I'm using a Procal to adjust some settings. One is tire size so I can her exact. MPH. I called discount t tier and all he said was the metric to inches confusion
I searched the form and saw discussions but no HOW TO.
So how to?

 

Read the problem instructions. Measure the tire, mounted, under normal load and air pressure. Round to the nearest quarter inch. From bottom of ground to top; use a ruler to dissect top at right angle to the measuring tape. 1st tire size mode is 24 to 38.75 inches tall. Set 1st 3 switches to proper mode. Size in inches - 24=A whole value, B=tenths value

 

With tire mounted on wheel, inflated to propper pressure. Tire and wheel mounted on the Jeep. And Jeep sitting on level ground:

#1 - Find a tape measure
#2 - Take tape measure to Jeep.
#3 - Pick a wheel / tire to measure.
#4 - Extend tape measure vertically to the ground and center of tire / wheel.
#5 - Read tape measure at top of tire.

Hope this helps.

 

Here's another easy way to measure the tire. and it will be what the computer wants to see.

Stick a short piece of chalk in the tread.
Move the Jeep until there are two chalk marks on the pavement.
Measure the distance from a point on one chalk mark to the corresponding point on the other chalk mark.
Divide by 3.1416.
That will be your tire diameter, with all other variables accounted for.

 

I asked Procal and they said loaded on the floor to top of tire. Not floor to center of center cap and double, no strings and chaulk etc. Just floor to top of tire that's what I did and I am dead on with my GPS at 70 mph.

 

Mine is dead on with the chalk method.
Either way is good. I just like to have a more exact measurement.