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If you’ve ever been corrected by a track nerd at a Cars & Coffee because you called your front lip a splitter, this article is for you. Or if you would like to avoid that awkward moment, then this article is for you as well. My name is Mike, welcome to my TECH Talk.

In today’s talk we’re going to discuss the difference between a front lip or front air dam, and a front splitter. The common confusion is that they are the same thing, and although they can look very similar from the outside, they are indeed two very different things.

The Simple Definitions

Front Splitter
First, let’s start with a front splitter. The reality is most front lips are modeled after front splitters, it is never the other way around. A front splitter is a functional aerodynamic piece that was developed for and used on race cars that want downforce. The short of it is, a front splitter is used to create downforce by creating a pressure differential on the nose of the car, building pressure on top of the splitter’s surface, and reducing pressure underneath, effectively “sucking” the front end of the car to the ground. But trust me, it can get a lot more complicated than that on modern day race cars.

Front Lip
Front lips, often look like front splitters if you’re standing outside of the car just looking at it, however most front lips are purely cosmetic and don’t add any meaningful additional downforce. They are purely a bolt-on piece that is made to look like a front splitter for aesthetic reasons. That’s not to say they can’t add any performance benefits. Some of them offer provisions for front brake ducting, which, if used, is a nice way to package that cooling modification. If your front lip sits close enough to the ground, it may also reduce front end lift by blocking airflow from getting underneath the car, and reducing lift is a lot like adding downforce, albeit they are technically different.

Aerodynamics Lesson: Why Splitters Work and Front Lips Don’t

The goal of a splitter, in the traditional sense, is to split the air it comes in contact with, hence the name, and create two distinctly different pressure zones with it. Air that goes above the splitter is forced upward and over the top of the car, through the front grille, etc. That change in direction the air makes slows the air down, creating high pressure. That high pressure builds up on the top surface of the front splitter, pushing the front end of the car toward the ground in the same way that if you were to stand on the top edge of a true front splitter, the car’s front springs would compress under the load. Pushing the front end of the car into the ground pushes the tire into the ground harder, equaling more grip.

The air that finds its way under the front splitter is directed under the car in as fast and as smooth a way as possible. That’s why front splitters are often completely flat on the bottom and extend backwards as far as the rule books will allow, creating a surface free of restriction for the air travel over without having to change direction. This reduces pressure under the splitter and makes it easier for the high pressure being created on top to transfer to the tires with as little resistance as possible. Some, more advanced front splitters will also curve up underneath in areas where they can, which accelerates the air underneath creating even lower pressure, and sometimes even downforce by way of “sucking” the car to the ground like a vacuum.

A bolt-on front lip does essentially none of that. At least not effectively. Does a front lip that is designed to look like a front splitter from the bumper forward still split the air above and below it? Yes. Does it still create higher pressure on top of it and give that high pressure air a surface to push down on? Depending on the design, yes. What I haven’t mentioned yet is that front splitters are usually always mounted to the chassis of the car directly so they can support the force being pushed down on it at the front end and transfer it directly to the chassis, where it counts. Front lips are never bolted directly to the chassis, they are bolted directly to the front bumper cover, and that front bumper cover is almost always a flexible material. So when the pressure on top of the front lip builds up, that force is merely being used to flex the bumper cover, it is not getting directly transferred to the chassis or the tires. Front lips also don’t extend backward underneath the car very much, if at all, negating the other half of what makes a splitter functional.

Different Splitter / Lip Designs And Their Purposes

If you look at race cars today, race cars through history, etc. you’ll see loads of different front splitter designs. Many were dictated and restricted by rule books. Here are some notable versions of a front splitter you might see, what they do, and where you might see them.

We’ll start with the humble air dam, which isn’t a splitter at all. It is merely a curtain extending the front bumper toward the ground, ideally as close as possible. You see this on cars that purely want to reduce drag, not necessarily create a bunch of downforce, or in series where the rule book restricts the use of splitters. You see air dams a lot in drag racing as well as vintage NASCAR. The purpose is simply to block as much air from going underneath the car as possible, reducing drag and reducing lift. Think of the under-side of a car like a riverbed of rocks. If you’ve ever swam in a river, you might have noticed that the water at the top is moving noticeably faster than the water at the bottom. The water at the bottom is being slowed down because it has to traverse around and over rocks and uneven surfaces. In aerodynamics, anytime you slow air down, it creates pressure in the direction of the surface. Air that goes under the car and gets slowed down by having to navigate around exhausts, and cross members, and fuel lines, and whatever else isn’t creating a flat surface is creating upward pressure, or lift as it slows down against that surface. Simply blocking as much air flow under the car as possible helps reduce that lift, and also reduces drag, which again, is a product of slowing air down by making it change direction.

Raised-center splitters are the complete opposite of that, on the other end of the splitter spectrum. These are used on cars with completely flat and/or tunneled underbodys. Cars where the floor actually accelerates the air, which you might be able to guess, has the opposite affect that slowing air down does. Speeding air up underneath a car creates downforce by way of creating negative pressure, like a vacuum, that sucks the car down. In the case of these cars, the floor of the car absolutely requires airflow in order to work and create downforce. That’s what the raised center is for, to continue to provide airflow to the floor and continue to create downforce. Without it, when a driver would hit the brakes or get to higher speeds where the car is being sucked down toward the ground, the airflow under the car would get cut off, resulting in an immediate loss of downforce, and therefore traction. So the raised center section ensures that under any condition, there is ample airflow getting underneath the car. But this only works if you have an aerodynamically designed smooth, flat, or tunneled floor, and a rear diffuser. Most production vehicles, aside from some high end exotics and hypercars, don’t have this.

Then there’s everything in the between those two, and everything in between those to is about compromise. In the time attack world for example, certain classes are limited in how far back their front splitter can go, usually no further back than the front hubs. So in cases like this you see a combination between an air dam and a splitter. The goal is to block as much air from getting under the car as possible, but the air that does get under there needs to be unobstructed for as long as possible before getting slowed down and creating lift. This is still more effective than a traditional air dam as downforce created forward of the front suspension has a multiplying effect on transmitting that downforce to the tires because of leverage. Think of a skateboard. Pushing down on the tail, behind the rear wheels, lifts the front of the skateboard up. Pushing with the same amount of force in between the skateboard’s wheels doesn’t push one end down or the other. This is simply the effect of leverage. So in terms of a front splitter, it is still more effective to speed up or maintain the air speed under the front of the car, even if it gets slowed down and creates lift in the middle.

So What Should You Do?

At the end of the day, figuring out what you want to do with your car is obviously up to you. Think of what you are building your car for, what is available to you via skills, materials, and budget, and how far you actually want to go. I am not really aware of anyone that sells bolt on aftermarket complete floors for normal production street cars. You’re going to have to custom make that. So 99% of us will end up in the compromise bucket. Unfortunately, there’s also not a lot of truly functional front splitters that you can just buy off the shelf either, so you’re probably going to have to make that too.

If you just have a street car, continue just bolting on your favorite looking front lip and call it a day. Just don’t call it a splitter, or don’t buy it thinking you’re going to be getting any noticeable performance gains from it.