Back on-topic...
Here's a real world example of how wheel/tire choice affects fuel economy. The new Mitsubishi Mirage is available in only 2 trim levels in New Zealand, with the only difference being wheels/tires and convenience options. Engine/drivetrain is identical.
The functional difference is in wheels/tires. (14's on the base, 15 on the fancy model):
Base car:
165/65R14
Uplevel car:
175/55R15
The base car's MPG rating is
6% better than the other car, due to a combination of:
- slightly narrower tire on the base car has a slightly better drag coefficient and smaller frontal area
- that flat plastic 14 inch wheel cover on the base car is more aerodynamic than the open spoke alloy wheel
- the different tires probably have different rolling resistance coefficients
- the bigger alloy wheels & lower profile tires may have more of their mass concentrated further away from the rotation axis, which need more power to accelerate
Not just speculation -- the impact of wheels/tires on MPG was confirmed by the manufacturer.
From:
How wheel & tire size and style affect Mirage fuel economy/mileage