anyone seen the radar guns on the lightpoles on I-95

[SharkD]

The 6 gets 25mpg at ~3250rpm in 5th gear... around 79mph. Any faster or slower and it drops to around 22mpg. (Or if I open a window, vent the sunroof or turn on the A/C.)

The 3 gets 8mpg at 5300rpm...

It used to be that there were days when I could leisurely cruise the E30 at 35+mpg.

[David Hicks]

It doesn't matter how aerodynamic your car is - drag increases with the square of velocity.

I stand by this statement when taken as a whole. Drag force increases directly with Cd and with the square of velocity, therefore velocity has a bigger effect on the total drag force than Cd.

I agree that a more modern, low-drag shape can go faster for X amount of drag force than a more brick-like shape of an older car. However, since velocity plays a bigger role than Cd, in a general sense, slower is more efficient from a gallons/hr standpoint.

That argument obviously leaves out the gearing and the efficiency of the engine at various RPMs. I wouldn't be surprised if automakers have changed the gearing to optimize fuel economy as world speed limits (and real world speeds) have gone up. I'd be interested to find out where an M52 or M54 produces the most hp/gallon. If you had that, you could do some minimax calculations to determine the greatest efficiency in terms of gallons/mile/hour, which would take into account speed and overall fuel consumption.

[ob325]

I've found the key to good mpg is to drive downhill as much as possible.

You have that right! I love to see the econometer go to the 50mpg+ range. Especially when I spent $43 for gas this morning.

[Dirichlet]

... when I spent $43 for gas this morning.

what was that, a half tank...