Shorter tires would not only throw the speedo off, but would also activate the speed limiter before hitting the "real" speed limit. That's one of my problems for the dragstrip. I want to run shorter tires to get a better overall gearing ratio but I can't go too short or it will think it's going faster than it is and shut everything down. I'm going to look for that link because all the controllers (VDC, ABS, and ECM) use a network cable for communication. Since there is no one wire to cut or put a speedo box calibrator on I'd like to know how that is done. Speed for the truck is measured from the wheel sensors.