Aerodynamics of buses and trucks
The amount of fuel used to push a heavy vehicle through the air increases rapidly with speed. The amount of fuel you need can be reduced significantly by making the front area of the vehicle smaller, and improving airflow with cab roof deflectors, side skirts and other streamlining devices.
- When to use aerodynamics
- Effects of aerodynamics
- Aerodynamic devices and treatments
- Preparing to use aerodynamics
There’s no one-size-fits-all solution, so it pays to spend time working out which options best suit your fleet. Aerodynamic additions won’t be suitable for all fleets. For example, if your vehicles mainly operate in 50 km/hr speed zones using aerodynamic devices will typically improve fuel consumption by only around 1%. Simple low-cost measures you can use to improve the aerodynamics when average speeds are greater than 70km/hr and achieve fuel savings up to 10% include:
- placing the load near the headboard whenever possible
- covering empty tipper bodies.
For example, linehaul vehicles can save up to 10% or more of their fuel bill through improved aerodynamics. That translates to 50,000 litres of fuel saved over the first million km of the life of the vehicle.
For a typical heavy vehicle with no aerodynamic devices fitted, you’ll need about 22 horsepower to overcome aerodynamic forces at 50 km/hr. This increases to 126 horsepower at 90 km/hr and over 170 horsepower at 100 km/hr.
This table shows the effect of aerodynamic treatments and devices on heavy vehicle fuel efficiency. Fuel savings are indicative only - actual savings depend on vehicle speed, the design of the device and other factors.
|Cover empty tipper trucks||Involves covering tipper bodies with a tarpaulin at all times when on the road.||3%|
|Aerodynamic design of prime movers||Choose prime movers with rounded front edges and streamlined shapes. Air cleaners and other objects under the hood can reduce the aerodynamic drag coefficient from above 1.15 to about 0.6.||10%|
|Load placement||Load is placed as close to the cab as possible on flat deck trucks.||3%|
|Cab roof deflectors||The height should be such that a straight edge extended from the trailing edge of the deflector or fairing passes over the front edge of the body or load. It’s better to set the deflector too high rather than too low. Setting it too high can increase the aerodynamic drag by 5% but setting it too low can increase it by over 15% compared to having it in the best position. Adjustable deflectors are recommended for trucks carrying containers that vary in height or that travel empty at times.||
1.2% to 2.4%
|Side flarings||These are used to bridge the side gaps between the cab and a curtainsider, container or van body.||0.6%
1 to 2 years
|Trailer side flarings||These flarings are used to direct air away from the side gaps between trailers.||>1%|
|Side guards and chassis body panels||These devices cover under-the-body areas on the sides of trucks and trailers. They are relatively expensive and are prone to damage from stone chips. They improve safety by providing side under-run protection.||
0.5% to 1%
2 to 5 years
|Air dam||Installed under the front bumper. Already installed on most modern trucks, and are often incorporated into frontal underrun protection.||
0.35% to 0.7%
< 2 years
|Exterior sun visors||Only effective in some circumstances. Some sun visors will reduce aerodynamic drag while others can increase it.||
1.6% to 3.6%
< 1 year
|Reduced roof height||Make the body only as high as it needs to be. If the body frontal area is smaller than the cab, look for a smaller sized cab when replacing the vehicle. When specifying replacement vehicles consider making the deck height as low as possible so overall height is reduced.||
The best options for a particular vehicle depends on your vehicle operation, road environment, annual distance travelled and other factors. Before making changes to your vehicles there are steps you should take.
- Do your research - to find out what has worked well for others in your type of operation.
- Start with the obvious treatments first.
- Consider a trial - 4 vehicles should be used in a trial, 2 fitted with aerodynamic features and 2 without.
- Swap the drivers of trial vehicles - to reduce the impact of different driving styles.
You’ll make the most savings by considering aerodynamics, engine performance and gearing together.
Read more about monitoring and measuring fuel use and biofuels.