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Where to Position the Trailer Axle?

When positioning a trailer axle or adding an additional axle, the key is to make sure that the axles are located in just the right position so that roughly 10 to 15 percent of the total trailer weight is placed on the tongue. Finding the correct axle location can take some trial and error, so it is best to mock up the locations for all the suspension components until you know everything is in the right spot. When building your trailer, it is best to have the layout of the trailer finalized before placing the axle. This will ensure that the axle is placed in the correct spot to accommodate any permanent weight placed inside the trailer, such as furniture, toolboxes, or shelving. The equations in this article can be used to adjust the trailer's axle location to offer the ideal amount of trailer tongue weight.


Steps to Determine Correct Axle Placement

Axle Placement Infographic Showing Steps and Equations



When Tongue Weight is Less than 10 to 15 Percent of Total Weight


If you find that your trailer's tongue weight is less than 10 to 15 percent of the total trailer weight, then the trailer axle will need to be moved further away from the trailer tongue, closer to the back of the trailer. To know how far back the axle needs to be moved, we want to subtract the trailer's tongue weight from 10 percent of the total weight. Then we will divide this number by the total weight. Then we will multiply this by the distance from the tongue to the axle.


For example, let's say we're building a trailer that has a total weight of 3,500 pounds. When weighed at the wheels and coupler, we find that the weight under the wheels is 3,400 pounds and the tongue weight at the coupler is only 100 pounds. With these weights, the trailer's tongue weight is only 2.9 percent of the total weight. The distance from the front of the trailer coupler to the axle center is 96 inches. Check out the equation below to see how much further back the axle needs to be moved.


Example 1
Example Equations when TW is Less than 10 Percent
For Boat Trailers
When building a boat trailer, the axle is often set back further than on a traditional 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.




When Tongue Weight is Greater than 10 to 15 Percent of Total Weight


If you find that your trailer's tongue weight is greater than 10 to 15 percent of the total trailer weight, then the trailer axle will need to be moved closer to the trailer tongue and the front of the trailer.


Knowing how far forward to move the trailer axle takes an equation very similar the the one mentioned above. However, this time, we will subtract the 10 percent of the total weight from the actual tongue weight. Next, divide by the total trailer weight. Finally, multiply by the distance from the coupler to the trailer axle.


To give an example of this equation, let's say we have another trailer being built that has a total weight of 3,500 pounds. This trailer weighs 2,750 pounds under the wheels and 750 pounds at the end of the tongue. This trailer has a tongue weight that is 21.4 percent of the total trailer weight. The distance from the very front of the trailer, the coupler, to the center of the trailer axle measures 96 inches. Check out the equation below to see how far forward the trailer axle need to be moved.


Example 2
Example Equations when TW is Greater than 10 Percent





Related Articles:

Double-Eye Trailer Suspension System Review
Slipper Spring Trailer Suspension System Review
Trailer Maintenance Schedule

Written by: Victoria B

Updated on: 12/19/2017





Ed S.

4/28/2022

Is there a rule of thumb regarding the distance the axle may be moved based on overall trailer length? I'm dealing with a 1500 lb trailer for 16' boat. There are very few things I can do to get to 10-15% tongue without moving the axle 12-20 inches forward.

Etrailer Expert

David B.

4/28/2022

What's goin on Ed? Let me link you to one of our expert answers that I think will help you out. If you need any clarification or have more questions let me know and I'll do what I can to help you out.

Dave H.

1/15/2022

Wouldn’t a person need the weight of the boat included in the weight number?

Les D.

1/17/2022

@DaveH yes you would want to determine axle location under a typical trailer load.

Hiss

1/15/2022

Would it be possible to locate a set of tandems at the rearmost part of a single wide snowmobile trailer? Pro’s/Con’s?

Les D.

1/17/2022

@Hiss I would determine axle location with a typical load on the trailer in its typical location. At the very rear would not likely be a good location.

Hiss

1/17/2022

@LesD just curious. On some tractor trailer combinations axles are located at the rearmost of the trailer. I am curious as to why this setup is not used in smaller applications…?

Les D.

1/18/2022

Depends on how the load is situated. For instance, a boat trailer has the axles most all of the way back as the most of the boat weight is in the rear with the engine. On a tractor-trailer the rear axles are manually adjustable by the driver to move the axles more forward or backwards as necessary to have a correct load on the fifth wheel hitch.
See All (4) Replies to Hiss ∨

Dave

1/7/2022

Not sure why weight below trailer makes a difference? If my wheels were 10,000 lbs or 200 lbs my tongue weight would be the same. Am I missing something?

Les D.

1/7/2022

@Dave when they say "under the wheels," they mean as if you were on a drive-on scale, or the weight on the axles. The tongue weight helps control the trailer, and the more the trailer weighs, the more control you need. In the typical experience, tires only have a few pounds difference in weight from one tire style to the other, so their affect on tongue weight would not have much impact. If you want to measure tongue weight, an easy way is to use a scale like Sherline # 5780 scale. Then you can put your Fred Flintstone wheels on there and check your tongue weight again. We are pretty sure it will be heavier. I would be curious to know.

Jd

11/29/2021

I have a small trailer 5'x6' to load a 600 lbs ATV, do I need to modify it ot it's fine. I am intending to go in a long ride. I just want to stay safe.

Les D.

11/29/2021

@JD What is the weight capacity of the trailer? What style of hitch does it have? What are you towing it with? How much does the trailer by itself weigh?


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