Rivian CS response to my questions...
"We are currently completing our EPA certification on all of our tire options and will publish more detailed range numbers once complete. When those get released, you will have a better understanding of the range difference of tires and the cabin decibel level. Rest assured, our innovation and engineer teams have ensured a great experience for our Rivian community.
We are waiting for confirmation on whether purchasing additional tires at the final configuration will be available, so when your guide reaches out in a few months, those details can be discussed and finalized. If the additional purchase can be made, then the need to buy extra tires depends on the Rivian owner and their needs.
In regards to the spare tire, if you live in a state where the spare tire is required, it is included with your vehicle, but if you live in a state where a spare tire is not required, one will be available.
We also understand the concern about the availability of Pirellis tires and appreciate the feedback on potential availability. While the 21’ was designed for Rivian, we are aware there will be aftermarket options available for the 20’ and 22’ that are not Pirellis."