Types of leaf springs

Leaf springs are key components in commercial vehicle suspension systems. They support payload, control axle movement, and affect ride comfort and durability. Modern leaf springs come in several types optimized for different applications, load profiles, and suspension systems. Below is a comprehensive overview of the most common leaf spring types used today.

1. Conventional Leaf Springs (Multi-Leaf Springs)

Conventional leaf springs consist of multiple stacked steel leaves of decreasing length, forming a pack. The longest leaf (master leaf) usually contains spring eyes for attachment to the chassis. These springs are robust and widely used in heavy-duty trucks, trailers, agricultural vehicles, and some pickups.

Construction: Multiple constant-section leaves stacked together.
Advantages: High load capacity, simple design, easy repair/upgrade.
Applications: Construction vehicles, commercial trucks with heavy payloads.

2. Parabolic Leaf Springs

Parabolic leaf springs use a variable thickness profile: thicker at the center and tapered toward both ends. This design reduces interleaf friction and weight while delivering smoother springing characteristics compared to conventional multi-leaf springs.

Construction: One or two parabolically tapered leaves.
Benefits: Lower weight, improved comfort, more even stress distribution.
Applications: Vans, pickups, and modern commercial vehicles prioritizing ride comfort and efficiency.

3. Z-Springs (Air Links / Beam Springs / Trailing Arms)

Z-springs are a specialized form of parabolic springs with a distinctive “Z” geometry. They are typically used in conjunction with air suspension systems as guiding elements for the axle while the air bellows carry the main load. These components are often called air links, beam springs, or trailing arms.

Features: Single-leaf profile, compact design, effective axle guidance.
Advantages: Light weight, good directional stability, suited for air suspension.
Applications: Vehicles with air ride suspensions and specialized trailer configurations.

4. Leaf Springs With or Without Eyes

Not every leaf spring has rolled spring eyes at the ends. Spring eyes allow attachment to the chassis via shackles or hangers, but in some configurations — especially in heavy multi-axle vehicles — springs are mounted between axles without eyes, serving as load-balancing elements.

With eyes: Classic mounting to chassis or hangers.
Without eyes: Used in tandem axle setups (balance/walking beam suspensions) and certain intermediate positions where springs do not connect directly to the frame.

5. Wrap Leaves (Safety Leaves)

Wrap leaves (also called safety leaves) are extended leaves that wrap around the spring eye area to provide a backup connection if the main leaf fails. They enhance safety by preventing axle separation or excessive movement in case of a primary leaf fracture.

6. One-Stage vs Two-Stage (Dual-Rate) Leaf Springs

Leaf springs can be designed with single or dual spring rates to balance ride comfort and load capacity.

One-Stage (Single-Rate): All leaves work together uniformly across the load range. Good for stable load conditions and smooth deflection behavior.
Two-Stage (Dual-Rate): Secondary leaves engage only under high loads, providing softer response when lightly loaded and higher stiffness under heavy load. Ideal for vehicles with varying payloads.

7. Helper Springs

Helper springs are additional spring elements that activate only under heavy load to support the main leaf springs. They improve load-carrying capacity and reduce bottoming-out without replacing the main spring pack.

Types: Additional leaf packs, coil helpers, rubber/air helper elements.
Benefits: Added load support while maintaining comfort when unloaded.
Applications: Pickup trucks, delivery vans, trailers with occasional heavy cargo.

Conclusion

Understanding the different types of leaf springs — from classic multi-leaf packs to modern parabolic and specialized Z-springs — is crucial for selecting the right suspension component for your vehicle. Each type offers unique advantages in terms of load handling, weight, ride comfort, and service life, and should be chosen based on vehicle type, application, and suspension design.