Why the air dam lip?

[BeatUpRanger]

Sport_Trac_Air_Dam_5.jpg

Why do air dams have this lip? Is it needed or just aesthetics? When (if) I build my own, should I incorporate something like above or is better to leave it straight like this one below?

Miata air dam.JPG

[wyatt]

They have them because NASCAR has them on lots of their cars. NASCAR has them for downforce. Effectively it is pushing the leading edge further forward and lower to the ground, forcing more air over/around the car, and allowing less under. It should be good for aero, but as all things aero, YMMV (literally!).

[Kodak]

From my understanding, it is to make it harder for air to get underneath the vehicle. I've seen some custom dams with it and some without. My plan is to include a small lip similar to stock design (just a lower dam).

Hey Ranger, if you build one will you post a little before/after thread?

I'm [very slowly] starting to finalize plans and collect materials for a dam. The more info the better.

[BeatUpRanger]

Thanks for the info. That's good stuff.

I'd like to build one myself, but no that I won't be starting any time soon...although I wish I was. I'll definitely post pictures when I do. Right now she's plenty beat up (front end, driver's side fender and door) after a recent deer ambush. Once that's taken care of, I'll start on my eco-mods. So far, I've removed the mud flaps, and have been working on my own driving habits.

[euromodder]

Originally Posted by BeatUpRanger

Why do air dams have this lip?

It keeps the air on the air dam while it's being pushed outward to the sides due to the airdam's slight curvature.

Without a lip, part of the air that hits the airdam is still going to spill underneath the car - while airdams are used to reduce the air going underneath.

[BeatUpRanger]

While Googling images of air dams, I came across this racing page, which summarized a lot of the aerodynamic add-ons of performance cars.

Here's the link.

[wyatt]

Originally Posted by BeatUpRanger

While Googling images of air dams, I came across this racing page, which summarized a lot of the aerodynamic add-ons of performance cars.

Here's the link.

I didn't read everything on their page, but at least one thing I saw was wrong. Their graphic "Car Underbody Aerodynamics" shows air coming into the underbody as being "Fast Low Pressure Air" and exiting as "Slower Moving Higher Pressure Air". If the air is going slower leaving the diffuser (which we could reasonably assume) the pressure is lower, not higher. This is why diffusers generate downforce, they are being pulled down by the low pressure air.
Due to this oversight, just make sure you keep a cautious eye when reading people's aerodynamics pages, as it's easy to get thing wrong.

[BeatUpRanger]

Help me out, Wyatt. I didn't see what was wrong with the graphic. It shows that the air moving under the car is faster moving and lower pressure.

I thought that was Bernoulli's law: lower pressure causes fast-moving air.

[wyatt]

Originally Posted by BeatUpRanger

Help me out, Wyatt. I didn't see what was wrong with the graphic. It shows that the air moving under the car is faster moving and lower pressure.

I thought that was Bernoulli's law: lower pressure causes fast-moving air.

About 2/3 of the way down the page, there is a picture of the underbody of a car. at the car's back end, it should say "Slower Moving Lower Pressure Air" (not higher as it does in the picture).

[winkosmosis]

Originally Posted by Kodak

From my understanding, it is to make it harder for air to get underneath the vehicle. I've seen some custom dams with it and some without. My plan is to include a small lip similar to stock design (just a lower dam).

Hey Ranger, if you build one will you post a little before/after thread?

I'm [very slowly] starting to finalize plans and collect materials for a dam. The more info the better.

Yeah it's called a splitter and that's what it does