A leaf spring is a simple type of suspension spring commonly used in vehicles. This type of spring is typically constructed of one or more flat, thin, flexible steel strips that are joined together in order to work as a single unit. The steel strips of a leaf spring are curved into an arc and attached at each end to the underside of a vehicle to help position and support the axle, and also to absorb shock.
Leaf springs are usually more able to evenly distribute the weight of a heavy load than ordinary coil-type springs. Although leaf springs have been in use for hundreds of years, they are generally only used for trucks and other heavy-duty vehicles today.
There are two basic types of leaf springs, mono-leaf and multi-leaf. A mono-leaf spring has only one arc-shaped steel strip, which is usually very thick in the middle with much thinner ends. A multi-leaf spring is constructed of several arc-shaped steel strips of varying lengths that are stacked together with the longest strip at the top, and the shortest strip at the bottom. Multi-leaf springs are generally able to support much greater loads than mono-leaf springs.
Leaf springs are sometimes referred to as semi-elliptical, cart, or laminated springs. The center of this arc-shaped spring is usually attached to the axle of the vehicle it supports, while the ends of the spring are attached to the frame itself. In some cases, a leaf spring may be attached to the vehicle frame on one end and the other end will be attached to a short swinging arm known as a shackle. This type of spring configuration often helps to provide a softer, less rigid suspension system. Some automobile manufacturers have recently developed a leaf spring that is constructed of a composite material similar to plastic in order to provide a softer type of rear suspension.
Leaf springs are probably one of the oldest forms of spring-type suspension systems, having been in use since Medieval times. Until recently, leaf springs were a common rear suspension component of most automobiles. The introduction of light-weight front-wheel drive vehicles has basically made the use of leaf springs unnecessary, and automobile manufacturers are now using coil springs for both front and rear suspension systems. Leaf springs are now generally used only for heavier commercial-type vehicles such as trucks, vans, trailers, and railroad cars.