Axle-Less Trailer Suspension

Customer Question:  “What do you think about the Axle-Less trailer suspension?  Is it good?”  Can I use it with the Mechanical Elements trailer plans?  . . .  You ask (actually a few of you are asking) and pointing to the eTrailer website, so here is some research and some answers about the Timbren Axle-Less trailer suspension.

If you have not seen it, the concept is a fully independent suspension that mounts on each side of the trailer.  The idea eliminates the axle tube that crosses the trailer.  In the pure form, it increases ground clearance and helps isolate axle input.  There are various methods of axle-less suspension, but in this post we’ll discuss details of one type with an elastomer in compression for spring force and damping.  It’s different from a torsion axle in the way the elastomer (rubber) compresses, but the properties are similar.

Other manufacturers use coil springs or airbags and sometimes shock absorbers for an ‘independent’ or axle-less trailer suspension.  Also, single side torsion axle stubs offer a similar axle-less function.  However, for simplicity, this article will focus on the Timbren suspension modules.  Other types may or may not be similar.

(To be complete, we will note that many multi-axle Air Suspension systems often look independent, but are actually internally linked.)

First Things First

Disclaimer:  This is NOT a definitive answer about the Timbren or any other products, because I don’t have first hand experience.  However, I do have experience with other Timbren products, like Suspension Enhancement Systems.  This post is about what I read and see, coupled with good engineering judgement and axles 101.  This is just one perspective, so use it with other available information as you make decisions.

The Axle-Less Trailer Suspension

From eTrailer, the Timbren Axle-Less Trailer Suspension PartsAs noted above, and in the images here from eTrailer.com, the Timbren product consists of 2 modules, a left and a right, that attach to a trailer frame and provide independent suspension for a wheel on each side of the trailer.  The design is a trailing arm style — generally good for stable action.  The image shows both the left side and the right side oriented as on a trailer.  They come with a neutral height like this one, or with a 4″ drop for a lower trailer bed height.  They also come with a lift for even more clearance.

In general, I like the product.  It’s not just a spring of rubber, they also include a chunk for rebound control.  Also, the overall construction seems well thought through and stout.

Things You Might See

On their website, Timbren is fairly clear in discussing benefits.  They don’t, however, get into details about where it will and won’t work, and they don’t address other things to consider with implementation.

On the other hand, retailers like eTrailer.com write a bunch.  The text below is a screen shot from the eTrailer site.  Normally I really like the great eTrailer info, but some of the info here is a little misleading.  See the circles in RED, then the comments below.  Remember, this is from eTrailer, not Timbren.

ALTS Description of Timbren Suspension

Comments About The RED Marks

“… Replace Your Existing Axle …”

Be very careful before you “replace your existing axle”.  As in the post on loads for suspension types, the forces are different with various suspensions.  These are no exception.  They function in some ways similar to a torsion axle, so the resulting forces to the trailer frame are NOT simple.  Just make sure the trailer frame strength is right for these forces before replacing an axle.  Also see the “Red Box” note below.

“… Safe, Smooth, Quiet Ride …”

Rubber definitely has some advantages for progressive spring rate and damping qualities – mostly very favorable for trailers.  Just don’t be fooled into thinking that statement makes these unique.  You can say the same thing about torsion axles, airbags, rubber isolators, etc..

The one downside to rubber is it hardens and changes (sometimes decays) with time.  That said, it takes a while.  I did not notice any of that with the Timbren rubber products I put on my van.  Just something to be aware of.

“… Lower Deck Height …”

For truth in advertising, please note that a lower deck height is comparative.  The lowest deck heights are typically available using torsion axles having arms at a neutral angle up.  Or, with special less common types using crank arms — like this low profile suspension.

“… Reduce Roll …”

Reduction of roll in corners must be qualified by suspension motion, hysteresis and damping.  If these have less total suspension travel (harder suspension), then yes, this is true to a level you might notice.  However, there are disadvantages to having less suspension travel.

Rubber suspensions have a natural hysteresis and a progressive spring rate.  That gives a different feel to the suspension that some equate with roll control.  Here’s a bad example video.  Though it’s not really a reduction in roll per se, it can “feel” more stable during certain dynamic events.

Real reduction in roll must include connectivity across the vehicle — like the torsion bars under your car.  Since these don’t have that, and they don’t have dynamic stability control (electronics), the claim to reduce roll is mostly false.  Even more to the point, Timbren does not make that claim, so it’s likely a false sales pitch by the writer for eTrailer.

“… Can …”

See notes below.  This is only true if the axle-less trailer suspension is installs straight and true.  Otherwise, the opposite will happen with the trailer less stable and increase wear on the tires.  From my perspective, these can be great, or, if installed just a little wrong, (or if the frame is not sufficiently stiff), they will be a disaster.  That means we, the DIY guys and gals, are the key to success.

“… Triple Axle Applications …”

While this is strictly true, it insinuates that tandem axle applications are OK.  That is NOT true.  I guarantee if these are in tandem on a trailer at capacity, you will have wheel, tire or bearing issues.  They don’t load share, so don’t do it.  Want more info?  Here’s the article with the engineering on the topic.

If you like this suspension type but want a tandem, use the very similar Silent Ride Trailer Suspension also by Timbren.  It is the same thing, yet made in a tandem axle system.

The Big Red Box

This is a very interesting note about the Timbren Axle-Less Trailer Suspension.  It basically negates some of the benefits by adding an axle beam.

Because the axle-less trailer suspension supports a cantilever wheel (off to the side), there are high twisting forces to the trailer frame.  With other suspension types, the twist forces are held by the “axle” beam.  However, for these, the trailer frame must handle them instead.  Of course, on a trailer made for these, it’s not a problem, but as in the Red Box note, you must make the frame for it, or add the axle beam.

I am glad they include this note because handling the cantilever suspension force is very important.

Axle-Less Trailer Suspension Installation Notes

Getting the installation right is the big hiccup, but also the key to success.  The literature makes it seem like a breeze, but I don’t believe it is.  Here are 3 important thoughts.

1.  The literature assumes your trailer beams are exactly parallel, and the hitch is perfectly at center.  That is often not quite true — especially with DIY trailers.  It also assumes the bottoms (mounting surfaces) of the main beams are coplanar (meaning flat and parallel).  Again, not always true.  And, not always a fault either, because often the main beam surfaces are not flat.

2.  How do you assure the spindles (left and right) align on the trailer.  Maybe with a jig so they fix true before attaching them?  If you guess (with a tape measure), and rely on the frame being square in all three directions, the wheels will not be parallel.  For slow speeds, like rock crawling, that doesn’t matter, but for highway use  . . .  A trailer with misaligned wheels will NOT pull stable and true.  And, it will increase tire wear.

Along with alignment, how do you set camber?  With a full load, will the wheels splay out a little because of deflection in the cross member or trailer frame?  I don’t know how much, but it’s worth considering.

3.  As mentioned, this suspension applies a strong twist to the frame.  That force is normally handled by the axle, or by the torsion beam of a torsion axle.  Counteracting that twist requires a substantial crossmember, or an added member in the provided pocket.  Make sure it is up to the task, because other cross members already have bed loads to contend with.  Adding the extra member Timken allows for will work, but truly, it’s no different than the beam of a torsion axle.

Summary

If you mount them perfect — with sufficient frame strength and stiffness — then I have no doubt this is a great suspension product.

Can I Put Axle-Less Trailer Suspension On Mechanical Elements Trailer Plans?

Good question.  With some adjustments to the plans, yes — for SINGLE axle trailers only.  Please don’t just slap them on in place of the defined axle.  ALSO, this system does not load share, so they are NOT good for tandem axles.  Use the Timbren Silent Ride walking beam suspension instead.

If you want this addition to our Mechanical Elements trailers, read about implementing it.  As mentioned above, you will need a cross member located nearby.  Then, stiffen the main beam above and around the area where the Axle-Less trailer suspension will mount.  See this article on mounting axles for more information.  The Axle-Less suspension loads the trailer frame more like a torsion axle, so adding a stress distribution member is a good idea.

Finally, figure out some way to align them.  Relying on frame members to be true and square is a bad idea – because they never are.  The materials we build them from are not guaranteed true and square, so even if we are extremely careful, the frames are true enough to align wheels.  Find a way to align them right.

What Do You Think?

Personally, I like it.  And, I might just build my next trailer with a set of these just to try them out.  Just have to make sure I mount the axle in the right position.  The only other hiccup I see is the cost.  They are not cheap.

Please leave a comment about what you think.  Let us know if you have them and what hurdles you find for installing them.  Do you like them?  Do they work well for you?

Next, for more on axles, read about Overslung and Underslung axles, or the article on rigid mount axles (for the full axle-less experience).  Thank you for visiting.

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