Leaf Springs

Leaf springs are commonly used for suspension in vehicles. It is one of the oldest forms of suspension and is used commonly in trucks and other heavy duty vehicles. Leaf springs are also available in most of the pickup trucks at the rear axle.

Design:

They are long and thin steel metal plates attached either above or below the axle. The metal plates are slightly curved and looks like a bow. The ends of the leaf springs are provided with eye-holes so that they can be attached to the vehicle body. Depending on the number of leaf and the number of eye holes, leaf springs can be divided into different types.

Based on the number of leaf:

·         Monoleaf Springs: These springs consist of only one steel plate in a curved shape. Such plates are thick at the center and get thinner on the edges. The shape is in the form of a semi-elliptical curve. They don’t offer good strength and suspension. Heavy duty vehicles require multileaf springs to provide the strength.

·         Multileaf Springs: It consists of various steel plates of different lengths stacked upon each other. The shortest leaf is kept at the bottom and the longest is kept at the top to give the same semi-elliptical shape that single leaf springs provide. Multiplate springs are provided with rebound clips to hold the plates together.

Based on the number of eye hole:

·         Double eye leaf springs: The longest steel plate in a leaf spring is provided with eye holes on both the sides so that it can be easily bolted to the body of the vehicle.

·         Open eye leaf spring: Only one end is provided with an eye hole. The other end is either flat or provided with a hook.

Purpose of U-bolts in a leaf spring:

Just by securing the eye holes of the spring to the hanger of the frame won’t be enough to steady the leaf springs. The leaf springs might be suspended or attached loosely to the axle of the vehicle. Such conditions lead to overslung and underslung. Overslung occurs when leaf spring is placed over the axle. Underslung occurs when the leaf spring is attached under the axle.

U-bolts are horse shoe shaped metal rods that avoid the overslung and underslung condition. A pair of U-bolts are fit around the axle and bolted to a metal plate that supports the leaf springs and also keeps the metal plates in the leaf spring intact without moving too much when carrying heavy load.

What makes leaf springs so strong?

The number and thickness of these leaves are what decide the spring rate and load capacity. The length of the leaves will decide the ride quality and the width decides the stability. Leaf springs are also known as progressive rate springs because of their tapered design. They grow stiffer when they are compressed which gives them the strength for carrying heavy loads.

Advantages of leaf spring:

·         It doesn’t require an anti-roll bar as leaf springs are twice as stiff in roll as it is in bump. Hence we can reduce weight and cost of extra material.

·         It provides great stability at high loads.

·         It is simple in design and easy to install.

·         The load distribution is even on both the sides of the axle. If a leaf spring is fitted with a shock absorber, then the load on the top of the shock absorber will be drastically reduced.

·         Leaf spring can be mounted in the centre, above or below the drive shaft without affecting the wheel movements. The advantage of this setup is that there will be no off-centre loads like we see in a coil spring.

Disadvantages:

·         Leaf springs are much heavier than coil springs. One leaf will weigh more than two coil springs combined together.

·         Takes up a lot of space.

·         Leaf springs cannot be tuned to adjust with the conditions. Coilovers have a modular design which makes it easy to adjust the ride height and spring rate.

·         Leaf springs are susceptible to noise.

·         Friction occurs between the contacting surfaces of the plates which wears out the leaves and can ultimately lead to a crack.

·         Life of leaf springs is lower than coilovers.