MPH change from old tires to new bigger ones
By David Steadman
Multiply by the ratio of the diameters of your new tires to your
old tires.
If you are talking about speedometer changes then;
Speed = indicated speed X New Diameter / Old diameter
So if you had 28" tires and now have 33" tires and are driving at 50 miles
an hour:
Speed = 50 X 33 / 28 = 58.9 miles per hour.
Or if you want to adjust the odometer or trip meter:
Actual miles = indicated miles X New Diameter / Old diameter
So if your trip meter shows 220 miles driven with the same tire sizes as
before:
Distance = 220 X 33 / 28 = 259.3 miles.