Quote:
According to Welburn, there are several drawbacks:
• The fender skirt causes tire pressure to increase. Although he did not say it, neither GM nor any automaker wants to create a design that increases the probability of tire failure.
• Removable skirts are difficult to keep in place properly, plus there’s the added cost of each skirt.
• Pick one: To use a fender skirt, the rear tires need to be narrower to fit inside the wheel well or the vehicle track needs to be narrower or the body needs to be what he called “pulled out” to accommodate the same size tires that are steering the car.
Welburn said pulling the body out, essentially widening the body where the rear tires are located, increases aerodynamic drag.
While Welburn didn’t explain the other two choices described above, a narrower tire would reduce vehicle capacity and a narrower vehicle track could slightly increase the probability of rollover.
Says Welburn: "The short answer is, skirts don’t help on a production car."
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If you have a heavily loaded tire it will tend to get hot. Pressure increases in a hot tire. If you have an underinflated- you know, like just about everybody drives around on- heavily loaded tire it will get even hotter. Yeah the pressure increase there would be nice but the heat is the worst enemy. If you then partially enclose it you can expect it to heat up more. If you partially enclose it and then use the brakes heavily I'd imagine that wheel well will really heat up. GM HAS to design for the worst case scenario, otherwise idiots and lawyers will sue.
Removeable skirts are fiddly. I think even if you have a robust mounting design, it is in a location often fouled by dirt, mud, and ice.
They'd probably want to paint it body color. Painted parts add cost disproportionatly.
It is undesireable to have front and rear tracks that mismatch by a little- I'd say, by less than 2x the width of the rear tires. This is because on a soft surface (yes people still drive on dirt roads in America) if the rear tires don't fall squarely into the front tires' tracks, they get squirrely. Believe me, it sux.
As always, if someone wants them badly enough, they can make them or the aftermarket can fill that void. (PUN!)
Last but not least, they aren't as great an aero device as we'd like. Mfgs have to scrutinize the pros and cons way more than the likes of us.