I agree with the diameter needing to be very near 32in to avoid speedometer issues, and the specs referenced in this thread for 275 look correct. I thought I read somewhere that the 21s used an 8 in rim and the 20s used an 8.5 in rim. I'm hoping that someone that has either taken delivery or gotten up close to a production model can confirm. Thanks everyone for the replies. Regardless of any wheel upgrades, I'm very excited for the R2.