Other effects to think about involve cooling efficiencies. The thinner air at high elevations can not cool the radiator as efficiently, so there will be more drag from heat transfer losses. This will be offset by less induced drag from the shape of the car through the air. I'm not sure what the net effect would be, and it probably depends on the car.
Also, while rolling resistance doesn't change with air pressure, it does change with temperature, and the tires and brakes will be hotter in the thinner air, especially at higher speeds, which will increase rolling resistance.
The only difference in these two scenarios is the altitude. The ground level one gives 35mpg, and the one at 3500 metres is 47mpg. This is entirely due to the extra 4hp required to overcome aerodynamic resistance at sea level.
>But for the real life factor, living in high elevations
>also usually means more hills. So that will throw that
>math out the window... LOL
The original poster (judacomadc) lives on a plateau. So no hills.
You have to isolate each factor and treat it separately. But then you have to combine everything back again to see the overall effect. You can't just hand-wave and say that there is only going to be a 0.1 MPG effect without any grounds to say that.
I should also point out that 3500 metres was just a simple example of the effect of altitude on MPG - it wasn't a specific example tailored for BogotÃ¡. The only thing I changed between the sea level example and the 3500 metre example was the altitude, it did not include temperature, or any specific factors related to the OP's vehicle or engine. But all these things can be added to the calculator as needed.