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Old 03-13-2009, 04:40 PM   #8 (permalink)
aerohead
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consistency

It probably doesn't effect consistency,but the higher initial speed allows the air drag to "emerge"dramatically from the velocity/time coordinates of the coastdown curve.Since the air drag force varies as the square of the velocity,if you take the car above 100 km/h and monitor the deceleration,the air drag is really significant and Newton's F=MA relationship will shine light on aero vs RR at these higher velocities.Down around 32 km/h Reynolds Numbers are falling apart and the RR portion from the becomes dominant,helping you to identify it from the aero.SAE recommends starting from around 112 km/h,begin taking your trace at 100,and continue down to 32,back-to-back in each opposing direction for a minimum ten runs.
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