Trailer Axle Position - Trailer Building: Where Does The Axle Go? (2023)

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.

(Video) How to Build a Utility Trailer Part 3 Axle Location and Axle Assembly

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 WeightWF — 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 LoadsWD — 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 LoadsWT — 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 Axle Position - Trailer Building: Where Does The Axle Go? (1)


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″

Trailer Axle Position - Trailer Building: Where Does The Axle Go? (2)

If we want 12% Tongue Weight . . .

Trailer Axle Position - Trailer Building: Where Does The Axle Go? (3)

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.

(Video) Tech Tips with Mike T - Trailers - Part 1: Axles

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).

Trailer Axle Position - Trailer Building: Where Does The Axle Go? (4)

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.

(Video) Everlast Trailer Project Build Pt 4: Axle Install

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?

Trailer Axle Position - Trailer Building: Where Does The Axle Go? (5)

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.

(Video) How to Fix a "flipped axle" in real time

And now you know how to calculate trailer axle position. We invite you to read Trailer Axles 101 and some extratips 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.


Trailer Axle Position - Trailer Building: Where Does The Axle Go? ›

Anywhere in between 7-10% is ideal. You may have heard of the 40/60 rule when it comes to positioning axles on a trailer. This is a very general rule of thumb where the axles are positioned so that 60% of the trailer bed is in front of the axle and 40% rearward of the axle.

Where should the axle go on a trailer? ›

On a traditional trailer, the heaviest items are loaded at the front, but with a boat the majority of the weight is at the back of the trailer, meaning the axle needs to be further away from the tongue for the trailer to have the appropriate tongue weight.

Do trailer brakes go on front or rear axle? ›

Typically trailers will carry more of their weight on the front of the trailer, so you would want to put the brakes on the front axle as it will most likely carry more weight while braking. Also, when braking, weight will shift forward from the inertia of the stop, so that would put more weight on the front axle.

How is an axle attached to a trailer? ›

Axles attach to a frame through the suspension. The axles are attached to the leaf spring stacks with a u-bolt kit and the leaf springs are bolted to hangers that are welded to the bottoms of the frame rails.

Which way should a trailer axle bend? ›

Should Trailer Axle Be Bowed Down in Middle A trailer axle should actually be bowed upwards in the middle and not downwards. When the trailer is loaded with your boat, that upward bow will flatten out and your tires will make even contact with the ground.

Why are trailer axles so far back? ›

This shorter overhang also helps when it's time for the horses to climb in for their ride. Since the rear won't move as much with the axles placed further back, there isn't going to be as much rocking back and forth on the trailer from their weight as they climb in.

Where is the 40 foot mark on a 53 foot trailer? ›

How to: measure the California bridge law (40ft mark) - YouTube

Do I need brakes on both trailer axles? ›

With all of this in mind, we always recommend adding brakes to both axles of a tandem axle trailer. This is simply because it's going to provide you with much better stopping power and will also keep the one set from wearing down quicker.

Do all tandem axle trailers need brakes? ›

Not only are tandem trailers required to have brakes whereas in most states single axle trailers are not required to have brakes, you have brakes on four wheels instead of two.

What weight trailer should have brakes? ›

In California, brakes are required on any trailer coach or camp trailer having a gross weight of 1500 lbs. or more. Usually the braking capacity on tow vehicles is good; however, it may not be good enough to safely stop the several hundred to several thousand additional pounds that your trailer weighs.

What does the axle sit on? ›

Axle spring seats are attached to the axle using a U-bolt. The bolt loops over the top of the axle and is attached to a plate underneath by a pair of nuts. The axle spring seat, which sits under the axle, is held in place by the plate and has holes that allow hooks on the leaf springs to be attached to them.

How do you connect axle to frame? ›

How to Attach Axles and Springs to the Trailer Frame - YouTube

How is hub attached to axle? ›

Purpose of Trailer Wheel Hubs

Tires are attached with studs to the hub assembly. The hub assembly then fits on the axle, which connects the tire component to the rest of the car. Because the wheel hub is the bridge between the tire and the entire vehicle, if one of its parts breaks down, it creates a ripple effect.

Are trailer axles supposed to be straight? ›

Are all trailer axles straight? Nope. As we explained above, a slight bow in your trailer axle is desired to help deflect the weight of the vertical load over it. This helps keep the wheels in the proper camber to avoid uneven tread wear.

Why are trailer axles arched? ›

The Camber ensures that the axle sits flat when under load. When the trailer is under load, the axle's weight pushes down, making the axles straighter, and the tires sit flat; this helps increase the tire's contact surface, even weight distribution, tire wear, and alignment.

Can you flip a trailer axle? ›

If your trailer travels securely on the road at all times, flipping the axles will not be a cause for concern. But if your trailer is sensitive to sway or has stability issues even on a good day, flipping the axles may not be such a good idea until the root cause of the poor ride has been fixed.

How far apart should trailer axles be? ›

Expert Reply: When installing tandem axles on a trailer you want to have at least 4 inches between the tires. So if you went with the part # A225R6SMQ which has an overall diameter of 28.31 inches you would need to have the axles set at least 32.81 inches apart.

How far back can I move my tandems? ›

When the distance between the first axle of your tandems is 35 feet from the rear axle on your tandems to the last axle of your trailer tandems, you will have to reduce the amount of weight that you load onto your truck.

How do you measure the axle spacing on a trailer? ›

Axle Spacing Report - Updated - YouTube

How do you measure the axle spacing on a trailer? ›

Axle Spacing Report - Updated - YouTube

Where should the axle be on a boat trailer? ›

The 60/40 rule is a great guideline for setting up axle placement on a trailer. But in reality the goal is to place the axles where the trailer will have 10-15 percent of the total trailer weight as tongue weight. The distance you would need to measure is from the center of the coupler ball to the back of the trailer.

Should my trailer axle bow up or down? ›

A trailer axle should actually be bowed upwards in the middle and not downwards. When the trailer is loaded with your boat, that upward bow will flatten out and your tires will make even contact with the ground.

Do trailer axles have a left and right side? ›

Expert Reply: An axle without idler hubs would not have a left or right side assigned to it. It could basically be ran either direction. If it has brake assemblies installed though then it would need to face the right direction.

How do you determine axle length? ›

TRACK LENGTH: measure your axle track length by determining the distance between the center of one tire to the center of the other tire. A more precise measurement can be made by measuring the distance from one 'HUB FACE' to the other.

What is hub face on a trailer axle? ›

Trailer axle hub face is the distance from the outside of hub mounting flange to outside of hub mounting flange, measured one-half way between top and bottom of the hub. The hub face is also known as the mounting surface where the wheel studs are located.

How do you check alignment on a tandem axle trailer? ›

You can check axle alignment by measuring from the center of the coupler back diagonally to the center of one of the wheels. Then take the same measurement to the other wheel center. They should be identical or within 1/8 of an inch, give or take 1/16 of an inch.

Where do you put axles on a gooseneck trailer? ›

The centerline of the axles should be placed 2/3 of the distance towards the rear of the trailer. If the measurement of the trailer box (A) is 30', the centerline of the axles (B) should be 20' from the front of the trailer box.

How do you install an axle on a boat trailer? ›

Trailer axle replacement for my boat trailer Starcraft - YouTube

How do you build a trailer frame? ›

Frame & Tongue Layout - Urban Logging Trailer Build Pt 2 - YouTube


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