What is the biggest tire I can put on my stock 18s without any modifications to the car? I'm looking at 255/55/18s. I want to have some more rubber fill up the wheelwell. Will these fit? I'm thinking of getting the tires from Sam's Club. I'm also thinking of going with Michelin. I want good...

What should be my tire pressure for a long trip (over 500 miles)? I have 255/60/18. Thanks for all the upcoming replies. :bigthumb: