On Tyres.co.uk, you can find BMW M8 Competition Coupé original fitment 20-inch staggered wheels, including 275/35 ZR20 front and 285/35 ZR20 rear. The Michelin Pilot Sport 4 S and Pirelli P Zero tyres are offered. Make sure to confirm the exact registration and keep to the specified XL design, load index and speed rating as alternative wheel choices may vary.
The specifications of M8 tyre sizes can be found on the driver side door inner panel tyre pressure information placard. They give the officially approved dimensions of front and rear tyres, and the cold tyre pressure of the wheel package on your vehicle. Prior to purchase, check this against the tyre sidewall info.
The BMW M8 does not require all four wheels replaced, however, every BMW M8 M xDrive (even those with a selectable 2WD mode) means all four wheels must be the same in terms of type, size, rolling circumference and level of wear. If this level of match is not possible, then all four wheels should be replaced. If only two wheels are replaced, replace the remaining two new wheels at the rear.