Function

The first thing one thinks of with a possible lining of the underbody is, wind resistance and perhaps also of noise reduction. The fact, however, that also the recycling of the car body has a lot to do with it, becomes clear when one discovers that under the lining, PVC protection has been saved.

How it works

At the very least, the same wind resistance which the car body offers to the wind on top, is also offered by the underbody below, because of the nearness to the road, probably even more. If it were possible, one would prefer to panel the complete underbody. Unfortunately, here there are a few restrictions. Apart from the freedom of movement for chassis and steering, most important is probably the exhaust system, because this needs a great deal of cooling. One can best see this on test benches, on which the engine must bring its full performance, the exhaust however, is cooled only by the air swirling around it from a blower. A red-hot glowing exhaust system is possibly the result. Therefore, a rear engine is, at any rate, a good choice for the underbody lining. Otherwise, only an exhaust shortly behind the front wheels (e.g., Mercedes SLR McLaren) helps in the front engined car. In all other cases a part of the floor must usually remain unpanelled.

Apart from the brakes, which often have their own air supply in the wheels, the engine, the gearbox and perhaps the final drive needs sufficient cooling. Either the designer lays out the cooling through lubricant accordingly more generously, or an oil sump with possible ribbing is included in the underbody design. Openings to sophisticated cooling channels are also possible. Vice versa, these can also be laid out as suction openings. They then accelerate, e.g., the air flow-through rate in the engine compartment. However, as a rule, all openings also increase the wind resistance.

This is also valid for a special species, the diffuser. This subject reminds us once again of the fact that low wind resistance cannot be the sole aim. Assuming that, although a super-sports car is very fast, but almost lifts off the ground when driving at high speeds, then this can not be at all healthy. Therefore, a part of the wind resistance avoidance is always sacrificed in favour of generating downward pressure. Large rear spoilers, e.g., can have the same affect as a half a ton of extra load. This is done more elegantly under the vehicle flooring, although not quite as efficiently. The simplest solution is to raise the floor height more and more towards the rear. Additionally, one can also attach air deflectors. However, in this case, the rear engine is, once again, at a disadvantage. 09/09

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