Torsion bar spring: What is it for? Operation, Damage and Adjustment torsion bar suspension

Torsion bar spring: What is it for? Operation, Damage and Adjustment torsion bar suspension
A torsion bar is a type of spring - torsion spring - used in the suspension of a car based on the mechanical torsion of a bar, usually of steel. Its operation is based on the torsional capacity of the metal; this is its ability to twist on its longitudinal axis storing mechanical energy that is then released in the form of rotation, recovering its original position without permanent deformation.

For this, one end of the bar is anchored solidly to the chassis of the vehicle, while the other is fixed to an arm of the suspension so that by means of a crank mechanism, there is a lever relationship such that the entire path of the suspension matches the desired torsion of the bar.

The elastic capacity of the bar will depend on its length, thickness and the material with which it is made.

What is the torsion bar of a car for?

The primary purpose of the torsion bar is to preserve the geometry of the car. In this sense, we can say that it supports and reduces the oscillations to which the chassis is subjected and therefore gives stability when driving.

This component is not installed in all cars, but as time passes, it is being included in many of the recent models. Sometimes it is installed longitudinally or transverse to the axis of the car.

Torsion bar operation

The operation of the torsion bar consists primarily of controlling the vibrating and balancing movements that occur during the turns, for this reason its implementation palpably influences the performance of a car.

This bar is attached to the frame in indirectly connected to the wheel. Sometimes the rear side of the bar is attached to the chassis and the front end to the suspension specifically to the control arm.

The torsion bar functions as a lever when the wheel moves vertically the bar twists and then returns to its position.

These bars can be installed longitudinally or transversely and are constructed of steel that during manufacturing are subjected to heat treatments and stretching to make them resistant to fatigue.

Torsion bars are very frequently found in armored cars since they generate great tension on the axles when maneuvering at high speeds due to the high weight of the armor.

Differences with stabilizer bars

These two devices should not be confused, because although both are based on the mechanical torsion capacity of the metal, their function is completely different and to some extent antagonistic. The torsion bars accumulate tension depending on the relative position of each suspension arm with respect to the body (for example when overcoming a pothole or loading the car), on the contrary, the stabilizer bar does so when the suspension arms of each side of the body move in the opposite direction, (when tilted by the effect of centrifugal force).

Torsion bars have the function of suspending the body of the vehicle to isolate it from the irregularities of the terrain. They can have an "I" shape and be directly coupled to the axis of rotation of an arm, or have an "L" shape, in which case they are fixed to the arm itself. In both cases, the bar acts as an elastic agent, capable of storing mechanical energy when it is turned on its axis that is returned in the form of a turning movement when the tension is released. This type of spring was very popular because of the space economy of its arrangement on the floor of the vehicle and the advantage of allowing the height adjustment of the suspension in a simple and economical way. Even today, it is a system widely used in tanks, having been used in many cars in the last century, or Simca 1100 on both trains, on the front train of the Alfa Romeo Alfetta or on the rear of the VW beetle, among others. At present the system is obsolete because its volume determines the shape of the monocoque body and because its action, although it is progressive, is not as easily controlled as with compression springs - coil spring - of varying thickness.

The tension to which the springs are subjected is stored in the form of kinetic energy, which is controlled by shock absorbers that transform it into heat energy, preventing its violent release in the form of oscillations in the body. Torsion bars were commonly used together with "lever" shock absorbers - lever arm shockers - a type of shock absorber that also employed a crank mechanism, the Morris Marina being the last large-series vehicle to use both systems.

The stabilizer bars on the other hand are auxiliary mechanisms of the suspension, whose function is not to suspend the body but to prevent its inclination by transmitting part of the compression force exerted by the centrifugal force on the outer wheel inside. They have the approximate shape of a letter "U" formed by two arms and a central axis, so that the movement of each arm is linked to that of a suspension arm, while the central axis is not solidly anchored, but can freely twist on its supports. Thanks to this arrangement, the axle will suffer a torsional demand only when the suspension arms move in the opposite direction - when the suspension of the outer side is compressed and the inner one is expanded - opposing the inclination of the body. In return, on bumpy terrain the suspension will be more uncomfortable because each wheel will be affected by the movement of the other.

A special type of stabilizer bar is the torsion axis , a type of semi-independent suspension where a "U", "C" or "H" shaped shaft is used, in which the central crossbar of the shaft itself acts as a stabilizer bar .

How to detect torsion bar damage?

As the name implies, these bars are always under torsion, for this reason it is essential that they have their complete integrity. Sometimes due to the effects of strokes or scratches of a stone, however small they seem, it removes the surface protection that is usually only paint and this makes possible the appearance of rust.

As time elapses at the rayon site, the oxide penetrates in some cases into the interior of the bar once there due to constant tensions, the bar will collapse breaking.

If the torsion bar that breaks is longitudinal, you will perceive it immediately because the car will fall on the same side of the bar that broke. On the other hand, if the torsion bar is transverse, the car will become very unstable when turning.

How to adjust the torsion bar?

Raise the wheel of the vehicle you wish to adjust by placing the rail of the frame on the jack stand, thus releasing the tension of the torsion bar facilitating the adjustment.

Position yourself below the vehicle, and then you must place the torsion bar support on the frame.

In the center of the mount, there is a bolt in the upward direction (adjustment bolt). Find the key that allows you to turn the bolt.

If you turn it in the same direction as the clock, you will press, raising the load that the bar can support, if you turn it in the opposite direction it will decrease the elasticity and lower the height of the car.

Exceeding any adjustment direction can cause problems, so read the manufacturer's specifications. Generally, just one bolt turn will be enough for the ideal fit.

Place the vehicle on the ground and check the height with respect to the ground; these should be even for both sides. If so, it is not necessary to make other adjustments.

The torsion bar adjustment can be done without lifting the car but the bolt will not turn easily.


  • You must be aware when you are under the car.
  • Do not remove the torsion bar without the proper tools.
  • The torsion bar adjustment bolt can be turned without lifting the carriage, but it will not turn easily.