New Tires...now what

[Longshot270]

Originally Posted by jetpilot2

Or from another post:

"The circumference is pi x D or: 3.141593 x 35 = 109.955755 inches.
You have to convert that to millimeters by multiplying by 25.4, which gives an unloaded circumference of 2792.88mm.

But now, your heavy truck flattens the tire at the ground which reduces its effective diameter/circumference. Usually, this reduction is about 3%, so multiply the last figure by 0.97 and you get 2709mm (rounded to the nearest whole number).

Try that last number. If the Gryphon's speed is slower than the real speed, increase it. If the Gryphon's speed is faster than the real speed, decrease it. Your dash speedo will always read about 2-3mph faster than the Gryphon, so your goal is to get the Gryphon speed correct (the same as a GPS). When you get the Gryphon's speed right, the dashboard odometer will be correct."

Good find


What I would do if you don't have a GPS is get the mileage of a non stop route that is at least 10 miles, I like to use google maps for distances. Also have the 2700 number programmed into the gryphon so that you already know your tire size. Clear your odometer and drive the route. When you reach the end simply plug and chug into the following formula:

map mileage / truck mileage x tire size

This should get you zeroed much easier than comparing speeds.