Is dirt stock car aerodynamics worth the effort?

I was reading today on the Accelerating Performance blog ( and the newest post on there was about aerodynamics, mainly concentrating on pavement late models. The basic principles that they concentrate on are the same basic things that are important on dirt stock car aerodynamics. If you run your car as close to the weight rule as possible the best way to get more traction, or make sure you don’t lose traction, is to use the air. Make no mistake, no matter what class you run, air always makes a difference. Yea, I know, everyone has seen people win races without an entire right side or the nose gone off the car, but the same balance on the car with good aerodynamics will always be faster.

Keeping air from under the car

The basic rule of thumb of stock car aerodynamics is to keep high pressure on top the car and low pressure under the car; or simply keep as much air from going under the car as possible, then manipulate the air going over the car to get the most down force in the areas you need it. The first thing the air hits is the nose and this should be the first consideration. On a smooth track, getting the nose as close to the ground as possible is the general rule of thumb. Remember this is in a dynamic state. If you car rolls hard onto the right front tire, the right front of the nose will need to be higher than the left. It seems general rule of thumb on a dirt late model nowadays is five to six inches on the left and nine to ten on the right. Also make sure the front of the tires are covered, you should not be able to see the tires when looking at the front of the car. In open air a tire will actually produce lift. Open wheel race cars are actually at a great disadvantage aerodynamically than stock cars, just because of the tires.

Wheel wells create vacuum

The next order of business is the wheel wells. The front of the wheel should be wider than the back. Basically when looking at the car from the back you need to see the rear of the tire. The air passing over the body at the front of the tire actually creates a sort of a vacuum, pulling air out from under the body. I’m would think there is a point of diminishing returns on this, but I don’t know what it is. I just make sure the front is out further than the back.

Dirt late model spoiler

Since we are talking about points of diminishing returns we will touch on the spoiler. I read somewhere, I wish I knew exactly so I could credit the source, that around fifty-five to fifty-eight degrees is about the maximum angle that stops creating decent down force and the drag starts getting too great. Also, spoiler uprights, a few years ago there got to be a trend of putting a bunch, five to six, spoiler uprights across the back of the car. Then sanctioning bodies cracked down and I believe they only allow four now. I got to thinking about this one day and I don’t know if more is better. OK, everyone thinks it acts like a rudder to make the back end of the car tighter, but hear me out. Could it be possible that when the car is in yaw that too many side boards block or at least dirties the air as it spills off the right side on to the spoiler. We normally think of a car going straight down the straight away, in which the air would attack the spoiler head on. Most dirt cars nowadays will traverse the straight at a slight yaw. Air, I think ,actually travels diagonally across the car, not straight on.

Well, these are just a few simple aero tricks to keep an eye on. Any work on air is better than nothing, but playing the air game will definitely pay dividends no matter what class of car you’re racing.

Till next time, Race safe.