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.

If you are putting high mileage on your rigs consistently week to week, you should look at removing steer tire flaps if you currently use them.  No doubt they look good, and they help keep steps clear of mud and ice.  These flaps however hang lower than anything else on the rig, catching the full force of oncoming air; and they represent another 2 square feet of surface area obstructing forward motion for the rig.  Kenworth published information early in 2009 confirming that their steer tire flaps generate ½% reduction in fuel economy over the road.  For a more aerodynamic profile, eliminate the use of steer tire flaps.

If you substitute a longer mudflap for trailer use, and you recut mounting holes to cinch up the flap and shorten it to a more practical length, don’t forget to trim off the excess you create at the top of the flap.  Once you remount the shortened flap, any material left above the hanger bar (3” to 4” typically) will drag serious wind in the path of the jet of air coming off the tires.  Remember that correcting little things like this really adds up aerodynamically to improve fuel economy at highway speeds.