Can I Use An Axle-Less Suspension

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

Yes, even the axle-less suspension has an axis (or axle with bearings) 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, this is a way of mounting a wheel on just one side of a trailer.  This makes it completely independent of the wheels on the other side.

Oh, and it has its own suspension.

Please Note: This product by Timbren is just one way to do it.  There are other styles of “Axle-Less” Suspension for trailers too, like torsion half axles from many suppliers for the same thing, but in a more compact form.  The image below shows a torsion half axle which does almost the same thing as the Timbren. It just mounts different.

Torsion Half Axle
A Torsion Half Axle Has Similar Axle-Less Function

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

Advantages:

The big advantage comes with removing the crossing axle beam.  While this offers several nice benefits, ground clearance under the trailer center is the big one.  If the axle beam 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 will 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 are 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, this is not as clean as it might first seem.  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 inherently align properly — from the factory.

So, if we take away the beam which crosses the trailer — using an 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, because it is not set at the axle factory.  See Trailer Axles 101.

3.  Axle-Less trailer suspension is great for Suspension Response because they have a low unsprung weight.  Comparing to a standard leaf springs, the axle beam is unsprung weight which slows suspension response.  While this is a little thing on a trailer, but worth mentioning.

Please Note, however, torsion axles are also independent, with even less unsprung weight.

4.  While it may be tempting, and in spite of what advertisements may say, axle-less is not for multiple axles.  (For the tech and illustrations of why, please see  “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, etc. support the wheel from just one side, then have structure to handle overhanging forces.  Super common.

Overhanging forces come from having the wheel off to the side of the mounts.  This first illustration below 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.  Overhang is the horizontal distance, the offset, from the arrow down to the arrow up – each side.  That creates a moment.  For a full beam axle, the overhanging forces are handled by the axle beam, green arrow.

Torsion with Full Beam

The next illustration shows an axle-less application.  This 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 moment load that we must now handle.  It was a job of the axle beam, but now we must now do it another way.

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 trailer frame rigidity to make it all work.  That is why Timbren (and torsion half-axles) require an extra crossing 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. (Interesting because that effectively makes it like a torsion axle.)

So, put a strong cross member in and use it as part of the mounting for the half axle or axle-less suspension 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 the use of the axle less suspension.  On the contrary, if you choose it, then I 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 is not a 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 is insufficient.  First there is no guarantee the beams are parallel.  Second, there is no guarantee sides of the frame are truly vertical and parallel.  (Steel stock is never truly square with perfect flat sides.  Rectangular tubes are not truly rectangular.  Sometimes the sides bow out a little, sometimes they bow in.  Same with channel and I-Beam.  They are not perfect.)  If the trailer is not dead straight perfect, the axle-less spindles won’t be either.

If you guess (with a tape measure), like most people, and hope the frame is square enough in all three directions, the wheels will not align.  (Yes, a tape measure is fine for a square enough frame for normal use, 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.  Perhaps laser alignment tools?  Then, mount the parts with shims or something to fix them in the aligned position.  Then, 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?
  1. The most likely outcome is bad tire wear.  If the tires directionally fight each other, the tires will wear prematurely.  If the misalignment is bad, they might get hot and fail by popping.  (Less likely.)
  2. The second most likely outcome is a trailer that is squirrelly to pull.  It may wander behind the vehicle — not because of stability concerns as we have discussed previously, but because each wheel wants 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 — especially if it is negative camber.  But, how can you tell?
  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 the very different overhanging load, 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.

Axle-Less Suspension Mounting

There are a number of ways to mount an axle, but most common is bolting.  Often, brackets weld to the trailer frame, then axles bolt to the brackets.  That allows removal if needed.

Welding is the other common way.  However, most manufacturers say DO NOT weld the axle to the trailer.  That is true of Axle-Less suspensions also.

The Timbren Axle-Less trailer suspension mounts with bolts.  But, where do the bolts go?

Look at the photo near the top of this article and see the 3 bolt holes.  Drill 3 matching holes in the trailer frame for these bolts.  Ah, but that means we drill through the trailer frame main beams – creating 3 problems:

  1. Holes in a tube, allow access for moisture.  Although it takes a long time to rust through from the inside, open tubes are not the best choice. On the other hand, for C-Channel or I-Beam frames, bolts conflict with the flange transition.
  2. If you torque the bolts on thin wall tubes, it will change the camber and alignment of the axles as it squeezes the tube.
  3. Drilling holes in the trailer frame main beams at the point of highest frame stress (right above the wheels) is weakening the frame at the most important point.

The easy idea of drilling through the main beams is not very good.  To solve it, use an additional bar of steel (or thick tube) under the frame for the bolts.

Bolt the Timbren to the added bar of steel.  That helps in more ways – like if you want a higher trailer clearance.  It also spreads the suspension load to the trailer frame which is great (so make this extra beam about twice the tire diameter).  Anyway, I just want to call this to attention so you know what is involved.

Other Options

A good torsion axle with a neutral angle down, will add ground clearance similar like 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 the come from separate suspension modules. It still needs a buffer to spread the stress to the frame, however, it does not have to be tall enough to support bolts.

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.)  This will give a lot of ground clearance on 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 our recommendation, the torsion axle trailer plans will also work with an 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 will be fine.


Question:

Can I use a Timbren Axle-Less Suspension for the 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.  Here is the article with the technical information – illustrations and explanation – about why that is a bad idea.  The article specifically talks about torsion axles, but the exact same is true for every other independent trailer suspension – including the Timbren Axle-Less 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 an axle-less suspension with the walking beam plans.  The main pivot pin will not handle the added 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 am 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 does not 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.  In most cases the final trailer will be a little heavier than with a full beam torsion axle.


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.  As noted in the article above, there are some bolting issues to overcome.

For frame stiffness, use the hole they provide for an added cross beam, 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 loads.  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, see the notes above.  We recommend a thick tube below the trailer frame for bolting.  However, if you must bolt to the trailer frame directly, it is 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 not to crush the tube.  Best to weld a bolt sleeve through the tube so it can’t crush.  With these precautions, it does not matter if you choose Tube or C-Channel.


Good Luck with Your Project !!

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