REPLACE BAFFLE LIKE HANGERS WITH ANGLE IRON.  Don’t use any tricky, solid steel hanger brackets to mount the trailer flaps.  All these do is block the high speed air flow on the highway that shoots across the top of your tires.  Choose a simple angle iron hanger bracket, and keep it close to the tires –  within 5” to 8” directly behind the tires.  This is the best aerodynamic spot for any kind of trailer flap.

SHORTEN YOUR FLAPS.  Trailer OEMs like to issue new equipment with 30” flaps.  (Resellers blithely pass these along, too.)  For most box vans and reefers, a 26” or 27” long flap will do.  Don’t run around with extra ‘real estate’ blocking wind behind your tires.  DOT requires the bottom of flaps mounted directly behind the wheels to be 9” from the ground, which is equal to the bottom of your wheel rim.  Also consider lowering your hanger brackets to accommodate a 24” flap.  The 24” flap represents 20% less surface area to drag wind.  Eco-flaps pull the road spray down and into the flap, so the starting height of the flap can actually be lower than that of a conventional mudflap, and still block more road spray.