I rented a 6x12' utility trailer yesterday and was surprised at how awful it pulled, especially empty. I ordered one without a ramp, but they substituted one with the ramp:
I normally get 20-22 mpg going 55-60 mph in my Tundra with no trailer. With the truck & trailer loaded with irregularly shaped items that were mostly level with the truck bed & trailer rails, I got 16-18 mpg.
Unloaded of the ~4,000 lbs of cargo I got even worse mileage -- 14-16mpg. There was a 5mph tailwind when loaded (so a 5mph headwind when empty), but I think most of the difference was trailer aerodynamics - especially with that damn ramp sticking up like an air brake and the cargo mitigating it by acting similar to tonneau cover.
When empty, that ramp really did show the effects of surfing bow wakes of big rigs. I've never noticed it before, but when a passing big rig is first coming up to my trailer, it actually would get sucked backwards into the wake. If you've ever gone surfing it feels exactly the same as when your board gets drawn backward into the ocean before you catch the wave and start surfing forward to the beach.
The scangauge updates kind of slow, but it looked like about a 7 horsepower drag (in addition to the normal 55-60 horsepower to maintain 55mph empty)
Then when the big rig was at my side, I'd get a bit of a draft - maybe 5 horsepower (50-55 hp instead of 55-60. And when the nose of the big rig pulled ahead of my truck by half a car length or so I'd get "surf" a big bow wake which saved 10-15 horsepower (45 horsepower instead of 55-60).
My awesome sketchpad skills of semi truck bow wake surfing/drafting effects:
Today's internet rabbit hole:
