EDIT: I was a derpy-mc-derpface and somehow missed this thread in my "spring-cleaning" of stickies... my bad
The 18-inch wheels were introduced into the Formula 2 Championship in 2020, to test what the changes to the tyre behaviour would likely be. It was originally proposed that the use of tyre warmers would be banned, but this decision was later reversed after opposition from Pirelli. Insteadm they're going to become a standardised piece of equipment and then eventually be phased out in 2024.
Particularly interesting to me, is the fact that the teams will have to run a flush wheel cover next season to minimise aerodynamic turbulence
The new tyres grow from 660 to 720mm in diameter, but the tread width of 305mm at the front and 405mm at the rear isn't changing.
F1 also asked Pirelli to make rubber that’s less prone to overheating and can be pushed harder for longer... here's hoping...!