Chucking?

richardcoxid.. You are correct about chucking. A software simulation using vector analysis is what an engineer would use to demonstrate it on a computer. It would take into account truck/trailer, speed, weight, harmonic/phase shift distribution, spring rate/dampening as well a leverage on the fifth wheel in three dimension which would be interesting to watch on a monitor. The vector sum would result in a back and forth movement of the truck. The pin box leverage on the truck is much different than a tow trailer which is the reason fifth wheel trailers call it chucking and tow trailers call it porpoiseing.
Chucking generally can not be compeltely limited unless the compenstion is very precise which is impracticle for all highways conditions and trailer/truck criticl dampening charactoristics. It can be minimized with some of the 5th wheel solutions like MorRide and TrailAir.

In my mind this is what happens- Chucking

Assume that you are going down the highway in a steady state condition. Level ground, constant speed, smooth pavement etc. this would take a constant amount of power (energy). Now you come to a concrete slab that is say 1 inch higher than than the previous slab.

When the front wheels of the TV contacts the higher slab the front of the TV has to raise which also compresses the front springs to absorb the 1 inch change. It takes energy to raise the TV and to compress the springs (i.e. the TV is going up hill). This energy is subtracted from the energy that is maintaining the constant speed which momentarily slows the TV. At the same time the RV momentum is pushing the RV ahead, Chucking! The same thing happens when the rear wheels of the TV contacts the higher slab, Chucking!

When the RV tires contact the 1 inch higher slab the same thing but opposite happens, the RV momentarily slows while the TV is continuing to maintain the constant speed. Chucking!

When the TV comes down off the higher slab the TV momentarily gains speed (i.e. It is going down hill) while the RV is maintaining your constant speed, Chucking!

When the RV comes off the higher slab, same thing except the opposite- The RV momentarily speeds up while the TV is maintaining constant speed, Chucking.

Of course the more slop there is between the hitch pin/hitch jaws and in fact the whole hitch assembly the worse the Chucking. From some of the TDR comments it seems that some outfits are worse than others. RV springs, shocks and tires probably also enter into "Chucking" but the basic problem is the unevenness (chuck holes) of the pavement.

I am sure that some member that is more of a mathematician than I am could calculate the energy gain/loss for say a TV with a 3,000# front axle/ 5,000 rear axle weight and a RV with a 10,000 axle weight.

A potential problem would be with the hitch. You may have to bug the hitch manufacture to come out and check out the hitch.
Once you cucking problem is under control you may want to consider a TrailAir pin box. Get the right one and it sofens the trailer up and down motion, as well as the front and back motion. I have one and it really works.
ken

Sabretooth007 wrote:
For what its worth in my opinion, the problem is created by poor manufacturing, the 5th Wheel axels are in the center of the trailer, which causes an easy up down movement. In retrospect a semi trailer, Horse trailer and the like have their axels at the rear which causes less up and down movement. Their is also the question of how the trailer is loaded and its weight plus levelness with the tow vehicle. A trailer which is high at the front (not level) affects the center of gravity and in turn having a poor center of gravity causes driving and stability problems. Also fresh water tanks don't have baffles so any movement of the trailer will cause the water to move in all directons (same with black and grey tanks)

One of the easiest ways to correct the problem is level the trailer to the truck, and slow down, 55 mph is a good speed as noted driving CA..
And if you don't want to slow down then don't complain..

I think "chucking" is a back and forth, jerking motion and not an up and down motion. That's why I don't think truck or trailer suspension has much to do with it. Shocks, springs, and air bags certainly has effect on up and down movement of the suspension/axles but won't have much effect on the back and forth movement of chucking.

For what its worth in my opinion, the problem is created by poor manufacturing, the 5th Wheel axels are in the center of the trailer, which causes an easy up down movement. In retrospect a semi trailer, Horse trailer and the like have their axels at the rear which causes less up and down movement. Their is also the question of how the trailer is loaded and its weight plus levelness with the tow vehicle. A trailer which is high at the front (not level) affects the center of gravity and in turn having a poor center of gravity causes driving and stability problems. Also fresh water tanks don't have baffles so any movement of the trailer will cause the water to move in all directons (same with black and grey tanks)

One of the easiest ways to correct the problem is level the trailer to the truck, and slow down, 55 mph is a good speed as noted driving CA..
And if you don't want to slow down then don't complain..

Best method to minimize "chucking" is to make sure your trailer is frame level when towing, weight is properly distributed, and the trailer suspension is fully functional with some type of energy dampening system (shocks, air bags, cushioned equalizers).

Many, many trailers have no suspension energy dampening systems(cheap OEM builders)-these trailers will have a propensity to chuck and have other poor handling traits because a harmonic cycle gets started and doesn't stop. These harmonic cycles are what you are feeling as chucking.

IBcarguy wrote:
I agree that masking the symptoms with a air or rubber pinbox is not correcting the problem. However, if I were to have tried every remedy suggested out there, it would have cost THOUSAND$+ and I still wouldn't be too sure what the "remedy" was. It may be a combination of things that cause this, not just one thing. Anyway, for me the $475 MORryde pinbox made enough difference in the ride characteristics that I can now tow without jerking my guts out and that's all I wanted in the first place. I'm sure it still chucks but I just don't notice it anymore.

That makes a lot of sense :-) BTY there is no cure for Chucking....

I agree that masking the symptoms with a air or rubber pinbox is not correcting the problem. However, if I were to have tried every remedy suggested out there, it would have cost THOUSAND$+ and I still wouldn't be too sure what the "remedy" was. It may be a combination of things that cause this, not just one thing. Anyway, for me the $475 MORryde pinbox made enough difference in the ride characteristics that I can now tow without jerking my guts out and that's all I wanted in the first place. I'm sure it still chucks but I just don't notice it anymore.

Denny & Jami wrote:
To the OP if you want to get ahead of the problem when you buy your 5th wheel get it with shocks and Mor/Ryde RE equalizer from the dealer. If the trailer doesn't have something like that make it part of the deal.

Denny

No. I do not agree with masking the problem. However, I do agree with others in that it is very important to find the real cause for the chucking. There is a problem somewhere, and you should find it. If you install an air hitch or TrailAir hitch. You may be masking the problem, but not solving the problem.
As I said on a previous post I had a real problem with chucking on my 5th wheel, and found out (after extensive searching) that the hitch (Reese 20K) was a little loose. Not that you could find it, but it was there. Reese put on a new hitch and my problem was solved. THEN I put on a better pin on the 5th wheel to really make the ride smooth (TrailAir).
You may have a hitch problem

So tell me how everyone's pet theory relates to this? https://www.youtube.com/watch?v=jDDQ4oMGeV4

This video is an extreme example, but some road surfaces and expansion joints do the same thing...