In technical documentation and professional environments, when it comes to how the rapids are properly called, the term “threshold” most often refers to the lower sidewall element connecting the front and rear wheel arches. This part is a critical part of the power structure of the load-bearing body, providing twisting rigidity and safety of passengers in side impact. In everyday life, drivers often confuse the metal structure itself with the linings installed on top for protection or decor, which leads to misunderstanding when ordering spare parts or discussing repairs with masters at the service station.
The correct name depends on the design of a particular vehicle: in classic passenger cars it is the same. sidewall, and frame SUVs - an element attached directly to the frame spars. It is a mistake to think that this is just a decorative strip, since in modern safety standards, such as Euro NCAP, the integrity of this zone is checked first. Understanding the differences between the load-bearing threshold, decorative lining and aerodynamic body kit is necessary for each owner for competent operation and maintenance of the machine.
Technical nomenclature: how to name elements in catalogs
When searching for parts in an electronic catalog or communicating with parts suppliers, it is important to use the correct terminology to avoid errors in the order. The main structural name of the element - sideways or lower body side memberHowever, in collapsible body catalogs, this knot is often referred to as a “threshold in the assembly” or “repair insert of the threshold”. It is important to distinguish between a single stamped part that is part of the body, and removable elements that can be part of the body kit.
Structurally, this knot is a complex spatial structure of high-strength steels, often having amplifiers and anticorrosion channels inside. It is this hidden part that is responsible for preserving the geometry of the doorway and the distribution of impact loads. The decorative elements that we see outside are technically called liner or moldings, and their replacement does not require complex body repairs.
In the catalogs of spare parts, you can find the following variations of names for related elements:
- 🚗 Lower sidewall lining a plastic or metal element covering the lower part of the door and the body threshold.
- 🛠️ Repair insert - part of the threshold intended to replace the rotten area without replacing the entire sidewall.
- 🔩 Threshold bracket - fastening element, often used on frame SUVs for fixing steps.
⚠️ When buying body parts, always check the VIN code of the car, as the form and method of fastening the thresholds can be radically different even within the same model, but different years of release.
Structural types: power, decorative and aerodynamic
The division of thresholds into types is based on their functional purpose and design. The primary and most important type is force-thresholdThese are an integral part of the safety framework of the car. They are made of high-strength steel, have a complex cross section and are often filled with polyurethane foam inside or have additional stiffness ribs to resist deformation in a lateral collision.
The second type is flat-layerwhich are installed on top of the factory metal. Their main task is to protect the paint coating from stone chips, sand and scratches during landing and landing. Such overlays can be made of plastic, aluminum, stainless steel or carbon. They do not carry a power load and in a serious accident often destroyed first, taking on the primary blow.
Production technologies
Hidden information about materials
Modern power thresholds are often produced by hot stamping from bore-containing steels, the strength of which reaches 1500 MPa. In luxury models and electric vehicles (such as Tesla or BMW i-series), the thresholds can be made of extruded aluminum or even magnesium alloy to reduce weight, while maintaining high torsional rigidity.
Type three: wind-stripping (Splitters) that are part of the body kit. They are designed to control airflows along the bottom of the car, reducing turbulence and downforce. Such elements are typical for sports versions of cars and tuning models.
Specificity of SUVs: steps and protection
In the off-road segment, the terminology is expanding, as the thresholds often combine the function of the footsteps. Drivers and owners of such vehicles as Toyota Land Cruiser, Land Rover Defender or Jeep WranglerThey are called “steps”, “footsteps” or “rannbugs”. run boards. These elements are attached directly to the frame or spars and must withstand the weight of a person.
A special category is expeditionary. These are massive metal structures, often with integrated bottom protection, that are designed to drive on heavy off-road. They protect the lower part of the body from impacts on stones, stumps and rocks, taking all the load on themselves. Unlike decorative analogues, such rapids can serve as a fulcrum for a jack (highjack) or even a winch.
When choosing thresholds for an SUV, pay attention to the method of attachment. Mounting only to the body (sidebar) during extreme driving can lead to the separation of part of the metal of the body. Look for models with frame or spars attached.
Key differences between off-road solutions from standard:
- 🏔️ fabrication thick-walled steel or aluminum profile, often with a polymer coating.
- 📐 Geometry - are located below the floor level for ease of landing, but should not reduce clearance at a critical point.
- 🔗 Integration - may have areas for installation of expedition trunks or additional lighting.
Manufacturing materials and their impact on durability
The durability of the thresholds directly depends on the material from which they are made, and the quality of anticorrosion treatment. Factory power elements are made of steel, which is subject to corrosion when the protective layer is damaged. This is why the rapids zone is one of the first to see rust, especially in regions with aggressive use of reagents in winter.
Overlays and decorative elements are made of various materials, each of which has its pros and cons. Plastic (ABS, polypropylene) is cheap and does not rust, but fragile in the cold. Aluminum is lightweight and resistant to corrosion, but soft and easily scratched. Stainless steel is beautiful and durable, but requires high-quality fasteners to avoid electrochemical corrosion in the areas of contact with the body.
Comparative table of characteristics of threshold materials:
| Materials | Strength | Corrosion resistance | Weight. | Cost |
|---|---|---|---|---|
| Steel (black) | Tall. | Low (requires painting) | Heavy. | Low. |
| Stainless steel | Medium | Tall. | Heavy. | Medium |
| aluminum | Medium | Tall. | Lightweight | Tall. |
| Plastic (ABS) | Low. | Tall. | Very light. | Low. |
| carbon | Tall. | Tall. | Very light. | Very high. |
⚠️ Warning: When installing metal sills (especially stainless steel or aluminum) on a steel body, be sure to use dielectric gaskets. The galvanic pair “different metals + moisture + salt” will lead to accelerated rotting of the body in the attachment areas in one season.
Problems of operation and diagnosis of hidden corrosion
The most common problem associated with thresholds is hidden corrosion. Water, dirt and reagents accumulate in the cavity between the outer sheet and the inner amplifier, causing the metal to rot from the inside. Externally, the car may look perfect, but when pressed or hit, the threshold is easily changed or pushed through with the foot, which indicates a complete loss of load-bearing ability.
Diagnosis of the state of thresholds should be carried out regularly, especially after the winter period. You should pay attention to the bloating of paint, the appearance of “redheads” in the lower part of the doors and on the rapids themselves, as well as the state of the drainage holes. Clogged drainage is the main reason for the accelerated destruction of the metal, as they do not allow water to escape.
☑️ Checklist of check of status of thresholds
To prevent destruction, it is recommended (periodically) to carry out anticorrosion treatment of hidden cavities with special compositions (oil or wax), which displace moisture and create a protective film. If corrosion has already begun, professional body repair is necessary with the cutting of rotten areas and welding of repair inserts.
Features of repair and replacement of body elements
Repairing thresholds is a complex technological process that requires qualifications and special equipment. Depending on the degree of damage, masters can choose the method of richting, digestion or complete replacement of the element. Replacing the threshold involves cutting out the old metal and welding new, which requires the use of a welding semi-automatic (MIG / MAG) and careful anti-corrosion treatment of the seams.
When replacing, it is important to observe the geometry of the body. Incorrectly set threshold will lead to the fact that the doors will be closed with difficulty, there will be cracks or the operation of locks will be disrupted. In modern cars with a high content of high-strength steels, it is often recommended not welding, but riveting or the use of special adhesive compounds, which requires factory repair technologies.
Quality repair of the threshold is impossible without removing the cabin and dismantling the seats, as access to the inside of the threshold and welding sites is often limited. Savings on disassembly of the car leads to poor quality results.
The cost of replacing the thresholds can vary widely and depends on the brand of the car, the difficulty of access and the type of metal used. The owner must be prepared for the fact that after body repairs will require high-quality painting and polishing of the entire board to eliminate the diversity.
Frequently Asked Questions (FAQ)
Can I drive without a rapid or with a severely damaged threshold?
Driving with a damaged threshold is dangerous. In addition to the loss of body rigidity and the risk of deformation of the doorway, safety is violated during side impact. Also through holes in the doorstep in the cabin will get exhaust gases, water and dirt.
What is better to close a hole in the threshold: putty or welding?
Putty is a temporary and low-quality solution that will quickly crack and fall off. The only correct way to repair is to cut out the rotten area and weld a repair insert of metal. Putty is used only to level the surface before painting.
How often should I update the anticor on the doorsteps?
The recommended frequency of processing hidden cavities of thresholds is once every 2-3 years for new cars and annually for cars with mileage or after body repairs. Visual control should be done every spring.
Does the installation of massive metal sills affect fuel consumption?
Yes, the installation of heavy power thresholds (especially steel) increases the weight of the car, which is insignificant, but increases fuel consumption. In addition, aerodynamics deteriorate, which at high speeds can also affect fuel consumption.
Why do the rapids rot faster than other parts of the body?
The thresholds are in the zone of constant contact with water, dirt, salt and mechanical damage from stone and sandblast. The design of many sills provides for internal cavities where moisture accumulates, which creates ideal conditions for electrochemical corrosion.