Elon, a series of coast down tests are good. The real issues begin when
trying to separate out the various parameters. Things like gear drag,
rotating inertia, brake drag, rolling resistance. You might be able to
quantify mechanical gear drag using a orque wrench and measuring the
torque it takes to rotate everything fron the rear axle tot he gear box
and then using the formula for finding lost horsepower. You would ned
to measure wheel rpm for finding that parameter. Then you need to try
and figure out rolling resistance. That requires that you weigh the car
in the as run condition and then getting the tires warm, measuring the
tire pressure. Brake drag wight also be measures similarly to the gear
drag technique. The for the aero drag, you will need actual air density,
wind speeds wind angle, roadway grade, the frontal area, and of course
the starting and stopping speeds. This is not a trivial task!
OR
You could just do the coast down and figure out the combined drag
coefficient for the car under the given conditions. Means that the Cd
would be a composite of all things above for this car and this car only.
Which woould work for determining enhancement changes to the car.
OR
Take it to a wind tunnel with a rolling road surface.
Things like this become fun into themselves.
Keep us oinformed of how and what you are doing with the dynamics of the
car.
mayf
Elon wrote:
<snip>
> But seriously everyone,
>Doesn't a coast-down tell you the product of the CdA and all the other
>variables? It doesn't tell you just the Cd or A, no?
>
>
><snip>
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