Trailer aerodynamics

Project output

A package of measures for improving the aerodynamics of single and double-deck refrigerated semi-trailers, including cab gap devices, side skirts, wheel covers, bumpers, wheel flow deflectors, optimised under-body flows and rear end taper.


A combination of an air deflector matched to the trailer height and a cab gap fin was found to reduce aerodynamic drag by 5%. Side skirts are very effective drag-reducing devices. Their optimum height is aligned with the wheel axis. Adding bluff bodies to the underbody does not necessarily increase drag and may potentially improve aerodynamics. Further reductions of approximately 7% may be obtained by tapering the rear, where the optimum taper angle is 9º.

% fuel saving

At highway speeds, a 5% reduction in fuel consumption may be achieved with cab gap devices and a further 7% with rear end tapering.

% CO2e Saving

% Carbon saving is equal to the fuel saving.

Cost of implementation

Aerodynamic double-deck trailers cost approx. £8,000 more than the standard vehicles, with an estimated payback period of 1.8 years.

Implementation strategy

Implement now. Designs are available from the research team.