Why Race Cars Use Splitters, Diffusers, Canards, and Wings

Introduction

If you’ve ever looked at a race car and wondered why it's covered with strange-looking flat blades and sharp corners, you're not alone. Splitters, diffusers, canards, and wings aren't just for aesthetics; they serve a real purpose and play an important role in managing a race car's airflow.

I'll soon be making aero components for my own car, using exotic materials like twill weave carbon fiber and CNC-cut 6061 aluminum. In this post, I’ll explain the four main types of race car aero, what each one does, how they interact, and whether they make sense for my Miata. I'll provide pictures and diagrams to help you visualize how each part works.

What Is a Splitter?

Quite simply, a splitter is a large flat panel that sits horizontally at the bottom lip of the front bumper on a race car. Commonly, higher-end splitters are made of carbon fiber and aluminum, while budget-focused splitters are often wood or plastic.



How it works: As a race car moves forward, air bunches up near the front bumper. This causes a high-pressure zone at the front of the car. This air is then pushed out of the way by the car. Normally, the air is pushed up, over the bumper, and down, under the bumper. With a splitter, however, the airstream is split before it reaches the high-pressure zone. Air below the splitter is also below the bumper and doesn't meet resistance from the bumper. Rather, it flows under the car, where it has more room to move, decreasing pressure and increasing airspeed. Air above the splitter is still pushed by the front bumper, but this time it can only go up, as the splitter prevents it from going under the car.

Thus, the slower-moving, high-pressure air above the splitter, combined with the faster-moving, low-pressure air under the car, both work to create front downforce. This improves front-end grip and braking performance.

Design notes: A bigger splitter generally creates more downforce but also introduces more drag. The bottom of the splitter should be smooth and flat, and the splitter should be sturdy. It should not deflect under heavy loads or it loses effectiveness.

What Are Canards?

Canards, also known as dive planes, are small, curved/angled fins that protrude horizontally on the front corners of a bumper. They are angled upwards and deflect air up and out.



How they work: By deflecting air upwards, canards create areas of high air pressure above, and low air pressure below. This creates downforce, pushing the front of the vehicle downward. Additionally, by deflecting air out, away from the car, air stays away from the turbulence created by the spinning wheels. This keeps it stable and makes the rear aero components, like a wing and diffuser, more effective.

Design notes: Canards are much less effective at making downforce with minimal drag than a splitter. Thus, they are mostly used for fine-tuning. A poorly designed canard can quickly increase drag, so placement and design are key.

What Is a Diffuser?

A diffuser is a ramped panel at the rear of a car. It transitions the car's flat underbody to the open air behind the car. Most diffusers also feature vertical splitters that travel the length of the diffuser. In all, the diffuser creates an increase in area for the air to flow.

How it works: Diffusers ensure a stable, smooth flow of air from the low-pressure region under the car to the higher-pressure region at the rear of the car. By gradually increasing the area for the air to flow, the diffuser slows down the air. This slower air pressurizes, causing a partial pressure recovery. This higher pressure is not quite ambient pressure, but increased enough that flow separation at the rear of the car is avoided. Overall, this decreases turbulence (and thus drag) and also slightly expands the low-pressure zone under the car.

Design notes: Diffusers work best with a flat underbody. Exposed suspension components or rough surfaces reduce efficiency because they disturb and slow down the air under the car, increasing pressure and turbulence.

What Is a Wing?

A wing is an airfoil that sits at the rear of the car, usually raised using pylons or upright brackets. Wings are usually relatively far from the vehicle's body and feature endplates (flat panels at either end of the wing).



How it works: The wing works just like an airplane wing, just upside down. The longer path below the wing encourages air to speed up, lowering pressure below the wing. The shorter path above the wing causes air to slow down, increasing pressure. This pressure differential creates downforce. The wing is often placed far from the body to avoid turbulent air from the body's airstream. Endplates on either side minimize vortices and increase efficiency.

Design notes: On most wings, the angle of attack can be adjusted. A greater angle of attack creates more downforce but also more drag. Every wing has a sweet spot of high downforce, low drag. Different cars use different airfoil shapes, some of which are great for high speeds, and others that are ideal for low speeds. Additionally, some wings have multiple elements for even more downforce.

Should You Add Aero To Your Car?

• Track Builds: Yes, but be careful. Aero helps the most above speeds of 60–80 MPH. Focus on balance, not just overall downforce.
• Street Cars: Maybe not. At legal speeds, most of these parts are more aesthetic than functional, and increase drag or reduce mileage.
• Mixed Use: Start small. A modest splitter and wing combo can totally increase performance and confidence. Just avoid bolting parts on without understanding their interactions, and don't overdo it.

Will I Add Aero To The Project Miata?

I will be dipping my toes in aero parts. However, I'm being careful not to overdo it. The wing I'm developing will have very small adjustment increments, meaning I can run it at 0-degree angle of attack, or in 2.5-degree increments. This means no big changes, and predictable handling.

As for a splitter, I'll be sticking with something reasonable with a mediocre travel. It won't have splitter ramps and won't be very long, keeping downforce manageable and predictable.

I will not be installing canards or a diffuser for the time being, as they are harder to manufacture and don't make as big of a difference as a wing or splitter. I may add these in the future though.