Hi, I am the owner of a 91 MR2 Turbo, and I had purchased it a couple months ago with 17's already put on it. I am unsure of how wide the tire wall is, but lets just say its about 1 inch in the front, and 2 inches in the back. I was doing 80 on the freeway the other day, atleast thats what my speedo told me. But I was flying past cars like they were nothing. I estimate I was really doing between 90 and 100 mph, and not 80. Cany any1 give me a rough estimate, how much mph my speedo is under rating my car?