Leaf Spring

A leaf spring is one of the oldest and most enduring forms of vehicle suspension, consisting of a curved strip of spring steel, or a stack of several such strips of graduated length clamped together, that flexes under load to cushion the chassis from the road. Its long history stretches back to horse-drawn carriages, and it survives in modern use precisely because it does several jobs at once with remarkable simplicity. Where coil springs only resist vertical compression, a leaf spring both supports the weight of the vehicle and helps to locate the axle, controlling its fore-and-aft and sideways position.

The spring works by storing energy as it bends. Mounted longitudinally, it is typically fixed to the chassis at one end through a fixed eye and at the other through a swinging shackle that accommodates the change in length as the spring flattens under load. The axle sits on the spring, usually near its centre, secured by U-bolts. When the wheel meets a bump the strips bend and flatten; as they straighten again the stored energy is released, returning the spring to its original arch. The most common road form is the semi-elliptic multi-leaf arrangement, in which the graduated leaves rub against one another as they flex, providing a degree of inherent friction damping.

The great strength of the design is its ability to carry heavy and variable loads dependably. Because the spring also locates the axle, it removes the need for separate radius arms or locating links, which keeps the whole assembly cheap, robust, and easy to repair. These qualities explain its continued dominance on pickups, vans, lorries, trailers, and commercial vehicles, where load-carrying capacity and durability matter far more than ultimate ride comfort.

Those same characteristics also explain its decline on passenger cars. The inter-leaf friction that provides natural damping also makes the ride firm and slightly harsh, and the spring's behaviour is harder to tune finely than a separately sprung and damped arrangement. The leaf spring is also relatively heavy and adds unsprung mass. As cars came to prioritise comfort and refined handling, coil springs with dedicated dampers and located axles or fully independent systems displaced leaf springs almost entirely from ordinary cars.

In service, leaf springs are generally long-lived but not maintenance-free. Individual leaves can crack or sag with age and heavy use, the shackle bushes wear, and corrosion or seized inter-leaf surfaces can stiffen the spring or cause squeaking. Variants such as the parabolic spring use fewer, tapered leaves that touch only at their ends to reduce friction and weight while preserving load capacity, reflecting continued refinement of a fundamentally traditional and trusted component.