In rec.aviation.piloting Montblack wrote:
("Charles Vincent" wrote)
According to SAE studies, aerodynamic drag accounts for 60% of the
resistance that must be overcome for highway cruise, with tires being 25%
and driveline friction making up the last 15%.


Semi:
Tires ........... 18
Footprint ..... big per tire
Weight ....... 80,000 lbs
Drag .......... HUGE!!
MPG .......... 5 (loaded)

Minivan:
Tires ........... 4
Footprint ..... smaller per tire
Weight ....... 4,000 lbs (for easy math)
Drag .......... MUCH less + no cab/trailer drag
MPG .......... 22

I've never really understood why an 800 lb motorcycle/rider gets (only) 50
mpg and a fully loaded semi can get (about) 5 mpg?

Motorcycle:
Tires ........... 2
Footprint ..... very small per tire
Weight ....... 800 lbs (with rider)
Drag .......... It's a motorcycle! g
MPG ........... 50


The coefficient of drag for motorcycles is usually pretty bad unless
they are faired, and it still ain't great.

The power required to overcome drag is 1/2(p*v^3*A*C)

p is the densitity of the fluid
v is the airspeed
A is the area
C is the coefficient of drag


--
Jim Pennino

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