3 Questions about Tandem Axle Trailer Suspensions
This article addresses three basic questions that you may have asked yourself about tandem trailer suspensions:
- Does my trailer need a tandem suspension?
- Which tandem setup is right for my trailer?
- 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.
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.
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.
“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:
- 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.
- 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.)
- 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
- Added stability
- Quiet rubber ride
- Smooth handling - loaded or unloaded