About a decade ago, they started putting spoilers atop semi tractors to lift the airflow above the trailer. A couple of years ago, I started seeing skirts on trailers to clean up the drag underneath. Just how much savings are they getting? I figure it has to be substantial. I mean, after all, a gallon of deisel/trip isn’t much, but when you operate 5000 rigs across the country, it adds up.
Any truckers on the board who can enlighten me?
Ehh, I read the thread title wrong at thought this was about slipstreaming a semi. I’ll post anyway and maybe save somebody trouble.
I slipstreamed a semi darn near all the way across New Mexico. I was glued to rear bumper. It was pretty harrowing at times.
Got less than a half-mile-per-gallon increase in mileage. :rolleyes:
Never done it since, and never will again.
Mythbusters did that one. If you’re too close, you’re off and on the throttle to avoid a collision. Get back about 10-15 feet and you get 40% better(appx), going by memory).
Also, it helps if you have nerves of steel and icewater in your veins like Grant did. 
It’s not that all efficient fuel savings wise. Less than 4%. Current regulations say when a fleet owner buys some quantity of trailers, a percent of those MUST have fairings. And those cost extra. When the fairings get beat up with use, there’s no regulation that they MUST be replaced.
They’ve been putting fairings on top of truck cabs for a few decades now. Recently they’ve also been adding devices to reduce the gap between tractor and trailer, side skirts, and a bunch of other things. This new stuff is part of the US Environmental Protection Agency’s SmartWay program.
If you add up all the features, it looks like you can improve fuel economy by something close to ten percent. If you’re crossing the country (~2500 miles) and you normally get 6 MPG, that’s 417 gallons of diesel. Cut that by 10%, and you’ve saved about 42 gallons of gas; depending on the price, that’s as much as $160. Five days per trip, so 73 trips per year, so total savings per year is $11,680, per truck. If you’ve got five trucks in your fleet, the savings is enough to pay somebody’s salary (once the mods are paid for). I’m probably being somewhat optimistic with some of these parameters, but you can see that the savings may be substantial.
I wonder what it costs to outlay each truck?
The claim at this site is $9,000 in savings every year (not far off of my earlier estimate), with payback occuring in 1-3 years - implying the cost is $9,000-$27,000.
Actually, if a company wants to drive in California, they better have any 53’ trailers going there equipped with fairings. As well as the rest of the stuff that is in the SmartWay program Machine Elf linked to.
Back in the 1930’s the NYC Railroad hired designer Raymond Loewy to design streamlined locomotives for its trains-many of these designs look very aerodynamic. But they seem to not have been practical-was it the low speeds that they operated at?
Streamlining locomotiveswas a worldwide thing. Once you’re going above c 80 mph the savings start to mount up.
All fast trains today are streamlined. France’s TGV trainslook a lot passenger jets from the front. Here’s a lineup of Japanese fast trains over the past 30 years. All very streamlined.
