I was curious to know what kind of "resolution" coastdown testing has: in other words, what magnitude of aerodynamic change can be revealed by repeated, timed coasting between two speeds.
We know that large changes will show up, eg, here's Skylark's coastdown results of his
Versa's Coroplast boat tail:
But what about the smaller things people are doing? Would they show up in coastdowns?
To try to answer the question, I chose
one open window as the aero modification I would try to detect.
The speeds tested were 100 km/h (~60 mph) to 50 km/h (~30 mph)
Test was AA-BBB-AA-B
The results seem to indicate that, for my vehicle, at those speeds, a single open window is
just at the edge of detectability - the average difference between the A & B results is just above the standard deviation in the control (A) set.
Any smaller aero "mod" would certainly disappear into the statistical noise / variation of the control runs.
Higher test speeds would presumably result in greater resolution.
