[alfa] Efficiency or economy?

["John Fielding" <johnf@xxxxxxxxxxxxxxx>]

Hi All,

This long lasting thread for some people seems to comletely miss the point.

"Efficiency" and "fuel economy" are not interchangable parameters, they mean different
things to different folks.

To get back to basics.  If you drive around at red-line in every gear you will have a poor
fuel economy, measured in miles per gallon, litres per hundred kilometre, or whatever
measurement system you care to use.  For the most miles from a tankful of fuel you need to
drive gently, not "foot-in-the-hook" as we say here (pedal to the metal - in American
speak!).  It is true that an engine running at WOT is the most "efficient", but it will
have a poorer mpg rating ("economy").  Aerodynamic drag goes up at a higher rate than
friction related losses in the wheels and transmission.  Hence, driving at 80mph instead
of  60mph will require more fuel to be used to maintain the higher vehicle speed because
the engine has to generate more power to overcome the extra drag.

Changing up to a higher gear sooner than later is one way to get the best fuel economy,
provide the engine has sufficient mid-range torque.  Lugging in a high gear up a hill is
not the most fuel efficent way to drive, changing to a lower gear allows the engine to
rotate at a higher speed where it can develop more torque and power and utilises the
mechanical advantage of the transmission to good benefit, which yields lower fuel
consumption.

my 2cents worth.

John
Durban
South Africa
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