Automotive Springs

The spring component in a suspension system can come in a variety if different configurations to suit any need the driver might have. Usually coming in three varieties. Coil Springs, which are what most people are familiar with when they think of a spring of any kind. Leaf springs are found in most heavy duty trucks, resembling leaves stacked on top of each other. Lastly, torsion bars, which mimic the vertical compression of a coil spring via horizontal twisting. Automotive springs come in a wide variety of shapes and sizes but mostly serve the purpose of bearing driving loads and providing a predictable and smooth driving experience.

Coil Springs

Leaf Springs

Leaf springs consist of several layers of sheet metal that vary in length, bound together to form a single suspension component. The leaf spring can attach to the frame either by the ends of the linkage or with the addition of a clamp in the center. This is one of the oldest forms of springs and does not offer the same suspension quality as coil springs but is still used widely today, mostly in heavy-duty and truck applications.

Torsion Bars

A torsion bar consists of a metal rod, usually steel, that is connected to the chassis on one end and is free moving on the other. Torsion bars twist in response to the vertical motion of the vehicle wheel to simulate the motion a conventional coil spring would. When the wheel travels upwards or downwards that motion is transferred through the control arm to the torsion bar which twists in response to absorb the shock. Just as a coil spring assembly the torsion bar provides a downward force on the wheels to maintain contact with the road. If you imagine a board on the free end of the torsion bar facing perpindicular, as you apply weight to the board the torsion bar twists slightly under the weight on the board. The bar doesn’t want to twist so it applies a rebounding force on the weight providing the same effect a coil spring does when weight is added to it. The chassis connecting portion of the torsion bar is usually splined so the bar can be adjusted to raise or lower a vehicle to compensate for natural suspension sag and whatever else you might be adjusting your suspension for.

Air Springs

Air Springs consist of a closed cylindrical chamber replacing the coil spring and the dampener aka the shock in its traditional spot in the wheel assembly. The compressed air inside of the springs absorbs shocks from the road and also maintains contact between the tire and the road. Some custom air shock setups allow for customization of the ride height at a moments notice via on board air compressors on the vehicle. These applications can also be seen in commercial use such as buses and semi trucks and is responsible for that characteristic hiss you hear from these vehicles. Lots of modified and VIP style cars are on air suspension systems to dial in their ride height for shows which in most cases makes the car so low it is un-drivable without damaging fascia and ego. So being able to raise the car protects suspension components and reputations.

Unsprung Mass

Unsprung mass is the mass of the suspension components not supported by the spring assembly of the vehicle. To make it easy, unsprung mass or weight is everything from the springs down. In most cases this includes the wheels, tires, and shocks if there are any,nuts and bolts included. Depending on the suspension setups some components that could also contribute to unsprung mass are the brakes, if mounted inside of the wheel assembly, portions of the driveshaft and some suspension linkage assemblies. Reducing your unsprung weight is what brings out the best in your suspension setup. lighter components such as carbon fiber wheels and control arms allow more of the suspension to keep your wheels in contact with the road. 

Sprung Mass

Sprung mass is essentially everything that rests on the spring assembly of the vehicle including but not limited to, the frame, body of the vehicle and internal components such as the engine and interior. Sprung mass can vary depending on the number of passengers and cargo. Track applications along with other hobbies usually recommend lightening the sprung mass of your vehicle so interior or engine component removals such as passenger seats, air conditioning or power steering units is common to reduce the sprung weight of a vehicle becauseracecar.

Spring Rate

Spring rates are defined by the amount of force it takes for a spring to be compressed one inch. The lower the spring weight, the softer the spring, making for a smoother overall ride but this makes for a chassis the rolls easily making it unsuitable for performance applications. On the other hand, a higher spring rate will result in an increase in performance as the stiffer spring will make it harder for the body of the vehicle to roll during hard braking or taking a corner at high speeds. The stiffer spring in turn doesn’t absorb shock as well as a looser spring would which diminishes ride quality on uneven surfaces.

Spring assemblies alone would not be able to satisfy both of the roles in a suspension. Springs are great for absorbing shock but aren’t ideal for the dissipation of the energy. This is why in most instances spring assemblies are used in conjunction with a shock or dampener or some kind. This creates a strut or coilover assembly.

Spring rates are measured in lbs/in. If a spring has a spring rate of 500lbs/in, that means it would take 500lbs of force to compress the spring one inch, and 1,000lbs to compress the spring 2″ respectively. Spring rates are usually chosen depending on the type of driving applications for your vehicle and should be matched accordingly to get the best performance.