Quote:
Originally Posted by Nautilus
If deflectors before front wheels really give a delta Cd of 0.01, this drops the overall Cd from 0.32 in the 0.28 range, which is actually very good for a daily-driven car.
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Quote:
Originally Posted by JulianEdgar
You cannot just ascribe Cd reductions to a car based on what the change did on another car. (Same as you cannot just add Cd reductions together to get an assumed total reduction.)
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I've also used the downloadable Excel Drag Coefficient calculator.
Frontal area for a Mk I Seat Leon has been published as 2.011, 2.20 or 2.28 sq m. Used an average, 2.16 sq m.
Weight of the car, with all bits and bobs as of Oct 2020, falls around 1364kg. Added driver weight and fuel weight (gasoline density average 0.748 kg/liter) for a total weight of 1471kg.
Tire rolling resistance for passenger car tires may be from 0.007 to 0.015. Tires were rated "E" in fuel economy, so I've assumed the worst and used 0.015.
After filling in the speeds with car coasting down in neutral, Excel formula gave a Cd figure of
0.29 (actually 0.290031, but sixth decimal place figures are too small to matter in Real Life).
As we can see, I had been too optimistic pulling a 0.28 figure from the hat, but my labors over the last few years had not been in vain.