“Some of your Trailer Plans do not use a standard axle size. Why not?” Good question, along with the also very common “Why should I special order the trailer axle? Why not design for off-the-shelf axle sizes?”
There are a few common-ish axle sizes that some manufacturers stock. Some people call these “standard” sizes. It is not really a standard because some manufacturers do one trailer axle size and other manufacturers do some different. It is more a matter of common use, than a matter of great thinking for standards.
While it is convenient to find your size in stock, there are limits in what the common axles include. Most important, there are limitations to having a common size trailer. This article talks about all of that, and about why we say it is good to special order the axle.
The Fallacy Of Standard Trailer Axle Size
One of my pet peeves is the trailer industry sizing paradigm. It is a little deceitful, because it is usually outside measurements. Take a 4 x 8 trailer for instance. You cannot lay a 4 x 8 sheet of plywood in a “standard” 4×8 trailer without damage. The outside dimensions of the trailer are 4 ft by 8 ft, but the inside, where it matters, is smaller.
To us, a 4-ft trailer should accommodate a 4-ft item. Same with 5 ft and 6 ft. After all, you normally think about what you need to haul (like 4×8 drywall), not what the outside of the trailer is. That is just a little thing, but it seems like common sense to us.
At Mechanical Elements, we let function drive the design. That means for some of our trailers, the axle is a little longer than a “traditional” axle for a trailer of the same size label. While it is a little different, many happy customers love the the ability to put 4×8 sheets easily in a Mechanical Elements 4×8 trailer. And, there is still enough space if they want to put a plywood lining on the sides.
Well, that seems sensible, so why is that not an industry standard? Because dimensioning to the outside is cheaper. They can sell you a trailer labeled 4×8 with less material. When you and I think about it, a few inches of material is not much, but when you consider cut lengths and high volume, the big boys find it easier to skimp. – Then deceive you with the labeling! I am not good with that.
To us, it is much more about the customer and about usability, than about skimping on materials or matching a skimp-ish tradition. Remember, our moto is:
“Build it Better than you can Buy It“.
That means making your trailer meet your needs — which are often different than a production batch.
What “Standard” Trailer Axle Size Fits You?
The details of the axle are more than just length (axle width). For every axle, there are many options. See this article for axle options and details.
The problem with off-the-shelf stock sizes is you do not get to choose the options. While one manufacturer’s choices may work for some, if you are building a custom trailer, we recommend you get the options that are right for you. Brakes for example. Do you need electric brakes or hydraulic brakes or no brakes? What size? Drum or disk? Underslung or overslung springs? Or the offset from spring seats to hub face? Camber or no camber? How many lugs for the wheels? The list goes on. They have these options because they all fit some need. The questions: What do you need? What will make the trailer best for you?
At Mechanical Elements, we recommend ordering axles with exactly the features you want. Order the trailer axle size and features made-to-measure. We even have a section on selecting the right axles and options in the instructions of the plans we sell.
In a world of instant ordering on the web, this may seem a little old fashion, but it is the right way to get the axle, and the trailer you want. Yes, to meet a certain demand, most manufacturers have some stock products, but that does not mean you should constrain your thinking, or your trailer, to someone else’s choices.
The Axle Type Matters
In this article we focus on the traditional leaf spring style axle and suspension. They are definitely the most common, and when we talk about standard trailer axle size, this is the axle type you can find.
There are many other trailer axle types, but not many that have standard sizes. For instance, almost all torsion axles are made to order. Most air ride suspensions are custom. Axle-less suspensions don’t need to “fit” the trailer, but they do have options like drop which can require special ordering.
Special Order Your Axle
Almost all manufacturers build to order, and that is what we recommend with our trailer plans. Yes, even when the axle length fits a common size. Ordering axles takes a little longer. But you do not need the axle(s) to start the project. Also, you will have the trailer for a long time, so it is worth it to wait a minute to get the features you want.
Another strong reason to special order the axle is for customizing. Our 4′ x 6′ Off Road Trailer Plans are a good example. Even if a stock axle length would match the frame rails, the traditional axle will not give the function we want. The standard axle overhang from Spring Seat to Hub Face is not enough for the big wheels and tires desired for an Off-Road trailer.
Whether you are building a specifically designed off-road trailer, or if you are making your own conversion to build an off-road trailer from standard plans, axle length, and specifically the overhang is important – in width for stability, and for large, wide tires.
So, to get the function we want, order the axle. That way we can build it the way we want it, made for the tires we want on it.
For more info about axle specs and options, please read the Axles 101 article.
Special order the axle size that makes your trailer the most useful for you. The additional cost is small, and you will get the features you want. Get it Made-to-Measure, for your fun.
Why Not Design For Common Axle Sizes?
It is a question we get once in a while. Often the standard features are fine, so why not use common-ish sizes? Hopefully by reading the above, you now understand that to us, function is more important than tradition. You come first.
That said . . . .
Making Your Trailer Fit A Stock Axle Size
Most of our plans are 2″ – 4″ wider than tradition. It is a little bit that makes the big difference in usability. However, if you want a traditional trailer axle size, you can very easily modify our plans for it. Just shorten the crossmembers to the trailer axle size you want. Slimming the width a little is certainly one way that is safe to customize the plans.
In general, the spring seat width (for leaf spring axles) matches the center-to-center distance of the main frame beams. If plans call for 62″ spring seat distance, but the axle you buy is only 58″ spring seat distance, then you must narrow the trailer width by 4″. (62″-58″=4″). That means all the cross members, and the front and back beams (if your plans have them), must be 4″ shorter than the plans say. Make any other width adjustments too.
For a torsion axle, the same general rule is true. Just compare the dimensions shown in the plans, to the dimensions of the axle you buy.
Please note that it is not as simple as JUST shortening the cross bars. Look at the blueprints, then make all the small adjustments. Update your list of materials, then you are good to go. It is not too hard, and that is one way to avoid a special order axle.
How Do I Get A Special Order Axle?
In the instructions with each set of plans, there are suggestions for places to get parts. I personally find it best to order from a local shop. Many manufacturers require that you work with a distributer or shop anyway.
Here are some main things for Leaf Spring axles. Again, read the Axles 101 article for all the details.
- Axle Capacity – How much weight will the axle carry.
- Spring Center Distance – Length between the spring seats. (This is often the reference value for trailer axle size, but it is only one parameter.)
- Hub Face Distance – Length between surfaces where the wheels mount, left and right.
- Straight or Drop Axle – For deck height. A drop axle lowers the trailer 4” from the straight.
- Brakes – Choose Hydraulic, or Electric, or no brakes. Also, many axles have size options for brakes.
- Hub style (including the style 0f bearings, seals, grease zerks, etc.).
- Bolt Pattern – and number of lugs (bolts) to match your desired wheel, and load capacity. Of course, it must match the trailer wheels you will use.
- Spring Type and Length – Double-eye, or Slipper style leaf springs (typically for higher capacity). Use longer springs for a softer ride, but note axle spacing for multiple axles.
- Underslung or Overslung – This also effects trailer height.
- Camber – We suggest Camber if the loaded trailer will see many highway miles.
Torsion axles have similar options, as well. Plus, there are some extra things like high or low bracket, neutral angle of spindle, etc.. Please see the Axles 101 article for a lot more information.
Almost any trailer parts store can special order the axle. If not, contact Aaron (sales @ JohnsonTrailerParts.com) and he will fix you up. Look at the available options and decide what you need, then order it. Normally it takes 4-6 weeks, but with all the COVID stuff, I hear some lead times are long.
Summing It Up – Special Order The Axle
The trailer axle size is just one of the features you need to consider. Another is the axle spring brackets and springs. For multiple axles, the equalizer link, the action and the relationship with the spring hanger brackets (or other load equalizing mechanism).
It is true, some of our plans do not use a stock axle length, when it works for the design. We deliver plans that are functionally to size, not to the skimpy industry “cheat” size. We recommend special order axles anyway, so you can get just the right features for your trailer. It is not that complicated, and the instructions with the plans will guide you. Make it GREAT !!
Next up, read the article about mounting axles straight. Make sure they align properly so you get the best performance and the most stable towing.
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