A Beginner's Guide To Spring Types
One of the primary topics of conversation within the pages of Four Wheeler, as well out on the Internet and amongst wheeling enthusiasts, is suspension. Suspension is one of the most important aspects of any four-wheel-drive vehicle, but can be an intimidating topic for anyone new to the sport.
To gather up all of the facts, we headed over to see our good friends and suspension experts at Deaver Spring in Santa Ana, California. Deaver has been around since 1982, manufacturing quality OE-replacement and custom suspension springs for virtually any application imaginable and has been an important resource on many of our project vehicles.
We'll walk you through what makes torsion bars, coils, and leaf springs different, and the pros and cons of each. Of course, you'll want to keep in mind that what we'll cover is in general terms, and there are exceptions out there.
A spring is any type of material that, when distorted, returns to its original shape. The job of the spring is to support the weight of a vehicle, maintain ride height, and keep the tires in contact with the road surface. Springs are used in conjunction with shocks, or dampers, which actually control the suspension movement. Three of the most common types of springs in use today are the torsion bar, coil spring, and leaf spring.
A good spring maximizes wheel travel, ride comfort and load-carrying ability. Springs are built with spring rate in mind. Spring rate is the amount of force that is required to move a spring and is measured in pound-force per inch (lb-in). Load rate is also a consideration, which is the amount of weight the spring is designed to carry at ride height.
The leaf spring dates back to medieval times and is one of the simplest and oldest forms of spring technology. Early leaf springs used leather instead of the metal we are familiar with today. A standard of automotive suspension systems for decades, the role of the leaf spring is slowly being reduced-even in applications where it has been the stalwart, such as pickups. Over the last 10 years or so, we have seen the leaf spring replaced by coils in Jeeps, in the front of heavy-duty trucks, and most recently in the rear of the light-duty Ram 1500.
Modern leaf springs use a series of steel plates of varying length and thickness, known as leaves, bound together in a pack. Some suspensions use a monoleaf design, which only uses one leaf in place of a pack. The number and thickness of these leaves are what dictate spring rate and load capacity. The overall length has an effect on ride quality, while the width of the leaf and whether it is mounted inboard or outboard all have an effect on stability.
Because of their tapered shape, leaf springs-including monoleaves-are progressive-rate springs. This means they grow stiffer the more they are compressed, which makes them superior for heavy load carrying than so-called single- or linear-rate (i.e., coil) springs. Leaf springs are also modular, meaning that if you desire a change in ride height or capability, all you have to do is add or remove leaves. The higher-quality packs will use multiple, thinner leaves to reduce friction. This stacking of leaves also makes for a more durable product because one leaf isn't holding the entire load, and if one were to break, chances are that the others will hold together long enough to get you home.
While all leaf springs are progressive-rate, some spring packs are two-stage. Two stage spring packs keep the progressive pack, but add an overload spring underneath to gain maximum load rating while retaining good ride characteristics when unladen. These packs are typically used in the rear of pickup trucks.
Although the design of a leaf pack itself is fairly complex, overall it is the simplest form of suspension design because the leaf packs both control and locate the axle without the need for control arms. Leaf springs also have the benefit of better stability, especially when hauling or towing at or near the rated maximum, by reducing sway and spreading out the load over a greater portion of the chassis. The downside is that they take up a lot of room to mount. Other leaf spring drawbacks are heavy weight and the susceptibility to axlewrap and noise.
Pros: Locate and control the axle, superior stability when loaded, simple, easier to lift.
Cons: Harder to tune for ride, heavy weight, prone to axlewrap, take up a lot of space, susceptible to noise.