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Today’s demand for reducing the fuel consumption of vehicles is one of the most challenging issues within the automotive industry. Together with the increased fuel price, the development of more fuel-efficient vehicles is escalating. Recent research about fuel reduction technologies for trucks states that aerodynamic improvements of the tractor unit and the semi-trailer, and thereby drag reduction, is one of the most important technologies for fuel saving.

The research shows that the largest effects of the trailer devices are achieved during 5° yaw, this especially applies to the undercarriage treatment. Furthermore, devices that were implemented in the undercarriage and base region presented the best results, which indicates that these regions are most susceptible to drug improvements.

Aerodynamic drag consists of two components, pressure drag (a force acting normal to surface) and friction drag (a force acting tangentially to surface). Friction drag is due to shear stress between the fluid and the surface, whereas pressure drag is due to a pressure difference between the front and the rear of the body. For a truck and other blunt bodies, the pressure drag contributes to more than 90 percent of the total drag. In addition to the tractor front, the regions that represent the main drag-contributing areas around a truck are the gap between the tractor and the trailer, the base wake behind the trailer, and the undercarriage.

Different types of roof deflectors, side deflectors, and chassis fairings are some good examples of aerodynamic improvements that possible to reduce fuel consumption.

The effect of the gap clearance between the tractor and the trailer is very much dependent on how large the gap is. One of the drag contributing issues with the larger gaps is that air goes into the gap and hits the trailer front, which results in increased pressure drag. This pressure becomes even greater if the trailer stands higher than the tractor.


It is beneficial to use a roof deflector with an angle adjusted to the height of the trailer. The main purpose of such devices added on the trailer front, is to prevent uncontrolled circulation and cross-flow in the gap, improve the flow over the gap, and to reduce the pressure acting on the trailer. A full-scale wind-tunnel test, performed with a speed of 100 km/h and over a yaw sweep to calculate the wind average, states that these devices reduce drag respectively by 2 and 34 drag counts.

cfrt nose fairing

The undercarriage flow encounters a large number of disturbances due to irregular geometries with sharp edges underneath the tractor and the trailer. Together with other disturbances, such as rotating wheels, this results in a reduction of velocity in the flow, so-called low-momentum flow, under the trailer with numerous separations and energy losses.


Different types of devices placed under the trailer can be used to improve the undercarriage flow by directing the flow along the side of the trailer. This is even more beneficial during cross-wind conditions since it prevents crossflow.

Side skirts have also demonstrated a drag reduction of up to 48 drag counts.

Trailer fairing is another undercarriage treatment for reducing disturbances as the air hits the trailer.

A smoother trailer bottom with less irregularity can also be a good adjustment to improve the undercarriage flow.

cfrt undercarriage 2

At the rear of the trailer, a dominant base wake is created, containing unsteady turbulent flow. This is a result of a low-momentum flow along the top and the sides of the trailer that separates at the trailing edge of the trailer. The low-momentum flow from the undercarriage interacts with the base wake, resulting in an even greater turbulent base flow. A consequence of this is a low-pressure region that is created behind the trailer that contributes to drag.


There are different types of aerodynamic devices to decrease and stabilize the base wake by guiding the flow at the rear of the trailer. By extending the rear with different types of angled plates, the flow attachment is maintained and the air can be guided into the center of the base wake. Other devices are added to the sides and the roof of the trailer to generate energized vortices to delay the separation and thereby decrease the base wake. According to wind-tunnel tests, these devices improve drag by respectively 51 and 44 drag counts.

cfrt base wake

Innovative car aerodynamic solutions can be completed in TOPOLO. The whole set of aerodynamic components including side skirts, nose fairings, and roof deflectors made of CFRT (continuous fiber-reinforced thermoplastic composite) can easily meet the demands of both lightweight and aerodynamic.

Aerodynamic Application Solutions
Gap Treatment Sealed Gap
Vortex Stabilizer
Gap Fairing
Base Treatment Side Plates
Base Plates
Frame Extension
Undercarriage Treatment Side Skirts
Sealed Wheels
Smooth Underbody


Features of CFRT Aerodynamic Devices in TOPOLO

√ Aerodynamic drag reduction

√ Elastic

√ Keep the vehicle stable

√ High mechanical property and elasticity modulus

√ The CFRT aerodynamic skirts can be installed on the top (roof deflectors), bottom (chassis fairings), and sides (side deflectors) of the vehicle, together to reduce the air drag force.

TOPOLO Composite Trailer Skirt