Chances are, at some point you’ve seen vehicles that were designed with streamlined little knobs on their hoods or roofs, to improve their aerodynamics. While such features have been shown to work, they generally haven’t been available as an aftermarket product. Now, however, if you want those knobs on your car, you can have them – in the form of GasPods.
Essentially miniature air foils, the pods were created by American industrial designer Bob Evans, using computer-simulated wind tunnel tests conducted by “one of the world's most respected independent engineering firms.” Those tests reportedly indicated that a vehicle with ten of the GasPods placed along the rear edge of its roof would experience approximately a five percent reduction in its drag coefficient.
Additional savings could be gained by placing pods on the sides of the vehicle to either side of the back window, or on the hood below the windshield.
Because different vehicles would likely benefit from different amounts of GasPods in different locations, one version of the product attaches to the car using padded rare earth magnets – in this way, users can experiment with moving them around to determine the optimum placement. Owners of cars with non-metallic body panels can opt for a permanent version, that attaches via automotive adhesive tape.
Evans is currently recruiting real-world testers, to report on how GasPods affect the mileage of their vehicles. If you just want to buy some, however, you can do that too. Prices range from US$29.95 for a set of three adhesive-backed pods in a stock color, up to $124.95 for a custom-painted set of nine magnetic pods.
Source: AeroHance
Furthermore, I'd be very surprised if the fuel savings generated by the aerodynamic gains made by such a device would ever surpass the initial cost. This type of device serves a function on something like a Mitsubishi Evo, directing the airflow more effectively onto the rear wing, but on your average family car I have strong doubts as to their usefulness.
This type of device belongs on ricer cars, just behind the painted black hood.
Tests in windtunnels have shown... ...typically the model used in windtunnels studies is laminar airflow. In such a steady state you can introduce vortex generators and work out their effect on the flow. But, when you realise that common cars move almost all of their time in turbulent air, these things really make no sense.
The other advantage is that there's only one basic model for the back end of a trailer.
One might use small toy magnetic checkers as well as these overpriced nubs and probably get a better result. Also a tape line kinda like a spoiler flap with the center stuck to itself and the edges on the car, with the flap going up to trip the airflow.