Speedometer & Odometer Correction

[GSatler]

after many tries (two dealers) i had my pinion factor set today.

works great. everything rite on.

it must be the first time my dealer did this.

do not use the size of the tires on your truck. measure circumference of tire first. do not go to the dealer until you do this.

insist u watch them do it in this fashion

tire size unknown or other

type of axle 10. 5 or 11. 5

revs. per mile 400 to 700 (to figure this, check below)



63360 divided by circumference in inches



this works every time

 

[JHardwick]

The only accurate way to measure rolling circumference is to measure the centerline of the axle to the ground with the tire mounted and sitting on the ground. Dynamic circumference versus static (laying on its side) circumference are two different animals!

 

[klenger]

You could also mark the position of the tire on the ground, slowly drive several revolutions while someone is watching and counting the revs and then measure the distance traveled and then do the math.

 

[thejeepdude]

It's easier to just put a little dab of paint in the center of the tire and drive forward a few feet, then measure between the paint dots on the ground. Extremely accurate and only takes a minute to do. That's how I calculate the circumference of my mountain bike tires in mm and the speedo is always dead on to the . 1 mph.