Jim,attempting to reduce the data from the last trip has forced me to revisit all the dynamics a vehicle can undergo which affect mpg,and it is a constant reminder of what you've had to fight over all this time.
So we all owe you the big thank you for good fight.
When CAR and DRIVER tested my CRX we had the luxury of a dead flat,tree-lined and windless straightaway at Chrysler's Proving Ground,where we could test un-molested by traffic.
C/D carries there own weather data acquisition hardware with them,so those variables were covered.
The Daytron Messtechnik optical fifth-wheel offers zero rolling resistance of its own,and the on-board computer was automatically recording all the speed/time data at 1/10th second intervals for later data reduction.
Speeds were started from above 70 mph,then coastdown data was captured between 70mph and 20mph.
The low velocity contour would help nail the power absorption coefficient for the tires to be compared later against the speed trace to 'see' the aero effects.
The car had been weighed on four, drive-on scales and was accurate to the pound.We knew the test mass with driver and recording equipment to the pound.
10,back-to-back runs were conducted as quick as the car could be
u-turned,with a weather check at the conclusion.
We ended up with Road Horsepower at 30-mph,50-mph,and 70-mph.
Knowing the R-R power absorption coefficient obtained,R-R power could be subtracted from the Road Load to isolate the aero contribution,and then by knowing the frontal area of the CRX,the Cd fell out of the data.
C/D used a custom program on a HP programmable calculator to do the data reduction.
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By using the Proving Grounds,we didn't have to deal with traffic,elevation,curves,wind spectra,etc.. With our own weather station those criteria was accounted for.As testing goes,it was good as it was ever going to get.
In hindsight,the only hitch,was the attachment of the fifth-wheel to the passenger door.
It was only when I reduced the C/D data that I realized that the fifth-wheel itself was aggravating the Cd,with its own frontal area and composite Cd.
No regrets,and it was a very interesting experience watching my car go around the high speed oval at top speed.
Since GM has moved onto a military reservation to escape the poveratsi (sp?)
perhaps they'll sell ecomodder.com their old Mesa Proving Grounds for cheap.
Then we can do our own proper testing out of harms way.
I want to personally thank you for all the hell you went through for all of us.
And I'll keep thinking of ways we can do these exotic tests and maintain our sanity.
Your a hero! Thanks,Phil.
