Calibrating Speedometer - 1990 Ford Bronco II

[idriveafordranger94]

I was using my GPS today to get somewhere and noticed that my speedometer is about 4-5 mph off at 45mph and 6-7 off at 65. The tires that are on my Bronco are 30x9.50 R15; They aren't stock. How do I go about recalibrating my speedometer? I have a perfect driving record and want to keep it that wa! Thanks!

 

[BRUTUS_T_HOG]

do the math, and get a new speedo gear to compensate. or just automaticly compensate like i do.

i have stock tires and its 5 mph off at all times