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Goosenecks
Dave, I have to disagrre with the statement that 'bumper pull' (tag-along) trailers are "a more unstable geometry".
The reality of it is that a gooseneck or 5th wheel trailer has a longer distance from the center of the suspension to the center of the hitch, that's all, the rest of the 'geometry' is basically the same. This added length means that input from the towing vehicle changes the direction of the trailer proportionately less.
That however can also work against you.
If you were to for instance put 2 identical trucks side by side, each hitched to a similar trailer, an 18' flatbed, one a gooseneck, the other a tag-along, and you took them through a slalom type course, or tried to follow each other through relatively narrow city streets, you would find a BIG difference in the tracking.
The fact that the trucks hitch swings out slightly, and follows the rear end, the trucks pivot, by a few feet, means that in a given corner, the tag-along trailer will not track to the inside as much as a gooseneck will.
In our fleet we have both types, in various lengths. If for instance, I want to take one of my units to my cottage, I cannot take a gooseneck trailer, it won't go in our narrow winding road, a tag goes in just fine, it's a little close in places, but it goes. In the spots that are a tight fit, the gooseneck would have 2 wheels completely in the ditch. I know, I've tried it. The only way I can do it is with my big TLB behind, forks down, and pick the back of the trailer up and shift it over.
The difference between a tag-along and a gooseneck also diminshes as the size of the tow vehicle goes up. My pickup doesn't handle a 5 ton load on a gooseneck as well as my big truck handles 10 tons on a tag trailer.
Best of luck.
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Goosenecks
Dave, I understand what you are saying, but I think you are missing a few critical details.
Using my truck as an example, becuase it's here and I know it well, I have about 38" from the centerline (C/L) of the rear axle to the C/L of the hitch, but the wheelbase is 172" so the hitch to axle length is about 1/5th (for arguements sake only) of the wheelbase, the length of the pivot. So to move the hitch 1", the front of the truck has to pivot 5" in the opposite direction.
If we take a forward speed of 50mph, if the front of my truck moved 1" suddenly, the hitch would move far less than 1/5" (becuase it's moving so it sort of slides over, it doesn't pivot like it was sitting on a turntable.
That movement gets even further diminished by the distance from the hitch of the trailer to the C/L of the trailers suspension, it's pivot point.
This doesn't make any unstability show up, the undulation caused by over-correction does that. A little touch of the trailer brakes soon ends that though.
I still agree that a 5th wheel is better overall, but it's also got it's drawbacks, some are big ones.
The hitch position ahead of the axle also helps by adding weight to the front axle instead of lightening it like a tag along does.
Best of luck.
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