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Old 09-04-2019, 10:26 AM   #24 (permalink)
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rule of thumb

Originally Posted by hat_man View Post
Most of the spats I see are on smaller passenger cars that are already fairly low to the ground. Vekke brings up a point about height of the spats making a difference. My question (being I know little about aero stuff) is this.....with shorter spats, is it that the spat covers less of the tire or that the spat is farther away from the ground that makes the difference.

The reason I ask is that I am trying some "reverse mud flaps" on my truck. They are definitely taller than anything I see on Festivas and Prii. But my truck also sits much taller than those. A shorter spat like those from a passenger car (at least in my mind) wouldn't work as well for my application. Or would they?

Is there an optimal "ground clearance" for spats and air dams and such? Or at least a general "rule of thumb"? I seem to remember JRMichler (at least I think it was him) that said he had the best results with an air dam that was 3" above the ground.
With the variety of vehicle designs I believe that a rule of thumb is impossible.And you might be looking at $50,000 in wind tunnel time to optimize a design for any specific vehicle.
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