When another car creeps up from behind, he is actually lowering the pressure on the back of the lead car. One cars low-pressure area cancels the high-pressure area of the other car so they both can run faster. The technique of reducing effective drag on one car by driving closely behind him is called drafting. .
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Figure 3 (Two Car Pressure Diff).
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Figure 4 (Two Car Pressure Diff).
The increased air pressure ahead of the trailing car fills in the wake of the lead car, and the air off the spoiler sees that pressure before it even gets there, so the streamline over the rear of the lead car is raised. Drivers call this "taking the air off the spoiler," and the shift can destabilize the car ahead. The lead car may get "loose" as its rear end loses traction. At the same time, the trailing car's stability also can be impaired. The same airflow that is reducing pressure on the rear of the forward car in the draft will lower the pressure on the front of the trailing car. This effect, called an "aero push," means the front of the trailing car wants to slide out rather than smoothly turning. .
If a car is driving 183 miles an hour and three more cars pull up in its wake, then you have four motors pushing and pulling the same air which will enable the cars to travel approximately 190 miles an hour.
Interference Drag:.
A fundamental fact of aerodynamic life is that drag increases with the square of the speed. Meaning when you double the speed, you quadruple the drag. So going a little faster makes it much harder. .
Graph 1 (Velocity vs. Drag).
A slowing phenomenon known as interference drag occurs when two cars are near each other. The sum of the drag of two bodies that are close to each other is higher than their individual drags. Essentially adding resistance to the flow and pressure to the nose of the car. .
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Figure 5 (Air Flow Side by Side).
Two cars traveling side by side are slower because air is blocked from flowing between them, forcing more air around and over both cars, giving them extra air to push.
