The wind drag created by conventional mudflaps is especially noticeable on the ascent and descent of hills at highway speeds. Eco-flaps can delay or even eliminate the need to downshift on the uphill side because the engine is not having to overcome the additional aerodynamic drag from the solid flaps to maintain sufficient RPMs and speed to climb the hill. On the downside of the hill, the rig reaches much higher top speeds because of the same reduced wind drag. On the highway, 53% of the usable power you get from burning fuel is used to combat aerodynamic drag. Clean up that drag around your mudflaps, and you can gain as much as 0.5 MPG improvement in your highway fuel economy.

On the highway, trailer skirts still leave residual wind drag surrounding the rear trailer axle, and this reduces your fuel economy, especially in cross wind conditions. Note the blow back air pressure on the conventional trailer flaps in this photo. Skirts also make handling and controlling the trailer in high winds very difficult. If you must operate with skirts, swap out your traditional mudflaps with Eco-flaps and you will improve your fuel economy by another 2%. Handling will improve, as well.

Wet weather provides a great opportunity to see the wind drag being generated at highway speeds by your rig. Spray is the result of standing water from the road surface being picked up and vaporized by turbulent air currents. The wind drag that creates this vapor is pulling down your highway fuel economy. High levels of spray around your vehicle mean you have some great opportunity to increase your fuel economy by reducing drag in all conditions, wet or dry. Even small changes that clean up air flow like Eco-flaps and Airtabs will greatly reduce this drag and the associated spray in inclement weather. Your fuel economy will improve significantly, as well. The trailer in the left photo is running with Eco-flaps while the trailer in the right photo is using conventional flaps. Both photos were taken a few minutes apart in the same light rain. Note the difference in spray.

Trailer OEMs make design decisions favoring ease of assembly and maintenance access sometimes. Don’t let the position of hoses, air tanks and brake boxes at the bogey create additional wind drag for your trailer. Most of these components can be tucked up into the bogey frame itself, removing additional obstructions to oncoming air flow. This far back on a trailer, every item creating drag reduces MPGs significantly.

When you use angled hanger brackets for Class 8 truck flaps, you create the same effect for 30% or more of the flap that using stiffeners create.  You restrict the top 1/3 of the mudflap from having any flexibility because it is anchored to the rigid angle design of the bracket.  This is a critical area of wind drag on mudflaps at highway speeds, as the high speed jet of air that flows over the wheels and tires has significant impact on this upper portion of a solid mudflap.  Consider changing over to straight brackets on the truck, and hanging those brackets slightly lower to clear any interference the angled brackets were designed to avoid.