The test is done on a rolling road in a lab, there is no wind resistance thus taping up any gaps and removing wing mirrors would have no effect.
A silly internet myth. The resistence of the rollers is set to include aerodynamic drag. It does not include 'wind', which could increase the aerodynamic drag and rolling resistence substantially.
Both wrong I think, if I recall correctly.....
Surprisingly, both rolling resistance and aerodynamic drag data is provided by the manufacturer to the test authority (which in some cases may be the car manufacturer itself). Rolling resistance and aerodynamic drag is supposedly tested by the manufacturer by a "standard procedure" where a "random" car is driven at a "standard speed" along a test track (the manufacturers usually) , then allowed to coast to a halt. The distance taken to come to a halt is used to calculate a combined drag/rr coefficient. I think they have to do the test in both directions to cancel out the effect of wind and gradient, and there are certain limits of wind/gradient stipulated..
Also the manufacturer also provides data as to how more economical the car becomes as it runs in. Basically the manufacturer makes a statement something like after 30,000km the car will, on average, use xx% less fuel because the engine/running gear becomes more efficient after running in and loosening up. The % provided is added to the tested result.
Again good faith and good methodology by the manufacturer is assumed.
Dont forget, heavy financial penalties are imposed by the EU on car manufacturers who dont acheive their EU directive emission targets - a very strong incentive to falsify data.
Edited by brum on 14/03/2013 at 20:58
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