Bob's Studebaker Resource Website

Specs on the Pirelli P225/60R16

225/60 relates to the aspect ratio, where in millemeters, the sidewall height is 60% the value of the treadwidth (225). 1 inch = 25.4 mm (tread is 8.85 inches wide)


To calculate the circumference for speedometer corrections:
225 X .60 = 135
135 divided by 25.4 = 5.31 (sidewall height in inches)
tire height = 2 sidewalls + rim size
2 X 5.31 + 16" = 26.62 inches (diameter)
Circumference = diameter X pi ( 3.1415)
26.62 X 3.1415 = 83.65 (6.97 feet)

5280 (feet per mile) / 6.97 = 757 revolutions per mile (tire)


The above ratios can be applied to any tire size if you plug the correct values in