With the bigger tires all bolted up, our speedometer was now off. We recently came across this little plug-and-play speedometer recalibration unit. Speedo Healer is a new player to the recalibration game, but the unit is waterproof and is super-easy to setup. Just plug it in line with your factory sending unit; it interrupts the signal, adjusts it, and sends it on the way to the computer or speedometer. You figure out how far off your speedometer is using a GPS or a stopwatch, and using the chart in the instructions, press the button until you’ve got that value on the LCD screen. It can be mounted out of the way under the hood. We just used a couple of zip-ties to hold it down.