Well we all look to race cars and F1 for inspiration but we forget that the appendages added to these cars have been carefully calculated and verified by lots of track testing and sometimes wind tunnel testing, and not just stuck on. Simply by copying something that looks OK does not necessarily mean it is going to have any useful function.
The problem with a car is that the distance air has to travel over its top surface is greater than the distance it travels under the car, therefore the airflow accelerates over the top of the car which creates low pressure (fast air has lower pressure than slower air) and hence lift. Any car therefore naturally generates lift. A splitters function on a race car is to restrict the airflow under the car and channel it around the car and works only in conjunction with a smooth flat bottom which is very low to the ground. This effect causes lower pressure under the car compared with over the top of the car and hence downforce through ground effect sucks the car to the ground.
Even if by pure chance and luck any splitter we add to our cars happens to be the correct shape to split the air in the correct proportions the problem is that our cars are too high up and to rough on the underside (thanks to exhausts, transaxels, spare wheel wells etc) to cause any meaningful downforce. Turbulent air kills any lift and any low pressure created under the car will just suck air from under the sides of the car (race cars also have side skirts that skim the track surface to minimise this effect).
So as you can probaly gather, I am very sceptical of the effect of any aerodynamic component on our cars (apart from the rear spoilers). They may cause better stability at high speeds, but that is a completely different thing to downforce. Any aerodynamic device that is designed to create lift needs very smooth laminar airflow to work. Any turbulence instantly kills any lift. Also with air not weighing very much you have to be going very fast. Even an F1 car's ultra efficient aerodynamic bits have very little effect below about 80mph - so what chance do the relatively tiny bits of foam and plastic on our cars have in creating downforce at any speed below about 150mph?
But they do look good though. The only reason i've not fitted a splitter is because it wouldn't last very long!
] on the motorway yesterday, I cannot honestly say that it had a marked impact on the stability or front end bite of the car so I'll 'fess up that I fitted it because I like the look - any aerodynamic benefit is just a bonus.
