Auto Motor und Sport reported that they had a source claiming that Red Bull used a secret infrared camera to check out the McLaren MCL39's temperatures and found its brake drums (the shroud managing airflow around the disk brakes) were a whole color cooler than anybody else's brake drums. Which means their brake operating temperatures are WAY cooler than anybody else's. And brake heat is a key contributor to tire heat, which 'splains (at least in part) why McLaren's tires are so long-lasting.
What it doesn't explain is how McLaren is doing it.
Piastri's MCL39 was given the full-blown anal exam by the FIA after Myjammy (one of 10 selected "at random") and given a clean bill of health. Which should put to rest the rumors that Red Bull has been circulating since Sao Paulo last year that McLaren was injecting water into their tires so they'd run cooler.
When the FIA announced the results they specifically mentioned that particular attention had been paid to TR 3.13 (Wheel bodywork) and TR 11.5 ("Liquid cooling of the brakes is forbidden."), even stating they had checked "at all four corners" and all was found to be in compliance.
I never understood why RBR was picking on water anyway, since the whole point of using nitrogen to fill F1 tires is that it's completely water-free. It's technically challenging -- and expensive -- to drive all of the moisture out of air, so compressed nitrogen is actually cheaper and more readily available than anhydrous air.
And being completely water-free is important to stable tire pressure because when water converts from liquid to steam, its vapor pressure increases 1700x! And dry slicks spend most of their working day at 210-230°F, so it's certain to reach boiling point sooner rather than later. So regardless whether they're filled with garden-variety air or nitrogen, even a minuscule amount of water in the tires could wreck tire management.
Red Bull's claim also doesn't explain how cooler tires are cooling the brakes, because that door only swings one way. Carbon-carbon brakes can get to 1800°F on the braking-heavy circuits, and they lose their bite if they get below 400°F. So brake heat DEFINITELY contributes to tire temperature, but the other, not so much.
But sometimes someone in F1 comes up with some really SciFi stuff, like the Lotus 56 4WD turbine car, and the Brabham sucker car, so I wouldn't completely discount the possibility that McLaren has magic water. Or Maybe Red Bull knows the secret of making magic water and suspects that McLaren has some of their own.
Anyway, McLaren's Zak Brown took the opportunity to take a dig at Red Bull over the accusations.
On a whim, I searched the TR and the SR for the term "Dry Ice" and could only find one mention in either, and that was a prohibition against using it in the driver cooling system in the TR. Which got me to wondering, is there a reg that forbids hiding a chunk of dry ice somewhere within the airstream through the brake cooling ductwork so that chilled air emerges?
An article at the-race.com states that after examining Piastri's car, the FIA emphasized that TR 10.8.4 prohibited the use of anything other than air to cool the brakes. I wasn't familiar with that passage, so I looked it up. And I have to say, the FIA's is a pretty twisted interpretation because the way I read it, 10.8.4 makes no mention whatsoever of "cooling" brakes, only of increasing or maintaining temp.
This is the entire unedited section:
10.8.4 Treatment of tyres
a. Tyres may only be inflated with air or nitrogen.
b. Any process the intent of which is to reduce the amount of moisture in the tyre and/or in its inflation gas is forbidden.
c. A complete wheel must contain a single fixed internal gas volume. No valves, bleeds or permeable membranes are permitted other than to inflate or deflate the tyre whilst the car is stationary.
d. The only permitted type of tyre heating devices are blankets that comply with the design prescriptions listed in Article 10.8.5. Any other device, system or procedure (except for driving of the car) the purpose and/or effect of which is to heat the wheels, hubs or brakes above the ambient air temperature, or to maintain their temperature if they are already warm, is prohibited.
I don't see a stinkin' word about "cooling," unless they're ruling is that cooling is a negative heating, which is come pretty contorted logic.
Anyways, I still have no idea how big a chunk of dry ice it would take to provide significant cooling for +/- 100-110 minutes (formation lap to checkered flag). Plus it's bound to make the FIA scrutineers suspicious if only two cars on the grid consistently lost a couple of kilos more weight than all the rest at every race.
But no matter because if the FIA says it's a rule, then it's a rule, at least until it isn't. Remember Red Bull's fuel consumption debacle at Melbourne 2014? I'm still convinced RBR's bench-testing equipment was more accurate than the FIA's was, which means Vettel's car was legal, but that's not how it's written in the history books.