What Are the Different Types of Semi-truck Suspension? (3+ Main Categories)

In this brief article we are going to discuss the different types of Semi Truck Suspension systems and the trucks that have these suspension systems.

What are the different types of Semi-truck Suspension?

The most common types of Semi Truck Suspension are:

• Leaf Spring Suspension
• Air-Leaf Suspension
• Air Suspension
• Tandem axle suspension

Leaf Spring Suspension

• The leaf Spring is the most common type of suspension on semi-tractor trailer trucks, especially as a front suspension.
• Earlier (pre-1970’s) truck models used Semi-Elliptic Type of leaf spring suspension
• Later models till date only use Parabolic Type of leaf spring; many trucks like Peterbilt, Kenworth and Freightliner also use a standard Parabolic front suspension setup
• Aftermarket suppliers like Henndrickson offer a Mono-leaf Softek NXT integrated front axle and steering assembly, which promises superior ride quality

• In the semi-elliptic leaf spring, each leaf is of constant thickness or, in other words, the cross-section of each leaf is constant throughout its length
• In a Parabolic leaf spring, the individual leafs of the pack are each of varying cross-section, except for the center clamping portion, where the leaf spring is flat. The cross-section varies in a parabolic shape from the center to the ends.
• In a Semi-elliptic leaf spring there is relative sliding motion between the leafs as the leaf spring travels between rebound and bump. For a Parabolic leaf spring, there is almost no contact area between one leaf and the other, except for the center clamping area and the 2 ends, where there is no sliding.
• The Sliding motion leads to a Damping effect in semi-elliptic, but there is almost no damping in the case of Parabolic suspension.

Air-Leaf Type Suspension

• The Air-Leaf type of Suspension is a combination of Parabolic leaf spring and Air bag suspension that works in combination to provide a soft ride. The leaf spring acts as a control arm and load bearing member for Low Frequency Vibrations.
• Air Trac is type of Air-Leaf rear axle suspension system used on PeterBilt Trucks with more than 46000 pounds GVW
• “Air Leaf” is itself the name of PeterBilt truck Air-leaf suspension system with Tracking Rods
• PeterBilt Low and Low-Low Air Leaf Tandem (built April 2004 or later) are variations of the ‘Air Leaf’ suspension which provide a choice of 2 lowered ride heights
• The Flex Air is a type of Air-Leaf type of suspension used on Peterbilt rear axle which is a combination of:
  • Leaf Spring, 
  • upper control arm and lower control arm
  • Air Bag

• The Kenworth AirGlide AG 130 Single Axle 4 Air Bag system as an optional package on the W990
• The Freightliner Airliner 

Air Suspension

Air Suspension will involve one two air bags per side on each axle and upper and lower control arms to constrain the axle in the longitudinal and lateral direction. In most cases the control arm would be triangulated to perform the dual function of longitudinal and lateral constraint. In some cases, a panhard rod or lateral rod would be used to constrain the lateral direction.

• Hendrickson – PRIMAAX EX Air single axle 2 air bag Suspension System on the Kenworth T270 and T370

Tandem Axle Rear Suspension

QuadraFlex 4

• The QuadraFlex 4-Spring Tandem Axle Leaf Spring Suspension in Peterbilt 90’s Model years.

Kenworth 8 Bag Suspension

• Kenworth 8 bag Air suspension is a Tandem Axle suspension that features 4 Air bags per axle
• 2 Air bags ahead of the axle and 2 Air bags behind each axle; Totalling 8 springs for a tandem rear axle arrangement

• The different versions of 8-bag air suspension found on Kenworths were the AirGlide 100, 200 and 400 models.

AirGlide Tandem

• The Kenworth AirGlide AG 400 Tandem axle 4 Air Bag system seen on the T680

Conclusion

In this brief article we have discussed the different types of Semi Truck Suspension systems and the trucks that have these suspension systems.

In case of any questions or queries, please feel free to ask.