Originally Posted by CliffordK

That is what one would think, but apparently not quite true.

It would be true with a spinnaker sail. But, the direct downwind cars are being driven by a propeller. But, rather than having the wind turn the propeller, the wheels turn the propeller which blows wind out the back. So, the faster the vehicle moves forward, the faster the propeller turns, and the more wind it blows against the blowing wind from the rear.

Or, perhaps one would say the greater the pressure differential between front and rear.

Here is a good explanation.
https://www.wired.com/2010/06/downwi...than-the-wind/

Apparently they have built upwind vehicles using the opposite principle.
https://www.wired.com/2012/07/wind-powered-car-upwind/