18 Comments

  1. leo
    February 6, 2019 @ 6:39 PM

    Thank you so much for sharing your information!

    Reply

  2. Ryan D
    March 14, 2019 @ 3:23 PM

    I am a big fan of this website. The knowledge you share here is very valuable to me. Thank you!

    I have a question that is more rooted in academic curiosity than practical application. Everyone discusses “tongue weight”. However, in a physics sense, is actual weight on the tongue the objective, in order to achieve stability? Or is the objective more about locating the trailer’s centre of mass (including the load) relative to the major pivot points (axle & coupler)? (If the latter, I understand that it would be translated to tongue weight rules of thumb, given average tongue lengths, so the layman can easily approximate the centre of mass and achieve a stable condition.)

    If it’s more about centre of mass location, is the primary factor the distance from the axle, or distance from both primary pivot points (axle & coupler)?

    As a thought experiment to illustrate my question, let’s imagine an 8′ utility trailer with an axle set a little back from the centre of the bed, with a tongue length of 4′, loaded evenly, with a result of 15% of the weight being on the tongue at the coupler. Now, ignoring the weight of the tongue material itself, let’s imagine we extended that tongue to be 12′ long. If I remember my math correctly, the weight on the coupler would be cut roughly in half; probably around 8% now. However, the centre of mass would still be the same amount forward of the axle. Would the second case be likely to tow stably, despite being outside the normal rule of thumb? (Let’s also ignore the other inherent stability benefits offered by the longer tongue, for the sake of this thought experiment.)

    Reply

    • The Mechanic
      March 14, 2019 @ 6:01 PM

      Oops, now you’re thinking. We can’t have that! — But these are great questions. How much do you want to know?

      Let’s play with your experiment. Let’s take your trailer and and move the load back so there is Zero tongue load. Now, as you drive your car goes over a bump. That pushes the tongue up fast, which throws the load back, which makes the trailer want to tip back (because the load is now behind the axle). As your car comes down from the bump, the process goes the other way. That back and forth switching causes some weird dynamics for the driver and he feels like it is “bucking”.

      So making the tongue (your 12′ experiment) long does work like you say, and actually it makes the bump feel (to the trailer load) like it’s half as high. A long tongue has other nifty advantages too — within reason — though your 12′ tongue will create other issues.

      All of this is part of why we avoid trailers with really short tongues.

      That’s the straight line dynamic. There’s much more to it. (Edit, new article on tongue length is https://mechanicalelements.com/correct-trailer-tongue-length/ )

      Reply

      • Ryan D
        March 20, 2019 @ 10:06 PM

        Leading me further down that thought experiment was helpful. By continuing to follow that though, I think I got some clarity: it’s more about the centre of mass and its location relative to the trailer axle, at least for straight-line dynamics. Brilliant, thanks!

        I relish the idea of an article that delves deeper. I’ll keep my eye out!

        Reply

    • nick hurst
      July 27, 2019 @ 5:01 AM

      Having built several trailers, a 6 x 4 single axle, an 8 x 5 tandem load sharing axle, a 10 x 5 tandem load sharing axle and two car trailers with 14 1/2 x 6 1/2 feet decks, 6 1/2 feet draw bars, tandem load sharing axles, all performed to expectation all axles were set no more than 1 inch aft of the deck centre, the difference between mine and others was that all of mine had considerably longer draw bars. All but one had no more weight on the draw bar than i could lift, for two very good reasons, excessive draw bar weight destroys the jockey wheel over time and renders the trailer almost impossible to manoeuver single handed and buries the jockey wheel in your just laid lawn. The trailer with more draw bar weight was my first car trailer I built to take my sprint car around, the reason for the excessive draw bar weight was that a cover was built from the front of the first axle up to half of the draw bar length, in the covered area were about 500kg of spares and tools. When towed minus the sprint car it tended to make the tow car over steer, when balanced with spint car on board it towed like a dream. My point being , have a good long draw bar, just enough weight on the ball to prevent bucking and ease of handling when empty, draw bar weight has little to do with handling, it is more the distance from the load centre to the tongue centre verses road speed. Incorrect weight distribution caused by placement, load shift, aerodynamic factors are the X factors and are probably responsible for as many if not more catastrophes than axle placement. Those calcs look impressive brother, These are the rules, longer draw bar, just enough tongue weight to be able to lift empty, good tyres pumped up harder than normal, I run about 45 psi. and place the load just forward of centre of the axle group, it’s just a trailer, KISS.

      Reply

  3. Will
    June 24, 2019 @ 6:15 AM

    I’m trying to build 48’ gooseneck trailer would like some information on this build

    Reply

  4. Autorama-7
    July 23, 2019 @ 9:23 PM

    Related to the earlier post about tongue length. I was looking at a trailer design with a 36 degree A frame coupler and calculating that changing the A frame coupler angle to a commonplace US 50 degree version reduces the length significantly but only has a small impact on tongue weight. From 10.7% to 11.5% in this case. (Ignoring the impact of the reduced mass of the shorter A frame for simplicity’s sake). (By contrast we are familiar that moving an axle (positioned close to the C of G) a matter of inches generates a significant change in tongue weight). I have read that the longer A frame of a narrower angle version gives greater dynamic yaw stability. Does this stability benefit outweigh the negative impact of the associated slight relative deterioration in hitch weight?

    Autorama-7

    Reply

    • The Mechanic
      July 25, 2019 @ 8:38 PM

      Interesting question. Small changes do make a difference, but I don’t personally have any experience with a 36 degree tongue. I doubt the angle has as much to do with it as the length. Just a guess.

      Reply

  5. Autorama-7
    July 28, 2019 @ 4:54 PM

    Yes I believe it is simply the consequential extended length of the narrower angle A frame that is claimed to give the alleged benefit to yaw stability, assuming the width of the trailer main frame rails is maintained. I don’t think there is any magic claimed in the angle used per se.

    Reply

  6. Gary Ford
    September 5, 2019 @ 3:03 PM

    Great article on axle loading. Thank you for very clear information.

    I understand what the end result needs to be in these calculations, but i am curious about the relationship of major weight items loaded on the trailer in relation to their distance from the axle.
    For this conversation lets assume a 30′ trailer with large permanently fixed water tanks that contain exactly the same amount of water.
    I see to extreme possibilities that could result in exactly the same tongue weight and i am curious if this matters.
    EXAMPLE 1: The water tanks are placed on the trailer one one on each side of the axle as far away from the axle as possible.
    EXAMPLE 2: The water tanks are place on the trailer one on each side of the axle as close to the axle as possible.

    If the tongue weight is exactly the same in both examples, how will the trailer handle in both examples.

    Thanks,
    Gary Ford
    Texas

    Reply

    • The Mechanic
      September 9, 2019 @ 5:46 AM

      Some of your answer is in this article about tongue length. In straight line action handling won’t be much different, but in dynamics, Example 2 will “feel” heavier because of the inertia moving the load in teeter-totter, and turning. Example 2 will be more pleasant to pull.

      Reply

  7. Jay
    September 18, 2019 @ 6:54 AM

    Thank you so much for these formulas. I work for a company that builds trailers. They did the lazy man way and used the 6″ to the rear from center as their go to setting. I will be designing trailers more accurately and safely now using your method. Cheers

    Reply

    • Dennis Ferderer
      November 7, 2019 @ 5:23 PM

      I have been lead to believe that the axle should be set back on the left side about a half inch from the right side to make turning better. What’s your thoughts on this.

      Reply

      • The Mechanic
        November 7, 2019 @ 10:18 PM

        Do you race NASCAR? I think it would work great if you always turn Left. Otherwise, the trailer will run behind you like a dog. If you’ve ever watched a dog run, their back end is off to one side from the front. You don’t want that with your trailer because it adds to instability.

        Reply

  8. Steve Arnall
    October 18, 2019 @ 2:20 PM

    Axle placement for tandem axles on a gooseneck or fifth wheel trailer

    Reply

    • The Mechanic
      October 19, 2019 @ 8:33 AM

      For tandem axles, use the center of the axle group with these same equations. Likewise, the process is the same for 5th wheel and gooseneck trailers except that the target tongue weight is higher — like 20% or 25% depending on your tow vehicle, trailer, and load.

      Reply

  9. Josh
    November 19, 2019 @ 8:05 PM

    Thanks for the article. I’m currently building a twin axle utility trailer 10′ by 5′. The tongue length 7.5′, I don’t know the frame weight is yet, but I estimate my maximum load (WD) is going to be around the 4,500lb. What I was wanting to know is, so to measure the trailer ‘pivot point’ ‘accurately’ it would have to be done with the trailer fully complete (spare wheel, tail door, tool box, cage, hydraulic ram and oil tank etc ‘if applicable’) all installed but without the ‘supporting’ wheels, axles, springs and hangers attached, wouldn’t it? Otherwise it’ll badly influence the ‘pivot point’s’ measurement doing the final sums at the end, thus null and voiding everything we stand for, right? For example, if you mounted the wheels as far to the rear of the tray/deck as possible, that would surely give a much different pivot point to, if you were to mount the wheels as far forward of the tray as possible, right? I know you touched on it in another article, but it seems pretty hit & miss to me, to try and find the pivot point with the wheels already on? Thanks.

    Reply

    • The Mechanic
      November 20, 2019 @ 4:42 AM

      Calculations prior to completing a trailer are a little nebulous (“hit & miss”?) if you really don’t know the weights, loads or positions. The beauty of calculating — you can try many scenarios to see the effect before building. Then, you can make an educated judgement for the actual build.

      Reply

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