Can I Use An Axle-Less Suspension

Axle-Less trailers.  Yes, that’s a thing, and we get a lot of questions about this unique suspension.  Some people ask if it’s any good?  Other’s ask if it will work with our trailers?  Still others ask about using them for tandems?  We even get questions about using it with our Walking Beam Suspension.  All are worthy questions, but they need a backstory to properly answer them.  So, here is a bunch more information — about Axle-Less suspension in general, and about the Timbren in specific.

By Definition . . .

Trailer wheels need an axle . . . kind of by definition.  That said, the play on words in the name “Axle-Less Suspension” is not really wrong.  Typically, this has reference to a product by Timbren that they call “Axle-Less Trailer Suspension”.  See the Photo below.

Timbren Axle-Less Trailer Suspension
Timbren’s Axle-Less Trailer Suspension

Yes, even the axle-less suspension has an axis around which each wheel turns.  However, these devices “disconnect” the left wheel from the right in the traditional way of thinking for trailer axles.  In other words, it’s a way of mounting a wheel on just one side of a trailer, independent of any other wheels.

Oh, and it has its own suspension.

Please note that this product by Timbren is just one way to do it.  There are other ways too, like the torsion half axles from many suppliers for the same thing, just in a different form.  The example below is a torsion half axle (image from SD Truck Springs).

Torsion Half Axle
Torsion Half Axle

And, there are other less known products that give a similar function too — like independent air bag lift systems.

Advantages:

The big advantage comes with removing the crossing axle beam.  While there are several nice benefits, ground clearance under the trailer is the big one.  If the axle is not there, ground clearance improves drastically.

A second cool advantage is they mount on any width trailer — they don’t care about how wide or narrow the trailer is.

There are more advantages, or touted advantages, which we will cover in context below.  We’ll get into busting some myths, and explain some things that are not immediately obvious.  In the mix, we will also talk about some disadvantages that are worth noting.

Axle-Less Suspension Caveats

1.  The biggest advantage of Axle-Less suspension is ground clearance, which comes by removing the “axle” beam.  We’re talking about the crossing beam under the trailer between the wheels.  Without the beam, ground clearance improves under the center part of the trailer, which is great, especially for off-road.

However, the “axle” beam crossing the trailer has 2 important functions:

  • First, it carries the overhanging forces that come from the wheels.  No matter what, we must handle those forces.  You might have seen a trailer going down the road with the wheels splayed out.  That happens when there is not sufficient support for the loads.
  • Second, a standard axle or full torsion axle from the factory uses the beam to assure wheel alignment.  Spindles (and bearings) mount at either end of an axle, making the wheels align from the factory.

So, if we take away the beam that crosses the trailer — with Axle-Less Suspension — then we must achieve those 2 important functions in another way.

2.  Things like axle Camber become more difficult to set and maintain, if it is not set at the axle factory.  See Trailer Axles 101.

3.  Axle-Less trailer suspension is great for suspension response because they don’t have a lot of unsprung weight.  With a standard leaf spring trailer axle, the axle beam is unsprung weight.  Full torsion axles are also independent suspension, and don’t have much unsprung weight either.  While this is a little thing on a trailer, it’s worth mentioning.

4.  While it may be tempting, and in spite of what advertisements may say, these are not for multiple axles.  (For the tech and illustrations of why — “Independent Trailer Suspension – Are You Being Taken For A Ride?“)

Overhanging Forces

Almost all wheels have overhanging forces.  The exception is a bicycle or motorcycle wheel with support on both sides of the axle.  Cars, trucks, trailers, trains, and a ton of other products support the wheel from just one side, and the structures handle the overhanging forces.  It’s something we know how to do.

Overhanging forces come from having the wheel off to the side of the mounts.  This first illustration shows a full beam torsion axle.  Red arrows under the wheels represent the load on the ground.  Red arrows pointing down represent load from the trailer.  The overhang is the horizontal distance, offset, from the arrow down to the arrow up.  That creates a torque.  For a full beam axle, the forces are handled by the axle beam, green arrow.

Torsion Axle with Full Beam

The second illustration shows an axle-less application.  This one is a torsion half axle, but the same is true for the Timbren and others – they just have a different shape.  For an Axle-Less suspension, the only connection from left side to right side is through the trailer frame.  The green curved arrows show the torque load that we must now handle.  It was done by the axle beam, but now we must use the trailer frame.

Axle-less Suspension Forces

With a standard axle (and a full beam torsion), the compensating forces naturally go to the connecting beam.  With Axle-Less, we have to add some trailer frame rigidity to make it all work.  That’s why Timbren (and torsion half-axles) require the extra cross member.

So, Where Do We Start?

Timbren is very clear that you need a stout cross member in the trailer frame at the location where the suspension mounts.  They even provide a hole where you can add a cross member through their mechanism if you don’t have one (or can’t put one) on the trailer frame.

So, put a strong cross member in and use it as part of the mounting for the half axle or axle-less units.  This will keep the trailer frame beams from twisting.  It requires more substance than a piece of angle iron, however.

I am not trying to discourage use of the axle less suspension.  On the contrary, if you choose it, then I do want you to be successful, and that means being aware of potential issues.  And, the solutions.

Wheel Alignment

Of all there is to love about the Axle-Less suspension, wheel alignment is the one piece of the puzzle I can’t get my mind around.  I can’t figure a good way to assure the two spindles are REALLY in alignment.

If you are making a rock crawler trailer that never goes fast or far, then it’s no problem.  On the other hand, if the trailer is for the highway, you will need to find a way to assure the spindles align.

Relying on a hopefully square and parallel trailer frame members is insufficient, IMHO.  First there is no guarantee the beams are parallel.  Second, there is no guarantee that the sides of the frame are truly vertical and parallel.  If you just guess (with a tape measure), like most people do, and hope the frame is square enough in all three directions, the wheels will not align.  (Note, a tape measure is fine for a square enough frame, but wheel alignment is much more critical.)

You will need to build a jig or something to make sure the wheels align and run true.  Then, you’ll need to mount it with shims or something to fix it in the aligned position.  Also, what about camber?  How do you set that?

I have not seen a good solution to assure alignment, but maybe you can figure out something.

What will happen if wheels do not align perfectly?
  1. The most likely outcome is bad tire wear.  If the tires directionally fight each other, the tires will wear prematurely.  If it’s bad misalignment, they might get hot and fail by popping.  (Less likely.)
  2. The second most likely outcome is a trailer that is hard to pull.  It may wander behind the vehicle — not because of stability concerns as we’ve discussed previously, but because the wheels each want the trailer to go a slightly different direction.  Basically, if the spindles do not align, then the trailer will not pull stable.
  3. Third, without careful alignment, one wheel will very likely have a different camber than the other.  See trailer axles 101 for more info on camber.  That will amplify the 2 issues above.
  4. Fourth, when the trailer is empty, it may tow fine.  With a load, it may have the characteristics above.  (Partly because the wheels have more traction when loaded, and partly because of insufficient overhanging load handling, see above.)

These are just some things to think about.  Best to know about possible things to care for when building, than to build it and find out you need to go back and fix things.

Other Options

As a side note, a good torsion axle with a neutral angle down, will add ground clearance similar to the axle-less suspension.  The spindles align at the factory, so just place the main torsion beam straight and square on the trailer frame.  This also eliminates other degrees of complication with separate suspension modules.

For off-road trailers, one option is a torsion axle that has a little more capacity than you need, then mount big tires.  (The over-rated axle will handle the big tires.)  You’ll have lots of ground clearance with a trailer that tows stable.

There are two articles on the topic worth reading.  The first, is a review of an advertisement for the axle-less product.  The second, is Axles 101 — scroll down to the part about torsion axles.

Questions About Axle-Less Suspension

Now for a Q&A.  We get a lot of questions on the topic, so here are some thoughts.  Feel free to ask more in the comments.


Question:

Can I use an Axle-Less Suspension with Mechanical Elements trailer plans?

And the similar Question:  I want to build a trailer with the Timbren style axle-less suspension.  Do you have a set of trailer plans with the necessary frame mods?

Answer:  While a torsion axle is the recommendation, our torsion axle trailer plans will also work with the axle-less suspension.  You will need to increase the size of the cross member near the axle, or use the crossmember adaptation from the suspension as Timbren recommends.  Follow the Timbren instructions for mounting the suspension, and make those mods to the plans, then you’ll be fine.


Question:

Can I use a Timbren Axle-Less Suspension for our 20′ tiny home trailer?

Answer:  I do NOT recommend using independent suspension of any style in a tandem or triple axle situation.  The axles need to share the load.  Do you want the technical data to back this up?  Here’s the article with illustrations and explanation about why that’s a bad idea.  The article specifically talks about torsion axles, but the exact same is true for Axle-Less (and every other independent trailer suspension style).


Question:

Hi, I am interested in the walking beam trailer suspension, but also looking to use the Timbren axle-less suspension.  Would the torsion effect from removing the axles affect functionality or create other issues?

Answer:   Please do not use the axle-less suspension with the walking beam plans.  The main pivot pin will not handle the additional offset forces.  Even Timbren highly recommends a cross member.  The pin in our walking beam suspension will hold the load, but it will wear that area out very fast.  It is definitely not for a Timbren suspension.  Even if you weld in a crossmember like Timbren recommends, I’m not sure how you would flexibly attach it to the walking beam.  The axle must attach to the walking beam in a flexible manner so when wheels move up and down differently on one side, it doesn’t bind in the suspension.


Question:

Will the Axle-Less Suspension make the trailer lighter?

Answer:  I have not looked at weights specifically, but even if it is slightly lighter, you must add things to the trailer frame that will offset any weight improvements of the suspension components.  If there is a net weight improvement, it will be very small — which is not a good reason (alone) to use it.  I personally think the final trailer will be a little heavier.


Question:

Is it better to use the Axle-Less Suspension with C-Channel or Tube for the trailer frame side beams?

Answer:  I don’t think it matters, as long as there is a stout cross member in the area.  Use the hole they provide, or put something in the frame at that point.  It will need to be more substantial than a piece of angle iron because of the large, frame twisting load.  Tube actually is better at handling torsional loads than C-Channel.  But either way, a good cross member is a must.

As far as bolting through a Tube or C-Channel, it’s easier to clamp hard through the flange of C-Channel than through a Tube.  That said, you can bolt through tube if you are careful to not crush the tube.  You can weld a bolt sleeve through the tube or something like that.  With these precautions, it does not matter if you choose Tube or C-Channel.


Good Luck with Your Project !!

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