some cars need a certain trye to cope with the load so they have to be the same across the whole car, not just axles
with the new space saver skinny things what would happen if oone of them blew out and you had an accident where you were going faster than the recommended 50 mph max and were 100 miles away from where you had the puncture?
if they don't have to pay out they won't as it'll cost them less to fork out for a assesor than it will to pay the cliam