Have you ever wondered what that one is called? flat side part car, which consists only of 4 letters? This term is often found in crossword puzzles, technical documentation or conversations among body repair specialists, but not all drivers know its exact name. Meanwhile, this part plays a key role in the design of the car - not only the appearance, but also safety in case of side impacts depends on it.
In this article we will not just give the answer to the riddle (spoiler: this word begins with "p" and ends with "l"), but we’ll also look at why this part of the body is so important. You will learn what it is made of in modern cars, how to repair it after an accident, and why improper care of it can lead to corrosion within 2-3 years. And also - practical advice, how to save on repairs and avoid mistakes when painting.
If you are the owner of a used car or are just planning to buy, the information below will help you assess the condition of the car according to one of the key criteria. Even small dents on this part can indicate hidden problems - for example, a violation of the body geometry after an accident.
What is a “threshold” and why is it called the side flat part?
The answer to the riddle about 4 letters simple: it's about threshold. This is a horizontal flat part of the body located between the wheel arches at the bottom of the doors. In most passenger cars, the threshold performs several functions at once:
- 🔹 Protective — absorbs part of the energy during a side impact, preventing deformation of the interior.
- 🔹 Carrier — in modern cars, thresholds are often included in the strength structure of the body, increasing rigidity.
- 🔹 Aesthetic — closes technological gaps and gives the car a finished look.
- 🔹 Practical — on many SUVs and crossovers, the sills are equipped with running boards for ease of entry.
Interestingly, in older cars (e.g. VAZ-2101 or Moskvitch-412) the thresholds were almost decorative - they were made of thin metal, and in an accident they crumpled like foil. Modern thresholds (for example, in Toyota Camry or Volkswagen Golf) are reinforced with high-strength steel or even aluminum, and are often lined inside amplifiers — additional metal beams to absorb energy.
Why is the threshold called flat side? The point is in its design: on the outside it is really flat (sometimes with a slight relief for rigidity), and on the inside it has a complex shape for attaching to the side members and the bottom of the body. At the same time, the threshold is not a homogeneous part: it consists of several layers:
- External panel (visible part).
- Internal reinforcement (often welded).
- Anti-corrosion coating (applied at the factory using cataphoresis).
Threshold design: from Zhiguli to premium cars
The material and design of the thresholds greatly depend on the class of the car and the year of manufacture. Let's look at the main types in the table:
| Vehicle type | Threshold material | Design Features | Examples of models |
|---|---|---|---|
| Budget cars (before 2000s) | Thin steel (0.8–1.2 mm) | Minimal reinforcement, prone to corrosion | VAZ-2109, Daewoo Nexia |
| Modern sedans | High strength steel (1.5–2 mm) + amplifiers | Integrated into the power structure of the body | Hyundai Solaris, Kia Rio |
| Premium and SUV | Aluminum or composites | Lightweight, but expensive to repair; often with running boards | Audi Q7, BMW X5 |
| Sports cars | Carbon fiber | Minimum weight, maximum rigidity | Porsche 911, Lamborghini Huracán |
In cars until 2010 the thresholds were often the “weak link”: in a side impact they were deformed, and the door could jam. In modern machines (for example, Volvo XC60 or Skoda Octavia) thresholds are designed so that they crumpled along a given trajectory, directing the impact energy downward rather than into the cabin. This is achieved through:
- 🔧 Programmable deformation zones (special “weak” areas).
- 🔧 Multilayer amplifiers (for example, with foam filler).
- 🔧 High strength welds (laser welding instead of spot welding).
Important: in vehicles with aluminum sills (e.g. Jaguar XE or Tesla Model S) repairs after an accident are 2–3 times more expensive than steel analogues, due to the need for argon welding and special rivets.
If you are buying a used car, be sure to check the sills for traces of welding or putty - this may indicate serious repairs after an accident.
Typical problems with thresholds: rust, dents, cracks
Thresholds are one of the most vulnerable parts of the body. Here are the main problems that owners face:
- Corrosion - occurs due to the accumulation of dirt, water and reagents. Thresholds rust especially quickly in cars older than 10 years, where the anti-corrosion coating has become thinner.
- Dents — appear when doors are opened carelessly (for example, in a parking lot) or from stone impacts.
- Cracks - most often in places of welds or fastening of amplifiers. They are dangerous because they can spread to the side members.
- Peeling paint - due to poor preparation before painting or the use of low-quality materials.
The most insidious problem is hidden corrosion. It starts from the inside of the threshold, where moisture has accumulated for years, but on the outside everything looks normal. It can be detected by the following signs:
- 🚗 The appearance of red spots at the junction of the threshold and the door.
- 🚗 Crunching or squeaking when you press the threshold with your hand.
- 🚗 Paint swelling (bubbles under paintwork).
What to do if the threshold begins to rust?
⚠️ Attention: Never paint over rust without completely cleaning it! This will speed up corrosion by 2-3 times. The correct algorithm is: stripping to metal → treatment with a rust converter → primer → painting.
For temporary protection (for example, before selling a car), you can use anti-corrosion mastics (for example, Dinitrol or Tectyl). But this is not a solution to the problem, but only a delay - in 1-2 years the rust will return.
How to check sills for hidden rust?
Use an endoscope (flexible camera) or simply shine a flashlight through the threshold from the inside. If you see red stains or holes, it’s time to go for body repair.
Repair of thresholds: when you can get by with local straightening, and when you need replacement
The cost of repairing thresholds varies from 3,000 to 50,000 rubles depending on the degree of damage and type of vehicle. Here are the main types of repairs:
| Type of damage | Repair method | Cost (RUB) | Working period |
|---|---|---|---|
| Small dents (without damage to paintwork) | Paintless straightening (PDR) | 3 000–8 000 | 1–2 hours |
| Deep dents with cracks | Straightening + welding + painting | 10 000–25 000 | 2–3 days |
| Through corrosion | Cutting out the rusty area + welding a patch | 15 000–30 000 | 3–5 days |
| Complete destruction of the threshold (after an accident) | Replacing the threshold assembly | 30 000–50 000+ | 5–7 days |
When you can get by local repairs?
- ✅ Dent up to 3 cm deep without breaking the metal.
- ✅ Small pockets of rust (up to 5 cm in diameter).
- ✅ Scratches or chips of paint without damaging the soil.
When needed complete threshold replacement?
- ❌ Through holes from corrosion.
- ❌ Deformation after a strong impact (body geometry changed).
- ❌ Cracks in the places of attachment to the side members.
⚠️ Attention: If, after an accident, the threshold was replaced using a makeshift method (without computer geometry), this can lead to uneven tire wear and poor handling. Always ask the master for a geometry check report!
☑️ Preparation for repair of thresholds
How to protect thresholds from corrosion: 5 proven methods
Prevention is cheaper than repair. Here 5 ways, which will help keep the thresholds in perfect condition:
- Regular washing - especially in winter, when salt and reagents accumulate on the thresholds. Use Kärcher with a nozzle for hard-to-reach places.
- Anti-corrosion treatment - apply once every 2-3 years ML-mastic or liquid plastic on the inner surface of the threshold.
- Installation of protective pads - plastic or aluminum linings (for example, from 3M) prevent chipping from stones.
- Checking the Drain Holes - if they are clogged with dirt, water will accumulate inside the threshold. Clean them every six months.
- Parking in dry spaces - Avoid prolonged parking on damp grass or in puddles.
This is especially relevant for owners of cars over 5 years old. processing of hidden cavities. For this purpose, craftsmen use special sprayers with long nozzles, which allow them to coat even internal amplifiers with anticorrosion. The average cost of such processing is 5,000–10,000 rubles, but it prolongs the life of the thresholds by 5–7 years.
Myths about anticorrosion that you should not believe:
- 🚫 “Bitumen-based mastic is eternal” - in fact, it cracks after 3-4 years.
- 🚫 “You can just pour oil into the threshold” - this will temporarily slow down the rust, but will not stop it.
- 🚫 “Plastic thresholds do not rust” - they do not rot, but can crack in the cold.
The most effective way to protect thresholds is a comprehensive one: washing + anticorrosive + linings. One method is not enough for long-term results.
Thresholds in tuning: from decorative overlays to LED lighting
Thresholds are not only functional, but also aesthetic part car. Many owners modify them to improve appearance or practicality. Here are the popular tuning options:
- 🔥 LED backlight — installed under the thresholds and turns on when the doors are opened (for example, in Audi A6 or Mercedes E-Class). The cost of the set is from 8,000 rubles.
- 🔥 Chrome trims - give the car a premium look, but require regular polishing. Popular on Lexus and Infiniti.
- 🔥 Wider sills - used in sports tuning to visually reduce ground clearance (for example, on BMW M3).
- 🔥 Protective “brutal” linings - relevant for SUVs (Toyota Land Cruiser, Nissan Patrol).
When choosing overlays, pay attention to material:
- 🔹 ABS plastic - light and cheap, but fragile in the cold.
- 🔹 Aluminum - durable, but expensive and can oxidize.
- 🔹 Stainless steel — the best option in terms of price/quality.
⚠️ Attention: Cheap Chinese linings made of “soft” plastic can become deformed after just a year due to temperature changes. Check reviews before purchasing!
If you are planning threshold illumination, consider the following nuances:
- 💡 For legal installation the light must be white or yellow (blue, green, and red are prohibited in Russia).
- 💡 Optimal brightness - 100–200 lumens (too bright light will dazzle).
- 💡 It is better to lay the wiring through
fuse box, and not directly to the battery.
How to choose spare parts for thresholds: original vs. analogue
If you have to replace the threshold, the question arises: what to choose - original part or analogue? Let's look at the pros and cons of each option:
| Criterion | Original thresholds | Analogs (non-original) |
|---|---|---|
| Price | Expensive (from RUB 20,000) | 2–3 times cheaper |
| Metal quality | High (meets factory standards) | May be thinner or less processed |
| Compatibility | Perfect Fit | May need some work |
| Warranty | Yes (from official dealers) | Rarely |
| Availability | Long wait (especially for rare models) | Fast delivery |
When to choose original?
- ✅ The car is under warranty (otherwise it will be removed).
- ✅ Threshold - part of the supporting structure (for example, in Volvo or Mercedes).
- ✅ Durability is important to you (original parts last longer).
When can you save on analogue?
- ✅ Budget repairs (for example, for selling a car).
- ✅ The threshold is decorative (not load-bearing), as in the old ones Okah or Tavriyah.
- ✅ You are ready for possible adjustment (welding, putty).
When purchasing an analogue, pay attention to country of origin:
- 🇪🇺 European analogues (for example, Febi, Meyle) - the best price/quality ratio.
- 🇹🇷 Turkish (Markal, Nipparts) - average quality, but affordable.
- 🇨🇳 Chinese ones are cheap, but often defective (check the reviews!).
Before buying a threshold, check it OEM number with a directory (for example, on Exist.ru or Autodoc). Even one model can have different thresholds depending on the year of manufacture!
FAQ: Frequently asked questions about car thresholds
Is it possible to drive with a rusty sill?
In the short term, yes, but it is dangerous. Rust weakens the structure, and in the event of an accident, the threshold will not be able to protect the interior. In addition, corrosion can spread to the side members, leading to loss of body rigidity.
How long do thresholds last after anti-corrosion treatment?
With high-quality processing (removing old rust and applying ML mastics) the thresholds will last 5–7 years without re-repair. If you simply paint over the rust, it will return in 1–2 years.
Is it possible to straighten the threshold yourself?
Small dents (up to 2 cm) can be straightened out yourself using reverse hammer or PDR set. But for serious deformations, it is better to contact a specialist - without experience, you can damage the paintwork or reinforcements.
What to do if the threshold is rotten through and through?
The only reliable option is cutting out the rusty section and welding in a new section. Fiberglass patches or putty will give a temporary effect (maximum 1-2 years).
Which anticorrosive agent is better for thresholds: mastic or liquid plastic?
Both options are good, but have differences:
- Mastic (for example, Dinitrol 479) - protects more reliably from mechanical damage, but is harder to apply.
- Liquid plastic (for example, Noxudol 700) - easier to use, but less resistant to stone impacts.
For maximum protection, it is recommended to combine both methods.