I just purchased a Hypertech econ programmer for my new truck. I installed a 2.5" leveling kit and put 35" xterrain tires on it. I followed instructions from Hypertech to adjust the calibration to reference the 35" tires. My spedo is off by about 6mph. Has anyone had this issue or have a resolution for me? I have been with Bully Dog for the past 6 years and never had an issue. Is Hypertech good because they dont have an answer for me.

 

You just have to play with the tire size settings a bit to get it dialed in. Borrow a GPS if you don't have one to use to get it spot on. Just because you are running "35s" doesn't necessarily mean they are true 35" tall. Also your air pressure and wheel width play a role in changing the real world tire height. On top of that, the data tables the programmer and ECM use to dial in the speedo aren't totally accurate so even if you plug in the real world tire height it still may be off a little. You just need to play with it until you get it dialed in. Every programmer is different, too. When I had my Bully Dog Power Pup, i had the tire settings at 33.25" to make my speedo correct. With the Bully Dog PMT it was 32.50" to get it spot on. With the Smarty, i've got it set at 34.25" to get within .5mph of GPS. All of these were running the exact same tires with the exact same pressure and exact same wheels.

Cliffnotes: trial and error with a GPS will get you dialed in right.