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Open torsion axle question to RTSmith

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hosspuller
Posted 2017-09-25 6:28 PM (#170699)
Subject: Open torsion axle question to RTSmith


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RT .. is there any practical difference in the starting articulation angle ? say 22.5 down when loaded the arm travels to zero, the arm exerts the most leverage. (hard to soft)
Or when starting from zero, the arm is at max leverage, then traveling up, the leverage is reduced. (soft to hard)
Or, Starting at 22.5 up, as the arm travels up the leverage is reduced. (hard to harder)

It seems to me, the starting angle affects the spring rate in a non linear fashion since the force doesn't change direction around the pivot.

Thanks for your thoughts on this..
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PaulChristenson
Posted 2017-09-26 2:06 AM (#170700 - in reply to #170699)
Subject: RE: Open torsion axle question to RTSmith


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While you are waiting for RT...here is something to peruse...
http://www.boler.ca/2017/05/19/torsion-axle/

The axle arm start angle is one of the primary factors that determines the ground clearance or ride height

The axle capacity is what determines the arm movement...If you put on an axle that has too high a capacity, the suspension will resist moving and again any bump will be sent through the trailer and frame.  Ideally you want the capacity so that the suspension is slightly compressed when the trailer is just sitting, when a bump is hit the suspension compresses and absorbs the impact rather that transferring it to the trailer and frame.

The rubber elastomer will deteriorate with use and age.  As the elastomer deteriorates the axle will start to sag, causing the trailer to sit lower, there can also be movement laterally in the torsion tube which will cause the wheels to toe out, this can cause slight swaying and tire wear. The most noticeable result will be a harsh ride

 

Edited by PaulChristenson 2017-09-26 2:08 AM
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RTSmith
Posted 2017-09-26 8:32 AM (#170701 - in reply to #170699)
Subject: RE: Open torsion axle question to RTSmith


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 I'm sure you have a valid point about some change. But the swing arm's length stays constant, so my ancient recollection of  physics makes me think the force stays the same. But- if you think about it,  to absorb shock by moving up- it also has to move forward which is against the force of the trailer's motion no less. So as you move farther from zero, as the wheel needs to move farther forward it is fighting to do so which would impact spring rate because it is hampered from moving forward and upwards in the arc.

I had a trailer manufacturer's engineer once share that a Dexter Axle engineer had said that torsion axles were originally designed at zero, and worked best at that build. But horse folks needed a lower height for loading, and thus the up angles were developed. As I recall, 22.5 degrees off of zero is as far as they will build, which may allude to your point as well.

But, all in all the torsion set up certainly is the best available at the moment, considering the cost:value ratio. They deliver a consistent ride throughout the range of carrying capacity. I love the air rides, but for the typical user just not practical.

ON EDIT- not sure why the phrase is highlighted. I did cut/paste it, but am not intending to highlight it.


Edited by RTSmith 2017-09-26 8:37 AM
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hosspuller
Posted 2017-09-27 9:09 PM (#170709 - in reply to #170699)
Subject: RE: Open torsion axle question to RTSmith


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RT ... Thanks for your post. So if I had my choice of axle angle ... Zero it is.

But it wasn't when I purchased my trailer. It had a 22.5 up start. Then I added 3 inches of blocking to level the trailer.

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PaulChristenson
Posted 2017-09-28 4:00 AM (#170710 - in reply to #170709)
Subject: RE: Open torsion axle question to RTSmith


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hosspuller - 2017-09-28 12:09 AM RT ... Thanks for your post. So if I had my choice of axle angle ... Zero it is. But it wasn't when I purchased my trailer. It had a 22.5 up start. Then I added 3 inches of blocking to level the trailer.

If you had switched from 22.5 up to 10 down you'd have gotten your 3 inches without adding blocking...
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RTSmith
Posted 2017-09-28 8:08 AM (#170711 - in reply to #170699)
Subject: RE: Open torsion axle question to RTSmith


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You're correct. But it generally isn't a choice. We deal with one mfg. that uses the different angles when building a new trailer to give the desired height. Another one, only orders 22.5 up, and adds blocks as requested. I do understand supply chain issues in production, so keeping only 1 axle makes sense.  

We have dealt with some older trailers that when needing an axle replacement, went ahead and did a different swing angle at the same time as many older trailers sit too low for newer trucks. The axles are all the same price with regards to articulation. So that aspect is handy, providing you are prepared to replace all the axles at the same time.
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PaulChristenson
Posted 2017-09-28 6:43 PM (#170713 - in reply to #170711)
Subject: RE: Open torsion axle question to RTSmith


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RTSmith - 2017-09-28 11:08 AM You're correct. But it generally isn't a choice. We deal with one mfg. that uses the different angles when building a new trailer to give the desired height. Another one, only orders 22.5 up, and adds blocks as requested. I do understand supply chain issues in production, so keeping only 1 axle makes sense.  



We have dealt with some older trailers that when needing an axle replacement, went ahead and did a different swing angle at the same time as many older trailers sit too low for newer trucks. The axles are all the same price with regards to articulation. So that aspect is handy, providing you are prepared to replace all the axles at the same time.

 Yes, I can understand the manufacturing issues, and the fact that simplified inventory provides cost savings for them...but as you and I know, it seems truck beds keep getting higher every year... Thank goodness, we have access to flatbed setups to tow these trailers...
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