, caliper etc. but not even a degree difference from ambient (which is 42F here presently). So I'm convinced there's no temperature sensor as such. It must be calculated from some combination of other data.

I'm going to log a lot of data later this week and try and cross check it again with my IR thermometer to see if it's accurate enough for track work.

 

[MasterC17]

I just tried heating up the area around the speed sensor with a heat gun. No change in reported temperature in SMT. I then went all around the front wheel arch with the heatgun trying different areas and also heating up the disc, hub, caliper etc. but not even a degree difference from ambient (which is 42F here presently). So I'm convinced there's no temperature sensor as such. It must be calculated from some combination of other data.

I'm going to log a lot of data later this week and try and cross check it again with my IR thermometer to see if it's accurate enough for track work.

Nice work, thanks for checking that out. It is likely then a calculated value using several variables as @destructure00 mentioned.

 

[Dangerous Fish]

Just for my own peace of mind, I disconnected a front wheel speed sensor and the (estimated) temperature was still being reported, so I think it proves conclusively that sensor isn't how it's done.

But it's taking a temperature measurement from something as a baseline and that number is less than the actual (cold) temperature of the brake disc I measured with an IR thermometer. It's also not the same as the ambient temperature SMT reports.

What's keeping me awake at night is how it adapts this est. brake temp. to the different pads I've used. With the standard pads I got brake temp. warning messages after a few laps. After I put in XT970s and went back to the same track, I wasn't getting the error messages. If it's using just braking pressure/time/speed/decelleration etc etc data then how is that going to give the car enough information so it knows I've put better pads in that day?

 

[destructure00]

With the standard pads I got brake temp. warning messages after a few laps. After I put in XT970s and went back to the same track, I wasn't getting the error messages.

Same. That's where my comment about brake fluid or pedal pressure variable came in...in my case I could feel that the pads were glazed and was on the brakes much harder with stock and 910 pads, wondering if that can be measured and accounted for in a calculation somewhere.

 

[Dangerous Fish]

Same. That's where my comment about brake fluid or pedal pressure variable came in...in my case I could feel that the pads were glazed and was on the brakes much harder with stock and 910 pads, wondering if that can be measured and accounted for in a calculation somewhere.

It's a very clever algorithm if it can come up with a fairly accurate temperature from those other inputs across different brake pad/disc combinations but I wouldn't put anything past the Tesla programmers. What we need is more people comparing the numbers from SMT with actual temperature readings off the rotors.

 

[Dangerous Fish]

OK I'm back from the track and what I've learnt today is that the temperatures reported thru SMT are lower than the actual rotor temperatures. For example, rotor temperatures measured at 350C front and 250C rear show as 250/180 in SMT.

This was with Carbotech pads, which I tried today for the first time. Maybe the accuracy varies depending on the pad used?

Anyway, the good news was that I saw temperatures on track well over 450C thru SMT which I reckon must have been over 550C rotor temperatures and the pads worked just fine (short track, 3 medium + 1 heavy braking corner).

 

[MasterC17]

OK I'm back from the track and what I've learnt today is that the temperatures reported thru SMT are lower than the actual rotor temperatures. For example, rotor temperatures measured at 350C front and 250C rear show as 250/180 in SMT.

This was with Carbotech pads, which I tried today for the first time. Maybe the accuracy varies depending on the pad used?

Anyway, the good news was that I saw temperatures on track well over 450C thru SMT which I reckon must have been over 550C rotor temperatures and the pads worked just fine (short track, 3 medium + 1 heavy braking corner).

Glad to hear the Carbotech Pads worked well for you! How did the wear on the pad/rotor look?

 

[Dangerous Fish]

Glad to hear the Carbotech Pads worked well for you! How did the wear on the pad/rotor look?

Haven't taken the pads out yet but rotors look the right color.

 

[destructure00]

Are you monitoring brake temperatures either with ScanMyTesla or with a IR thermometer on the rotors?

My OBD2 adapter harness finally showed up, got the OBDLink MX paired and SMT downloaded. I can see all of the standard parameters but can't find brake temp anywhere. How are you accessing that data?

 

[Dangerous Fish]

My OBD2 adapter harness finally showed up, got the OBDLink MX paired and SMT downloaded. I can see all of the standard parameters but can't find brake temp anywhere. How are you accessing that data?

I'm guessing you're sitting in the car in park looking at the variables in SMT?
Press the brake pedal to wake the car up and more variables, including the est. brake temps will appear.

 

[destructure00]

I'm guessing you're sitting in the car in park looking at the variables in SMT?
Press the brake pedal to wake the car up and more variables, including the est. brake temps will appear.

Yep, I just did that as you were replying I think, found them. Thanks!!

 

[destructure00]

Just tried to let TrackAddict connect to the MX and the car went nuts....heards motor under the car spin up, contactors were clicking back and forth, got all kinds of error messages on the screen. Unplugged MX and powered car off....hoping all is normal when I power back on in a few minutes. Weird. Guess I won't be doing that again.

 

[destructure00]

All good now....phew. It went nuts when TA started scanning for parameters.