Beat to death: But..... tires.

[desertPOS]

I have a '69 C20 with stock suspension and no intention of dropping it. It has the 16.5 factory (I think) rims, but the tires are mismatched rollers that need to be replaced. I do a decent amount of fwy driving in the truck, would like to fill the wheelwells and get something a little wider, at least in the back. Looking for tire recommendations, I can't wrap my head around the proper way to measure tires when they're not measured in inches yet. Looking at the BFG T/As, but something with a decent warranty would be good. Not opposed to running smaller in the front, as long as they all use the rims I have. Any insight would be great...