Mine read wrong until I put on 31's...then it read perfectly.

I have 33's now, so it reads really wrong.



I use the GPS to see my real speed/distance.

BTW - Go with 32's, or 33's, not 31's....ESPECIALLY with the 3" lift...the 31's look really puny under the lift, and the larger tires make it all work better.



So - A GPS will replace the speedometer, or you just time a few mileage markers, figure your % error, and pick a new mental cruise speed for your speedo (Like 55 on the speedo is 65 real speed, so to go 65 on the free way, drive the speedo on 55..., etc.)

After a few miles, you will know anyway.