Well the very short answer is in the title.
A slightly longer version, after testing coastdown times from 70 to 50 MPH in bidirectional testing, one cannot discern any improvement or penalty in using Moon wheel covers.
The longer, data version. I selected an essentially level course of about 1.5 miles where I could find convenient turnarounds. I tested over a course of about 3 hours, beginning at 11 am. The data:
No Moons:
East 33.89sec
West 36.01sec
E 32.4 sec
W 38.56 sec
E 35.19 sec
W 37.33 sec
Ave 35.72
Moons
E 34.03
W 35.95
E 36.87
W 36.53
E 37.25
W 37.51
36.35
No Moons
W 38.5
E 36.10
W 37.67
E 35.48
W 38.81
E 35.84
AVE. 37.24
There was a fairly linear minor increase in coast down times as the day became warmer. Anyone who drives an Insight will be well familiar with the improving MPG with temperature. In this case this is entirely dure to the warming ambient temperature and NOT to car warm up, as the car was thoroughly warmed before all segments.
If one averages the first and last segments to take out the temperature gradient, one gets 36.49 sec, no Moons. The Moon cap time was 36.35.
I'm left with several conclusions:
1. Stable temperatures, like still winds would be nice if we could get god to cooperate.
2. The Insight loves warm temperatures.
3. When compared to stock Insight wheels, Moons are a wash - no better, no worse.
Lots of time invested for no improvement in the end, but then there are never any guarantees.
Moons MIGHT improve on the stock wheels at much higher speeds, but that is not the hypermiler's world
