Most information on this site relates to modifications to the powertrain (engine & gearbox), since that is my field of expertise. But I am regularly asked about the benefits (or otherwise) of aerodynamic fuel saving modifications.

Unlike many of the gadgets I mention here, there is a sound theoretical basis to the idea of reducing aerodynamic drag and so improving fuel economy. In many cases, the saving is sufficiently large to justify the cost of buying and fitting the device, so in general I would say they are worthwhile. A good analysis of one common modification - a cover for the open bed of a pickup truck - can be found on the SEMA website.

Having said that, a couple of caveats apply:

• The savings will very much depend on your type of driving - aerodynamic mods are far more effective if you spend your time cruising at high speed, than if most of your driving is stop-start round town

• It's very hard to know if a particular modification is or is not helpful, because vehicle aerodynamics is such a complex matter. The SEMA report shows that some modifications could even make drag worse

If you found this page helpful, you may like to support my work. If you think I have made a mistake, or am talking complete nonsense, please take a moment to read the Response to Critics before saying so in public (on discussion Forums and the like).