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Old 08-23-2014, 04:11 PM   #15
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I don't own either one of these hitches, (though I think I'd like to), and so haven't inspected one of them that closely.

I take it the geometry of the 4-bar linkage is not adjustable? In other words, it's a fixed projection amount? You can't dial it in to put the pivot point where you want it?

A lot of Fifth Wheel setups I've looked at have had the hitch point actually about a foot ahead of the axle.

To me, having it behind the axle just isn't as good. Certainly, any amount you can move it forward of the ball is helpful. But I would want to have it at the axle "pumpkin" at a minimum, and preferably a foot ahead of that.

I've never tried to make a hitch, but I have read quite a few books on auto suspension design and using long arm/short arm "double wishbone" suspensions to move the roll center as low as possible. These hitches are the same science, just rotated 90 degrees.

They really are a good idea, at least to my "P.E. in Mechanical Engineering Geek Brain" way of thinking

Although, I'm still not convinced that a modern version of the "Slimp Dolly" wouldn't be a great and wonderful thing too. I know there are at least two of them being produced right now. If you had one of those with a little electric motor on it, so that when you went to park the rig, you uncouple the tow vehicle and just back it on its own with the dolly....that could be pretty handy for getting into tight spots Not to muddy the waters though...just got me thinking here.

See ya on the road,

- Jim
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Old 08-23-2014, 04:19 PM   #16
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Hensley and ProGlide Questions

As far as fifth wheel installations go way back when I first started doing one ton conversions, the rule of thumb was to put the center of the king pin one inch forward of the center of the rear axle,

Over time and experience I stated inching forward.

Now I put the king pin about 3" in front of the axle center line.

This improves steering stability going down the road and it helps to minimize front end lift of the tow vehicle when starting a heavy load from a stop. ( the second factor is moot with tongue mount trailers)

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The other day I did a very quick and imprecise measurement of the Hensley on my short bed Chevy, on my setup 54" from the ball is very close to the centerline of my rear axle.

The fact that I am opinionated does not presuppose that I am wrong......

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Old 08-23-2014, 10:17 PM   #17
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Originally Posted by JimGolden View Post
I take it the geometry of the 4-bar linkage is not adjustable? In other words, it's a fixed projection amount? You can't dial it in to put the pivot point where you want it?
That's correct, the geometry of the 4-bar linkage is not adjustable, and the "projection" distance is fixed.

Based on the information I have, the centers of the linkage pivots are 7.125" apart at the front and 7.875" at the rear. The linkage bars are 5" between the pivot centers at their ends.

The virtual pivot point is at the point of convergence of lines projected through the left linkage pivot centers and the right linkage pivot centers.
The virtual pivot point lies about 52.3" forward of the linkage bars' rear pivot points when the TV and TT are aligned straight ahead.

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Old 08-24-2014, 03:18 AM   #18
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Reducing the length of the shank with a Hensley or PP does improve handling somewhat. Mainly due to increased weight transfer to the front wheels and a reduction in the effect of the movement due to shank/receiver play. The ride is definitely improved.

With a pp it is hard to move it closer unless you convert the shank to a welded one. On a Hensley the straight shank can be shortened considerably but of coarse only if the heights work out to use a straight shank.

In some cases we have added a second receiver tube below the factory one so that a straight shank could be used. Though this was more to reduce the weight of the shank for the customer the handling was a secondary benefit.

Here is a picture of a straight shank shortened to reduce overhang.
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Andrew Thomson
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Old 08-24-2014, 06:35 AM   #19
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Great information guys! Thanks!

J, that's very interesting what you did with the fifth wheels. I have seen some that were a foot ahead, but most were just a little ahead, just like you came up with.

Ron, thanks for the measurements.

And Andy, with the short overhang on that sedan, a 52" forward projection should put you up near the back seat somewhere. I would think that would really make a huge improvement.

Good stuff!
- Jim
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Old 08-24-2014, 07:49 AM   #20
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Thanks all for you very informative comments. If my future includes another Airstream, there is no doubt I will purchase one of these two hitches. I do have one more question, does anyone know where I might be able to have one of these installed in Houston area? I prefer not to do it myself.

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