I just bought a '96 F150 and it needs tires badly. It has the tiny 235/75-15 on it now, but the factory upsize was a 265/75-15. I would like to go to the larger tire, but I want the speedo to read correctly and since I am a Mopar guy I do not know how the Fords adjusted for tire size. How do you make the speedometer adapt to tire size changes? Thanks!