As far as car suspension goes, leaf springs are pretty much dead and buried. But when it comes to the suspension of vans, trucks, trailers and other heavy duty, commercial vehicles, leaf springs continue to be one of the primary choices for supporting suspension.
In this article, we will look at a brief history of leaf springs and the advantages and disadvantages of the modern day leaf spring, before summarising the reasons why you would choose leaf springs for your van, truck, pickup, bus or trailer.
Leaf springs are a basic form of suspension made up of layers of steel of varying sizes sandwiched one upon the other. Most leaf spring setups are formed into an elliptical shape through the use of spring steel which has properties that allow it to flex as pressure is added at either end, but then returning to its original position through a damping process. The steel is generally cut into rectangular sections and then once held together by metal clips at either end and a large bolt through the centre of the leafs. It is then mounted to the axle of the vehicle using large U-bolts, securing the suspension in place.
The elasticity of the spring steel allows for a pliancy within the suspension for comfort and control of a car while moving, and a leaf spring setup has been proven as a viable option for cars for many decades, despite only really being found on HGVs and Military vehicles these days.
As an entity, you’ll be able to trace leaf springs right back to the Roman times, where they were first created for damping chariots for when they were used on rough surfaces. For many years, the springs stayed the same, up until after the 1900's when the first version of the shock absorber was created and then produced in mass with the Ford Model A in 1927.
Modern day leaf springs haven't evolved a great deal. They have been developed to be more robust and hard-wearing, although the overall duty of the leaf spring and the way it functions remains the same. But what are the leaf spring advantages and disadvantages?
Due to the sheer amount of metal layered together, leaf springs offer a large amount of support between the wheels, axles and the car's chassis. They can take huge vertical loads being applied to them due to their tight-knit structure, hence why heavy duty industries still use them. Vertical loading is also distributed throughout the length of the leaf spring rather than acutely through a small spring and damper, which can potentially create a concentrated force too large for the suspension to handle.
In a car, damping can be an extremely important characteristic. If the suspension is under-damped, the car will wallow and bounce around well after hitting any bump or pot hole in the road. This was a significant characteristic in cars that used helical springs before the dawn of the shock absorber and was disadvantageous to cars when driven at any real pace. Leaf springs coped much better with vehicle damping due to the friction between each plate of steel which made the response time after a vertical flex in the suspension much quicker, thus making for a much more controllable car.
Leaf springs were simple in design and cheap to produce in comparison with the early springs and dampers therefore it was the go-to setup once cars were being fully mass produced to ensure reliability while keeping costs low. Monoleaf springs were the simplest design of the lot, using only one leaf of spring steel which tapered from thick in the middle to thin at the edges (known as parabolic leaf springs) to distribute the vertical loads appropriately. A single leaf setup could only however be used on extremely lightweight vehicles due to the lack of strength within the bar.
• The way the suspension is constructed is really simple and strong, acting as a linkage that holds the axle in position without the need for separate linkage.
• Extra weight and costs are reduced because of the rear axle location. This eliminates the need for trailing arms and a panhard rod (AKA track bar).
• Leaf springs support the weight of the chassis, making them ideal for commercial vehicles.
• They also control axle damping.
• The chassis roll can be controlled more efficiently due to the high rear moment centre and wide spring base. If the springs are mounted wider apart, the roll tendencies will be less.
Although there are many key advantages of the modern day leaf spring (especially when installed in commercial vehicles), there are also a couple of disadvantages which you should be aware of.
A big downside of leaf setups is they aren't brilliant when it comes to suspension tuning. In racing and performance car applications, it is vital to be able to manipulate a suspension setup for the driving conditions and for different driving styles, something that is much easier nowadays through adjustable coilovers. This lack of adjustability of leaf setups is emphasised by the fact that the ends of the leaf springs are attached to the chassis, which leaves very little scope for shortening or lengthening of the leafs. Adjustments can therefore only really be made through the strength and flexibility of the material used to make up the leaf springs.
Leafs also allow very few directions of motion and are only really designed to move vertically, while a spring and damper combination can be manipulated into a much larger range of motion. Leaf springs are firmly clamped together and bolted to the chassis as well as clipped to the axle, thus giving little to no scope for any other direction of motion which can lead to heavy wear on the joints and connections holding the setup together.
This connection with a live rear axle can cause comical dynamic characteristics in a car when compared to a more modern independent suspension setup, something that older Mustangs are famous for. The rear axle will simply bounce around high speed corners as the suspension and axle are forced to move around together, when a modern damped system would add much more composure to the driving experience.
In comparison with a helical spring, leaf springs are generally much stiffer simply down to the steel construction and the tight package that they are bolted and clamped into. Ride comfort is therefore not a feature of vehicles that use leaf springs which made their popularity decrease dramatically after proper dampers were introduced in the 1970s to everyday cars in a cost-effective.
• They aren't always the easiest to install – but there is a clear process to follow that makes life much easier.
• The ride comfort isn't as great because of the inter-leaf friction between each leaf.
• Over time, the springs tend to lose shape and can sag. When the sag is uneven, it can alter the cross weight of the vehicle which can affect the handling slightly. This can also change the axle-to-mount angle.
• Wind-up and vibration can be caused by acceleration and braking torque. The wind-up can also cause nose-diving and rear-end squat.
Before making any purchase it's important to consider the advantages and disadvantages, especially when it comes to vehicle performance. Tips for maintaining and extending trailer leaf spring lifespan?
Large layers of metal are what make up the basic anatomy of a leaf spring, meaning they can deal with huge vertical loads. They offer a huge amount of support between the wheels, axles and the vehicles chassis, making them perfect for commercial vans, pickups, trailers and trucks, where the need to support greater weights is essential. We could design and produce any type truck & Trailer & Car leaf spring as per customers' drawings and samples. Tell us what you need or were expecting to find. Get in touch for more information regarding Leaf Springs!
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