# Why are vehicles not pitted like golf balls?

I have read that non-laminar flow reduces drag on blunt bodies.

Given that, why is pitting not used on motor vehicles?

• Presumably the answer in the context of airplanes (see here) applies to most other vehicles. Jul 5, 2015 at 13:17
• But trucks and cars are much blunter than aircraft? Jul 5, 2015 at 13:21
• I think Mythbusters covered this one a long time ago. Jul 5, 2015 at 13:36
• Jul 5, 2015 at 15:38
• Excuse me if I’m wrong, but aren’t the dimples on a golf ball a form of vortex generator? Apr 12, 2020 at 8:41

Mythbusters covered this one. They found significant fuel saving at constant speed. Assuming their findings are correct I can only guess that the technique is not used for cosmetic reasons ie few people would want to drive a car that looks like it has been in multiple accidents and covered in dents

• According to Adam Savage, one of the big three automakers tried to reproduce that episode with a wind tunnel on one of their own clay cars. The automaker was unable to reproduce Adam's results, though the automaker was using a different type of car. Jan 9, 2021 at 1:20

Major classes of drag:Two main factors of drag are friction and flow separation. This friction drag is dominant in streamlined shape and pressure drag (drag due to flow separation) is dominant in bluff body.

Ways to reduce friction and pressure drag: Turbulent flow has more momentum than laminar flow so they reduces flow separation so pressure drag is reduced that is main cause of drag in bluff body. So such mechanism is used in gulf balls (since gulf ball is spherical there is no way to streamline it!). In streamlined bodies friction drag can be reduced by increasing smoothness of surface.

Why vehicles are not pitted: Car is not a complete bluff body ( length of car is more than height)and not a good streamlined body( length of car not very much than height). Usually pressure drag causes more drag than skin friction drag in most of the flows. If we put pitting in cars that may lead to flow separation and increase the drag. Structure of car can be easily streamlined by avoiding flow separation. That can be archived by increasing steepness of front and back side glasses. We can reduce skin friction drag by using smooth body surface or painted surface. If u consider some part of car where separation can occur, example convex corners of car surface where dimples can reduce drag!. Manufacturing and maintenance cost of the vehicle will increase if vehicles are pitted. But the main reason is dust may accumulated in those holes and increases weight and purpose of those dimples. ( Pls, note that aerodynamics of bluff body and streamlined body is different)