how does it work?? in the door of my 97 ram it says the tires are 255, i bought it last year and it had 265 on it. now i put oon some 285s. i cant really tell because i think it thorws off the odometer. if so which way does it change it? are you going farther of shorter distance than it says when you increase in tire size? my speedometer says that im going slower than i actually am.