Why do heavy hauls have an extra trailer at the back?

[}OwO{ Trashcan]

Can anyone tell me why American trucks often have an extra trailer at the rear with nothing on it when hauling oversize or heavy loads?
https://imgur.com/a/42hcdy5
As far as I can tell this trailer at the back (like the one in the image link) won't actually be bearing any significant weight, and just adds to the overall length. I'm probably missing something, can someone clear this up?

[Red Wolf]

it spreads the weight over all the axles evenly

[Reese]

Without going into significant detail, I'll do my best to explain the purpose.

This little bit is called a "Stinger." The Stinger came about because the United States has a law regarding weight spread often referred to as the "Bridge Formula Law." In short, weight is limited per axle over a specific distance.

In the configuration in your image, the stinger can pivot left-right, but not up-down. It is locked in place with a pin. Some trailer manufacturers have this pin replaced with a hydraulic ram to make it adjustable during movement. The stinger can also be locked to go backwards without it turning. ATS does not have that specific functionality though. The stinger does hold weight, my personal guess without any hard facts is probably like 20% overall in that configuration.

This is also why there's a short trailer in front of the load trailer, known as a "Jeep." The jeep takes up some of that weight on its axles as well, to spread them over a larger distance. Which brings us up to the truck which may also have additional axles, spreading the weight over even more of a distance. So instead of 120,000 pounds over 5 axles of a standard truck and trailer, you're now spreading 120,000 pounds over 10+ axles, reducing the concentrated weight in a singular spot on the road.

Edit: There are downsides to this approach, as seen by Europe just putting axles the full length of the trailer, but this is the legal solution in the US.

[}OwO{ Trashcan]

Originally posted by Reese:

Without going into significant detail, I'll do my best to explain the purpose.

This little bit is called a "Stinger." The Stinger came about because the United States has a law regarding weight spread often referred to as the "Bridge Formula Law." In short, weight is limited per axle over a specific distance.

In the configuration in your image, the stinger can pivot left-right, but not up-down. It is locked in place with a pin. Some trailer manufacturers have this pin replaced with a hydraulic ram to make it adjustable during movement. The stinger can also be locked to go backwards without it turning. ATS does not have that specific functionality though. The stinger does hold weight, my personal guess without any hard facts is probably like 20% overall in that configuration.

This is also why there's a short trailer in front of the load trailer, known as a "Jeep." The jeep takes up some of that weight on its axles as well, to spread them over a larger distance. Which brings us up to the truck which may also have additional axles, spreading the weight over even more of a distance. So instead of 120,000 pounds over 5 axles of a standard truck and trailer, you're now spreading 120,000 pounds over 10+ axles, reducing the concentrated weight in a singular spot on the road.

Edit: There are downsides to this approach, as seen by Europe just putting axles the full length of the trailer, but this is the legal solution in the US.

Ahh I see! I didn't know it couldn't pivot up and down, if it can't I can see why it would be contributing to holding weight on the rear axle. Thanks!

[MagnusA]

I have also wondered about that little extra trailer. It sure looks like it bears only its own weight and nothing of the main trailer. Like "Oh crap, too few axles for the law! Let's add some more by adding this little pup." :-)

Didn't thought about the trick of no up-down movement.

[Tom Johnson]

Originally posted by MagnusA:

I have also wondered about that little extra trailer. It sure looks like it bears only its own weight and nothing of the main trailer. Like "Oh crap, too few axles for the law! Let's add some more by adding this little pup." :-)

Didn't thought about the trick of no up-down movement.

It bears weight, and even though you have more axles, to carry the weight, you still can not exceed a certain weight per axle, and that also depends on how many tires per axle. That is why most scales are small, they are designed to weight each axle, and combine all those axles to get your overall weight.
https://oversize.io/regulations/axle-weight-calculator