Trailer Build: Where Does The Axle Go?

Trailer axle position?  This is a good question.  Unfortunately, there is some popular, but misleading information around.  So, how do you know proper trailer axle position?  Here’s the whole answer, from The Mechanic.

There once was a boy who came to his mother and asked “How do rockets get to the moon?”  She replied “Ask your dad.”  To this, the boy mumbled “I don’t want to know that much about it.”

If you’re looking for a simple — maybe misguided or incomplete answer — this is not the right article.  If you really want to know about trailer axle position, then you’ve come to the right place.

Trailer Axle Position Goals

For this discussion, we will focus on trailers with a traditional tongue attached to the rear of the tow vehicle.  (Bumper Pull.)  5th Wheel (and Gooseneck) trailers are similar, but are not the focus.

These are The Goals that drive trailer axle position:

  1. Stable, predictable towing.
  2. Proper weight balance for both the tow vehicle and the trailer.

There is a lot in these goals including construction (straightness, flatness, perpendicularity, etc.), proper stiffness and more.  However, with respect to axle position, we follow some well proven guidelines.

  1. Follow manufacturer specifications for the tow vehicle.  Note:  there are 2 different limits — trailer weight, and tongue weight.  Don’t exceed your tow vehicle limits.  Enough said.
  2. In general, more weight on the tongue is better for stability.  Example:  Over-the-road trucks (ie., a Semi or Lorry) trailers have roughly half the trailer weight on the hitch.  It works because the tow vehicle is built for it.
  3. For a 5th wheel (or gooseneck) trailer, weight at the tongue should be in the 20% – 30% range of total trailer weight.  (Perhaps we’ll dive into this in a future post.)
  4. For rear connecting trailers (traditional, bumper pull), weight of the tongue should be in the 10% – 15% range of total trailer weight.  (10% minimum, 12% – 15% is great.)

As a side note, many manufacturers and products assume 10% tongue weight so they can inflate their tow numbers.  Just be aware of this trend and adjust for a higher % for better towing.

Stable Predictable Towing

The guideline above for 12-15% of trailer weight on the tongue is time tested for dynamic towing stability.  If tongue weight is too low, the trailer will buck more over bumps, and wag around corners.

I won’t go into all the engineering, but the summary is inertia.  If there is not enough tongue weight, a change like a bump or turn or steering correction leaves the trailer mass pivoting, and it takes additional energy to get things back to stable.  As a driver, you feel this motion as bucking or a wagging of the trailer.  In bad cases, it is very unnerving.  In severe cases, a crash can result.

If there is significant tongue weight (above 10ish %) gravity serves to help settle things back to stable.  The more tongue weight, the faster stability is achieved, because the Center of Gravity is further from the axle.

Measuring Tongue Weight

One technique for setting axle position is by measuring tongue weight.  Most of us don’t have a scale that will go high enough, so take the trailer to a vehicle scale.  (Or use this DIY method for a good approximation.)

For an existing trailer, load it for travel.  (This is difficult for utility trailers because you never know what it will haul.)  Drive onto the scale where only the trailer wheels are on the scale.  Take a measurement.  For example, 2250#.  Unhook the trailer on the scale so it measures the full trailer weight (tongue and axle).  For example, 2600#.  Subtracting:  2600# – 2250# = 350# tongue weight.  For percentage, divide:  350/2600=13.5% which is great.  Adjust axle position if needed.

When building a trailer, one easy way is to set the axle in place under the trailer, but don’t mount it.  Clamp it in place, then measure as above.  Move the trailer axle position forward or back as needed, then verify loading.  This technique works well when you have a defined load for the trailer — like a boat, or ATV for instance.

On the other hand, for something like a Tiny House Foundation or a Utility Trailer, this method for trailer axle position doesn’t help much because you don’t have the actual load when constructing the trailer.  See the Calculation Method below.

That said, using this measurement technique helps when locating bigger loads like a battery pack or water tank for a Tiny House.  You can set an axle position that suits the overall design, then place the bigger loads where they measure for proper tongue weight.

Calculating Tongue Weight And Trailer Axle Position

We can also calculate trailer axle position.  I’ll give an example below.  However, for existing trailers (if you want to check the axle position or maybe move the axles), please read this other article also about Calculating Axle Position.)

This calculation example uses a “balanced lever” approach for loading.  First, we sum forces in a vertical direction.  There are only 2 points that support the vertical forces (tongue, FT; and axle(s) FA).  Then, there are several “loads” (depending on your trailer):

  • Trailer Weight — WF — Weight of the trailer including frame, sides and flooring can be measured or calculated pretty easily.  You must also know the position of the center of that weight, L4.  (Measure this by placing a board on edge under the trailer frame, then move it till the frame balances on the board.)  This is NOT the geometric center of the trailer.  It’s the center of MASS.
  • Evenly Distributed Loads — WD — Loads that can be assumed as even along the length of the trailer bed.  For a utility trailer this may be rocks, or firewood.  For a Tiny House, this is the walls and roof.  A good estimation is OK, but more accuracy gives a more accurate final answer.  The location of this load, L5, is the center of distribution.  If you don’t have an evenly distributed load, leave this out of the equation.
  • Points of Specific Loads — WT — These are big loads at specific locations.  The image shows one as a toolbox in front of the bed, but these can be on or under the bed as well.  For a utility trailer it may be an ATV, or lawn tractor, or tank.  For a Tiny House, maybe water tanks, battery packs or kitchen cupboards.  You may have several loads, giving more variables like WT1, WT2, . . .  and L1a, L1b, . . .

Trailer Loading Diagram

Measurements are from the center of the hitch ball to each load (center of mass for each load).  If any of these are not present, just leave them out.  If you have more point loads, just add them in as illustrated.  Obviously, Tongue Length L2 has a big effect, so it’s worth reading this article too about Choosing the Right Tongue Length.

Axle Position Example Calculation:

Let’s use a utility trailer rated for 3000 Lbs.  Also written 3000#.  We will assume an evenly distributed load of rocks, lumber, or whatever.  It also has a mounted toolbox.

Weight of the Toolbox:  WT = 300 Lbs  @  L1 = 30″
Length of the Tongue:  L2 = 42″
Trailer Bed Length:  L3 = 96″
Trailer Frame Weight:  WF = 450 Lbs  @  L4 = 83″
Distributed Load:  WD = 2250 Lbs, Center  @  L5 = 90″

Calculate Trailer Axle Position

If we want 12% Tongue Weight . . .

More Axle Position Calculations

If there are more load points, just follow the example and add them in.

Now we know the loading if the tongue has 12% of the load.  If that works for the tow vehicle, then we can move to the next step.

On the other hand, let’s say our tow vehicle can only handle 300# tongue weight.  By dividing the max tongue weight, 300#, by the total trailer load, 3000#, we get 300/3000 which is 10% tongue load.  That is on the margin, but it can work.  So,  FT = 300#  and we calculate  FA=3000#-300# =2700#.

Summing Moments (Load by Position)

Now we know the forces, the next step is to figure out where the axle goes so all the forces balance.  We do that by summing the moments — basically, summing the loads multiplied by their distance from the ball.  By setting the moments with forces up equal to the moments with forces down, we can solve for axle position.

For equation 2, please note that the distance from the tongue (ball) to the tongue load is Zero (so the multiplication of that Zero * FT = Zero).  We take advantage of that nice fact so we have only one variable to calculate — which is why FT is not in the equation.

Back To Our Example:

Using the values and solutions from above . . . Noting that the distance from the tongue to the tongue load is Zero (so that multiplication is Zero — which is why it is not included).

Equations for Trailer Axle Position

So, our Axle position is 94.3″ from the hitch.  Of course the numbers don’t have to be exact, because loading will vary.  With fewer rocks, the load is less.  Or, if there are not 300 pounds of tools, then that makes a small difference too.

From the example above, if we remove the toolbox, the calculated axle position changes to 100.9″
Or, using the example, if WT is 15% (instead of 12%), the axle position becomes 97.6″

When building your own trailer, run the calculations a few times with different load scenarios, then design for the maximums.  After evaluation, make a judgement call to choose the final trailer axle position.

That’s it.  Now you know how to calculate proper trailer axle position.

Trailer Axle Position for Multiple Axles

What is different for multiple axles?  Nothing.  Use the central position of the axle group for all the measurements and calculations.  Treat them as a single axle.  Note:  This simplification works for loading and trailer axle position on load sharing multiple axles, but not for stress or stiffness calculations.

What about torsion axles?  Use the location of the wheel center, NOT where the axle attaches to the trailer frame.

Proving Or Disproving The Common 60% Rule

On the internet there are several websites and YouTube videos saying to position the axle at 60% of the trailer bed.  What do you think?

% of Trailer Bed Length

In our example above, the trailer axle position is ~55% of bed length.  If we put it at 60%, the tongue weight becomes 501 Lbs, ~16.7%.  Or, if we take the toolbox off and went to 15% tongue weight, the desired trailer axle position is 65% of the bed.  These examples show that the 60% guess-of-thumb is not always best.

In some cases it makes the tongue load below 10% which borders on dangerous.  Other situations it can make the tongue load too high.

My Opinion?  Setting the axle at 60% is the lazy way.  In many cases it gives a reasonable answer, but why settle for a lazy guess when you can simply run the numbers and gain understanding.  Sometimes the answer is near 60%, but calculate and be confident.

All that being said, I recommend biasing the trailer axle position a little farther back for trailers where the load will change — like utility trailers.  It improves towing stability, maneuverability, and safety.  You can place the load appropriate for the conditions.  Just make sure you have the right materials and design safety factors for the loads you intend to carry.

And now you know how to calculate trailer axle position.  We invite you to read Trailer Axles 101 and some extra tips on mounting a leaf spring suspension.

Good Luck With Your Trailer Building Project!!

A Word About Center Of Mass

This seems to be a point of a little confusion, so here’s a quick explanation on the difference between the Geometric Center and the Center of Mass.  Think about a Hammer.  The Geometric Center is approximately half-way down the handle.  The Center of Mass is where the hammer will balance — say on your finger.  That balance point is the Center of Mass, and it’s much closer to the head.

The same is true of a trailer.  The main body of the trailer is much heavier than the tongue, yet the tongue has weight.  So, the Center of Mass is not the Geometric center, nor is it the center of the trailer bed.  While it’s nice to think about, the only real way to find it is to balance the trailer on something like a pipe or 2×4 as mentioned above.  Hopefully this explanation helps.  Have a wonderful day.

58 Comments About “Trailer Build: Where Does The Axle Go?”

  1. 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
    • 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 tongue length.

      Reply
      • 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
    • 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
    • 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
  2. 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
    • 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
  3. 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
  4. 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
    • 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
  5. 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
    • 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
      • 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
    • 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
    • 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
      • I would like to know what effect it would have if I would move the tandem axles on my 5th wheel toy Hauler 3″ farther apart. I went to larger tires and now they only have about an inch between them.

        Reply
        • You do need some space between tires. 3″-4″ minimum is recommended. In general the “issue” with wider axle spacing is resistance to turning. Not a big deal if your trailer is long. The added benefit is it spreads the load a little more (assuming the same springs). In your case changing to shorter springs and a longer equalizer link will accomplish the task without welding new spring hanger brackets. The ride will be a little rougher with shorter springs, offset in some degree by the bigger tires, so probably not enough to really notice. Good luck.

          Reply
          • Thanks for your input. I purchased a Morryde CRE-3000 Rocker kit, 3 1/8″ shackles and 4 new spring hangers to modify the suspension. I prefer to use the existing springs. The plan is to weld the new hangers on the outside ends of the existing hangers hence buying 3 1/8″ shackles in lieu of using the 2 1/4″ shackles.

  6. 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
    • 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
      • I’m building a tandem, deck over tilt trailer. 4’ tongue, 4’ stationary deck, 16’ gravity tilt deck… is the thought. 6” C from tongue to rear axle bottom frame with 3” cross members. 3” support laid inside bottom frame with 3 “ top deck over bottom frame. Plan on tilting over rear axle… a mouthful I know.
        Having hard time with axle placement and making tilt work! Thanks! Enjoying this

        Reply
        • That is the crux of design. Finding the right ‘balance’! Pardon the pun. There are always opposing requirements, so keep thinking and fiddling. Good luck.

          Reply
  7. 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
    • 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
      • 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
      • 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
        • 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
          • 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.

          • 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.

  8. 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
  9. 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
    • 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
  10. 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
  11. 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
  12. 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
    • 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
  13. 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
    • You are on the right page, or for a different perspective of the same thing, try 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
  14. 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
  15. 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
    • 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
  16. Great information: question: Range Rover discovery , max 3500kg trailer capacity with max tongue weight 150 kg. This makes it only possible to have 4.2% nose weight.
    If I push to 200kg nose weight and 10% bias then I can only tow 2000kg.
    How can it be stated that 3500kg can be towed with 150kg nose weight?

    Reply
    • I don’t know their reasoning. Many manufacturers push the limits of what works well to promote and sell their products. That might be what’s happening here. I can only tell you for sure that I would not pull a 3500kg trailer with a tow vehicle that can only carry 150kg tongue weight. It means the tow vehicle is too small for the trailer. (150kg is the weight of 2 people! If it can’t handle that weight on the end, then it has no business pulling 3500kg – IMHO.) Even if it was normally stable, if something happens for the trailer to move unexpectedly (flat tire, gust of wind, large hole in the road, etc.), the tow vehicle can be tossed. I don’t want to be in that vehicle.

      Reply
  17. Gday, interesting reading…I’m about to build a caravan chassis…..because it’s not built I cannot work out Wf…..I know approx what the weight will be but not where it will be centered ..what to do?
    Thanks Jeff

    Reply
  18. Hi, I am designing a trailer for a high school engineering project and came across your website. Its very useful, especially this article.
    I am a bit confused about tongue weight though. I am not planning to have any weight in front of the trailer bed itself (eg like the tool box you show in your diagram).
    For info, tongue length is 1.1m and bed will be 2.4m long. I would anticipate load spread of 50kg at 1.45m from the tow hitch and another 50kg at 2.5m from the tow hitch. The rear of the trailer will carry two bikes, so circa 15kg each.
    The trailer frame weight will be 115kg and the laden weight will be a maximum of 335kg (including weight of the trailer).
    I’d like to include some calculations to show how I’ve positioned the axle based on these loads, but how do I do that using your formula if I don’t want to put any weight infront of the bed?
    I can send you a dimensioned diagram if it would help to explain better.
    Can you help me figure this out please?

    Reply
    • Fair question. The equations allow you to add or remove loads as needed for your situation. Make the toolbox load =0, then create a load at the right distance for your other things. Put as many specific loads at the appropriate distances as you need. If each load is matched with a distance, the equations all work out. Good Luck.

      Reply
      • thanks for your help, I’ve managed to do this now.
        Another question – the worst case loading scenario for my design (ie max weight at front of the bed) indeed puts the optimal axle weight at 61% of the trailer length.

        However, if I load the trailer differently, eg different configuration of weight distribution or lower loads for each one, I see that the axle position can shift foward quite significantly.

        I am presuming however that I need to position the axle for the “peak” load design, ie full load condition? And having the axle further back even when not fully loaded will still be a good thing as it will help the stability of the trailer, right?

        Reply
  19. Hi I’m having a trailer custom built. It weighs 2200 lbs. However, the tongue weight is 900 lbs. I brought up my concern to the builder, and he said he already pushed the axle to 55/45 from 60/40 and that moving any farther forward will cause sway. My tow vehicle is rated to 350 lbs tongue weight. Can the axle be moved forward to achieve 10-15% tongue weight even if that means the axle could be at 50/50 or less? From my understanding preventing sway is about a minimum tongue weight, not a minimum axle distance. The axle can be anywhere, correct?

    Reply
    • Sounds to me like there is a more to the story — like what is so heavy in the trailer front? As humans, we like to boil things down to one thing, but stability is more complicated than just tongue weight. It makes a nice measurable and it’s certainly a significant factor. With all other things equal it’s often the determining bias, but when we get out of the “all other things equal”, it’s time to think carefully about what’s happening. Going from 900 to 300 when you only have 2200 to work with, will likely push the axle much closer to the tow vehicle. Again, it sounds like a re-think is needed.

      Reply
      • You are right to question why the tongue is so heavy. I got a call yesterday from the manufacturer, and they explained the new guy still had the jacks on the rear when he measured the tongue weight. They remeasured with video for proof, and the actual tongue weight is 250 lbs. I was quite relieved!

        Reply
  20. Why are there no travel trailers designed using the wagon principle – two main axels with the front one on a pivot? Does it have to do with stability or weight capability? Just a stupid idea?

    Reply
    • Good question. They still appear frequently on farms, and you sometimes see them in multi trailer rigs on the highway, but almost never for RV’s and such. Stability is certainly a concern, and they are near impossible for a layman to back up. (Can you imagine the jam in an RV park!) Anyway, here’s an article explaining more.

      Reply
  21. Why would a trailer have an axle to the extreme rear. I’m looking at buying a trailer and I found one that looks to be an old generator trailer.

    Reply

Leave a Comment

58 Comments About “Trailer Build: Where Does The Axle Go?”

  1. 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
    • 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 tongue length.

      Reply
      • 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
    • 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
    • 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
  2. 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
    • 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
  3. 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
  4. 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
    • 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
  5. 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
    • 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
      • 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
    • 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
    • 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
      • I would like to know what effect it would have if I would move the tandem axles on my 5th wheel toy Hauler 3″ farther apart. I went to larger tires and now they only have about an inch between them.

        Reply
        • You do need some space between tires. 3″-4″ minimum is recommended. In general the “issue” with wider axle spacing is resistance to turning. Not a big deal if your trailer is long. The added benefit is it spreads the load a little more (assuming the same springs). In your case changing to shorter springs and a longer equalizer link will accomplish the task without welding new spring hanger brackets. The ride will be a little rougher with shorter springs, offset in some degree by the bigger tires, so probably not enough to really notice. Good luck.

          Reply
          • Thanks for your input. I purchased a Morryde CRE-3000 Rocker kit, 3 1/8″ shackles and 4 new spring hangers to modify the suspension. I prefer to use the existing springs. The plan is to weld the new hangers on the outside ends of the existing hangers hence buying 3 1/8″ shackles in lieu of using the 2 1/4″ shackles.

  6. 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
    • 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
      • I’m building a tandem, deck over tilt trailer. 4’ tongue, 4’ stationary deck, 16’ gravity tilt deck… is the thought. 6” C from tongue to rear axle bottom frame with 3” cross members. 3” support laid inside bottom frame with 3 “ top deck over bottom frame. Plan on tilting over rear axle… a mouthful I know.
        Having hard time with axle placement and making tilt work! Thanks! Enjoying this

        Reply
        • That is the crux of design. Finding the right ‘balance’! Pardon the pun. There are always opposing requirements, so keep thinking and fiddling. Good luck.

          Reply
  7. 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
    • 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
      • 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
      • 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
        • 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
          • 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.

          • 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.

  8. 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
  9. 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
    • 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
  10. 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
  11. 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
  12. 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
    • 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
  13. 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
    • You are on the right page, or for a different perspective of the same thing, try 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
  14. 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
  15. 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
    • 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
  16. Great information: question: Range Rover discovery , max 3500kg trailer capacity with max tongue weight 150 kg. This makes it only possible to have 4.2% nose weight.
    If I push to 200kg nose weight and 10% bias then I can only tow 2000kg.
    How can it be stated that 3500kg can be towed with 150kg nose weight?

    Reply
    • I don’t know their reasoning. Many manufacturers push the limits of what works well to promote and sell their products. That might be what’s happening here. I can only tell you for sure that I would not pull a 3500kg trailer with a tow vehicle that can only carry 150kg tongue weight. It means the tow vehicle is too small for the trailer. (150kg is the weight of 2 people! If it can’t handle that weight on the end, then it has no business pulling 3500kg – IMHO.) Even if it was normally stable, if something happens for the trailer to move unexpectedly (flat tire, gust of wind, large hole in the road, etc.), the tow vehicle can be tossed. I don’t want to be in that vehicle.

      Reply
  17. Gday, interesting reading…I’m about to build a caravan chassis…..because it’s not built I cannot work out Wf…..I know approx what the weight will be but not where it will be centered ..what to do?
    Thanks Jeff

    Reply
  18. Hi, I am designing a trailer for a high school engineering project and came across your website. Its very useful, especially this article.
    I am a bit confused about tongue weight though. I am not planning to have any weight in front of the trailer bed itself (eg like the tool box you show in your diagram).
    For info, tongue length is 1.1m and bed will be 2.4m long. I would anticipate load spread of 50kg at 1.45m from the tow hitch and another 50kg at 2.5m from the tow hitch. The rear of the trailer will carry two bikes, so circa 15kg each.
    The trailer frame weight will be 115kg and the laden weight will be a maximum of 335kg (including weight of the trailer).
    I’d like to include some calculations to show how I’ve positioned the axle based on these loads, but how do I do that using your formula if I don’t want to put any weight infront of the bed?
    I can send you a dimensioned diagram if it would help to explain better.
    Can you help me figure this out please?

    Reply
    • Fair question. The equations allow you to add or remove loads as needed for your situation. Make the toolbox load =0, then create a load at the right distance for your other things. Put as many specific loads at the appropriate distances as you need. If each load is matched with a distance, the equations all work out. Good Luck.

      Reply
      • thanks for your help, I’ve managed to do this now.
        Another question – the worst case loading scenario for my design (ie max weight at front of the bed) indeed puts the optimal axle weight at 61% of the trailer length.

        However, if I load the trailer differently, eg different configuration of weight distribution or lower loads for each one, I see that the axle position can shift foward quite significantly.

        I am presuming however that I need to position the axle for the “peak” load design, ie full load condition? And having the axle further back even when not fully loaded will still be a good thing as it will help the stability of the trailer, right?

        Reply
  19. Hi I’m having a trailer custom built. It weighs 2200 lbs. However, the tongue weight is 900 lbs. I brought up my concern to the builder, and he said he already pushed the axle to 55/45 from 60/40 and that moving any farther forward will cause sway. My tow vehicle is rated to 350 lbs tongue weight. Can the axle be moved forward to achieve 10-15% tongue weight even if that means the axle could be at 50/50 or less? From my understanding preventing sway is about a minimum tongue weight, not a minimum axle distance. The axle can be anywhere, correct?

    Reply
    • Sounds to me like there is a more to the story — like what is so heavy in the trailer front? As humans, we like to boil things down to one thing, but stability is more complicated than just tongue weight. It makes a nice measurable and it’s certainly a significant factor. With all other things equal it’s often the determining bias, but when we get out of the “all other things equal”, it’s time to think carefully about what’s happening. Going from 900 to 300 when you only have 2200 to work with, will likely push the axle much closer to the tow vehicle. Again, it sounds like a re-think is needed.

      Reply
      • You are right to question why the tongue is so heavy. I got a call yesterday from the manufacturer, and they explained the new guy still had the jacks on the rear when he measured the tongue weight. They remeasured with video for proof, and the actual tongue weight is 250 lbs. I was quite relieved!

        Reply
  20. Why are there no travel trailers designed using the wagon principle – two main axels with the front one on a pivot? Does it have to do with stability or weight capability? Just a stupid idea?

    Reply
    • Good question. They still appear frequently on farms, and you sometimes see them in multi trailer rigs on the highway, but almost never for RV’s and such. Stability is certainly a concern, and they are near impossible for a layman to back up. (Can you imagine the jam in an RV park!) Anyway, here’s an article explaining more.

      Reply
  21. Why would a trailer have an axle to the extreme rear. I’m looking at buying a trailer and I found one that looks to be an old generator trailer.

    Reply

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