sorry for the newbie question... just not familiar with how this is done on the newer vehicles.

when you guys are going to a larger diameter tire, how are you adjusting the speedo/odometer to reflect the new tire size ??

on my old 4x4 Samurai I just figured out what speed it shows and then what I am really doing with a GPS and call it a day.

 

most modern vehicles include a setting in the PCM to update the diameter of the tires. Changing that will allow the computer to calculate everything from speed to MPGs properly. Most offroad and performance shops can do it for a small fee. Or you can include it in a more complex tune... might even be worth buying a tuner once they become available. For now, your best bet is going to the dealer for the PCM update to tire size.