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Originally Posted by sendler
Back to the original topic. This also shows the insignificance of skin drag.
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yes,with automobiles,the surface friction contributes 9-12% of the overall aerodynamic drag,depending on body design.
The Coefficient of surface friction drag is 0.003.
On automobiles,the wetted area is estimated at 10X-frontal area,yielding Cd 0.03 average skin friction drag,based upon frontal area of the car.
If you could smooth the finish beyond that of glass it wouldn't make any difference to skin drag.
It all has to do with air viscosity and Reynolds number effects.
Since drag coefficients on bikes begin at Cd 0.9 they're absolutely dominated by separation induced pressure drag and until the bikes are streamlined,skin friction is essentially meaningless.