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

Motorcycles have a terrible coefficient of drag given their shape and
the shape of the rider. A fully faired bike is much better, but still
much worse than most cars. My K1200LT is one of the better motorcycles
and its Cd is above 0.5 with the windshield fully lowered and I believe
it is closer to 0.6 with the windshield at the highest setting.

So even with the relatively small frontal area as compared to a car
(although not as much smaller as you might think as the bike is taller
than most cars), the drag coefficient is so high that the total drag is
quite high in comparison.

Matt