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
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
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
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Written by: Victoria B
Updated on: 12/19/2017
Sebastian C.
1/18/2024
Is tongue weight to be considered in this rule the weight of the trailer on the front of the front axis?
Mike L.
1/18/2024
@SebastianC Tongue weight is the amount of downward force the trailer would place on the trailer ball. The tongue weight is influenced by the placement of the axles and where the load is carried on the trailer.
Nathan D.
5/14/2023
So how am I to determine the position of the axle if I'm still in the process of building the trailer? therefore i haven't finished and don't have a final weight, and can't take it to the scale because the axle isn't attached, because i know know the location to put it...
Anonymous
7/10/2023
So rule of thumb that I have noticed on "off the shelf" trailers is...
The distance from the centerline of the last axle to the end of the trailer is equal to ½ the distance of hitch ball to the centerline of the first axle.
This is true for both of my 2018 trailers (14'+4' tongue and 18'+4' tongue). Both have standard equalized tandem leaf spring axles. If you're building with torsions or spread axles or axle-less, you'll need to make adjustments to this rule of thumb. Single axles seem to be set further back a tiny bit than the center hangers between tandems (centerline between the two axles) for what it's worth.
Both my trailers have approximately 10% tongue weight empty when they are level.
Jason
3/9/2023
I googled how much weight should sit on the trailer and the consensus is 60%. Now I read you saying 85%. That is not even close. Who do I beleave.
Anonymous
7/10/2023
You might have found a guide of how to load your trailer, aka load at least 60% of your payload ahead of the axle(s). The numbers are trailer-carried weight (85%-90%) + tongue-carried weight (10%-15%) = trailer weight (100%). This is for "bumper pull" style trailers. Gooseneck and 5th wheel take a lot more % on the "tongue" because this weight goes directly on the truck's rear axle, rather than behind the truck's axle like on a bumper pull style trailer. Lots of physics involved with this, but it is true.
Too much tongue weight will cause your tow vehicle to squat excessively and unloads your front axle (steering affected) while overloading the rear one. This will cause an unpleasant to dangerous tow. Too little tongue weight will lead to trailer sway and excessive porpoising. If you don't handle these appropriately while driving, you will have a massive accident, because your trailer will begin to steer the back of the vehicle in all directions as speed and road imperfections increase.
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.
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.
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Luis A.
2/9/2024
Hello, do you know if there is a security standard that indicates that percentage 10.15%? Do you know any design standards for light trailers? (ISO, etc.). Finally, are those photographs from a book? I am very interested in learning about the subject of design.