I just swtiched to 35's actual 315 70 17 which measure 34.69 say 34.75 for pro cal use. when I program the the new tire size in my speedometer is still 9 miles per off at 60 mph. so when my speedometer reads 60 I am actually doing 69. I have checked this 3 ways 2 with gps speedometers on my i phone and also outhouse signs with radar that always tell me to slow down. I can't figure out what to do. should I reset the speedo with a larger tire size that would match the 9 mph error. or is there something else I am missing .