Aerodynamic fences?

[John Milmont]

What ever happened to the aerodynamic device known as 'fences' that use to be on a lot of old race cars? They use to be found on the sides of the car and go down its entire length. It seems that they would be great way to keep airflow over a car and produce more downforce. Were they banned? are they just inefficient? ineffective?

 

[Randy V]

From what I know there are effective but I would imagine that you'd need a pretty deep wallet to do all the wind-tunnel testing to get them right. NASCAR had mandated them on the roofs of the cars to act not so much in a positive manner as much as they were to be spoilers that cause the air to burble over the roofs should the cars go sideways in a wreck - this would minimize the opportunity for the car to get airborn...