Quote:
Originally Posted by JRMichler
.....Your top speed was only 40 MPH, which is not fast enough for accurate results. A 5 MPH headwind increases aero drag by 27% at 40 MPH, and more at lower speeds. A 5 MPH head or tailwind will change my trip mileage by about 2 MPG.
Averaging several runs is good. Starting at a much higher speed is even better. The best starting speed is where the aero drag is at least ten times higher than the rolling resistance. Coasting down until almost stopped will also improve accuracy.
MTA: OK, I see that you already spotted some of this. You calculated that air drag is equal to RR at a speed higher than your highest test speed. That means that it is difficult to accurately estimate Cd from your data. Your Crr should be pretty good because the test data is almost all rolling resistance, with very little contribution from air drag.
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Actually my top speed was closer to 60 mph (over 25 m/s), so that should be pretty useful for getting the split between Cd and Crr.
The rest of your comments are based on the assumption that my maximum speed is only 40 mph, and because of this, these are not correct because my start speed was actually higher than that.
Jim.