* At 'normal' driving speeds, designers like to build understeer into the vehicle.
If a side wind pushes the nose leeward, the driver simply turns the wheel 'upwind'. It's intuitive for the average driver, driving on, with the steering wheel 'crabbing,' as with the rudder on an aircraft in a crosswind.
* In a high-performance sports cars, or race car, if understeer was built in, at high speed, a side gust would push the nose leeward, increasing the relative wind from the side, increasing the yaw-moment, requiring even more steering correction. In extreme crosswind gust, the yaw moment might overwhelm the reaction time and steering effort, ending in a crash.
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* The addition of rear fin / capping plates, creates 'arrow feathers' / 'weather-vane' into the vehicle.
* If you're hit by a strong crosswind gust at high speed, the car will automatically steer the nose into the crosswind, canceling out the yaw moment.
* This high speed oversteer can be a lifesaver.
* At the Bonneville Salt Flats, the added rear tray and capping plates help provide a cleaner flow region for the pilot-chute to 'grab some air' in which to deploy the drogue parachutes. ( last September, our Gumby79 volunteered at World of Speed, and had to respond to one race car that had a #1 parachute deployment failure at the finish line ). It can take eleven miles for some of these cars to coast down to a speed at which the brakes can be applied.
