What are those long mudflaps on semi's

[Thump553]

Goggling gave no answer so I thought I hunt for knowledge here. I've seen a few semi trailers recently with something that looks like a pair of long mudflaps, starting inboard at the trailer's front wheels and extending to outboard just before the rear wheels.

What are these things and what are they supposed to do? I'd think they make the trailers even more susceptible to crosswinds but they must have some positive function.

 

[Zenmervolt]

Those are "skirts." They greatly reduce turbulence underneath the trailer and by doing so reduce fuel consumption by 7.5% to 8.5% depending on the design.

ZV

 

[ThatsABigOne]

It's all about aerodynamics.

 

[DVad3r]

They aren't mudflaps they are for aerodynamics and improved fuel economy. I believe some states like California now have a mandatory requirement for all trailers registered there to have them.

 

[TridenT]

http://www.northcountrypublicradio.org/news/images/trailer-tail.jpg

I've never seen the rear portion, but the bottom portion I've seen a lot. I thought it was actually opening the bottom of the trailer. (It looked like something you would use for emptying the contents of the trailer)
http://www.northcountrypublicradio.org/news/images/trailer-tail.jpg

 

[phucheneh]

I've wondered why those rear bits aren't more common. I don't think I've ever seen them on a normal monocoque trailer out on the road. Only on 'specialty' stuff like enclosed car haulers, where they're put on at the factory. But it seems like the fuel economy benefit of a 'suggestive wedge' would outweigh the cost of freight companies buying piles of them. It's basically the same idea as the back of a Prius- get a lot of the benefit of a true wedge (or teardrop, which is, functionally, kinda like two perpendicular wedges) shape without having to give the back of the vehicle/trailer a long 'tail.'

 

[Tsavo]

Little known fact, but these cut down 'Ring times by two minutes.

 

[phucheneh]

Little known fact, but these cut down 'Ring times by two minutes.

...so, it's like, a 58 minute lap now?

I'd like to see one of those crazy 'racing semis' do Nurburgring. Or even better, one of those weirdass baja garbage truck things.

 

[JulesMaximus]

They are for mounting disgustingly sexist naked women with pointy boob placards to.

 

[Zenmervolt]

I've wondered why those rear bits aren't more common.

Mostly because they make it a pain in the ass to open the rear doors. The operational difficulties outweigh the savings in most cases.

ZV

 

[brainhulk]

i've been thinking about putting those on my prius to get more mpg

 

[Demo24]

http://www.northcountrypublicradio.org/news/images/trailer-tail.jpg

I've never seen the rear portion, but the bottom portion I've seen a lot. I thought it was actually opening the bottom of the trailer. (It looked like something you would use for emptying the contents of the trailer)
http://www.northcountrypublicradio.org/news/images/trailer-tail.jpg

I've seen 1 or 2, but not for a couple months now. All clearly on trucks with great effort made to improve aerodynamics and efficiency.