Re: Tyre size question
Hi. I put 245/40/19 on the rear of my XF. I did this because I wanted to get a little more sidewall height to give a somewhat smoother ride. I didn't go to a 255/40/19 because I did not want to throw off the speedometer so much. After the change, I see no appreciable change in the speedometer.
As far as the cats go, many people in states other than California gut the cats or remove them. It should not affect the operation of the car.