Microsoft has allowed me into their AI and I've been annoying it. I found (I think) that you can work out some interesting things for your own car. For example, I have been calculating the specific drag of my vehicle (well, using my particular weights, height on coilovers etc).

My mpg has for some reason gone through the roof, following a dealer oil change and a greater mix of country, city and highway driving (max speed is 55 mph), my lifetime mpg is now 50.2 (up from 42mpg). I think that's .3 above Mini spec?

Using AI, I asked pretty basic:

"Can you tell me the differential drag acting on a road vehicle if it travels at 60 mph and at 55 mph, based on a vehicle with a drag cx of 0.31, a weight of 1360kg, and height of 54in and width of 67.99in and an ambient temperature of the air 17.5c "

The AI says that at 60 mph the drag is 21.18% greater at 60mph that at 55 mph, so perhaps the 5 mph speed cut has give me my c. 19% mpg increase?

What do you think?

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Full AI response:

Assuming that the vehicle has a drag coefficient of 0.31, a weight of 1360 kg, a height of 54 in (1.37 m) and a width of 67.99 in (1.73 m), and an ambient temperature of the air 17.5 °C (290.65 K), we can calculate that:

- The cross-sectional area of the vehicle is:

A=height×width=1.37×1.73=2.37m2

- The air density at 17.5 °C is:

ρ=RTP=287.05×290.65101325=1.19kg/m3

assuming that the air pressure is 101325 Pa and the air gas constant is 287.05 J/kg K.

- The drag force acting on the vehicle at 60 mph (26.8 m/s) is:

Fd=21ρv2CdA=21×1.19×26.82×0.31×2.37=282N

- The drag force acting on the vehicle at 55 mph (24.6 m/s) is:

Fd=21ρv2CdA=21×1.19×24.62×0.31×2.37=228N

- The differential drag acting on the vehicle between 60 mph and 55 mph is:

ΔFd=Fd(60)−Fd(55)=282−228=54N

This means that the vehicle experiences an additional drag force of 54 N when it travels at 60 mph compared to when it travels at 55 mph.

To calculate the percentage difference between two values, we can use the formula:

Δ%=2x1+x2∣x1−x2∣×100

where x1 and x2 are the two values.

Using this formula and plugging in the values of the drag force at 60 mph and 55 mph, we can calculate that:

Δ%=2282+228∣282−228∣×100=25554×100=21.18%

This means that the vehicle experiences a 21.18% increase in drag force when it travels at 60 mph compared to when it travels at 55 mph.