Tires: tires on AWD vehicles, awd vehicles, flat tires

Question
I am in the process of researching AWD vans to purchase for my wife and 3 children. After talking with a friend, and a tire store I have used many times, and your reply to an AWD audi owner I am starting to have second thoughts. My question is: if the tires on an AWD vehicle need to be the same diameter to avoid damage to the differential do you rotate tires on these vehicles? Also the AWD van I am contemplating buying comes with "run flat tires" and I know nothing about these. Any advise would be helpful. Thank You Peter
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Answer
Peter,

Yes, in fact tires on AWD must be rotated (if possible) to avoid the tires wearing differently and arriving at different revs per mile.

If you are contemplating a van with Michelin Pax, I would do a lot of research.  There have been many complaints about how expensive they are to replace - particularly considering the recommendations that they not be repaired.