12 Comments

  1. David Avard
    August 25, 2019 @ 12:29 AM

    One other factor you didn’t mention is the sensitivity of tandem torsion axles to hitch height (and the axles being level).

    My club has a custom 28′ trailer that the builder unfortunately put the axles in the center of, and some people had no problems towing it and for others it was a nightmare. Someone who works on trailers (for semis) suggested that it was related to the height of the hitch changing the effective length of the tongue (ie: when the trailer was tongue low, the front axle carried more weight and when tongue high, the rear axle carried more weight. This changed the load center of the trailer and made it unstable when tongue low or less unstable when the tongue high.)
    We confirmed some of this by measuring the weight on the hitch at various hitch heights. With a 10,000# trailer, the tongue weight varied by 500# (800#-1300#) over a 6″ variation in hitch heights (3″ +/- from level), with it weighing around 1050# when level.

    I’m sure I didn’t phrase that in correct engineer-speak, but you should understand the idea.

    Reply

    • The Mechanic
      August 28, 2019 @ 4:28 PM

      You communicated the situation, and that’s more important than the “engineer-speak”! You bring up a great point, and you’re exactly right. Thanks.

      Reply

    • James Wohlford
      June 10, 2020 @ 11:27 PM

      Yes you are correct as to hitch/tongue height causing towing problems.
      No matter the axle type… you NEVER want to tow a trailer tongue high.
      You want to be level (Always the best situation as to stability and tire heat/wear as well) or even a bit low in the front, if you have to go one way or the other.
      Otherwise the trailer will always sway all over the road.
      Never tow a trailer high in the front.

      Reply

  2. Travis, KC Slider LLC
    September 27, 2019 @ 4:24 PM

    Love everything in this articular. We specialize in building a product to load and unload cars in the trailer. I also tow a lot of miles each year myself. I have seen and experienced the damage to many different manufactures trailers that use tandem and triple torsion axles. What are your thoughts about putting an air bag on each end of the of the walking beam? My thought is to help spread the load better across the beam rather than concentrate that load at the pivot.

    Reply

    • The Mechanic
      September 27, 2019 @ 4:36 PM

      Thanks for the endorsement. Yes, you can use air bags with the walking beam suspension, but make sure they are linked — as the front one compresses, it puts the air to the back one — so they both stay the same pressure. Yes, that would spread the load. Incidentally, that center pivot is high load, but it’s big & fat — designed to take it. Load is then spread with the underpinning beam between the trailer frame and the pivot.

      Reply

  3. John D
    May 1, 2020 @ 2:50 PM

    Thanks for a great article. I was planning to replace the rough spring suspension on my horse trailer with rubber torsion (which is what nearly everyone recommends) But now I am leaning towards Timbren silent ride. The trailer weighs about 2000# and the maximum load it would ever have would be 2 1500# horses. Though much more likely 1 or 2 1000# horses. The number one priority is smooth ride for the animals. It seems that the Silent Ride would be the best of both worlds. Do you concur?

    Reply

    • Mechanic
      May 1, 2020 @ 4:33 PM

      I like the look of the Timbren Tandem axle Silent Ride Walking Beam Suspension. I’ve never had my hands on one, but I like what I see. Speaking from experience with a different walking beam, that does a great job of smoothing the ride. Good luck with your project.

      Reply

  4. Dave P
    July 10, 2020 @ 9:50 AM

    Firstly I want to thank you for this article. I’m currently in the market for a new race car trailer and see a lot of the tandem axle trailers with torsion axles, so as an ME myself I appreciate informed information like this that cuts through the marketing hype. Overbuilding is common, and a trend I’m noticing is “spread axles” where they move the axles farther apart than you would see on a leaf spring multi-axle trailer, apparently in an attempt to mitigate the single wheel loading problems you mention when traveling uneven roads. How effective is this?

    Reply

    • Mechanic
      July 10, 2020 @ 10:06 AM

      If you can support a long trailer at more separated points, then the structure does not have to be as strong and stiff. So, if the axles load share properly, then “spread axles” are great, but that’s not what I see. As in the article, independent suspension does not make sense for a trailer. Why do people do it? This is my warped opinion: They are trying to make the trailers cheaper and lighter while ignoring that trailers do not travel on even flat ground all the time. I think there’s some amateur hour in the engineering at the source. FEA looks great if you input easy conditions, but as we know garbage in = garbage out.

      Reply

  5. STEVAN J WHITE
    September 16, 2020 @ 2:17 PM

    Question: I have a single torsion axle on my boat trailer. My boat is a 21′ fiberglass center console with a 150 hp Yamaha outboard. The weight means the tires continually look flat though they are properly inflated. The boat pulls exceptionally well as is but I was considering adding a second axle to re-distribute the weight. After reading your article I’m thinking leave well enough alone. A misguided attempt may actually make things worse. your thoughts would be appreciated.

    Reply

    • Mechanic
      September 17, 2020 @ 5:23 AM

      Interesting question. I’d do a few things: 1) Weigh the boat and trailer fully loaded. There are vehicle scales at truck service centers, recycling centers, garbage dumps, etc. 2) Check the weight compared to the axle capacity and the tire load ratings. 3) I assume the trailer came with the boat, so the axle is probably good. Maybe it just needs higher capacity tires? I recommend a load rating that is 20% or so over the actual load. Go a little larger diameter if you have the room.

      Reply

  6. Shawn Simcheck
    October 5, 2020 @ 9:35 AM

    Very interesting Article on Torsion Axles. I just replaced the torsion axles on my 1973 Argosy (Airstream) travel trailer with tandem axles. They lasted 47 years before losing almost all their travel and going lob-sided. Looking at your article, it appears what Airstream did to handle the overloading problem you mention was to totally over-engineer it. The trailer itself weighs 3400lbs- Axles were rated at 2600lbs apiece. 4 Bias-ply tires rated at 2900lbs each. When you consider probably over 400lbs would be in tongue weight- it would be nearly impossible to overload an axle. Even so, I bumped the new Lippert axles up to #2800lbs each. If they last as long as the original; I wont have to replace them until I am 106 years old:)

    Reply

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