Car spar: what is it, what does it look like and where is it located in the car

Any car consists of a structure in which each part has its own location and purpose. The spars play an important role in this. They perform supporting, protective and other functions. Many car owners are faced with this concept, but not everyone knows what a spar on a car looks like, what it is intended for and what significance it plays. The operation of various car systems depends on the integrity of this part. Let's consider what spars are, what advantages, functions and tasks they have.

What is a spar?

Spars are two metal elements, longitudinal stiffeners, that are part of the resistance structure of any car. These parts, made from special ultra-high-strength steel that is six times stronger than conventional steel, absorb the load of a severe impact and reduce the impact of an accident on passengers. Externally, the parts are similar to metal profiles or box mesh. On trucks, the spars are presented in the shape of a “P” figure, slightly tilted to the side.

A minor accident will never require the side members to be balanced throughout the entire process. The collision must be very serious and destroy many elements, not only the bumper, headlights or radiator, but also the steering gear or even shock absorbers.

If it is impossible to visually assess the function of the part, then it is worth finding out what will happen to the side members if they wear out or break:

The bottom sheets will “slip” from under the passengers’ feet.

What are they for?

The parts are made of very hard metal and can withstand heavy weight. They absorb shock loads and vibrations received by the car when moving on various roads. Spars are needed to strengthen the elements of the bottom and floor of the trunk (passenger cars) or to completely take on all the loads (trucks, frame SUVs).

Another function of the side members is shock absorption. By taking on vibrations, the part distributes the load across all parts of the machine. Pipes effectively absorb deformation distortions. Therefore, they are made as rigid as possible, but not everywhere. In fact, a modern spar is a structurally very flexible unit with programmable deformation zones. Otherwise, it would not soften the shocks, absorbing them, but transmit them to the cabin.

Thus, the side members of the front part of the car are specially made with a greater ability to deform. Thanks to this, during a collision, the parts absorb the destructive shock wave, preventing it from going further.

Origin

Spars were invented quite a long time ago. Their appearance is associated with the creation of frame body structures. They were considered the main supporting systems of a car, but they were improved and other elements were added. If in ancient times cars were assembled from wooden parts, then over time they became metal. The same thing happened with the spars, which took the place of the frames.

The frame, which has a cross-section in the shape of an “X,” was introduced by a company from the USA at the beginning of the twentieth century. The spar had two beams parallel to each other, as well as cross members. The appearance of the part was similar to a ladder. By the way, this production technology is still used today. “Staircase” structures are installed on trucks.

The car does not work without a side member, despite the fact that the element is not visible behind the wheels. To see the structure, you will need to lift the car.

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

Front and rear side members

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

Functions

Spars are a structure that bears the weight of the body, engine, and passengers. In addition, suspension elements are attached to it. That is why they are created from very durable materials with shock-absorbing functions. Due to their light weight, they provide good handling and high dynamics characteristics.

The spars have the following functional features:

They connect body parts and chassis into one structure.

The load-bearing function is that the structure can withstand heavy loads.

The parts take on kinetic energy during impacts, which means they play the role of a kind of damper.

Provide passive safety by absorbing energy from impact during a collision.

To absorb vibration evenly, the side members have weak zones. The main feature of these sections is the thin profile walls and the presence of technological holes. During an impact, the parts seem to “fold,” thereby absorbing kinetic energy. The deformation of the spar itself can occur for years.

Additional functions of the spar include shock absorption and reinforcement of the bottom and mudguards. In the first case, driving comfort is increased by reducing the rigidity of the beam. In the second case, the underbody with mudguards is constantly exposed to strong impacts from bad roads. It is the spar that prevents serious damage.

The disadvantages of the spar element include low maintainability.

Main types

The spars are installed in different positions, which depend on the type of car:

Parallel and horizontal.
Horizontally and at an angle.
Curved elements arranged vertically.
Curved power beams placed horizontally.

Horizontal parallel beams are installed on trucks, while on SUVs they are placed at an angle, due to which the steering axis of the wheels is larger. Elements curved vertically allow the car's center of gravity to be lowered. The vehicle's horizontally curved side member improves passive safety in the event of a side impact.

Design and varieties

The appearance of the spar resembles a frame, but from a domestic point of view it looks like a ladder. The part can be composite or integral. They are necessarily installed in the front and rear of the car, but sometimes there are designs without rear elements. Solid ones, compared to composite ones, are stronger, but not as repairable.

The spar design is represented by a metal profile, but with a different cross-section. It can be a round pipe, an I-section or a box section, a channel or a Z-shaped profile. The channel is considered the most common. It has increased rigidity. Areas of high loads have an increased area, and in areas of low loads, on the contrary, a smaller cross-section. Box spars are installed on sports cars. Thanks to their shape, the parts help reduce the weight of the machine while maintaining increased frame rigidity.

What are side members in a modern car? This is a structure made of high-alloy steel with the inclusion of aluminum and titanium alloy. Production technologies have changed over the past few years. Composite materials with unique characteristics are increasingly being used to create.

Types of existing load-bearing structures

The biggest difference is the direction of the load-bearing part and the location of the side members. The type of design differs depending on the role and tasks of the vehicle, as well as the decisions of the manufacturer.

Today there are a number of common types:

completely horizontal placement with elements parallel to each other. Most often installed on vehicles that require high cross-country ability;
with slight bends. The curvature is located throughout the bottom, the spars bend around the shape of the bottom, creating a single contour. Improve passenger comfort and effectively reduce vibrations;
vertical position. The peculiarity of the type comes down to the possibility of creating a flat floor with a significant reduction, greater than that of traditional car models;
angular views. Increases the passive safety of the vehicle.

The load-bearing part differs according to the transverse type, arranged in all cars. Their role is reduced to creating stiffening ribs, but structurally they are designed differently: inserted perpendicularly between the channels, in the shape of the letter K or X-shaped models. Cross members are almost always made of steel and then bent. In passenger cars, the transverse set is welded to the side members, and in truck models, the riveting method is used. Next, brackets for attaching machine units are attached to the structure.

Spar on Infiniti FX35

Possible faults

Spars become unusable for two reasons: as a result of natural wear and tear or in the event of a severe accident. In any case, there is no need to delay repairs, otherwise the engine and suspension will partially move. If the body is not visually damaged, then you still need to carry out an additional check of the side members.

We list the typical faults of the part:

Deformation that occurs during long and heavy use of the car. Due to old age, the structure can “crack”.

Failure of side members as a result of an accident. Fenders and body elements suffer from deformation, the shape of the suspension is disrupted and cracks form on the outside of the body.

Bursting parts cause the body to collapse completely. In practice, after an accident, 90% of cars require repair of the front side members.

Repair work depends on the severity of the damage. For example, it is easy to change part of the junction with the frame. If the spar that is part of the body is severely damaged, then most likely it will not be possible to replace it.

For minor problems, you can resort to an alternative repair option. It consists of pulling out the load-bearing part of the body. Then the parameters will return to the original data.

If a driver wants to buy a used car, then he should check the accident history of this vehicle. If a car looks normal on the outside, this does not mean that all the systems in it work harmoniously.

To determine if a side member is damaged without lifting the car, you need to get behind the wheel and drive a little. A slight pull of the car to the side when moving in a straight line, as well as less coordinated turns of the steering wheel indicate problems.

Is it necessary to strengthen

Reinforcement of technically sound side members is required only in sports and when operating vehicles in particularly difficult conditions for which the bodies are not designed.

Sometimes reinforcement is carried out after an accident, when they are trying to avoid complex repairs with the replacement of load-bearing parts. In these cases, the geometry of the body is restored by drawing on a slipway, and since the deformed spar is no longer able to work normally in the future, external reinforcements are welded onto it.

The same technology is sometimes used to repair corrosion and fatigue cracks.

Risks associated with repaired side members

It's hard to believe that a person can buy a used car whose condition has not been affected by time. Wear and tear on moving parts or the most exposed elements inside is normal, but hiding some of the deformations in the vehicle's resistance structure is a long way off. Driving a car that has undergone unprofessional intervention exposes the owner to serious risks. They can affect the stability of the vehicle on the road and the safety of passengers.

Having understood what side members are needed for, the driver is more attentive to buying a used car. Here's what will happen if the car has repaired side members:

Instability. With an insufficiently rigid chassis, the car may deviate slightly from its trajectory, even without a heavy load or without a crosswind. Also, when driving on an uneven surface, the driver will experience discomfort. He will have to repair the entire system several times in order to correct the trajectory of the car.

Premature tire wear. The uneven pressure that a vulnerable chassis puts on the shock absorbers causes the tires to wear excessively, but not evenly. Thus, there is an additional risk of deviation from the trajectory during braking, as well as an increase in the distance required to stop safely.

Noisy move. This phenomenon is caused by the chassis and shock absorbers working synchronously with the help of the side members. If the latter are questionably repaired and the high-strength steel is damaged due to welding interference, the driver will hear sharp sounds that will be felt during more complex maneuvers.

In other words, if a person decides to have a used car inspected before purchasing it and the mechanic reports signs of repair to the side members, it would be wise to cancel the purchase. And this is even with the restoration of the airbag system and the belt pre-tensioning mechanism, which, however, does not guarantee exemplary safety.

Advice from professionals on operating a vehicle's side member

Evolution of the frame. “At first, hardwoods were used for the frame, and sometimes metal pipes. In the 1910s frames with an open profile began to be used on trucks.
If you know English terms, then it won’t be difficult to understand what a side member looks like on a car. It is often called staircase because it looks like a staircase. Elements located longitudinally are usually made from an open profile. Cross beams can be different in shape: K- and X-shaped, perpendicular. Frame pieces can be connected to each other using welding (in passenger cars), rivets (in trucks) or bolts (made to order).
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Today, riveted frames are used for trucks and pickups. Some engineers consider X-frames to be spar frames because they are much lighter. Such devices were used in American cars of the 1950s, in the Soviet Chaikas (GAZ-13 and GAZ-14). The main advantage of the spar frame is its manufacturability and simple configuration. The disadvantages are bulkiness and heavy weight, which leads to a reduction in usable space in the car.”
How to check a car's side member before buying.
“If you buy a car second-hand, you need to check the side members. If they are led, the body may become deformed. As a result, the camber will become incorrect and tire wear will increase, and the gap between body parts will become larger. In addition, you need to remember that driving a car with a burst or rotten element is dangerous. At high speeds, the car loses control because the rigidity of the body is compromised. During an accident, this element provides passive safety, preventing the body from being crushed.
Finding a slight curvature of an element and a change in the geometry of the body is possible only on a stand. At the same time, global deformations can be detected independently. You need to check:
Read also: Replacing the steering gear on a VAZ 2101, VAZ 2102, VAZ 2103, VAZ 2106

Camber and toe . If the part has a problem, then the alignment of the car's wheels will be incorrect. Even if you make adjustments, it will constantly go wrong, and the tires will begin to wear unevenly.
Gaps between body parts . If the side members are faulty, the gaps between them will be uneven. Such problems are visible even to the eye.
External defects . Problems with parts are easy to see with the naked eye: the geometry of the body is broken. You can also look from the viewing hole. Elements must not contain welds, defects, or cracks. Usually the front part holds the power unit. The rear side member of the car goes under the trunk, and the rear bumper and tow bar are attached to it.”

How to check the status?

A set of repaired or replaced side members is easy to identify, regardless of whether the car has to be lifted or not. Knowing where the side members are located in the car, the driver can quickly find them and check them.

A careful visual inspection from top to bottom with a flashlight will reveal whether there are weld marks or cuts where paint has been applied over the top. Moreover, if you look at the ends of the side members and see cracks or irregularities on them, it becomes clear that after a severe impact there was a mistake in the safety design of the car.

Another indicator is the condition of the bolts and fastenings, both side members and shock absorbers. If they seem suspicious compared to others, then the buyer has no reason to throw money away.

Therefore, it is vital that special care is taken when purchasing a used car. The tips above will help you avoid getting into a car accident.

conclusions

Analyzing all of the above, it can be noted that the spar should be considered the most important part of the car body. Damage to it in an accident can lead to the most unpredictable consequences, and therefore you should not buy used cars that have been in serious road troubles.

The spar is responsible for the safety of the car, as it is the main load-bearing element. Therefore, the resistance to deformation and rigidity of the body is entrusted to it. The owner needs to regularly monitor its technical condition, being aware of all the sad consequences of destruction. Inside, the spars are hollow. This leads to the accumulation of dirt and moisture - companions of advancing corrosion. Therefore, it is recommended to carry out diagnostics at least once a year, and to apply anti-corrosion mixtures before the winter months.

If you have any questions, leave them in the comments below the article. We or our visitors will be happy to answer them.

Repair and restoration

Drivers, having realized what a car spar is, begin to more closely monitor the condition of their car. When a breakdown occurs, they should immediately contact the workshop. In practice, the majority of requests are for the restoration of front parts, since the rear parts are deformed extremely rarely. The bent elements are pulled out using the installation. But the catch is that the craftsmen have to almost completely disassemble the car. Not every person will take on such work.

A burst spar can be restored by welding, but only if its main part remains in good condition. You need to understand that the quality of the parts will no longer be so impeccable. At the seam site, the strength will decrease.

Brackets will help facilitate the repair of side members. Sometimes they are used to attach parts to the body instead of welding. It becomes easier to replace items, provided they are in good condition. If the parts have undergone severe deformation, then repair will be futile.

Sometimes drivers try to strengthen the side members by adding stiffeners to them. But in this case they deprive the parts of their shock-absorbing properties.

The main advantages and disadvantages of the spar

The key advantages of the spar are its low weight parameters, flexibility and reliability. Transport does not lose maneuverability, it becomes easier to drive, and thanks to the use of modern technologies, passive safety can be achieved. If the first car bodies used a heavy and durable frame, today frameless elements are used, the basis of which is flexible spars, which are the key power body parts.

Not without its drawbacks:

If an accident or severe collision occurs, all units installed on the side members suffer, from the engine to the suspension and gearbox.
The product is difficult to repair because it has a specific design.

The front and rear side members are firmly connected to the body by welding. Long before the production of a car begins, engineers calculate the level of body rigidity and the degree of resistance. It is for this reason that after significant damage, the original parameters of the part change and it can no longer cope with its previous functions. During repair work, ensuring the basic properties of the spar becomes impossible. The beam must be reattached to the body by welding, which is very difficult to do if there is damage. It is much easier to remove the old one and install new material.

Rail saver repair tool

Tim Gerhards, an American auto body repair specialist who has been working in this field since 1986, has come up with a tool that helps remove dents and bends in side members by attacking the imperfections from the inside. This is a fairly new invention. The tool is called Rail saver (literally translated as spar saver). It is a metal body, to one end of which a hydraulic cylinder connected to a pump is screwed. There is a metal pipe inside the housing.

A hydraulic cylinder acts on one end of this pipe, and at the other end there is a wedge, which gradually lifts the part of the body where the wedge is also located. It turns out something like a long jack, which is inserted inside the spar to the place where the bend is located and the bend or dent is applied from inside the spar. Anvils of different shapes, which are included in the kit, can be screwed to the place in the tool that rises. Thus, this tool can work on dents and folds caused by the displacement of the side member from the inside.

The tool for straightening the side members from inside the Rail saver is placed inside the side member. The arrow shows the place where the fold is located, which the tool will straighten.

If necessary, the unevenness is tapped from the outside with a hammer, and the tool for straightening the side members acts as support. Since a hydraulic cylinder with a pump is used to operate the tool, it is possible to remove deformation on the metal of a spar of any thickness without much effort. The most important thing is to correctly position the tool in the right place. To do this, you need to measure the location of the deformation and position the tool inside the spar to the desired length. There is a measuring scale on the body of the instrument.

Depending on the size of the spar, you can place wooden blocks in its cavity to position the tool as best as possible.

The Rail saver tool has been tested and approved by General Motors for repair of salvage vehicles at authorized service centers. The advantage of this tool is that it eliminates the need to cut segments in the spar to access the reverse side of the damage. There is no need to heat the metal, especially since modern high-strength steel is sensitive to heat and is significantly weakened and loses its properties.

The design of the Rail saver tool is quite simple and if it is thoroughly understood, you can make such a tool yourself.

On the left, at the top of the tool body, you can see a wedge on which another wedge acts, lifting it. The pipe with the wedge inside the housing is pushed by a hydraulic extension. The place with the wedge, which rises when exposed to hydraulics, must be installed opposite the fold, inside the spar. Special anvils/supports can be screwed to this part of the tool.