Speedo
After slapping on the new tires, I needed to recalibrate my speedo. I know most folks use a FlashCal or a ProCal, both of which are fantastic devices, but earlier this year I picked up an
Aeroforce Tech Interceptor gauge to go in the center of my sPOD. This gauge also features two way communications, a feature that I have yet to take advantage of until now. I flipped through the internets and found an older thread, but still
a good read on JK Forum that gave a good description on how to set your speedo for your new tire size. He says "The Tire Size is entered based upon circumference in millimeters. Here's a little chart to make it easier: (You should round the number e.g. 2656.8 = 02657)"
This chart is from the post referenced above. I did not make it.
Starting with that calculation pic, I went to the garage to measure the circumference of my tires using a very scientific method... I wrapped a string around my spare to get 2788 mm. When I tried using that setting, my speedo was waaaaaaaaaaay off. On a side note, for those of us with OEM NAV's, the speedo on the instrument panel and the speed display on the NAV come from the same source. One isn't a GPS based number.
After quite a bit of trial and error testing, the perfect measurement to get the speedo to line up with a GPS was actually 2643 mm (or the same revs as a 33.125" tall tire). Either there's a been a change to how the 2013's calculate speed and distance (possible, but unlikely) or a tire under weight actually does compress
THAT much. Wow! Did I just learn something new? If anyone has a stronger grasp on physics and can go into additional detail on tire compression calculations depending on weight, pressure, and ambient conditions (yeah, I know... I'm a bit of a nerd!), please feel free to PM me.