Ok, I set my tire size to 19.5
I called Trail tech to see if that right.
They told me to do this.
mark tire and ground
roll 5 times
Measure distance and convert to MM. (1' = 25.4 mm)
Then multiply that by 25.4? they told me that
then devide it by 5.
Enter that number they said it should be like 15.5 for setting
Well, i took the diameter and used the circumferance rule 2*pi*r
well my tire was 19.5 tall so r = 9.25
that came up to 58.1 inches per roll and 290.597 in 5 roles
if i reverse the calcs it come back to exact tire diameter.. so my guess si 19.50 should be the settings.
THER WAY
290.597 in convert to mm = 7381.168
Then devide that by 5 for rolls = 1476.232 MM per roll. GREAT yippy!
so what the BLANK should the darn thing be? I just put 19.5..
I have stock tires and such..

 

their way takes into consideration the tire sagging from bike weight, thereby changing circumfrance. its a more precise means, because you're actually looking at the exact conditions that will be giving the computer its signal to calculate from.
With you saying your diamater is 19.5, well if its actaully 19.62, or 19.43, or something like that, then through conversions and math, eventually the trailtech will end up being miles off of its accumulated odometer reading. Such a small differnece won't effect spead reading much, but the long term mileage would be effected.

 

Mark the tire and ground.
Roll one (1) complete time with you on the quad and mark the ground again. No need to roll 5 times.
Measure from mark to mark in inches and convert to mm. (x 25.4)
Input this four digit number into the computer.
In your example you should enter 1476