So I was looking into going with a 245/45/18 on the SC. I was surprised to learn that you cannot adjust the speedometer via techstream to accommodate a different size tire other than came OEM? Even back in 1999 on our Ford F350 Dully when we went from a 205/?/16 to a 235/?/16 the Ford Tech hooked up the laptop and changed the tire size so the speedometer was correct.

Dennis

 

Funny you mention this. The speedo read high with the 40’s exactly correct with the 45’s.

 

Calflashbob

Really given the car came with 245/40/18's I would have thought it would have been spot on with OEM tires.

Dennis

 

That is interesting. Mine also reads a little high on stock. Can't wait to get rid of these run flats. I did something similar to my old LS400 with a larger sidewall than stock and the same thing happened. Speedometer was more accurate with the slight oversize.

 

My ls460 is also off. Reads high. Tried the tire calibration and no change.

i have a set of 19”s to put on when the 18’s wear out and may go slight oversized to correct it also