Side Duct

Overview

Side air ducts are aerodynamic features typically found behind the front or rear wheels. Originally adapted for racing coupes, the concept involves creating an aerodynamic opening on the side of the car that allows air to flow out of the vehicle. Since aerodynamic efficiency requires that wind flows smoothly around the car, speeding it up rather than slowing it down, a side duct further reduces wind resistance by providing a vent for air to pass through.

Side duct on Audi R18 9-L LMP car

Function in Racing Cars

Side ducts are primarily seen on race cars for two reasons: brake and engine cooling is crucial, and most serious race cars use a front underbody diffuser that channels airflow toward the rear of the front wheel well. Conventional fender designs trap much of the turbulent air coming off the top and back of the tire, generated by the counter-rotation of the tires and wheels. Combined with hot air moving through the engine bay and brakes, this generates losses and drag.

Side ducting not only provides a smooth outlet for these hot and turbulent gases, but also turns the flow to exit smoothly along the side of the car instead of directly outward, which would interfere with the turbulent curtain generated by the canards and vortex generators. This reduction of air stagnation inside the tire bay also helps pull more fresh air through the cooling system.

Road Car Applications

Air ducts are also available as aftermarket modifications for road cars. They can improve airflow efficiency and slightly reduce fuel consumption. The openings on the air ducts are usually large enough to prevent obstruction from objects encountered during normal driving. Mesh or similar grille and vent covers can enhance the appearance but are often difficult to apply once the body kit is already on the car, so spending time planning the installation beforehand can save considerable fitting effort.

Citroen C4 side ducting

Side duct on Nissan GT-R road car