help on tires/gearing effect on speedo and odometer

I know this is late but I wanted to chime in since I just went through this process and would like to help someone else. I have a 2006 4x4 trd automatic. I purchased 265/75/16 and found that on the gps the speedo was correct. So like most have said from the factory the speedo is programmed for 265/75 or 31.6 and most factory tires are 30.5 or 30.6. So you will be off just a little reading faster than you are going and racking miles a little faster.


So then I purchased an arb up front with 4.56(went from 3.73). After the install my speedo was dead on again. I was blown away and could not understand after making this kind of gear change. When I use to work on f-bodys(99-02) this was not the case because the speed sensor was on the trans. I found out that on this truck the speed sensor is at the tires which make sense. GEARING has no affect on trucks with wheel speed sensors. It calculates from tire rotation and not driveline rotation.


So then I purchased some 285/75/16 and found that my gas mileage went way down or so it appeared, but then this is when I found out about the speed sensor and realized that I was off about 3mph. So I installed the hypertech which is a little expensive, but I didn't have to cut anything and the usb is still in the dash easy to get to so I can make changes at anytime.


thanks