Coil spring

coil spring, also known as a helical spring, is a mechanical device which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces. They are made of an elastic material formed into the shape of a helixwhich returns to its natural length when unloaded.

Under tension or compression, the material (wire) of a coil spring undergoes torsion. The spring characteristics therefore depend on the shear modulus, not Young’s Modulus.

A coil spring may also be used as a torsion spring: in this case the spring as a whole is subjected to torsion about its helical axis. The material of the spring is thereby subjected to a bending moment, either reducing or increasing the helical radius. In this mode, it is the Young’s Modulus of the material that determines the spring characteristics.

Metal coil springs are made by winding a wire around a shaped former – a cylinder is used to form cylindrical coil springs.

Coil springs for vehicles are typically made of hardened steel. A machine called an auto-coiler takes spring wire that has been heated so it can easily be shaped. It is then fed onto a lathe that has a metal rod with the desired coil spring size. The machine takes the wire and guides it onto the spinning rod as well as pushing it across the rod to form multiple coils. The spring is then ejected from the machine and an operator will put it in oil to cool off. The spring is then tempered to lose the brittleness from being cooled. The coil size and strength can be controlled by the lathe rod size and material used. Different alloys are used to get certain characteristic’s out of the spring, such as stiffness, dampening and strength [1]

A compression coil spring

A tension coil spring

A selection of conical coil springs

Oxy-cut spring showing deformation due to loss of tempering in adjacent turn

Spring Rate

Spring rate is the measurement of how much a coil spring can hold until it compresses 1 inch. The spring rate is normally specified by the manufacture. If a Spring has a rate of 100 then the spring would compress 1 inch with 100lbs of load. [2]


Volute spring suspension on an M4 Sherman tank

Types of coil spring are:

  • Tension/extension coil springs, designed to resist stretching. They usually have a hook or eye form at each end for attachment.
  • Compression coil springs, designed to resist being compressed. A typical use for compression coil springs is in car suspension systems.
    • Volute springs are used as heavy load compression springs. A strip of plate is rolled into the shape of both a helix and a spiral. When compressed, the strip is stiffer edge-on than a wire coil, but the spiral arrangement allows the turns to overlap rather than bottoming out on each other.
  • Torsion springs, designed to resist twisting actions. Often associated to clothes pegs or up-and-over garage doors.


Coil springs have many applications; notable ones include:

  • Buckling springs in computer keyboards
  • Mattress coils in innerspring mattresses
  • Upholstery coil springs in upholstery
  • Coil Springs in Car Suspension
Coil springs are commonly used in vehicle suspension. These springs are compression springs and can differ greatly in strength and in size depending on application. A coil spring suspension can be stiff to soft depending on the vehicle its used on. Coil spring can be either mounted with a shock absorber or mounted separately. Coil springs in trucks allow them to ride smoothly when unloaded and once loaded the spring compresses and becomes stiff. This allows the vehicle to bounce less when loaded. Coil spring suspension is also used high performance cars so that the car can absorb bumps and have low body roll. In off-road vehicles they are used because of their range of travel they allow at the wheel. [3]
  • Coil Springs in the engine
Coil springs are used in the engine. These springs are compression springs and play an important role in lifting the valves that feed air and let exhaust gasses out of the combustion chamber. The spring is attached to a rocker that is connected to the valve.

Coil Spring in valvetrain

Tension and extension coil springs of a given material, wire diameter and coil diameter exert the same force when fully loaded; increased number of coils merely (linearly) increases free length and compressed/extended length.


  1. “How Springs Are Made”. Thomas. Retrieved 19 April 2018.
  2. “Street Performance & Racing Spring Rate Tech”. QA1. Retrieved 19 April 2018.
  3. Zahl, Timothy. “Coil, Leaf, & Torsion Bar | Describing The 3 Different Kinds of Springs”. Carid. Retrieved 18 April 2018.
Transverse leaf spring and solid axle front suspension of early Ford cars Transverse leaf spring and solid axle front suspension of early Ford cars is a type of automotive front suspension that has been most common in early Ford Motor Company products. "Suicide front axle" is a term that has been used for it. The configuration consists of a one-piece axle (solid front axle), to the ends of which the steerable front wheels are mounted. The axle receives its vertical and transverse support from a transverse leaf spring (leaf springs were often used for support in more than one direction), and its longitudinal support from fore-aft links sometimes called "radius rods" which are attached (via pivots) to the ends of the axle at their forward end and to the sides of the chassis (again via pivots) at their aft end. The ends of the transverse leaf spring can either tie to the top of the rods, or to the top of the solid axle. The transverse leaf spring is attached at its center to the center of the chassis's front cross member. 1919 Ford Model T Advantag...
Corvette leaf spring Corvette leaf spring commonly refers to a type of independent suspension that utilizes a fiber-reinforced plastic (FRP) mono-leaf spring instead of more conventional coil springs. It is named after the Chevrolet Corvette, the American sports car for which it was originally developed and first utilized. A notable characteristic of this suspension configuration is the mounting of the mono-leaf spring such that it can serve as both ride spring and anti-roll spring. In contrast to many applications of leaf springs in automotive suspension designs, this type does not use the spring as a locating link. While this suspension type is most notably associated with several generations of the Chevrolet Corvette the design has been used in other production General Motors cars, as well as vehicles from Volvo Cars and Mercedes-Benz. Fiat produced cars with a similar configuration, using a multi-leaf steel spring in place of the FRP mono-leaf spring. Design The C5 Corvette's rear suspension ...
Leaf spring A leaf spring is a simple form of spring commonly used for the suspension in wheeled vehicles. Originally called a laminated or carriage spring, and sometimes referred to as a semi-elliptical spring or cart spring, it is one of the oldest forms of springing, appearing on carriages in England after 1750 and from there migrating to France and Germany.   A traditional semi-elliptical Hotchkiss leaf spring arrangement. On the left, the spring is connected to the frame through a shackle. Leaf springs front independent suspension, front-wheel-drive Alvis1928 Independent front suspension by transverse leaf spring Humber 1935 Independent front suspension by semi-elliptical springs Mercedes Benz 230 W153 1938 Leaf spring on a German locomotive built by Orenstein-Koppel and Lübecker Maschinenbau A leaf spring takes the form of a slender arc-shaped length of spring steel of rectangular cross-section. I...