The "k" value is the number of pulses the speedometer needs to register 1 mile. The pulse generator in the dif creates 6 or 7 pulses per axle revolution. You can do the math to check this after you measure/calculate/estimate the tire circumference.

To check speedo accuracy, set cruise control and measure time required to travel 5 miles using milemarkers on interstate. MPH = (Miles travelled)/(Time in hours).

What size tires are on your car?

Paul Shovestul



Quote Originally Posted by cschollum
Can someone explain how alterations to wheel sizes affect speedo calculations?

my car has different wheels from standard and ive always suspected that the speedo was out - im aware electronic speedos, especially bmw have a small difference in speed stated to actual due to allowances for errors, meaning you are going slower than stated but im guessing wheels play a major part in this

do the markings on the speedo allow calculations to be made as to what size the wheels should be for the speedo to be acurate? it says something like k=

any help would be good
chris