Roger Mills wrote:
In an earlier contribution to this discussion,
The Natural Philosopher wrote:

aerodynamic drag is the cube of
velocity. Or it might be the square.


Either - it depends on what parameter you're talking about!

Aerodynamic *force* is proportional to the square of velocity. The *power*
(force x speed) needed to overcome aerodynamic drag is proportional to the
cube of velocity.

Right, So on a per mile basis, the work done is the force times the
distance? So in theory the *consumption* is affected as the square of
the velocity?

If you lump the two things together, you get that the frictional losses
are constant..so there is a fixed amount of gallons per mile you need
to burn just to keep moving irrsepective of speed, and the only way to
reduce that is with skinnier tyres and smaller cars and engines, and
pumping the tyres up harder..and a part which is related to the velocity
squared, which starts at zero, and increase accordingly.

So given a *uniformly efficient* powertrain, in cruise the slower you go
the less fuel you burn. Although the effects of aerodynamic drag are not
that great up to 50mph or so.

The next point is where are engines most efficient?