soft ride fifthwheel hitches

[Dave e Victoria]

Rich, I am never in favor of adding second order spring mass systems on top of each other if they have similar natural frequencies. I think this is the case with the systems that add an air suspension uncder the fifthwheel hitch. To me this is just asking for a new natural frequency not too different from the old. To be sure, there are nonlinearities that happen when springs are completely depressed or axles bottom out. But, I believe one should start with a good linear system design and then deal with extremes. I would love to model this mathmatically and see if we could actually see what is happening. In addition, anything we can do to keep the suspensions within range linear behavior will help these systems perform to their best.

I'm going to do a bit of a brain dump here. If I am on to something, help me out. If it comes across as just more technobable, let me know. I find this whiole discussion fascinating.

Given the current knowledge, lets consider a couple of facts. The fore aft action called chucking is a result of angle changes coupled through the off alignment connection between the truck and trailer. The mass field of the truck and trailer are coupled at this connection. The mass we are talking about is on the order of twenty or more thousand pounds. The other sytem in play is the vertical suspensin over the three (or four) axles at work. Here we are dealing with masses more on the order of five to seven thousnad pounds. It would seem desireable to avoid anything that added to the translational couping of these systems. In addition, it would seem like the 4 to 1 difference in the mass behavior of the two axis suggests that the needs and corrections in the two systems are different.

This is not to say that a careful analysis of each situation might not reveal a peculiar solution having equaly peculiar results. Unfortunately, such solutions likely imply very suboptimal results for other situations. In other words we need to look for simple, generally and generically beneficial solutions

Bottom line, I think we should deal with vertical ride issues in the vertical ride systems. This is springs, airbags, shock absorbers and tire pressures (this includes the trailer axles) as well as looking at weight distribution over each of the vertical suspension systems. Then, deal with the fore aft chucking effect in the fore aft direction with elastic systems at the foreaft connection.point. Actually, in developing this arguement, I have come to another conclusion. That is, it is better to optomize the vertical suspension before addressing the fore-aft connection. This conclusion comes about from the simple fact that if the truck trailer connection were to remain level in all conditions, there would be no chucking effect.

In a seperate note to Bob Grissom (firetrucker) I suggested it might be interesting to try the modeling exercise. Since then, I have found a couple of industry colleagues who have rather intimate knowledge of the behavior of suspension systems. I would be very interested in getting a small group together over the internet to discuss and develop such a model. The ultimate goal would be to reduce the findings to a set of understandable observations more helpful to our membership than these sort of intuitive speculations.

Again, sorry about the verbosity
Dave

[richfaa]

Comment on the Trailer saver hitch. Dropped by CW this morning to ask a few questions about hitches..They have the trailer saver hitch in the catalog for 1799.00 plus installation.By chance a fellow in the waiting room overheard our conversation.He was there with his 04 Long bed Chevy and Hitchhiker and he HAD the trailsaver on the truck. he took me out for the tour and when he was done I asked him ..so..how do you like it...his reply was..well it does what it is advertised to do..however..there are better ways to spend 2K.He did not feel he got the expected results for the $ spent..just one opinion but one that carries a lot of weight .

[Dave e Victoria]

Rich,
I think $1800 to $2000 is in the ballpark for putting 4 wheel independent suspension on the trailer axles. Some here on the forum have gone that route and have given good reports. This, to me, is an excellent place to improve trailer ride. Most trailers, Montana included, have really poor suspensions. They have limited freedom of movement (like 3 inches) and tend to be overloaded which reduces freedom even more (to an inch or less in many cases). Dragging this arrangement over mildly rough roads will definitely result in the kinds of effects you were describing above.
Dave
PS: The cambridge does not have independent suspension but does have a suspension that is far superior to the standard Montana suspension. I suspect it is responsible for much of the good ride we experience.

[richfaa]

Since we have nothing and a few months before we will have the camper we have the advantage of doing some homework/ research
and devising a plan of attack on what we feel is a critical issue (suspension) since we will be doing a lot of traveling.We agree that the vertical issue(up and down movement is the best place to start and the cause of most of the problems..That is why I had all the ??? after airbags/mor-ryde. Our previous TV was a 1/2 ton chevy pulling a 32 ft Terry TT . We solved the up and down motion with heavy duty shocks and air bags.It removed 90% of the vertical motion. My thought was that in installing ther Mor-ryde hitch and air bags we are doing the same thing twice, Howver all this equipment is far to expensive to experiment with. Now I am not a engineer of any kind. In my previous life my title was "Engineering technician" which means that I took two years of really heavy math, which is my weakest subject and I did not enjoy ,but the title got me some better jobs.My specialty in the National airspace system was electronics..I am just a old Electronics technician but I do have a little schoolen and having worked with engineers most of my working life I can sort of translate what they say into things I can understand. I would jump at the chance to be part of a work group on Rv suspension systems..

[Dave e Victoria]

Rich,
Excellent.
I will prepare a seperate subject on the forum later tonight and see if we can entice a few more.
Dave

[Montana_4391]

Although I don't have experience with air hitches, I have lived in Alaska all my life and the roads up here can be some of the worst you will ever come across - many of which are barely considered "paved" (some not even that good!)

My recommendation is to talk to jrgwdenner about what they used - they just completed a pretty extensive tour of Alaska and I'm sure they came across more than one of Alaska's infamous roads in their travels.

[jrgwdenner]

Funny that I noticed this thread right after your comment, ak traveler. I can't join in on the technical aspect of this thread but I will share our experience. We added the TrailAir hitch just before we started our two month drive through Canada and Alaska. And we're glad that we did. The roads are notoriously bumpy and we feel that the hitch saved wear and tear on the frame of the Montana as well as contributing to a more reasonable(comfortable) ride through Alaska. Nothing will take away all the bumping and chucking movements, but we do feel that the TrailAir hitch helped a lot. We had very little flying missles out of our cupboards. Cost? Less than $1000.00.