[Blue Bomber Man]

As I said earlier: Your main concern should be about first finding your most fuel efficient tire, most of the best seem to fall in the 15-16" size. These tires have an overall lower average RRC (rolling resistance coefficient). Your RRC effects fuel economy significantly as this number is multiplied by the mass of the vehicle to calculate the total loss of energy.

Once you have an efficient tire it would be time to address ride height (as we already know that lower height improves both handling and aerodynamics) and then seperately deal with your gearing issues to maximize energy efficiency.