Making headway: the importance of aerodynamic devices for trucks and trailers

With operators looking for ways to decrease fuel consumption and emissions, aerodynamic devices for trucks and trailers are becoming more important

One of the biggest truck launches in the past few years came when DAF unveiled its new XF, XG and XG+ trucks in June 2021. As the first to take advantage of new EU regulations on truck lengths and widths, DAF’s designers took full advantage to create trucks that could deliver up to 10% fuel savings over the previous iteration of the XF – of which much was derived from improved aerodynamic efficiency.

This article was originally published in the August 2021 issue of Commercial Vehicle Engineer magazine. To read the full issue, click here.

DAF’s focus on aerodynamics shows the importance that truck manufacturers are now attaching to it as they seek to produce trucks that are ever more fuel efficient and, as a result, produce less CO2 emissions.

DAF redesigned its exterior cab, with all three new models featuring the same distinctive tapered cab shape. They also have seamlessly fitting body panels, and sleekly mounted windscreen and doors for improved aerodynamic efficiency.

The cabs also feature a curved windscreen, elliptically shaped corner panels, streamlined A-pillar covers, along with a bottom plate with integrated air deflector and wheel bay deflectors, which all add to the aerodynamics.

To enhance engine compartment and under cab airflows, there are closures around the charge air cooler and the radiator, flow guides and recirculation barriers and closed wheel bay covers. All this has resulted in 19% better aerodynamics, which accounted for more than 6% out of the overall 10% fuel efficiency improvement, according to DAF.

This is further enhanced if the optional DAF Digital Vision System is fitted, which substitutes the main mirrors for in-cab cameras and monitors.

The focus on aerodynamics has been increasing for some years. Mercedes-Benz was the first manufacturer to replace traditional mirrors with internal cameras in 2018 when it launched its new Actros, which brought fuel savings through reduced drag. Other manufacturers have since followed with their own internal mirror system.

Whenever a new or refreshed version of a truck model is launched, aerodynamic efficiency is always a feature. For instance, when Renault announced details of upgrades to its T, T High, C and K range in April, it included improvements to the aerodynamics around the front grille and the addition of wheel arch extensions to improve airflow.

Drive to reduce emissions

Ryan Kingston, managing director of truck aerodynamics company Aerodyne, says that this reflects the global drive to reduce carbon emissions, which means that truck aerodynamics are as important as they ever have been. “Reducing carbon emissions is a significant part of this, but there is also an excellent economic benefit from fuel-saving making it an easy area for fleet operators to focus on,” he says.

Kingston adds that benefits from fitting aerodynamic aids can be derived in all sizes of truck. “Typically, larger artics use more fuel so aerodynamics are very important at higher speeds,” he says. “However, lighter vehicles such as 3.5-tonne Luton vans can get a fuel-saving at speeds as low as 25mph, so it is well worth fitting aerodynamics for vehicles predominantly doing urban work.”

Unsurprisingly, demand from operators for aerodynamic aids is steadily increasing, particularly spurred on by fleet operators becoming more environmentally conscious, Kingston says. “They are looking for bespoke products to suit their vehicle size/design rather than the ‘one size fits all approach’ that most of the OEM’s offer.”

Aerodynamic add-ons

Specific aerodynamic add-ons can also bring significant savings. These include 3D fairings, which sit on the top of a cab and deflects air upwards, and side wings, which are fitted to the rear vertical corners of a cab help to push the air out around the width of the body as well as fill in the cab to body gap, which is particularly effective when the vehicle is in a yaw.

“On an artic, there can be anything from a 3-10% fuel-saving, depending on the trailer size,” explains Kingston. “For smaller vehicles such as 3.5-tonners, we see fuel-saving in the range of 7-20%. This is because the vehicles are much lighter, and the aerodynamic benefit kicks in at lower speeds. Fitting side wings can increase fuel-saving by an additional 2.5-3%, so we always encourage fleet operators to do this.”

Side skirts, which fit around the perimeter of a trailer, are also becoming more popular, Kingston adds. “These are well worth considering for box body rigids and trailers with a high average speed,” he says. “Fuel savings vary but tend to average about 4% depending on the vehicle type and operation. They also offer added protection for pedestrians and cyclists as they cannot go underneath the trailer.”

Another popular aerodynamic product is a smaller ‘top spoiler’ for rigid vehicles, adds Tim Vincent, commercial director of Kuda (UK) Ltd.

Vincent adds that automatic spoiler adjustment systems, such as Kuda UK’s LaserEye, are also attracting operators. “LaserEye is a system that requires zero driver input and ensures that the spoiler is set to the correct height for the optimum fuel efficiency at all times,” he says. “LaserEye is fixed to the upgraded spoiler on the roof of a tractor unit, it then ‘looks’ for the trailer to be coupled and then, using the installed actuator rams, adjusts the spoiler to the optimum height. All before the driver has finished connecting the suzies or coupling.”

Vincent adds that many operators of larger articulated fleets take an ‘off the shelf’ product, as the trailer/load heights in the UK are pretty consistent, being 4.2m upwards. “We developed our iAM (Improved Air Management) product range to ensure we covered off as many options in height as possible for these operators, giving them maximum flexibility when it comes to vehicle use,” he says.

Aerodynamic add-ons can make a significant difference, Vincent says. “Aerodynamic devices, such as our iAM air management kits for trucks and trailer side skirts or bulkhead spoilers all come together creating savings of more than 9% in many cases. As truck manufacturers create more aerodynamic and fuel-efficient vehicles for the European market, the savings are still available in the UK market due to the increased overall vehicle height allowed on UK roads.

“In the world of tractor unit aerodynamics, the maths is pretty simple; for every 20cm of exposed trailer bulkhead, the vehicles fuel consumption increases by 3%. When you take into account a more than typical set up in the UK, with a truck, with a factory fitted spoiler (at 4m in height) pulling a high-volume trailer (4.6m), that’s an increase of 9%!”

If a tractor unit is travelling 100,000 miles a year, that 9% increase equates to thousands of pounds worth of savings in fuel. With full air management kits often costing less than £1,500, it can pay for itself in a matter of months.

Teardrop brings smiles

The aerodynamic properties of trailers are also important to consider. Don-Bur developed the concept of the Teardrop trailer – where the roof of the trailer initially rises from its start point, then reduces again towards the rear – more than 15 years ago, and this has become very popular since for its fuel saving potential.

A recent study by the University of Surrey investigated whether the Teardrop trailer works and, if so, why? Comparing a Teardrop against a 4.1m high standard box van trailer, the project summary confirmed an aerodynamic drag reduction of 15% and an expected reduction in fuel of 7%. At today’s bulk diesel prices, that would save an operator thousands of pounds in fuel costs and result in a CO2 reduction of more than six tonnes every year, according to Don-Bur’s calculations.

Previously, Don-Bur had only collated real-world proving ground and operator trial results; however, numerous variables can skew those results, prompting a more scientific approach. Titled ‘Could Teardrop Trailers Reduce Drag on Articulated Lorries?’, the University of Surrey project report was carried out by Andrei Stylianou and used SimScale Computational Fluid Dynamics to carry out the analysis. The purpose of the study was to ‘investigate the drag reduction capabilities of an articulated lorry hauling a teardrop trailer as opposed to the conventional box trailer’.

Contrary to some previous beliefs, the study uncovered that the key mechanism behind the Teardrop’s success was “keeping the main flow attached to the roof of the trailer and directing the upper shear layer downwards towards the ground. This effectively reduces the size of the wake by improving velocity recovery.

“Qualitative analysis of pressure distribution showed a significantly larger pressure recovery in the wake region of the Teardrop trailer, responsible for the drop in pressure drag, and hence the drag coefficient, when compared to the conventional trailer.” For a standard trailer, the length of absolute wake was more than 3m whereas the Teardrop only had a wake length of just over 2m.

Richard Owens, marketing manager at Don-Bur, says that this independent research proves how much of a difference aerodynamics can make. “The Teardrop is a fundamental way to be able to account for less CO2 and consumption of less fossil fuel. If a vehicle does 80-100,000 miles per year, the figures are quite substantial and when you apply it across a fleet, it isn’t a couple of pounds or tonnes of CO2 you are saving, it is significant quantities.”

Simple idea

Owens was there when the concept was originated in 2006, and, as with many innovative ideas, it began with a simple sketch. “We were going to a fuel saving forum at a local football stadium and had invited about 100 guests and I was in an office with the engineering manager as he was then and were chatting about ideas to stimulate interest. The engineering manager said: ‘what if we put a curve on a double deck?’ We had already done sloping rooves at the front and knew that presented quite good fuel economy but we hadn’t done curved rooves as such, it was a cheese wedge shape.”

The idea was mentioned at the forum, and one operator asked to have one produced to test. It was, and he came back with savings of more than 11%.

With concept proved, the Teardrop launched to the market in 2007, with DHL and Marks & Spencer the first operators to put it on the road. Since then, the Teardrop has consistently produced fuel savings for operators – although Owens admits the savings can vary markedly depending on the work the operator does, with greater savings coming for trucks involved in long-distance work driving mostly on motorways – and has become a familiar presence on the UK’s roads.

Other manufacturers

Other trailer manufacturers have followed suit by manufacturing more aerodynamic trailers, such as SDC, which has its Aeroliner, where the airflow that comes from the tractor unit flows smoohly over the trailer surfaces and trailer has a curved rear end to the chassis, as well as a rear roof slope that incorporates vortex generators to help reduce drag behind the trailer.

Additional fuel-saving features include an air deflector at the front of the trailer, as well as aerodynamically optimised curtains and mud flaps.


As countries around the world look to decarbonise transport as much as possible in the future, aerodynamics is set to become increasingly important, especially in the years before zero emission drivelines take over.

“We expect to see the truck and trailer combination of articulated units to become more and more integrated, with closer gaps between the prime mover and trailer and additional aerodynamic aids like rear trailer wings,” says Vincent.

“We do however believe there will be a requirement for additional devices for a number of years to come yet. We expect to see more operators look at the aerodynamic set up of their operation as the push for a carbon neutral world becomes more and more pressing.”

This article was originally published in the August 2021 issue of Commercial Vehicle Engineer magazine. To read the full issue, click here.

Dan Parton
Dan Parton
Dan Parton is a former editor of Truck & Driver, the UK’s biggest selling truck magazine. He is now writes for The Van Expert and The Truck Expert.