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06-08-2017, 02:32 PM
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#1
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Rivet Master 

1956 22' Caravanner
Don Pedro Island
, Florida
Join Date: Apr 2013
Posts: 623
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Why Shocks on a Torsion axle?
Trying to understand why install shocks on a torsion axle. My understanding is that torsion axles are designed to be shock free.
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06-08-2017, 02:50 PM
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#2
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Half a Rivet Short
2017 30' Classic
2022 Interstate 24X
Carlisle
, Pennsylvania
Join Date: May 2017
Posts: 16,746
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Hi
Simple answer: With a torsion setup, you get a very fixed amount of shock absorption (or damping). Adding a real shock to the mix lets you better control the rock and roll of the trailer.
Bob
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06-08-2017, 02:57 PM
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#3
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Rivet Master 
1973 21' Globetrotter
Houston
, Texas
Join Date: Sep 2009
Posts: 3,389
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The torsion axle replaces a metal leaf or coil spring with a rubber one, but it is still springy. The shock absorber is basically a motion dampener, thus it takes the "bounce" out of the system.
A torsion axle may be less bouncy than a metal spring, but the system can still benefit from additional dampening. If you look around on these forums, there are several threads debating whether a shock absorber makes any difference, and there are definitely some believers out there who can attest to the difference they see in handling with a functioning shock absorber in place.
good luck!
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06-08-2017, 03:04 PM
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#4
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Rivet Master 
2014 20' Flying Cloud
Sag Harbor
, New York
Join Date: Jun 2015
Posts: 17,523
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A lay non-expert comment -- probably unclear -- but here goes . . .
Shock absorbers and torsion axles perform different functions.
Shock absorbers dampen according to the rate of acceleration of the moving part, the trailing arm of the axle/wheel assembly. If it moves very slowly the shock absorbers will not dampen the action much. Quick movement gets dampened.
The torsion axles are just like regular springs, in that they resist motion in a linear fashion according to the distance of movement. The more the tire/wheel moves up from road force, the greater the resistance from the torsion axle (or spring in the normal set up). It really does not matter how quickly (acceleration) the motion occurs.
If the road action results in fast motion, the shock absorber kicks in to dampen the action, in addition to the axle's linear resistance.
Sorry -- this makes sense here!
Lay comment over . . .
PS -- Just noticed Post #3 by Belegedhel -- similar IMO.
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06-08-2017, 03:07 PM
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#5
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Rivet Master 

1956 22' Caravanner
Don Pedro Island
, Florida
Join Date: Apr 2013
Posts: 623
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Quote:
Originally Posted by uncle_bob
Hi
Simple answer: With a torsion setup, you get a very fixed amount of shock absorption (or damping). Adding a real shock to the mix lets you better control the rock and roll of the trailer.
Bob
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Okay I understand that much (thanks). I guess the next part of the question is the benefit worth the extra fabrication and cost.
If you listen to the axle manufacture they say thats the reason you have the torsion axle.
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06-08-2017, 03:14 PM
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#6
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Rivet Master 
2014 20' Flying Cloud
Sag Harbor
, New York
Join Date: Jun 2015
Posts: 17,523
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Quote:
Originally Posted by islandtrader
. . .
If you listen to the manufacture they say thats the reason you have the torsion axle .
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It would be interesting to know where you saw this, as Airstream has not offered such an overview that I know of.
As I just posted, the torsion axles and the shock absorbers have different functions IMO, and our AS's benefit from having both.
A trailer without a torsion axle, or without shock absorbers, would probably not work all that well, under all real world road conditions, including off-road.
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06-08-2017, 03:20 PM
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#7
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Rivet Master 

1956 22' Caravanner
Don Pedro Island
, Florida
Join Date: Apr 2013
Posts: 623
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Quote:
Originally Posted by OTRA15
It would be interesting to know where you saw this, as Airstream has not offered such an overview that I know of.
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Sorry for the confusion ...axle manufacture and not Airstream.
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06-08-2017, 03:36 PM
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#8
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Rivet Master 
2014 20' Flying Cloud
Sag Harbor
, New York
Join Date: Jun 2015
Posts: 17,523
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Thanks, I would still be surprised if an axle manufacturer said not to use shock absorbers. I see on other forums posts about adding shocks to torsion axle assemblies for off-road use -- FWIW.
PS -- Our FC20 has small shocks forward of the wheel assembly.
PS2 -- nice rebuild thread!
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06-08-2017, 03:56 PM
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#9
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Rivet Master 
1988 25' Excella
1987 32' Excella
Knoxville
, Tennessee
Join Date: Oct 2010
Posts: 5,246
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Actually Dexter does say that shocks are not needed with their axles and they manufacture them without the mounts. So I think at least one manufacturer does say that.
I would want shocks added to mine.
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06-09-2017, 07:12 AM
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#10
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Half a Rivet Short
2017 30' Classic
2022 Interstate 24X
Carlisle
, Pennsylvania
Join Date: May 2017
Posts: 16,746
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Quote:
Originally Posted by OTRA15
It would be interesting to know where you saw this, as Airstream has not offered such an overview that I know of.
As I just posted, the torsion axles and the shock absorbers have different functions IMO, and our AS's benefit from having both.
A trailer without a torsion axle, or without shock absorbers, would probably not work all that well, under all real world road conditions, including off-road.
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Hi
Well, they *used* to make them that way. Our original (1930's vintage) trailer was set up with a conventional axle and no shocks. I never rode in the back. I'm sure it was quite a bumpy ride  Needless to say, it was not an AS. It also did not have trailer brakes. That lead to it's retirement long long ago.
Bob
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06-09-2017, 07:16 AM
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#11
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Half a Rivet Short
2017 30' Classic
2022 Interstate 24X
Carlisle
, Pennsylvania
Join Date: May 2017
Posts: 16,746
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Quote:
Originally Posted by islandtrader
Okay I understand that much (thanks). I guess the next part of the question is the benefit worth the extra fabrication and cost.
If you listen to the axle manufacture they say thats the reason you have the torsion axle.
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Hi
Matching shocks to a given vehicle is a bit complicated. You need to get things right for them to do you any good. Getting it wrong can damage things. You can use the "try it and see" method. That may involve buying quite a few shocks. If you are handy with mechanical analysis software (and have a few months to spare) you can get pretty close.
Bob
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06-11-2017, 07:47 AM
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#12
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Rivet Master 

1956 22' Caravanner
Don Pedro Island
, Florida
Join Date: Apr 2013
Posts: 623
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Quote:
Originally Posted by uncle_bob
Hi
Matching shocks to a given vehicle is a bit complicated. You need to get things right for them to do you any good. Getting it wrong can damage things.
Bob
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I tend to agree with you. I remembered when I was building street rods and trying to get the shock thing figured out. Even with the manufactured aka. Mustang II Heights suspensions...We had a lot of trial an error. For the time being I will stick with what I have.
However let me say that all the discourse really adds to the knowledge base.
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06-11-2017, 12:02 PM
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#14
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Rivet Master 

2017 26' Flying Cloud
Tampa
, Florida
Join Date: Feb 2017
Posts: 8,118
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The torsion axle provides spring.
Shocks help tame the spring so the wheels stay in contact with the road.
Many years ago, as a teen, my dad's car had bad shocks, so I thought, "Rather than listen to the clunking, I'll just take the bad shocks off."
Ha, the first stop had me bouncing up and down until I thought I'd get seasick.
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06-11-2017, 12:14 PM
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#15
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Rivet Master 
2008 22' Safari
Spicewood (W of Austin)
, Texas
Join Date: Mar 2015
Posts: 3,021
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Shock absorbers don't actually absorb shock. They prevent wheel "bounce". If you've ever driven down the road and seen another vehicle's tire bouncing like a basketball dribble... it's the shock absorber which has failed. Good shocks will keep the wheel on the pavement.... and improve braking thereby....as well as directional-control.
Torsion axles do not suffer from the same harmonics of spring-rate as other axles do, so they rarely need shock absorbers. If your trailer was designed with shock absorbers....keep them in good order and replace them when necessary.
If yours was designed without shock absorbers, it's unlikely you will benefit from adding them ...and may damage your trailer and/or suspension if adding them without the benefit of proper engineering support. Trial and error will likely prove expensive and maybe even damaging.
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06-12-2017, 03:50 PM
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#16
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Half a Rivet Short
2017 30' Classic
2022 Interstate 24X
Carlisle
, Pennsylvania
Join Date: May 2017
Posts: 16,746
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Hi
If we want to get very complicated about it, shock absorbers add damping to the system. They lower the Q (typically below 0.707) of the spring + mass. Their damping function acts for either extension or compression. Indeed the "how does it act" is why there are so many different shock absorbers. A spring + mass without a shock absorber would wobble back and forth for quite a while after energy is supplied by a bump. (They convert the energy to heat slowly). Shock absorbers speed up the energy to heat process.
Bob
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