well for us who came with 18's stock 245's wont really throw the speedometer off much. i think its like a 1 MPH off or so which aint nothing. yeah 245/40/18's are deff alot better. i launched my car today after getting the clutch in better condition by shifting at 3k around town and let me tell you its so much better. i didnt really notice any wheel hop so im set on this size. now all i need is a better clutch and to put my traction bars back on so i can really test them out at the track.