Yesterday i tried to do the Coast Down Test for Cd evaluation:
-7 test from 180kph* (about 112 mph) to 90/80Kph* (about 56/50 mph). *Speed from speedometer. ( 7 test, 4 in one direction and 3 in the opposite direction, because the trial road isn't very flat)
- I use elm 327 interface + Forscan to record all data (time, fuel, real speed)
- Several months ago I found an excel file that models the experiment for the evaluation of Cd and the resistance rolling coefficient, by inserting some characteristics of your car like mass, frontal area, etc plus the insertion of the actual speed that you find.
I edited this file because i don't like playing with two variables to minimize the error between the model speed and the actual speed, so i modeled the Crr with the Stuttgart rolling resistance coefficient which depends on Speed and Tire pressure.
The results are:
Cd= 0.272 ( i think it's quite reliable)
Error= 0.37 ( i think it's acceptable)
What do you think about it? Any suggestions?
After finish the diffuser, i'll try again of course!