Here in Ky they don't really regulate the tags on a personal vehicle. Two of my trucks have the same tags on them as my wife's car. The amount you pay is calculated by what the vehicle books for. Now if you are running commercial then you buy tags that are large enough to cover the weight of the truck and the trailer that you would possible tow. So in other words if your truck weighs 10,000# solo and you pull a trailer that has the capacity to weigh 20,000# and you plan to load it to that then you will need tags on your truck that will cover that 30,000# which in turn puts you in CDL licence territory. My person F350 service truck that I drive for the company has 26,000# tags on it.