What is and why are spars in a car?

The design of any car is clearly thought out and each element in it has its own specific purpose. Spars play an important role in the body structure. These elements are assigned not only to a supporting function, but also to protect and absorb external influences. In this article, we will understand what a car spar is, its functions, position and the consequences of deformation.

Purpose and device

The spar is a longitudinal profile or channel, which is located in pairs in front and behind the car body.

In the structure of the monocoque body, they are at the bottom level, parallel to each other. In some models, they may be located at a slight angle. If the supporting part is frame, then the parts are located along its entire length as one-piece elements. In the figure you can see the position of the parts. They are marked in red.

The safety and controllability of the car largely depends on the integrity and strength of these elements. The side members are designed to withstand different pressures and loads. This is the weight of indoor units, passengers, cargo, as well as external shocks and vibrations while driving. As you can see, these elements perform an important load-bearing function in the body structure.

Side member functions

Thus, the side members perform the following functions:

• Connective. They combine various elements of the body and chassis into a single structure.
• Carrier. One of the main functions. The elements are able to withstand heavy weight and loads. During movement, they are continuously affected by static and dynamic forces.
• Damping vibrations. The parts also act as a damper, absorbing a certain amount of kinetic energy upon impact. These are a kind of connecting elements between the body and the suspension.
• Passive safety. Some designs have special programmed crumple zones that dampen the impact energy in a collision.

Design features and types

In heavy duty vehicles and SUVs, a frame structure of the supporting system is used. This is due to the increased load. In such designs, the spars are parallel to each other along their entire length. Solid elements are interconnected by special jumpers. For the peculiar shape of the frame, drivers often call this design a "ladder".

In modern passenger cars, the body itself is the supporting part. Therefore, the side members are already integrated into the body structure and are part of it. They can be either solid or separate and must be installed in the front and in the rear, although there are structures without rear load-bearing elements. The rear side members do not carry as much load as the front side members.

One-piece side members can also be used in a monocoque body. This has its advantages. The structure becomes more rigid and reliable, but it has a complex shape. This affects the manufacturing technology.

Thus, side members can be divided into two types:

• composite;
• whole.

If the advantage of solid ones is in rigidity, then composite ones are more practical. In a collision, the side members are most often affected. They bend, break. Composite elements will be easier to replace with new ones.

In turn, much depends on the geometry of the elements. Additional bends allow for increased structural strength in a side or front impact. Bends also improve the vehicle's maneuverability and steering angle.

Position of side members in the body

The position of these elements will depend on the body structure and vehicle model. There are several options:

• parallel to each other or at a slight angle;
• vertically at an angle;
• horizontally at an angle;
• with a horizontal bend.

The first option, as already mentioned, is found on the frame structure of heavy vehicles. The other three options are found on load-bearing bodies of different brands.

Possible malfunctions

For the manufacture of side members, only special aluminum alloys or titanium are used. The strength of the structure is very important as the elements are subjected to constant stress.

Such exposure over time can lead to their deformation. During operation, microcracks may appear on the metal. This effect is often referred to as metal fatigue. Damage, bends and cracks can affect the geometry of the body and many other parameters of the vehicle. For example, the angles of the wheels will change, an incorrect gap will appear when the doors are closed, all sorts of creaks in the cabin, and so on.

Also, these important elements can be deformed during an accident. These are the most common cases. The bending of the side members threatens with serious repairs, or even disposal of the body. There are cracks, gaps, the geometry of the body is violated. It is unsafe to operate the car in this case. Even repairs do not always give the desired result. Damage to the geometry is likely to increase tire wear and damage the factory steering settings.

On the other hand, side members are also passive safety elements. They have zones of programmed deformation. In the event of an accident, the part will bend exactly in this place, taking away part of the impact energy.

Features of repair

In most cases, it is the front side members that are dealt with, the rear ones are not deformed so often. Bent elements "pull out". This is done using a special installation. The difficulty also lies in the fact that you have to disassemble most of the car. Remove the engine, suspension components, bodywork, and so on. Not every master undertakes such a complex repair.

If the spar has burst, but its main part is in good condition, then the repair can be done with welding. In this case, it should be borne in mind that even after high-quality welding, it will no longer be possible to achieve the previous state of these elements. The strength will decrease precisely at the seam. In frame structures, it is much easier to replace these elements.

In some bodies, the side members are not fastened by welding, but by brackets. It also makes repairs easier as it is easier to replace the part. But if the elements are badly damaged or bent, then there is often no point in repairing.

Some drivers try to reinforce the side members in advance by adding additional stiffeners. In this case, you need to understand that the part loses its shock-absorbing properties.

Side members are one of the most important parts not only of the body, but of the entire vehicle. They may be hidden in the depths of the body, but do not forget about their meaning. They play an important role in the safety and handling of the vehicle. If these important elements are deformed, it is imperative to contact a car workshop in order to avoid possible costly repairs in the future.