A local guy has a set of factory 18's for sale and I've been thinking about switching out the 20's on my Limited to open up some more tire choices. However, while reading some posts I've seen a couple mentioning a difference between the 18's that came on the Base vs Premium as far as load rating. Then I've seen some other posts where people talk about switching to the factory 18's with no mention of a difference between them. Just wondering if all factory 18's are created equal and if not how to tell the difference. Thanks in advance for any advice.