I did a write up on the speedo error a while back. Here is the program that is built into the factory speedometer. 30's is 3 high 40's is 4 high 50's is 5 high And so forth. I have verified this with 2 different gps's and a few thousand miles. This is with the stock front tire. The 70 front tire is said to bring it back in line some. Remember the readings are not random, but programmed.