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Decided to go do some more "A-B-A" testing of fender skirts today. Headed up to my 4.4 mile course in Washoe Valley - elevation 5200 ft. and a bit of a west wind blowing (mostly a cross-wind to my course). Speed - 50 mph, cruise control regulated. ScanGauge "trip" reset at beginning of each section - northbound, then an "equal and opposite" southbound:
"A" tests... grille block, mirrors folded back, roof rack off, 60psi in the tires...
speed - n.bound - s.bound - avg.mpg
50 - - - 29.3 - - - 30.1 - - - 29.7
50 - - - 29.2 - - - 30.1 - - - 29.65
50 - - - 29.2 - - - 30.0 - - - 29.6
overall "A" avg. = 29.65
"B" tests... same as "A" tests, but with cardboard "fender-skirts" taped over back wheel openings...
speed - n.bound - s.bound - avg.mpg
50 - - - 29.0 - - - 30.0 - - - 29.5
50 - - - 29.2 - - - 30.2 - - - 29.7
50 - - - 29.5 - - - 30.3 - - - 29.9
overall "B" avg. = 29.7
"A" verification tests. Same as others with cardboard fenderskirts removed
speed - n.bound - s.bound - avg.mpg
50 - - - 29.4 - - - 30.2 - - - 29.8
50 - - - 29.4 - - - 29.7 - - - 29.55
2nd "A" avg. = 29.675
If I average all 5 "A" runs, I get 29.66mpg for a 0.04mpg improvement from the fender skirts. Wow - that's almost negligible. In fact, I tried a less rigorous test a couple weeks ago, and it showed the fender skirts actually DECREASING my mpg!!!!
So - - - how is this possible? Has anyone else done fender skirt tests that showed almost no, no, or even negative gains?
Confused & baffled?
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