[Cd]

I know we have discussed this in the past and I searched this forum using the keywords " skin friction " as well as " car wax " , but didnt get anything specific.

I have read conflicting articles regarding the importance of skin friction on an automobile.
Some experts claim that the boundary layer is actually pretty thick on an automobile, and therefore things such as hood pins have little to no effect on drag.

On the other hand, I have read about HPV bicycles where the surface is polished to a smooth finish. The article stressed that this was important in the reduction of drag, and this was from a scientific source - not just someone speculating.
( I'd have to search for the article )

So this is this due to the fact that the racer has such small dimensions right ?



With cars such as the AeroCivic, there are several dents and protrusions ( caulking ) on the car.
I'm confused because the car has its gaps filled in with caulking to reduce drag , but supposedly the boundary layer is thick enough that the surface irregularities go unnoticed by the airfow.

( Basjoos, the video of you talking about the sand on the car not blowing away due to the thick boundary layer comes to mind )

Enlighten me please folks . I'm clueless.

BTW, I have read conflicting statements about body gaps too . Both from aerodynamic experts .
Some say body gaps can contribute quite a bit of drag. Others say they have no effect on the Cd.

My guess is this is due to the tightening of the gaps on modern cars versus older cars.
I had a 280Z that had body gaps large enough to stick your index finger into. Not on ly this, but the fit was off as well and the body panels did not create a smooth body at all.