The Sprung Axle vs The Torsion Axle
Do a little research and you’ll find diehard fans for each axle option: torsion or sprung. But there isn’t a right or wrong answer – both have benefits and disadvantages. What’s most important is to make an educated decision on which option is best for your towing application. Let’s decipher the facts…
The Scoop on Sprung
Leaf spring axles are the most common axle type, especially in the industrial utility trailer and RV markets due to its affordability and ability to service the system. Leaf spring axles have curved metal leaves stacked on top of each other acting as the shock absorbers for the trailer. Because of the moving parts, leaf springs lend to a ride that is typically louder and rougher than a torsion axle.
Leaf spring suspension systems are more versatile than torsion, suitable for single, tandem, or triple applications in capacities ranging from 2,000 lb up to 27,500 lb. Springs are either double eye – where both ends of the spring are mounted to the frame with hangers, or slipper spring where one end is mounted and the other is allowed to “slip” or slide back and forth to cushion the ride. Double eye would be used in trailer applications 7K and under where slipper springs works well with higher weight capacities. Double eye generally rides a little more smoothly than slipper; but more moving parts means more maintenance.
Leaf springs can be mounted two ways – underslung where the spring is mounted under the axle or overslung where the spring is mounted over the axle. Overslung is typically used when space is limited between the bottom of the frame and the top of the trailer.
Spindles are offered in both straight and drop versions. This helps obtain different ride heights which are determined by the manufacturer. Leaf springs are less compact than torsion axles, which affects ride height.
While leaf springs will have more wear and tear because of the moving parts, replacement kits are readily available, (i.e. shackle straps, spring seats and hanging parts). Tandem, double eye applications can be enhanced with an equalizer system. It help absorb road shock and provide a smoother ride and longer fatigue life. Equalizers are typically available for quick install during manufacturing or as a replacement kit. This affordable option does not affect the overall ride height.
The Low Down on Torsion
Torsion axles are made with rubber cords (typically 4) inside an axle tube surrounding a solid inner bar. The rotation of the trailing arm attached to the inner bar compresses the rubber cords between the inner wall of the axle tube causing resistance. Various start angles are available for the trailing arm which helps to control trailer height. Torsion axles are mounted to the trailer frame with metal brackets. The system adds rigidity to the trailer frame reducing flex with cross wind or rough terrain. Torsion axles can also act as a cross member.
Because they are more compact than leaf springs, trailers with torsion axles are often lower to the ground. This lower center of gravity offers improved handling, especially cornering. This also makes torsion axles ideal for boat trailers where a lower trailer makes it easier to launch on shallow ramps. Torsion axles work best in fully loaded conditions and may not perform as well in extreme cold where the rubber is not as elastic.
Due to each torsion axle being independent, the trailer is not equalized, increasing the importance of towing the trailer level. This independent suspension will mitigate side-to-side transfer when one side of the trailer encounters uneven terrain, reducing stress on the load. Triple axle systems are also not recommended unless axles are specifically designed for triple applications.
There is nearly no maintenance required for a torsion axle beam since it is mostly a self-contained system therefore replacement parts are not characteristically available. Removable spindle options have recently been introduced to the market reducing field service costs by allowing the replacement of only the spindle in the field instead of the whole axle. Torsion axles with removable complete trailing arms are also available which allows the start angle to be changed.
Torsion axles can be upgraded to an air ride suspension system offering an improved softer ride. This high end feature is used most often in horse trailers or race car trailers due to cost. It’s usually available on 7K or 8K torsion axles in single, tandem or triple applications.
Warranty coverage for torsion axles is generally longer than leaf spring. Most manufacturers offer a 5-year limited warranty on the suspension system where sprung axles are usually a 2-year limited warranty. Few manufacturers extend warranties to 3 years with the use of matching HAP (hanging and attaching parts) kits.
While most agree that torsion axles are less suitable for rough terrain, off road use, or heavier loads, the agricultural and specialty markets are seeing an increase in torsion axle use for high vibration applications. In some heavier vibration uses – such as wood chippers – extreme duty torsions are preferred over sprung axles because the rubber will remove the metal to metal contact factor that could result in potential damage.
Satisfaction = Happy Customer
Torsion axles will provide a smoother ride with less maintenance where leaf spring axles are more durable, less expensive and easier to repair. Your overall satisfaction will depend on selecting the axle and trailer that best meets your intended use based on the load and application. And as always, properly loaded cargo coupled with periodic maintenance will assure a long axle and suspension life.
*warranties provided vary based on manufacturer. Warranty information stated is typical for the axle market. Check with your axle manufacturer to verify warranty duration.