Executive Summary

A variety of mud flap alternatives have been on the market for many years offering improved aerodynamic performance and fuel savings. The consensus is that these devices should be beneficial but the amount of fuel saved is hard to determine in individual tests.

One critical aspect of mud flap aerodynamics is specifying the correct width of mud flap for the tires. There are differences between wide-base singles and duals so that one size mud flap does not fit all. A mud flap that is too exposed to the airflow will increase aerodynamic drag and downstream issues.

Trailer Aerodynamics
Common Fleet Strategies

Each area of the trailer represents an opportunity to reduce aerodynamic drag.

Both industry and government aerodynamicists have shown that the maximum aerodynamic improvement comes from a combination of sealing the tractor/trailer gap, sealing the trailer underbody, and adding a boat tail.

As each device is added, the performance of other devices will be impacted. The airflow over each device changes the operating conditions for the other devices. The performance of a combination of devices will not simply be the additive total of each device operating alone. However the greatest aerodynamic drag reduction comes from using devices in three main areas: gap, underbody, and rear. Addressing the aerodynamics of all three points of drag should give the greatest fuel savings for the vast majority of fleets.

What Fleets Are Saying

The overall perception of the savings offered by trailer aerodynamics is positive. “They are really effective devices now,” one fleet owner said.

Fleets stated that aerodynamic device construction, design, and materials have all vastly improved in the past five to seven years. They have become lighter and more robust.

Some fleets feel that drivers have become more accustomed to having aerodynamic devices on trailers and when combined with fuel economy incentive programs, actually appreciate having them.

Fleets were uniform in stating that the devices should “require no driver intervention.” One fleet owner said, “Any statement that starts with ‘All the driver has to do is…’ should be questioned.”

Fleets have been investing in trailer skirts as their first choice for aerodynamic improvements. However, now having done that they are looking at the next steps and are debating the merits of tails versus other options.

Decision Making Tools

The study team developed several tools to help fleets make their decision about trailer aerodynamic devices.

  • The Confidence Matrix, below, is used to inform fleets of the study team’s confidence in the technology being studied vs. the payback the fleet should expect to receive from the technology
  • An appendix of SmartWay verified trailer aerodynamic devices, found at the end of the full Confidence Report
  • A simple payback calculator, shown below, has been developed for aerodynamic devices

Decision-Making Tools

Conclusions

•    There is significant data showing fuel savings for the various trailer aerodynamic devices. The priority for device adoption by fleets is skirts, tails, front, and then other devices.
•    Devices have matured and will continue to improve. Skirts have become lighter, less expensive, and more robust improving their payback. Other devices are maturing but need continued development to improve their total cost of ownership.
•    There are unique challenges with trailer aerodynamics. These include the trailer to tractor ratio, the fact that the purchaser of the aerodynamic device is not the one buying fuel, and the fact that some devices need driver intervention.
•    Performance for each fleet is difficult to determine. 
•    Regulations will drive great adoption