I didn't rotate because someone said that I would then need 4 tires fast. It looks like the thread is wearing evenly but not much left. Don't need an alignment or any thing like that. Don't know how to calculate the tread depth.Dang, 20k miles!! What are you doing burn outs? Geesh, I got 75k out of my stock Michelins. Did you ever rotate? Drive in circles all day? In what way's are you tires worn? What's the tread depth? Shoulder wear? Are the cords coming through? Are they dry rotted? More details would help, thanks.