Sponsored Links (Register now to hide all advertisements)
4.50-21 tires have a diameter of 30", so their circumference is 94.2". 4.74-19 tires have a 28.5 diameter, so their circumference is 89.5. The percent difference is +5.1% for the 2.50-21 tires, so that also is the percent difference in MPH. For example, at 1000 RPM where the car with 4.75-19 tires does 25 MPH, a car with 4.50-21 tires will travel at 26.3 MPH (25x0.051=1.275; using 1.3 thus 25+1.3 = 26.3 MPH).