i'm pretty sure 52's are as big as they go... michelin has special duty 52's that are all the rage on the big trucks like that.
edit: unless they're monstertruck tires or god damn tractor tires...
you can buy those tires aftermarket. its just mil spec tires. 52" is correct tho.i'd like to know where to get those bronco's. always liked the 4 door version. just never saw one for sale.