I can interchange the tire sizes? The surface part the width of the treads. Hubby's 2000 Dakota, cab V8 wears the 255/70R15 Can I drop the first three numbers down to 235? Or it must be the exact tire treads it had on? Yep it is going bald and time to get some new tires. I was hoping some sales on tires but the cheapest I can find are at WalMart.