[i heart square bodys]

okay so i have come to find that there are 7.5'' wide rally wheels as well as 8'' and 9''. whats the deal here ! why so many different sizes? did it have to do with the year of the truck or were the 7.5''s for vans, 8'' for trucks and 9'' for jimmys and burbs? im confused here! im planning on putting 2 of the wide ones in the back and 2 of the 8''s in the front. someone clear this up as i have only one 9'' wheel and need to find a mate for it !