Quote Originally Posted by Matt View Post
ESP issues are associated to tire diameter changes. What diameter did you program into your computer? And whats the "effective" tire diameter? Measure from the center of your hub to the ground, that's the effective radius; double that for the effective diameter.
Yea I know that the ESP issues are related to tire diameter. When I installed the 33's I programmed the new tire size with the flashpaq before the XK even left the garage. I measured the tire diameter two ways. First I measured from the ground up to the top of the tire. Then I measured by making a chalk line on the ground and tire and pulled the XK forward until the chalk line on the tire made one complete rotation and extended the line on the tire to the ground. Now that I had to line on the ground I measured the distance between the two lines and used the formula to compute the tire diameter. That number was within 1/2 inch of just measuring the tire from the ground to the top of the tire. I then took the average of the two measurements and came up with a solid number for the tire diameter. Plugged that number into the flashpaq and the speedo is dead on with gps. I also paced a stock vehicle to make sure both speedos were reading the same mph. I can't remember what they measured but I think it was somewhere around 32 inches for the 33's.