I wasn't aware of the fact this is done with real race cars. I read about this in reference to an article about Corvette's testing of this years C6.R GT1 lemans style race car.

The method used is to install multiple infrared sensors in each wheel well of the car to measure temperatures across the width of the tires.

According to that article, the pit stall has 23 flat screens, as many lap tops as will fit in a double decker pit stall; some watching video feeds, the others tracking telemetry. The car's onboard computer can be expanded to support up to 280 channels with up to 96 of them being live feeds (the rest are downloaded post test or race). The other interesting fact was that a lot of air sensors are used on the car to measure airflows inside and around the car (almost a virtual wind tunnel).

Corvette is probably glad that Aston Martin with their faster but more prone to break DBR9 is racing GT2 class this year leaving them almost to themselves in the GT1 class.

Interesting. I wasn't aware the thermal sensor bit was being done either, but am not all too surprised. Calspan does this at their tire testing facility. There are three sensors just after the contact patch.

Someone told me about an IR camera that was mounted to an Indycar pointed at one of the tires for testing at the Indianapolis Motor Speedway. I don't know how common that is or when it was done, but he said the videos were very interesting. This wasn't for sorting out the car setup like the sensors you describe are probably for, but rather for the tire engineers to look at.

Granted, the temperatures you see with both of these systems are surface temperatures rather than the pyrometer readings down near the cord, but still a very useful thing to have, especially for the tire compounding guys. I wonder if there are any cheap types with reasonable accuracy to play with on a road car.

So, are the days gone when the instant a car enters the pits, the first thing that happens is the tyres getting prodded with a heat probe? (after they've been changed in a race, obviously).

No, the heat probe is still totally valid, because that gives a far more representative tyre temperature from the core. The surface temp is relatively useless, but pretty much all you can get off a moving tyre [Although I suppose a thermocouple embedded in the rubber, with miniature wireless senders inside the wheel might work, if you have the money for special tyres].

F1 use them in testing. In fact, I think Renault installed IR pyrometers inside a hollowed out winglet on the front wing endplate to monitor changes during races.

To get an idea of how useless they are, press Ctrl-Shift in LFS whilst driving with tyre temps show, and see how they vary a lot, but without really telling you much at all. At the level of F1 it can show the onset (and recovery) of the mystical 'graining', and early(ish) warning of impending tyre failure/delamination.

its all a far cry from what I used in my karting days, we would get the pressure right by looking at the contact patch size, which you can see by looking at the dark area of the tyre surface, the rears where checked from trackside in the same way, we had a probe but honestly by the time we got through the weigh bridge to the pitstall it wasn't much use.

Considering the tire temps are being constantly monitored, and fed via a live stream back to even more computers, it's possible that the GM team's software can approximate core temperatures based on telemetry inputs, knowledge of the tire's physics, and the temperature readings.

Quote from JeffR :

Corvette is probably glad that Aston Martin with their faster but more prone to break DBR9 is racing GT2 class this year leaving them almost to themselves in the GT1 class.

Offtopic: that GT2 car is DBRS9, not DBR9. That one DBR9 in American Le Mans GT1 is Bell Motorsports entry. Le Mans is the only race Prodrive / Aston Martin Racing does this year, so Corvette can try have their revenge at them in Le Mans.

For anyone interested in real life data the sample files that are included with the free Motec download have tyre temp data channels.