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Old 01-18-2006, 08:38 PM   #1
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Leaf Springs vs. Torsion Axles

I just finished reading an excellent book, "Airstream - The History of the Land Yacht". In there, they talk about how Wally Byam went to work for the aircraft industry during WWII when aluminum was considered a "govt. priority" material and not to be "wasted" on civilain travel trailers. They went on to describe how Wally learned many lessons from the aircraft industry concerning simplicity and light weight.

They alluded that he came up with the idea for the torsion axle to reduce parts count and eliminate the need for lubrication.

My question is this: Do the torsion axles really ride any better than the leaf spring types? What year did they make the switch to torsion axles? In the book, they show a 1964 model trailer on one of larger caravans and it's got leaf springs. The major caravans were over by the mid 60's. Most of the big ones were mid 50's to early 60's, and those trailers apparently had leaf springs.

So, do the torsion type axles really ride any better than a properly sprung leaf spring trailer?

It would seem to me that, all things being equal, the leaf springs are less trouble as you don't have to jack the trailer up for fear of the rubber axles taking a permanent set and going up-angle on you.

I realize the claim is that you get independant suspension with the torsion type axles. And I agree that that is true. But, if you have a leaf sprung suspension with the proper spring rate, would the independant suspension really be that superior? They still use leaf springs on our tow vehicles.


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Old 01-18-2006, 09:30 PM   #2
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All springs lose their original ability over time if they have weight applied, leaf types included. If you don't believe me, find a 30 year old car and put a new set of springs on it. The difference in ride and handling is amazing.

The Henschen axle doesn't actually use torsion bars, in the sense that the spring action comes from twisting a piece of metal (like the suspensions in old Porsches and Jaguars, among others). It's compression of the rubber pieces that resist the torques, as far as I can tell. It seems to me that the rubber has to add some damping of the axle twist, and some shock absorption too.

But regardless of operating principle, these axles have other things going for them. They are simple and compact, and that counts for a lot. They aren't hanging out where they can get rusted by road salts either.

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Old 01-19-2006, 06:13 AM   #3
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Torsion springs

You also get the advantage of 4 wheel independent suspension with torsion
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Old 01-19-2006, 06:42 AM   #4
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The advantages of the rubber-rod torsion axle are legion on these trailers. Airstream switched to torsion axles incrementally across the lineup of trailers in 1960-1961. The engineered lifespan of a rubber torsion axle is from 15-20 years depending on the weight applied and the rating of the axle in the application. Many folks have seen as much as 30 years out of them. That is pretty phenominal, I think.

Dexter warranties their torsion axles for five years; their leaf-spring axles for one. That ought to tell you something about the stability and durability of the design of the torsion axle. The fact that there are now a number of manufacturers of torsion axles, and that more and more trailers are switching to them should also be an indication that they are believed to be superior in this application.

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Old 01-19-2006, 06:45 AM   #5
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One of the primary reasons the Airstream TT's tow and handle so well is the 4 wheel independent suspension and their "state of the art" torsion axles.

The many advantages are:

compact design
low ride (handling advantage)
long life

Yes they are expensive but you get what you pay for.
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Old 01-19-2006, 07:23 AM   #6
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Advantages of torsion suspension

Two biggest advantages of torque suspension are:

1. Independent suspension with minimium of unsprung weight. Each wheel can independently react to the irregularities it encounters and follow the road. Much like a sports car.

2. Torque bars do not require solid live axles (with required vertical suspension movement) to be mounted under the trailer. Therefore, the flat trailer floor can be constructed lower to the ground. Thereby lowering the center of gravity of the trailer and make it less tippy and follow the road better. It also presents less of a frontal profile above the tow vehicle, lessening drag. Somewhat negated by the large air conditioners they put on the top of them nowdays.
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Old 01-19-2006, 07:25 AM   #7
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It's interesting to note that a couple of other trailers use this axle. Note most Uhaul tandem axle trailers use torsion axles. That's why they are so low to the ground. In the RV industry Hi-Lo travel trailers also use the torsion axle. I owned an '82 Hi-Lo for 14 years and I remember the dealer telling me that I had the same axle as an Airstream. As a matter of fact during my trip up to Jackson Center in 2001, I had a Hi-Lo set up next to me at the Service Center campground. They were there for an axle alignment.

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Old 01-19-2006, 08:03 AM   #8
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Another advantage is that a good quality torsion axle does not allow for much side to side flex, which would translate into sway, eventually.
Leaf springs do allow a certain amount of side-to-side wallowing, by the nature of their design.
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Old 01-19-2006, 08:08 AM   #9
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Can you change from leaf to torsion on 60 Pacer

I have a 60 Pacer that is sitting lower than spec. Can I replace the leaf-spring axle with a new torsion axle? Do you have to use a Henschen axle? I can get a Dexter axle for half the price from an RV Surplus.

I replaced an axle on a 1977 Argosy Minuet with a new Henschen axle ordered from Inland RV and it was a perfect fit. Job took less than 2 hours. I assume a Dexter axle would have to have the mounting brackets welded on to fit the trailer. Has anyone done this with a Dexter axle? Thanks!
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Old 01-19-2006, 10:57 AM   #10
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Well, I do have a '72 Dodge that's got leaf springs in the back. If it has sagged some, it's not showing it. Not like my Airstream, that has axles that are basically flat to abot 5 degrees up. The trailer looks like a low rider.

My only beef with the torsion type axles on travel trailers is the requirement to have to jack them up all the time. On a Wells Cargo or something like that, you've probably only got 30% of the possible weight normally resting on the axles, so they don't sag so much. With a travel trailer, you've got probably 80-90% of the possible weight on the axles all the time and I think that causes them to sag.

Maybe I'm overstating the problem here. I've only ever owned this one trailer with the dura-torque type axle. Maybe they will go for 20 years without taking the permanent set. And maybe the new axles won't take the set like the old ones did because they have better polymers to make the elasic cords from. I don't know.

I've never seen a leaf sprung trailer, though, sag to the point that my Airstream has. My axles are definitely shot. My granddad has a '58 Airstream with leaf springs and it sits up high just like it did 48 years ago.

Just wondering if the dura-torques really do ride that much better. The book implied that Wally went to that axle for simplicity rather than performance. Just trying to verify.

That was an excellent point about the side to side motion. You'd have to use a panhard rod to get that same sway resistance on a beam axle.

It'd be nice if Dexter or somebody put shock mounts (maybe they already do unbeknownst to me) on the swing arms such that you could put vertical mount air shocks on there. When you get to where you're going, just pressureize the shocks from an internal switch. When you want to hit the road, depressurize them. The airshocks could relieve the load on the rubber cords.

It would be relatively straight forward to convert from leaf springs to a dura-torque. It may require a little cutting and welding, but nothing major at all.
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Old 01-19-2006, 12:59 PM   #11
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I'd be shocked if your 72 Dodge wouldn't feel completely different with new springs, assuming it still has its originals.
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Old 01-19-2006, 01:16 PM   #12
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Has anybody done double wish bones with coil springs on a trailer? That would be the true A-Ticket. Awful lot of trouble to go to on a trailer though. That's usually reserved for true performance cars.

I've also got a '65 Plymouth Sport Fury. I did put new springs on the back, but that was because I went to a different rear. It wasn't sagging when I changed it. It's got the original Chrysler torsion bars up front, but they're adjustable for height so I'm not sure about sag on them either.

I'm looking to have a completely new frame built. The supplier that does it normally uses leaf springs. It'd be a logistical nightmare for me to get a set of dura-torques and put on this new frame. However, if it's truly worth the trouble, I'd do it.

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