The spar is the main structural element of the car, located along the entire length of the car. Two spars connected by transverse elements form a frame to which the body, suspension and other vehicle units are attached. The lintels give it the appearance of a staircase, for which it is called a staircase.
Most often, the spar is a metal profile, box-shaped beam. In other words, a spar is a rectangular tube. Paired side members are located at the front and rear of the vehicle or run along the entire length of the vehicle structure. This is one of the most durable parts of the car, as it carries the loads of the body, engine and passengers, and also perceives shock loads from the wheels.
The spars that are part of the ladder frame, as a rule, have a profile of the letter "P" laid on its side. You can examine the frame and the side members that are part of it on any truck and many models of heavy SUVs. Most passenger cars are manufactured with a load-bearing body structure (without a frame), but side members are always included in the structure. Thus, any car is equipped with spars. You can see them when looking from under the car.
Under the influence of loads, the spar can deform, fatigue and crack. In this case, the most important parameters of the machine can change: the position of the units relative to the body (motor, suspension), the line of connectors of body parts, doors and fenders. In addition, the spar can deform in an accident. At the same time, important dimensions of the body's structural structure are violated, irreparable gaps appear on the outside, and the suspension geometry is violated. The car ceases to obey the steering wheel, there is increased tire wear, there is a risk of destruction of the body's structural structure if the spar bursts. Therefore, when examining a car after an accident, first of all, they find out the integrity and correct position of the spar.
A slightly damaged spar can be corrected at the caroliner stand, having previously disassembled half of the car. And it is not always possible to achieve the desired result. Replacing a spar is also an expensive and difficult undertaking. At the same time, when welding a spar, the quality will almost always be worse than the factory one, and this reduces the strength of this element. The spar, which is part of the frame, can be changed, but there is no point in changing the heavily removed spar of the supporting body. The way out is to change the whole body. All proposed options for replacing a heavily deflected spar in a monocoque body are not considered due to their poor quality.
