[M_a_t_t]

+1 for California98Civic's response. The air immediately touching the body panels is stagnant. As you get farther away from the panel the air speed increases until you get to freestream which is the air speed of the air that is not close to the car. That should be equal to the car's forward speed.

See attached pic for maybe a better explanation. The bottom black line is the surface of the car. The longer the arrow the faster the air is moving along the surface. There aren't any units because it's not something to be set in stone (I think) and is partially dependent on the situation (car in question, speed, etc.). It's called viscous drag. This is also why clay barring a car doesn't really do much (if anything) because the air is stagnant anyway.


My brothers motorcycle was bedlined before he got it. It's an interesting thing to do, but it's held up really well including spilled gas and a few drops. Conversation starter for sure though