Issues addressed in this article:

  • What is a car frame design
  • What are the advantages and disadvantages of frame designs
  • What is the purpose and types of frame structures
  • What is safer and more convenient – a frame structure or a supporting body
The first car was an open crew driven by an internal combustion engine. It was based on a trolley – a frame with four wheels, on which a power unit was mounted. The structure of a steam locomotive consisting of a massive platform and wheelsets looks similarly. Most production cars in the last century were made according to the same “recipe”. It was based on a frame uniting aggregates and components of a car. The frame design of the car has been preserved to this day, but it is used much less often and slowly disappears in its pure form. What is the frame structure of the car

What is the frame structure of the car

audi a8

The car’s frame structure is a supporting system on which an internal combustion engine (ICE), transmission and suspension parts, and, in fact, a body are mounted. Such a device provides maximum reliability of the machine when operating in real road conditions. Do not forget that rail transport became the prototype for automobile vehicles, and, accordingly, the relative position of the elements initially migrated from there. The locomotive moved such volumes of cargo that the car did not even dream about, so the frame structure of the car has a very large margin of safety.

The frame design of the car clearly divides the elements into power and decorative. The frame accepts loads from the engine, transmission and wheels. It also plays an important role in passive vehicle safety. The chassis is a combination of a frame and a power unit with a gearbox and suspension. It, in principle, can move without a body.

Body panels form the appearance and form a cab for the driver and passengers. Some elements of the body can be reinforced with an additional frame, but this mainly concerns the safety of people and does not affect the damping of loads from the motor and the road surface. The scheme was constantly improved, and over time, several separate subspecies appeared that characterize the power structure. Spar, spinal (including fork-spinal), peripheral and trellised types are distinguished, bearing and semi-bearing varieties stand apart.

Purpose and types of frame structures


The frame structure of the car includes a system of profiles of rectangular, T-shaped, H-shaped or other sections, interconnected by welding, rivets or bolts. The chassis and the motor, which is aggregated with the transmission units, are mounted on the frame through elastic suspensions. The combination of the above details is called the chassis. From above it is covered with a body intended for the driver, passengers and, separately, for the cargo compartment.

Cars with a frame have a large mass compared to the supporting body layout. But due to its presence, they have significant bending and torsion strength, and, accordingly, are better suited for operation in off-road conditions and the transportation of heavy loads.

An important incentive for car manufacturers is the interchangeability of parts from different machine models. The frame design of the car allows you to maximize unify the dimensions of the units and their mounting points. Ultimately, different models could only differ in exterior body panels with identical chassis.

How Car Frames Are Made

It is customary to distinguish several frame types that differ in the relative position and cross-section of structural profiles. Each of the varieties described below is characterized by its own specifics:

  • Spatial frames.
  • Spar constructions.
  • Spinal and spinal-forked.

The frame design of the car can be combined and combine to one degree or another all three basic types.

  1. Spar and its subspecies .The most proven scheme consists of two longitudinal beams (spars), stretched from beginning to end of the chassis and pulled together by transverse ligaments.Spars are made of steel alloys. For stiffness in cross section, several stiffeners are created. They are closed (square or rectangle) and open (T-shaped or H-shaped profile).The longitudinal profiles on the very first products were smooth, but in the process of technical evolution, they acquired bends in both vertical and horizontal planes. This was done to optimize the placement of mounted units and reduce the center of gravity of the car.

    In addition, on SUV frames having a slope with respect to the horizon can be used.

    The longitudinal profiles of the frame are pulled together by cross members, which usually have a similar section. Transverse frame beams are located either at an angle of 90 ° – the classic “staircase” layout, or at an acute angle – the so-called K- and X-shaped schemes.

    Between themselves, the longitudinal and transverse side members are fastened with welding or rivets. In some cases, a bolted connection is allowed. Additional brackets are mounted at the points of attachment of the power unit and suspension.

    The frame structure of the car with widely spaced longitudinal spars is called peripheral. It allows you to increase resistance to side impacts and, accordingly, increase its safety. In addition, the units can be lowered below (between the beams), thereby reducing the center of gravity and increasing passive safety.

    The spars, reduced to the center of the frame in a horizontal plane, are a connection in the form of the letter X. This shape allows you to place in the center only the transmission shaft and the exhaust pipe.

    Least of all is a variety of two longitudinal profiles connected not by separate screeds, but by a whole metal sheet. This is also the frame structure of the car, despite the fact that this sheet may be the floor of the cab or body.

  2. Spinal frame The spinal frame variation was used on the Tatra truck. The longitudinal pipe was only one and had a circular cross section. Branches departed from it by analogy with the spine and ribs. The engine and gearbox were also a kind of amplifier due to the robust metal casing.The middle spar rigidly connected the motor and transmission (gearbox, transfer case, final drive). Transmission shafts connecting the units to each other passed inside this pipe. The design was very advanced and compact, but practice has shown its operational and repair futility.An important advantage of this arrangement was the ability to provide independent suspension of all wheels.Dependent drive axles could not be put in principle, and the torque on the wheels was transmitted using cardan shafts, not the axle shafts.The increased torsional rigidity allowed to increase the carrying capacity of the spinal frame with a smaller thickness of the metal side members in comparison with traditional schemes. The pipe system made it possible, if necessary, without complex modifications to increase the length of the platform and the number of drive axles by connecting additional modules.

    The high center of gravity due to the peculiarities of the attachment of the units allowed the spinal frame to be used only on trucks. For cars traveling at higher speeds, such a frame structure threatened to tip over in corners and on rough roads. The main drawback that did not allow further development was the low maintainability. Repair of worn shafts and other transmission units lasted a very long time due to the need for almost complete disassembly of the frame. For commercial vehicles, such downtime is unacceptable.

  3. Space frame .The frame structure of the car is called spatial, when the frame made of steel pipes is not a flat part at the base of the car, but combines a chassis and a cabin. This type is typical for sports cars that get into accidents much more often than others, and, accordingly, should better protect their passengers.Facing body panels are fixed directly to the power frame, as well as the engine, transmission and other components.For example, buggies are initially made with a spatial frame. And civilian specimens are converted into sports by welding a tubular frame inside an existing body, so this safety cage cannot be considered a full-fledged frame. The most expensive sports cars are a carbon capsule (a type of reinforced plastic), which is not inferior in stiffness to a metal frame with a significantly lower weight.
  4. Combined types.The frame design of the car is not always a certain type. The combination of different types is used by many manufacturers.For example, the symbiosis of the spar and spinal frames. A pipe goes between the two longitudinal spars in the center. Units are attached to the side members in the front and rear. The pipe is rigidly attached to the periphery, but unlike the spinal structure, it does not hide the drive shafts of the transmission.

    The fork structure has several different combinations of basic types. For example, a bent X-shaped spar frame equipped with a continuous metal coating. Or a spinal base with a central supporting tube to which the crossbars are welded, but not along the entire length, but only in front and behind.

    The integrated frame combines the actual frame structure of the car and the body in a single form factor. At the same time, body panels, in addition to performing a decorative function, are power parts of the bearing base. Spars in their pure form are present only in the front of the car and are intended for mounting the motor and gearbox and at the rear for mounting the suspension and rear axle elements, if any.

    It is widespread, especially on SUVs, to attach the power unit to the body through a subframe. It is a lightweight version of the frame structure of the car. That is, the frame is not located under the entire car, but only under the front and is bolted to the body. This significantly increases the rigidity of the latter.

    Finishing the excursion into the history of the development of the frame structure of the car, it should be noted that the frame as a separate power element is used only for certain types of cars operated in difficult road conditions or for the transport of goods. Modern passenger vehicles use a truncated version in the form of a subframe or side members welded into the body structure.

Advantages and disadvantages of frame structures

car frame

The frame structure of the car is very convenient for conveyor assembly, as there is free access to most units. Service workshops also give preference to such cars, because it is much more convenient to dismantle parts and entire assemblies for replacement and repair. Owners of frame SUVs can safely drive not only on asphalt roads, but also in “directions”, without fear of distortions of the body, jammed doors and bursting windshields. After all, the frame takes up the whole load.

Frameless designs prevail among cars due to a number of advantages. Firstly, functionally spaced chassis and bodywork significantly increase the weight of the car, which results in increased fuel consumption and poor dynamics. The layout of the cabin with side members along the sides suggests either high sides through which it is inconvenient to climb over when boarding a car, or a high floor that reduces the ceiling height in the cabin.

Recently, stricter safety standards for the driver and passengers do not allow the frame structure of the car to provide the same high rating on crash tests as for analogues with an integrated circuit. A separately mounted body shifts relative to the frame during an accident and inefficiently absorbs impact energy.

Scope of frame constructions

Automakers settled on a frame structure for trucks, heavy SUVs and, in some cases, buses. Premium cars are a separate article, especially in armored versions.

Initially, the parts of the bearing base were fastened with rivets or in one piece. Riveting technology is quite simple and convenient. It does not require expensive equipment and highly qualified assemblers. Currently used only for trucks. Frames made by the method of integral casting were distinguished by high strength, but due to their high cost and complexity of setting up equipment and accessories, they finally went down in history.

Welding technology has taken its place and has all the prospects for further development. Such work is easy to automate, and welded elements are much easier to cast and transport than the whole frame. Most trucks and off-road vehicles are made using this technology.

Vehicles with frame design:

  • UAZ “Hunter”;
  • UAZ “Patriot”;
  • Jeeps “Great Wall”;
  • Jeeps “Hawal”;
  • Some jeeps from Korean manufacturers.

smart car frame

The opinion of car owners about the frame design of the car

  1. Do not confuse sour with salty .A classic sedan or hatchback car certainly does not need a frame. But if you need a large carrying capacity, increased wheelbase, the ability to drive on the road, you should pay attention to the car frame design with a minimum number of bells and whistles and auxiliary electronics. With such a machine, you can safely leave civilization and not be afraid of unexpected breakdowns. And if there are any, then they can be eliminated on the spot. Modern crossovers are created only to storm the curbs for parking on the sidewalk. They can not go far from the branded service.
  2. Modern “frames”, on the contrary, can be considered high-security cars .For an SUV, the frame is more a plus than a minus. Low torsional rigidity leads to the fact that riding on rough terrain can result in a skew body. An increased wheelbase is necessary to improve stability on the road, but at the same time insufficient strength leads to poor handling. Reliable cross-country vehicles still have a frame structure.Each manufacturer lays its own “zest” in the body structure: one has an integrated frame, the other has high-strength steels, the third has both. It is almost impossible to single out a leader. The frame has not gone down in history because of its indispensability for large-size jeeps and pickups. Commercial vehicles will also never change orientation. And everything that is smaller will cost a frameless layout.