Willie via EV wrote:
On 5/18/19 12:38 PM, Haudy Kazemi via EV wrote:
drag and increased energy consumption (and reduced range). Simply
raising a
vehicle increases frontal area by virtue of the tires being more exposed.
I believe the under car air speed is also increased. Or, maybe
increased turbulence. Anyway, I think it is worse than just exposing
more tire.
I think that is true. Keeping the car low is a way to reduce the amount
of air and turbulence underneath. Of course, a smooth bottom would help;
but that costs too much.
Big fat tires with lots of tread have lots of wind resistance. And, the
tops of the tires are moving forward at *double* the speed of the car!
Paul MacReady (of Aerovironment) talked a lot about auto aerodynamics
when he was designing the Impact (aka GM EV1). Things I recall:
- Aero testing is in wind tunnels, with car and tires not moving.
- The roughness of the bottom of the car is usually ignored.
- Spinning tires have much more drag than stationary ones.
- Most cars are more aerodynamic in reverse.
So, he designed the EV1 with a smooth bottom, with wheel wells optimized
as "ducts" to minimize turbulence, and a shape that actually *was*
aerodynamic (instead of what some stylist thinks will "look" aerodynamic).
If you need more ground clearance sometimes, maybe adjustable air bags
are an answer?
--
Fools ignore complexity. Pragmatists suffer it. The wise avoid it.
Geniuses remove it. -- Alan Perlis, "Epigrams on Programming"
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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