Your right narrower tires probably perform better on the snow. But that was not my question. I don't have a narrower choice with Nokian WR G4 at 19 inches with a similar diameter. Also, I wanted a compromise of all-weather traction and performance not just snow. Anyway, I was just trying to find out if 255/40/19 set up would have any issues at all in terms of front fender clearance with increase tire diameter. As far as speedometer accuracy goes I know the actual speed will be faster by a mile or two then indicated on the speedometer.