Hucho?
Darin,I believe that Hucho's book has CdA vs MPG tables/curves for both N.America and European test cycles.Sorry,don't have my book with me.
If one presumed that the Cd was unchanged and only the frontal area went up with wider tires,then the drag relationship would be arithmaic.Say,a 2% increase in frontal area would mean a 2% drag increase.
At 55 mph ( 88 km/h ) mpg would suffer by 1%.
At 70 mph ( 112 km/h ) mpg would suffer by 1.2%.
