What don said. On 31" tires, my speedo is 7% off, therefore, at 65mph displayed on my speedo, I'm actually going more like 70mph. Can the same percentage be directly applied to mpg though? ...becuase if it does then I'm happy. <img src="/forums/images/graemlins/smile.gif" alt="" /> (16.7mpg is actually 17.9mpg)