How to choose a shock-absorbing Hitch ?

[femuse]

We had started a similar discussion in "Axle, Brakes, Wheel & Tires" and wyhjr started one in "On the Road".
Along the way, both threads took a lot of side trips. On many bumpy roads.

We think it may be a good idea to start a new thread concentrating on the more technical aspects of this problem. (the 2 original links are found at the end of my note).

Let's start again, then:

We are replacing our 29 ft Airstream with a 32 footer. Trailer weight is going from 4,850 lbs to 6.350 lbs. (dry weight), a minimum gain of 1,500 lbs. This has us wondering if we need to look into major changes to our hitch.

The tow vehicle is an International 4700 series (Medium Duty) truck. We use a fabricated hitch with a 2 inch receiver mounted with (what I think is) a Drawtite version of a Reese head. We use 1,000 lb. Dual Cam leveling bars.

The truck itself, is equipped with air ride suspension and we load it, including the tongue weight of the trailer, to about 25 or 30% of its 12,000 lb capacity. This means the suspension is underloaded. However, the Air Ride suspension adjusts the ride height to the same level regardless of the load. It occurs to me that this conflicts with the leveling function of the Dual Cam bars. Now I am thinking that I might want to dispense with the leveling and use only the sway control. A service person at an AS dealership tells me that even this may be unnecessary with a rig like ours. He has seen several trucks in the same class as ours, pulling AS, without any special hitches. (don't know more, they were just going trough).

Originally, we towed with a one ton Chevy Van, but the inadequate brakes encouraged us to look for something more capable. The 4700 certainly is capable, but from the beginning I've wondered if a tow vehicle in this weight class, with its stiff (and underloaded) suspension might not deliver too much shock to the tongue of the trailer. That in mind, we've started to look into some sort of shock absorbing hitch, but we haven't talked to people who use that.

We have already tracked down 3 makers of air hitches for TT ( Advanced Air Hitch Inc; Air Ride Hitch, Inc. and My Air Hitch), at a cost of about $1000. We will be looking as well into CaseDMI as mentioned by John HD (thanks again) and Andy Inland RV suggestion about carnival people.

I'd be please to hear any opinions or ideas regarding any of the points I've laid out. Especially if anyone knows anything about shock absorbing hitch and the need for it.

Thanks,
Mike



Any of you clowns know anybody working in the Circus ?

Chantal


"tires balancing ...and more": http://www.airforums.com/forum...&threadid=3679

"towing dread": http://www.airforums.com/forum...&threadid=3634

[Pick]

Chantal & Mike:

I believe that the DMI hitches absorb shock in the back and forth or horizontal plane. They do have some of these at Tractor Supply, but I do not know the ratings. I think the RV type shock/air rides absorb in the vertical plane, which is what I believe you are looking for, and are, of course the most expensive. I think if your truck has air ride suspension on the back axle you would be ok. If it was mine, I'd run it for a while and see what happens. How did your other AS fair towing this way?

[3Ms75Argosy]

Chantel,
I did recently read in Trailer Life magazine about the "Blue Ox" hitch system. It did have two springs on the trailer that suspend the hitch, isolating the trailer / truck combo to only verticle movement. It seems like the Case DMI hitch moves laterally (horizontal) only? The drawback that I noticed with the Blue Ox was that I think you'd have to relocate the propane tanks closer to the hitch, increasing tongue weight. However, on your rig, that probably wouldn't be an issue.

While not a mathmatician (I did stay at a Holiday Inn Express though....), I would think you would not need the weight equalizer. The idea of the springs is to put even weight front to rear of the truck, eliminating rear sag. In your case, I think the more weight over the rear, the better the ride and less jolts to the trailer. I doubt the air suspension would even know there's a trailer back there without the bars.

Out of curiosity, what kind of mileage do you get? Gas or diesel?

P.s. - Cirque de Solie (sp?) came to town, excellent show. Their form of "air ride" will get you shot out of a cannon! Big semi's, no airstreams noted.
Marc

[femuse]

Thank you, 3Ms75Argosy & Pick

We had heard about the "Blue Ox", I think I just pased a discussion on the RVnet forum. I will look into that too.
It looks like you both agree about the DMI not being the solution to our problem.
Mike is pretty sure about the leveling bars fighting the effect of the air ride.
We used the van from 1992 to mid summer 2001 (starting with our 25', then the 29' in 1996). With the truck, we noticed our 29' bouncing in the back more than with the van. In front and kitchen, very good.
Maybe we shouln't use the bars then. It's sometimes difficult to know if the problem comes from the truck or the bad roads at high speed.
A Goodyear dealer replaced a tire, and us being "young and inexperienced" we believed his "you don't balance TT tires" (Goodyear's web site has instructions for its distributors about the necessity to balance TT tires. I know were this guy lives, Syracuse, NY). This was one week after we started to use the truck.
SO ? I think this really screw-up our data.
The other problem was: the 29' is a rear bath. [somebody should tell Andy that I have already read everything on the subject: "it's not the rear bath fault, it's the balancing,...."...... please....I heard it.....This one too....]

what kind of mileage do you get? Gas or diesel?

we get about 9, diesel, unfortunately A/T . Our van (1990 G30, 454, A/T, 145" wheel base) gets about 10 without the trailer, about 7 with. When towing, we had to use mid grade gas, premium in mountain. An a quart of oil/200 miles. Chevy told us that was normal ?!?! (even when we got it in 1992)
Le Cirque du (or de?) soleil, if they are pulling white box TT and they don't fall apart, I guess an AS could make it too. I believe smaller circuses may use older crapier trailer though and may be a better study. I don't thing they are gonna be easy to catch.

Thanks again,

Chantal

[john hd]

mike/chantel

since it sounds like the dmi may not be what you want, consider having some one custom fabricate one.

then you could design it for your truck and possibly incorporate both the up and down AND the in and out springs!

with the long distance from the rear axle to the hitch you would have plenty of room.

my 4700 international at work has regular springs with overloads on it. it rides nice, but then it scales out around 18,000 lbs. (42 foot bucket truck)

like pic sez, with the air ride, run it for a while and see what happens. i certainly think you don't need the load bars. i hardly need them on my 2500 chevy!

john