Recently did my first track day in a new-to-me GTR Pro. From looking at the Cup 2 tire wear vs the tire-temps shown in the console, I'm guessing that the below-surface tread temp is about 10-20 deg C more than the tire-temp shown on the console ... 10 deg at lower temps and 20 deg at higher temps. It was a warm day (about 30 deg C/85 deg F) and the track is a short track that's brutal on tires (and brakes).

Reviewing all the WIS docs I could find on the TPMS system, I only found one mention of the temperature indication:
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The 4 tire pressure sensors send out data telegrams during a journey every t = 60 s to the tire pressure monitor control unit.

These data telegrams contain the pressure, tire air temperature, wheel identifier (wheel ID) and status information (direction of rotation, operating mode, etc.).
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On track, when I saw one or more tire temps shown as 80 deg C in the console, I backed off as, from my experience, when Cup 2 "below the surface" tread gets much over 100 deg C, they start to shed rubber very quickly ... too much over and they start to shed tread in chunks, effectively destroying the tire quite rapidly (I've experienced this). Even when backing off, at about 80 deg C console indication, it would always continue to climb into the high 80s, at which point I pitted. This is consistent with the WIS info that the temp measured/shown is the air temp inside the tire so the air's temp would continue to heat (up to the inside tire-carcass's temp) and there'd be hysteresis/lag.

An after-track-day detailed look at my tires showed something like this, on the fronts ... which, to me, says I wouldn't have wanted to get them any hotter:


QUESTION
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Does anyone have any additional info, comments, etc. regarding the operation of the TPMS system's tire-temp display and/or use of the console-shown tire temps when running on-track?

 

Side question - would a non GTR/GTR Pro show tire temps on the internal screen or dash screen? Those tires look like they’re about to give lol - I remember having cheap tires at some of my first autocross get togethers years ago that ended up looking like this

 

Only if the model has that capability.

Actually, I'd say they were right at the limit. Though I wouldn't want to get them any hotter, they did have significant grip at that point. #;-)

Here's what happened when I got a Cup 2 tire too hot (the fronts on my C63 S) ... you can see that chunks of the tire were starting to shed and expose the top of carcass to which the tread compounds are bonded (my track day ended early, that day):

 

This is a completely normal look for a Cup 2 ZP tyre that has been used on track

 

that looks completely normal to me as well. My ZPs looked just like that after a hard session.

I don't trust the console display, always used a pyrometer to check the actual temperature at hot pit. It really depends on the tires you are using, track condition, driving style etc.

 

I don't have a pyrometer, but have used the infrared temp gun to get a rough idea. While I know it's not as good as a pyrometer, it does provide good comparative data if used consistently (e.g., immediately after pitting). I'm now fairly familiar with what those readings mean relative to tire wear.

QUESTIONs:
Since you've been using a proper pyrometer, have you developed any sort of feeling for how the displayed (inside-tire air) temperatures relate to the pyrometer readings? Does my guess of a difference of 10 deg C at lower temps (say 40-55) sliding up to 20 deg C at higher temps make sense?

I agree that my Cup 2 tire looks perfectly OK but, from looking at the "granularity of the melting" on the leading edge of the tread blocks, I do think it was about to get too hot ... if others have different experience, I'd be interested (more data, more data!).

When you look at the pic of the destroyed C63 S tire, the "granularity of the melting" is much more coarse and the melting has occurred across the entire tread blocks. I'm guessing that the coarseness of the "granularity of melting" correlates to the maximum tread temperature. Higher temp means rubber rolls off more readily and in larger pieces and, at some temp, may separate in "chunks" ... though the "chunking" may also be being "helped" by some debris/curb-running/whatever.

FYI, that tire was also not MO, but was homologated for BMW M2, which is probably 350-400 lb lighter on the front end than the C63 S ... so the tire always tended to have outside-edge roll-over, even at 40 PSI (which is too high). That didn't help the situation. I've learned to buy track tires ahead of time, lest the correct ones not be available, when needed. $;-)

 

I actually didn't do that comparison, I was more relying on the console display of tire pressure and then coming into the hot pit to use pyrometer for the actual temp of the tires. I think the TPMS monitoring of temp might give you an understanding at a high level, but definitely wouldn't be accurate. Do you feel any push or other abnormal feedback from the tires close to the end of a session? If you over push them, these tires do get very greasy and can really tell.

 

Yes, when I've overdone it with the C63 S, I also noticed that the Cup 2s got greasy. That meant increased understeer from the fronts slipping and if powered, increased oversteer from the rears slipping.

On hot days, I find that about 6 consecutive aggressive laps will max out the Cup 2s for temperature and 8-10 such laps on a cool day. That seems to be the same for both the C63 S and the GTR. I've gotten pretty good at guessing the starting temps and always do an adjustment immediately upon arriving at the track. The hour+ drive to the track means I'm not starting from cold tires if I set them before sitting through the driver's meeting, etc. I noticed that the GTR pressures varied much less than I was used to with the C63 S.

Typically, I bleed off another 1-3 PSI after each of the first 2 sessions. The GTR remained within pressure range much longer and I didn't have to add pressure for the drive home (but did the next day, of course). Maybe the outside temp was more consistent throughout the day, maybe the larger tires hold their heat more ... whatever it was, it was nice not to be fiddling with pressures all the time.

 

Depends on the track, but 6 laps is about what I could get from the cup2s as well before they starting to get greasy and needs a cool down. Our cars are definitely on the heavier side of a track car, that contributes a lot to it. I do drive to track as well and use similar bleed off after each morning session approach as you do.

 

Understand and agree. If you ever do gather some data that would help correlate the console temp display numbers with pyrometer readings, it'd be valuable data to know. For now, I'll continue to work with my "10-20 C deg over" guess as it seems to be useful. More track days will help refine. Thanks for your responses.