40 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

    • Thomas
      January 17, 2020 @ 9:20 AM

      General rule for a gooseneck trailer is 70% back from the front of the trailer, as far as doing these calculations unless you are putting the same thing in the trailer in the same locations I don’t see where it would help. Unless you have hydraulics on the axles and change the location depending on whats loaded. LOL

      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

    • Josh
      November 24, 2019 @ 12:09 PM

      Hi Jay, how does the 6″ set back theory work in practice, do the trailers, your company produce, perform alright? To be honest I’m not mathematically adept, therefore all this theory is kinda wasted on me and although I usually like things perfect, working this out takes a better mind than I have, therefore I am looking for that ‘quick fix’! Thanks.

      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

  10. Darby
    December 4, 2019 @ 7:30 AM

    Thank you so much for sharing this information. It is extremely helpful. Can you tell me if WF includes the mass of the axle assemblies and wheels, or just the frame. In my case the tandem axles & wheels account for about 33% of the trailer weight and it makes a notable difference. Thank you!

    Reply

    • The Mechanic
      December 4, 2019 @ 8:46 AM

      Good question, with a 2 part answer. 1) 33% is a lot, so I assume that’s the empty trailer weight, so the axle position won’t matter that much empty. Make the calculations based on a loaded trailer, the way you expect it to be fully loaded. 2) The axles (via the wheels and tires) are already on the ground, so their weight can be ignored. Their weight is important for total capacity, however. My experience says when calculating axle position for a loaded trailer, the axle(s) weight will only make a small difference for placement, and it biases the CG back just a little which is good for stability. Good luck.

      Reply

      • Darby
        December 4, 2019 @ 8:11 PM

        Thank you for the quick response. You are correct the 33% is for empty frame only with no load. My trailer is a special purpose build for a fixed position 5,300 lb pizza oven and a reasonable payload of ~1,000 lbs for firewood and supplies. I am basing my calculations on WF @ 1,200 lbs (without axle assemblies), WT @ 5,300lbs and WD at 1,000 lbs. I’ve been crunching the numbers for empty vs loaded and wanted to make sure if the 600 lb for axles should be included. Thank you for clarifying that!

        Reply

      • Josh
        January 19, 2020 @ 10:03 AM

        To ‘The Mechanic’. The second answer you gave here appears to contradict itself slightly. Firstly, you say the wheels and axles are part of the ‘supportive’ weight, so their weight can be ignored. Then you go on to say the “their weight is important for total capacity”! Should I take it then that, the wheels and axles ‘SHOULD BE INCLUDED’ in weight at the weigh bridge, for example, total loaded trailer weight is 4000lb, that should be taken as 4000lb and not 4000lb less 500lb for the wheels and axles, making the total loaded weight measurement 3500lb? If that makes sense? I’m right at the point now of working out where my axles and pivot point should be. I’m getting a full load of firewood within the next two weeks, then heading for the scales. Thanks.

        Reply

        • Mechanic
          January 19, 2020 @ 6:57 PM

          Thanks for writing again. Hopefully I’ll do a better job answering this time. I can definitely see what you mean by contradictory. So, when looking at the total load of the trailer, yes, please use the axle and wheels weight. That is real weight on the tires and on the ground. Argumentatively you could say hitch weight is not on the axles, but if you are that close in terms of capacity, then it’s best to move to a higher capacity axle. Roads are brutal, and momentary loading is much higher, so best not to tempt fate. Now, for calculating where the axle goes, ignoring the weight of the axle and wheels is helpful to simplify equations because the axle weight is always right at the axle, no matter where you put it. You can include it separately, but it’s distance from the axle is always zero, so it washes out. This can be confusing, I know. Here’s another way of looking at it. If you think about balancing on a teeter-totter, the balance point does not include the stand that the teeter-totter is mounted on — but, when you pick up the teeter-totter to move it some place else, you also have to pick up and carry the stand it mounts on. Does that analogy help? I think the real issue with my writing is the context of theoretical and practical. I’m trying to give enough of the theoretical for understanding, but focus primarily on the practical because that’s what really matters in the end. Let me know if I should try again with the explanation.

          Reply

          • Josh
            January 20, 2020 @ 10:06 AM

            Thanks so much for taking the time to get back to me. I can’t pretend my head’s not spinning, I’m just a simple meat worker. I’m now understanding that, when checking the final weight on the scales, I include the axle and wheels weight. But, I’m still unclear, despite your intricate details, as to whether or not I get the pivot point with or without the axles and tires in place so, if you could just answer with a simple ‘yes or ‘no’. ‘Yes’ for they should be on the trailer, ‘no’ for they should be removed from the trailer, that would make it simple for me. Thanks again, Josh.

          • The Mechanic
            January 20, 2020 @ 9:13 PM

            Ignore the axle weight when you do the calculations for axle position — only for calculations. I think that’s “No” based on what you asked.

  11. Josh
    January 19, 2020 @ 9:53 AM

    I’ll try and cut to the chase for I feel you misunderstood my question above. When checking for ‘The Pivot Point’, owing to the fact that the wheels and axles are ‘supportive’ weight, and not ‘load’ weight, should they be on or off the trailer, when finding the ‘Pivot Point’? Thanks.

    Reply

  12. Jesse Kurtz
    January 20, 2020 @ 4:53 PM

    Ok..maybee this was discussed in previous comments but I am new here and I feel my issue is unique…I have a tilt body trailer with a cargo area of 5×10..when trailer is empty it would sway almost out of control..I would drive my golf cart on (forward) and it would still sway..I back it on and no sway. I figured load c.o.g. was in front of axle…Now I will be eliminating the tilt basically welding it so tilt will not be available. My plan was to go with the 60%/40% method however,I briefly read that this method would not work.A friend of mine builds trailers for a side hustle and he said that is the rule he goes by..I have flipped my trailer over to make easy to move axle and by my measurements I will need to move the axle back 13 and 1/2 inches to meet the 60/40 rule. I understand that the axle was that far forward to not have so much of and angle when driving on or off.Math is not my strong subject so I was wondering if that method would be my best bet or should I not move it that far back in Hope’s of not creating to much tongue weight…I think my wife’s car would only handle about 400 pounds tongue weight .not worried about tongue weight for my truck ,it has a tongue capacity of 1200lbs.

    Reply

    • The Mechanic
      January 20, 2020 @ 9:17 PM

      As mentioned in the article, those rules of thumb are pretty generic. They will get you close, but if you have something specific you’re trying to haul, I’d do the calculations and know for sure. Sounds like the back tires of your golf cart carry more weight, so figure out how you prefer to drive it onto the trailer, then do the math with that. Get a friend to help with the calculations if you don’t like doing math. Good luck.

      Reply

  13. khalid
    February 16, 2020 @ 5:52 AM

    hello MR. mechanic , i have a trucks and trailers spare parts shop and i wanted to know the main component of the trailer so i can have a basic idea if you can ,

    thanks,

    Reply

  14. Graciano Diosdado
    May 24, 2020 @ 10:43 PM

    Hi I have a question, I got 60’ frame it was from amobile home three axels were in the frame I cut 20 feet to the back of the frame cuz I want To make a Tinay home on it, my question is now I need to move the axels since they were place for a 60 feet frame now its only 40 feet frame how can I calculate to where to move the axels now? Please help

    Thank you
    Graciano Diosdado

    Reply

  15. Chuck Williams
    June 14, 2020 @ 10:36 AM

    I have a 16ft car trailer I want to extend 6ft to add sleeping quarters and convert to goose neck. Will I need to add an axle? How muck can I add without add or moving axles? Still will convert to goose neck.

    Reply

    • Mechanic
      June 15, 2020 @ 9:50 AM

      Adding 6′ plus the goose neck will almost certainly require bigger main beams. At some point it’s better to start with a platform that comes closer to your end goals instead of chopping so much. I’d sell this one and buy one with the length, goose neck and axle placement already there. The integrity and weight will be much better in the long run — instead of all the manipulation you’d need in converting.

      Reply

  16. lonny
    June 19, 2020 @ 1:56 PM

    I am building a 56’x13′ trailer for tiny home. This will be traveling only a total of 5 miles. approx. weight of house is 32,000 lbs. Trying to figure out location for axles.

    Reply

    • Mechanic
      June 24, 2020 @ 5:52 AM

      You are on the right page, or for a different perspective of the same thing, try https://mechanicalelements.com/calculating-axle-position/ You will need to know more than just the total weight, however. You really need to know the center of mass also. Another thought — for a tiny house that won’t move almost ever, the exact axle position is of less importance because that is mostly for dynamic (towing) stability. In other words, do your best with weights and locations, then don’t worry about a few inches one way or the other.

      Reply

  17. Jan
    July 23, 2020 @ 10:17 AM

    Got a 22’ pontoon boat trailer , box frame is 13’2”. It had a single axle but shop replaced with tandem axle. After change out and loaded boat back on, when pulling it feels like it’s dragging the whole truck to one side, very hard to pull: we did the measurements of when axles should sit. Center of tandem axle spring assembly bolt is at 5’2” from back of frame (40%). Back axle is at 46” from back and front axle at 78.5” from back. Everyone seems to think not enough tongue weight: Should I move axles both or forward? Or is that the problem?

    Reply

  18. Wali
    September 9, 2020 @ 6:19 AM

    Start by measuring the length of the trailer cargo box or platform, but do not include the trailer tongue. Multiply this length by .4. The resulting number is the distance from the rear of the cargo box to the center of the axle. For example, the math for a 10-foot box is: 10 x.4 = 4. So, in this example, simply mount the axle so that the axle center point is four feet from the rear of the trailer.

    PLEASE tell me what you think of this guy’s method. (A google search listed this second under your site being #1.
    My project is simply a DIY bicycle trailer kit using 1″ square alum. tubing for frame. I’ll be towing camping gear. The bed
    is 8′ long w/a 4’8″ tongue. The ball hitch is connected to the rear of the bike rack on my Mongoose Dolomite fat tire bike,
    so the tongue connector is raised up 2′ from the end of the tongue to accomodate the distance needed to connect to the
    ball connector. Just wished I could send you pics.

    Reply

    • Mechanic
      September 10, 2020 @ 8:26 AM

      As mentioned in the beginning of the article, you can use the 60% thought (which is the same as the 0.4 you mention) if you’re looking for a simple — maybe misguided or incomplete answer. Or, use the equations offered. It’s entirely up to you. A bicycle trailer isn’t really different than an automotive trailer, just lighter duty. Same principles apply. Good luck with your project.

      Reply

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