Key Questions to Ask When Ordering tandem trailer suspension types

This article addresses three basic questions that you may have asked yourself about tandem trailer suspensions:

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1. Does my trailer need a tandem suspension?


2. Which tandem setup is right for my trailer?


3. Which one will give my trailer the most stability?

“Does my trailer need a tandem suspension?”

The concept is simple. If you need to carry more weight, you put more axles under the trailer. Capiche?

“Okay, but why not just buy a stronger single axle?”

There are four big reasons for adding extra axles:

• Tires To carry more weight you need bigger tires. But higher capacity tires are usually bigger in diameter which affects bed height, not to mention a few other details.


• Safety With a single axle, regardless of how hefty it is, if you damage one tire, you’ll have a major problem. But with an extra tire on each side, you can usually pull over before serious damage occurs.


• Load distribution With more than one axle, the load is spread over a much broader portion of the frame, which adds more strength.


• Ride quality With more than one axle, the load is distributed over more points, so when a tire encounters a bump or pot hole, the load-sharing linkage (the equalizer) helps lessen any bouncing or jarring of the trailer. This produces a smoother ride.

“Which tandem system is right for my trailer?”

Axles for trailers and the accompanying hardware are readily available, and come fairly standard. The challenge is to choose the best tandem suspension setup for your trailer. Let’s take a look at some of the various designs.

Leaf Spring

The leaf-spring suspension system is the most common, and also the least expensive. When looking for a tandem leaf-spring setup, the choice comes down to either “Slipper” style (fastened with a bolt at one end), or “Double-Eye” (fastened with a bolt at both ends). As a rule of thumb, think “Slipper” for heavy loads (6000 lb axles and more) and “Double-Eye” type for lighter applications (4000 lb axles and less).

Both leaf springs need to be placed in tandem using an equalizer. This will help to distribute weight more evenly between the two axles.

Torsion Axles:

Two torsion axles side by side should be referred to as “Twin Axles” rather than “Tandem Axles.” Why? Because the two axles do not interact with each other. Therefore, they can’t equalize (load share) when the road is uneven.

Basically, if you hit a bump or pot hole, the front axle will take the entire load, forcing the rear axle up into the air. Depending on your capacity, this might become a serious overload issue. While it’s true that torsion axles handle overload conditions better than leaf springs, the tires and the frame do not. 

Hybrid equalizer using rubber

One of the advantages of using rubber torsion axles is the vibration damping. Similarly, by adding rubber to the equalizer for a leaf-spring tandem setup, much of the same effect is achieved. The rubber provides vibration damping and equalizing, allowing the axles to share the load when the road isn’t level while offering vibration damping.

Center Pivot / Walking Beam:

An entirely different approach to a tandem axle setup is the Center Pivot – also called the “Walking Beam” suspension – to accommodate equalization. A good example of this type is the Silent Ride suspension from Timbren. This is a quality system and more expensive than a conventional leaf-spring suspension. Also, much of the load is concentrated in a relatively small area, so the trailer frame might need to be strengthened where the hanger is installed.

https://www.youtube.com/watch?v=B4BXxfcR6X4

“Which one will give my trailer the most stability?”

There are a number of factors that contribute to axle / trailer stability. Here are just a few of them:

1. Proper placement of trailer axles along the frame can make the difference between a trailer that tows safely and one that is a danger to everyone on the road.

Axles mounted too far to the rear puts too much weight on the trailer hitch causing undue wear on the tow vehicle's suspension and tires. Too far forward and the tongue weight won't be enough, causing the trailer to sway badly.

The mounting point for a single or tandem-axle setup is 40% the length of the trailer bed, measuring from the back end (length x .4). For a tandem axle setup, the 40% mark lines up with the center of the equalizer.

2. A trailing arm is a very stable way to mount an axle. It’s one of the reasons people like the feel of torsion axles. (But as we said before, twin torsion axles – although very stable – don’t offer any equalization.)

3. When two leaf-spring axles are mounted without an equalizer, the back axle acts like a leading arm, which is not a stable setup. But if they are connected with an equalizer in the center, the back axle becomes more stable. 

One word about Silent Ride…

If the lowest price is what you’re looking for, there’s plenty to choose from.

But… if you’re ready to upgrade your trailer to a quality, top-of-the-line product, the Silent Ride tandem suspension might be exactly what you’re looking for.

Some of Silent Ride’s features are:

• Easy installation


• Built-in camber


• Equalization


• Added stability


• Quiet rubber ride


• Smooth handling - loaded or unloaded

Click here for more information on Timbren’s Silent Ride suspension.

There are a number of choices for suspension on a trailer that is practical and enduring and while there are other options such as swing arms, coil and shock absorber style suspension available, the following are the most popular.

Leaf Springs

Leaf spring suspension has been around in one form or another since Roman times and steel leaves have been used since the 18th century. You might think that using leaf springs on your trailer is a bit old fashioned, believe me, it’s not. The reason why is we still use them is because they are so damn good. They are relatively cheap to manufacture, long-lasting, easy to repair or replace and depending on the spring setup, they can carry huge loads while reducing stresses on the trailer chassis and axles.

Springs are built to an upper load limit and need to be matched to the total trailer and load weight. Too low a load rating and the springs will bottom out and quickly fail. Too heavy and the ride will be stiff and harsh causing stress to both the trailer and load.

Leaf springs are available in almost any combination from very light duty single leaf to behemoth 12 leaf plus monsters.

For more information, please visit advantages of suspension system.

Find a spring that matches your load rating and find one that has a reasonable camber that suits your axle position. Springs are normally available painted, but galvanized leaves and also proprietary corrosion coatings are also available. Just remember that leaf springs are designed to slide against each other and wear between the leaves is inevitable and unpreventable. Galvanized springs, due to the nature of the heat treatment process may be slightly weaker overall and lose their camber quicker than painted springs.

Poorly galvanized springs are prone to cracking and failure - always purchase from a reputable supplier.

Slipper Leaf Springs

(Eye/Slipper)

This spring has the least moving parts of all springs although there can be a bit of wear where the springtail rubs against its slipper. An anti-rattle version is available as this spring can be very noisy over bumpy roads if the standard version is used. Using the slipper to retain the spring gives good lateral stability to the trailer and is especially good on a trailer with 2 or more axles because of this extra constraint. An advantage of these springs on a single axle is that the distance between the chassis and the spring is quite compact and can be helpful if you are after a lower deck height.

Double Eye Leaf Springs

(Eye/Eye)

This is another common type of setup that rather than 2 loading points on the chassis with the slipper style, the dual eye has 3 distributed points which minimize stress in the chassis and to some point to the axle. The spring requires a correct set up to ensure correct operation. I have seen these springs tuck themselves in between the hangers and jam up due to very bumpy roads and overloading of the trailer. They are ideal for single axles but due not give as good side to side stability as the slipper style on a multi-axle setup and reduces their load sharing capacity.

Another possible disadvantage is they take a bit more room up under the chassis and can limit how low the deck height can be.

Parabolic Springs

The Parabolic spring is the modern version of the leaf spring. It is normally a single leaf with a thicker center tapering out to the ends in a parabolic curve. The advantages of this spring are that there is no interleaf friction, they weigh a little less than standard leaf springs and are not as stiff as leaf springs so give a much smoother ride. Disadvantages are that they tend to take a lot of room up under the trailer so this can limit how low the deck height will be and the single leaf version has a lower load capacity compared to standard leaf springs.

Multi parabolic springs are available and these are set up with spacers between each leaf to prevent contact due to the shape of the leaves. These will take more weight but again add more to the underside of the trailer raising the deck height considerably.

Torsion Suspension

Torsion suspension is basically a swing arm style axle that pivots within a rubber or elastomer enclosure.

As load is applied to the axle the torsion arm turns within the rubber causing the rubber to compress on one side and roll on the other and as the load is released the rubber moves the torsion arm back to its original position.

This type of suspension can give a very smooth ride as the trailer rides over the bumps with independent suspension. Another advantage is that the trailer deck height can be significantly lower due to the lower profile of the torsion unit.

There are a few disadvantages to torsion suspension as follows. Torsion suspension load capacity normally maxes out at 2500 kg towing capacity as a tandem setup, but due to the independent nature of the suspension and the way it is mounted on the trailer, axle load sharing is non-existent which can stress the chassis considerably. For this reason, when mounted on a tandem trailer, the axle rating should be reduced by around 25% to avoid bearing and suspension failure. For example, over a bumpy road, one axle may be constantly working overtime while the other axle will be fully unloaded. The overloading can cause premature failure of the bearings and axle.

Contact us to discuss your requirements of car axle for sale. Our experienced sales team can help you identify the options that best suit your needs.