Le Mans prototypes will have to carry Formula 1-style fins from 2011.
The move, decided following a CFD study by Delta Motorsport, is the latest attempt to prevent LMP1 cars from getting airborne during spins or accidents.
Nick Carpenter, who led the research, said: "We found that bigger is better. The point at which the fin starts to become effective is different on open and closed cars, but once you get above a certain height, it works on both. The size of the fin overcomes any effect of differences in sidepod or wheel-arch geometry between cars.