Incorrect....
Tire size only affects where power is made and the overall torque number because of it.
JetPilot and I spent a day with various tire sizes at DGR along time ago and all we did was move the HP number up or down in the curve and raise and lower the torque number.Larger tires tend to kill torque and smaller tires will elevate the number..
Sounds like winter fuel and air quality made the changes on him.