CARB (California Air Resources Bord) is now(2009 all exemptions expire January 1, 2018) REQUIRES skirts and low rooling resistance tires on all 53' box/refer trailers .
http://m.truckinginfo.com/article/25...pliant-trailer
Why ? Because they work 4% improvement at 55mph (California truck speed limit) and bigger the faster you go (70-85mph Mt. , Id. ,Ut. Truck speed limit)
From what I have read .
3" off the deck/ground , or
1/2" lower than the lowest thing hanging down.
Any thing lower has a diminishing return till about 3/4" off the ground.
Eg . Many new cars have less air dam (more clearance) in the center were the suspension duse not hang down. And larger wheels that alow more ground clearance under the lower control arm.
Side skirts only should help but much less effective , and like kach22i stated could destabilize your rig under the right wind / driving conditions.
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1st gen cummins 91.5 dodge d250 ,HX35W/12/6 QSV
ehxsost manafulld wrap, Aero Tonto
best tank: distance 649gps mi 24.04 mpg 27.011usg
Best mpg :
31.32mpg 100mi 3.193 USG 5/2/20
Former
'83 GMC S-15 Jimmy 2door 2wd O/D auto 3.73R&P
'79 Chevy K20 4X4 350ci 400hp msd custom th400 /np205. 7.5-new 14mpg modded befor modding was a thing
87' Hyundai Excel
83 ranger w/87 2.9 L FI2wd auto 18mpg on the floor
04 Mitsubishi Gallant 2.4L auto 26mpg
06 Subaru Forrester XT(WRX PACKAGE) MT AWD Turbocharged 18 plying dirty best of 26mpg@70mph
95Chevy Blazer 4x4 auto 14-18mpg
04 Chevy Blazer 4x4 auto 16-22mpg
