It's true that a smaller wheel completes more rotations than a larger wheel, but that has nothing to do with fuel economy, even in a conventional vehicle. Fuel consumption isn't directly proportional to engine rotation; it's the amount of fuel burned in response to power demand, and engine efficiency at those speeds. For example, shifting from drive to over-drive may actually burn more fuel, due to the greater load placed on the engine. Depending on the optimum RPM range, the engine may be less efficient running at a lower RPM. With a variable-speed transmission, the best drive-ratio is determined by the computer. In the case of the Prius, the computer can actually run the engine at the optimum RPM to achieve the best fuel economy. In this case tire size is nearly irrelevant.
i forgot to mention one other advantage with the solar powered fan: The fan running/drying the vents after you leave insures you won't get that musty/rotten smell from an undried AC dehumidifier.
