The above pictures show the 2019 Pirelli P Zero F1 tyres working windows for all compounds, which were in the 13-inch wheel format. Although this is not accurate, we could guestimate and thus extrapolate that the 18-inch tyres from 2022 onwards are almost in the same ballpark figures.
What is important to notice from the above pictures is the fact that:
- There are 5 tyre working window ranges – WWR – and for this year, there are 6 WWR.
- The softer compounds have a smaller WWR, usually some 20 degrees Celsius, and the harder compounds have a wider WWR, usually in the 25-30 degrees Celsius ballpark figure.
- There is a common WWR for any successive 3 tyre compounds that are designated for a particular race, and this is narrower for the softer tyre compounds
Based on the below graph and picture, in case of using a bimetal strip solution (or better say temperature harvesting store) acting as a thermostat, there are at least 5 bimetal strip variants that are needed, bearing in mind that in the race usually are used 2 tyre compounds. And each bimetal stripe should be designed/tailored for the WWR main tyre or for the common WWR of those 2 tyre compounds used in the race.
These bimetal strips must have the temperature triggering point – TTP - (when they are starting, thus entering temp harvesting mode) higher each time the tyre compound is harder. This could be done either by altering the volume of the material or by changing the material itself with one that has a higher TTP. Knowing that in F1 the best solution is one that weighs the least, that means the optimum solution is to change the bimetal composition. But here is another important catch: you need to tailor both the TTP and WWR mostly for those 2 tyre compounds designated for the race. And this is a trade-off of a usual characteristic in F1.
For instance, Pirelli designated the C1, C2, and C3 tyres for a race. According to the graph below, the common WWR for all 3 tyres is between 110 and 135 degrees Celsius, but only C2 and C1 are usually the race tyres that will be raced, C3 tyre being designated mainly for the qualy. Now the main question is where to have the TTP? If you set the TTP at 140 degrees Celsius, the C2 tyre would be overheating, but if you set the TTP at 135 degrees Celsius, you`ll narrow the C1 tyre WWR. The answer is that in common practice, they choose the conservative/safer option, going with the 135 degrees Celsius value for the TTP.
(As a disclaimer, all below values are relative and based on the 2019 Pirelli P Zero F1 tyres)
We could go deeper into the solid-state chemistry area if we are to talk about the composition of those bimetal strips, but I think it`s not the appropriate place here to do so. All I have to say is that it`s a complex matter and those bimetals stripe/changing phase material/temps harvesting store could be three, quarter, and multiple metals alloys that require deep knowledge in the bi, three, quaternary system a specific to the solid-state materials …
In conclusion, I think this solution it`s a doable thing to do and has nothing to do with a movable device rule, thus it`s a perfectly legal device according to the regs. But unfortunately, this solution is both time and resource-consuming. For starters, you need to hire someone who has a degree in solid-state physical chemistry, and particularly an engineer with lots of practice in the physical metallurgy field. And last but not least is worth doing coz this could also be used in 2026 and beyond, thus it is not a waste of time and money ...
P.S. Regarding the water filling tyre story, my best guess is just water or moist/dew spots on the wheel rim. This is due to the condensation phenomena triggered when there is enough high temperature difference between the internal and external sides of the wheel rim. And this big delta temp occurs due to that material that is harvesting temperature for a long time, something that is very useful in addition to the race after they change the tyres …
