Noticed a large dump truck driving around a construction site at the airport and the dump trailer it was carrying had a hitch almost as long as the trailer. Why is this? Maneuverability? Helps with leverage when dumping the trailer?
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Gives space to dump both loads without unhitching the trailer. The truck bed load dumps in the space freed up by that long tongue.
I’d have to see the one you’re talking about but the dump trucks I know have quite a lot of overhang behind the rear tyres. The tyres are where the pivot point is when it’s turning. If the trailer is too short, the rear part of the truck will collide with the trailer when making turns.
If they had a short hitch, they would have to unhitch to dump both loads. Instead they can just pivot the trailer out of the way to drop the second load.
That setup would be a unicorn in Michigan. I do see that long tongue setup a lot on the West coast. Maybe load limits play into it. I Gotta think Mountain roads would be easier with long tongue too.
Some special law allows 180k GVW in Mich [https://flic.kr/p/9qtbvJ](https://flic.kr/p/9qtbvJ)
The tandem(two back axes) dump truck can pull a couple kinds of trailers. I know them as “Truck and pup” and “Truck and trailer”
The Truck and Pup is what you’d consider a normal trailer with a long hitch and its own box to dump. This box is about 1/2 – 3/4 the size of the dump trucks. As /u/ginger_whiskers says, with the long hitch, it can dump both loads without unhitching. https://youtu.be/AGQl07__CtM?t=7m7s
The truck and Trailer is more interesting IMO. This is a dump truck, pulling a trailer with a set of wheels and a hitch for another full size dump box. These like of look like a mini train. The driver can back up and twist the truck, trailer and dump,trailer into a U shape and dump the main load. It’s really impressive to watch. (Halp, I can’t find a good video of this)
Some states have weight laws on how mush weight can be on each axle, the weight can be increased by the spread of the axles. The distance between axles allows one truck to carry more weight in a single trip. The truck can also “jack knife the trailer and dump both loads if the site has enough space. But mostly it is about the weight distribution.
Another cool setup with a really long hitch is a set of transfers. They truck will drop the trailer, maneuver into a smaller area and dump the load. He will then take the empty dump truck, back up to the trailer and the entire container will slide and lock into the dump truck, he can then take that and dump it!
The hitch has to be long enough to swing the trailer out of the way so that he can dump the truck with the trailer out of the way – without unhooking.
Also a longer hitch gives easier control when backing into place.
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