We used to put 7.50x17 tires on the back of our 3/4 ton and they would run 70 all day long and of course the 7.50x17 carry more load. It looked a little goofy, but it was practical for us. Here is a picture of the last one of them that still saw limited service when I remodeled my house 30 years ago.

http://www.flickr.com/photos/crenwelgeoil/2847834566/in/photostream