I'm not sure why everybody's is off. When I went to 35s I recalibrated my speedo to be accurate at 70mph. (Oddly that required setting Superchips to 33.75" tires, running 35X12.50 MTRS @ 30psi). Anyways my neck of the woods is flat as a pancake, and while I am not the Stig or a Grandma behind the wheel, my dash reads dead nuts compared to old school measuring.
YOU CAN'T HANDLE THE TRUTH!