I work at a tire shop myself, and the policy there is that we aren't allowed to put on any tire that isn't specified by the Manufactuer, that means no oversized tires,
The correct size or optional sizes are listed in Tire Books, or you can just look at the sticker on the doorjam of your vehicle, one way to get around this is just to bring the rims in separated then you can put whatever ####ing size you want on the rims, then we don't have anything to do with the safety of the customer because he himself is installing the rims onto the vehicle.
and i was reading in my Explorer Manual the other day, and it says that only A/T tires are supposed to be installed on this vehicle, that means no M/Ts or H/Ts and whatnot, but I always see Explorers running around without A/Ts but i plan to keep A/T/s on my vehicle