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Vehicle Drag Reduction

A design for the rear of vehicles that reduces drag for increased fuel efficiency

Published: 19th April 2021
Vehicle Drag Reduction


When an object moves through a fluid its forwards motion is opposed by drag forces. This force increases with increasing speed so that at higher speeds a significant proportion of the energy used to move the object is lost to drag. In the context of transport systems this translates into lower fuel efficiency, increased running costs and greater emissions from non‑electric vehicles.

In particular, Heavy goods vehicles (HGVs) comprising a front cabin and a trailer, are responsible for approximately 17% of the UK’s transport CO2 emissions. At motorway speeds up to 50% of the fuel consumed by a vehicle is used to overcome aerodynamic drag. At the rear of the HGV trailer, separation from the blunt trailing edges forms a large wake immediately behind the vehicle which produces lower pressures that act to resist the vehicle’s motion. The rear of the trailer is responsible for 30 – 35% of the total vehicle drag.

Over the last 10 years vehicle design modifications to reduce drag have focused mainly on the front of vehicles, however attempts to reduce drag from the rear of vehicles have been largely unsuccessful

Technology Overview

Boat-tail designs attached to the rear of the vehicle for reducing drag are well known however, these:

(a) suffer with the structural integrity of the attachments;

(b) are largely impractical due to the difficulty of loading and unloading a vehicle fitted with such a device as it impedes access to the rear doors.

(c) have safety and regulatory concerns over the stability of vehicles fitted with these devices.

The Brunel technology is not attached to the rear of the vehicle but is embedded into the walls of the vehicle. This eliminates all of the difficulties above.

The design involves the combination of a single embedded trough at the rear end of the vehicle roof and asymmetric troughs at the rear end of each side of the vehicle (Figure 1). Drag reduction of up to 10% has been achieved using such design at 1/24th scale models. Smaller benefits are achieved by using only the roof or sides designs separately. The technology is currently at TRL level 4.

On a typical HGV the side troughs would be around 5‑30 cms long and 2‑15 cms deep, and the design only impacts the trailer width and height by 10‑15 cms. As the side designs are asymmetrical they are best placed towards the roof top thereby minimising any interference with loading of trucks.


This design enables up to nearly 10% reduction in vehicle drag with a resulting positive impact on fuel efficiency, cost and emissions.

The design does not extend beyond the vehicle rear therefore does not suffer from the existing technology issues of structural integrity, impracticability and safety concerns.


The work to date has primarily focused on application to the trailers of Heavy Good Vehicles. However the design can be applied to other modes of transport particularly where high speeds are common or mileage is very high.


Brunel University London is looking for companies interested in taking this design to the pilot scale and to develop it into a full scale prototype. This could be in the HGV trailer manufacturing industry but also in the manufacturing of cars, particularly high performance/speed vehicles, coaches, train carriages and boats.

Opportunities exist for collaborative R&D projects or to license the technology for specific applications.

IP Status
  • Patent application submitted
  • Development partner
  • Commercial partner
  • Licensing