TST recommends a tire size of 245/40R20 for the 20x9 wheel (front), and a tire size of 275/40R20 for the 20x10 wheel (rear). I actually disagree with that recommendation.
The standard tire diameter for the Model S is 27.7", which is a circumference of 86.9", and 729 revolutions per mile. Any tire that is fitted on the Model S should be as close as possible to these numbers, since this is what the car expects for speedometer calibration, auto-park distance estimates, and energy calculations. Ideally, the tire fitment should be within 1% of these numbers.
The 245/40R20 tire (front, for the 20x9) wheel is 27.7" diameter (0.0%), 86.5" circumference (-0.4%), and 732 revolutions per mile (+0.4%). This is well within the 1% tolerance.
A 275/40R20 tire is 28.7" diameter (+3.6%), 90.0" circumference (+3.6%), and 704 revolutions per mile (-3.6%). This is a fairly significant difference, and I wouldn't want to put this tire on the Model S, especially with a significantly different size tire on the front axle.
The 275/35R20 is 27.6" diameter (-0.4%), 86.6" circumference (-0.4%), and 732 revolutions per mile (+0.4%). This is within the 1% tolerance for the original fitment tires, and nearly exactly matches the front 245/40R20 tires.
I would fit the TST staggered setup as:
245/40R20 front
275/35R20 rear
Tire rack carries several brands in this size combination. My recommendations for summer performance tires would be:
Michelin Pilot Super Sport
Bridgestone Potenza S-04 Pole Position
Continental ExtremeContact DW
Pirelli P Zero
I think the first 3 choices are better than the Pirelli in this category.
If you want an all-season tire, look at the
Continental ExtremeContact DWS 06.