We bought a 1997 Chevy Suburban and recently put new tires on at Walmart. The associate there told us that we had the wrong size tires. Rather than worrying about different rim sizes or something I just had them put the same size tires on that were already on there, since I knew that size had already been on there.
However, I also somewhat recently got a flat tire and discovered that my spare tire is 245/75R16, which is also the number found on the placard inside the drivers' side door. (It also suggests a proper PSI of 45, and all the tires I've bought have a max PSI of 44).
Is there a huge difference between the tires that are on there and the tires that are supposed to be on there? Will there be a problem if I get another flat and say, have to drive 300 miles to the nearest tire repair place?
(These are my specific circumstances, but if there's a general formula for comparing tire size and advice for driving on a different sized tire/wheel (aside from "don't", which I assume is the correct answer), that would be great!