My 35/12.5/17 Toyo Open Country tires on 8.5" wide Hutchinsons were programmed at 33.5" into the Hypertech.
I since changed them to 33.75" and the speedometer is almost dead on.

 

To measure the exact tire running diameter put a chalk or piece of tape on the tire and ground at the exact centre bottom. Move the jeep until the tire moves exactly one revolution- mark at bottom centre again. Mark this new position and then measure the distance between. Divide this measurement by 3.14 to get actual diameter. Example 106 inches divided by 3.14 = 33.75". Set your tire pressure to normal running pressure before measuring. This will give you an accurate measurement for programming. It is amazing how much smaller say a 35" tire actually runs. Hope this helps someone.

 

just measured my 35x12.50 grapplers and they measured out to 33.75 running 34psi.....i was a bit amazing and dissapointed until i found this thread...whew im glad thats kinda normal...

 

Not all rubbers are created equal in size Some account for shinkage

 

I believe the width of the rim affects the tire height also, myself and another member were looking at our bfg km2 35's and his look at least an inch taller then mine, I have 9in wide rim and he has the stock 7.5

 

So, I'm basically seeing that most 315/75/R16 tires are basically 34.5 or so. I kind of expected that from looking at Quadratec's website because they give an "actual size" statistic with each tire. I'm just wondering how much of a difference does a load range C tire make vs. a load range D? Besides that the C's will ride "softer" on road, is there a noticeable size difference between C and D tires both 315/75/R16??

 

Tires are measured at a specific wheel width. Multiply the actual wheel width difference by .4 then add for narrower wheels or subtract for wider wheels than the manufacturer stated tire height at their given wheel width.

 

Great info!!! thanks.

 

bump, anyone know the answer???

 

less "squish" on the D lr than C lr maybe 1/2 inch in height.
"squish" is amount the tire settles with weight on it