letterman7 wrote:No. The wings are strictly visual.
Not necessarily true. This test was conducted when roof spoilers first became popular in Europe - you can see by the shape of the VW Passat that this is from the 80s. But this is a test done by VW in their full-size wind tunnel, so you can't get much more definitive than this:
That's a 15% reduction in drag for this particular car/trailer combination, so would give around a 15% fuel economy improvement.
If you want the same results, you need to find a wing that works as well for your particular car/trailer combination and that's the tricky bit.
