Speedo Calibration Chart

SPM MPH KPHLapsed Time

Seconds Per MileActual

Miles Per HourActual

Kilometers per Hour68 52.9 85.267 53.7 86.566 54.5 87.665 55.4 89.264 56.3 90.663 57.1 92.062 57.1 93.561 59.0 95.060 60.0 96.659 61.0 98.258 62.1 100.057 63.2 101.856 64.3 103.555 65.5 105.554 66.7 107.453 67.9 109.352 69.2 111.451 70.6 113.750 72.0 115.9

MPH Formula:

MPH = distance ÷ time or MPH = (distance x 60) / time

Simple Equation: 3600 = Seconds Per Hour (KPH = 5796 ÷ SPM)

SPH ÷ SPM = MPH: 3600 ÷ SPM = MPH: 3600 ÷ 68 = MPH: 3600 ÷ 68 = 52.9

SPEEDOMETER PROBLEMS

Speedometer slow (on dash) head Speedometer fast (on dash) head1. Increase the teeth on the drive gear 1. Decrease the teeth on the drive gear2. Decrease the teeth on the driven gear 2. Increase the teeth on the driven gear

Usually, there is a 3-5 mph change in each tooth The drive gear in on the output shaft on most vehicles The driven gear is usually in the extension housing Most GM vehicles have both replaceable drive and driven gears Most Ford and Chrysler vehicles have their drive gears cut into the output shaft Most conventional 4x4’s are driven at the transfer case