Thresholds are one of the most vulnerable parts of a car body, but many drivers don’t even think about their existence until they encounter rust or mechanical damage. These elements not only form the appearance of the car, but also perform important design functions: they protect the interior from moisture, dirt and noise, and also increase the rigidity of the body during side impacts. However, due to constant contact with road chemicals, stones and water, thresholds often become the first source of corrosion.
In this article, we will look at where exactly the thresholds are located for different types of cars, what tasks they solve, and why their condition directly affects the safety and resale value of the car. You will also learn how to diagnose problems yourself and what protection methods will extend the life of these body parts.
Contents of the article:
- 🔍 Where are the thresholds on a car and how to distinguish them from other elements
- 🚗 Design features of thresholds for sedans, hatchbacks and SUVs
- ⚙️ Functions of thresholds: from protection to safety
- ⚠️ Typical damage and why they are dangerous
- 🔧 How to check the condition of the thresholds yourself
- 🛡️ Protection methods: from anti-gravel to “liquid fender liners”
- 💰 The cost of repairs and when it’s better not to save
🔍 Where are the thresholds on a car and how to distinguish them from other elements of the body
Thresholds are external panels located between front and rear wheels in the lower part of the body, right under the doors. They are easily confused with other elements, e.g. pallets (lower engine protection) or wheel arches, but the thresholds have key differences:
First of all, they are always parallel to the cabin floor and visually “flow around” the lower edge of the doors. Secondly, on most modern cars the thresholds have plastic or rubber pads (often called "moldings"), which are attached over a metal base. These covers not only improve the appearance, but also protect the metal from minor scratches.
On classic sedans (for example, Toyota Camry or Volkswagen Passat) sills are usually straight and narrow, whereas SUVs (like Toyota RAV4 or Nissan X-Trail) they are wider and may have integrated running boards for ease of landing. In sports coupes (for example, BMW 4 Series) the sills are often made more streamlined to improve aerodynamics.
🚗 Design features of thresholds for different types of cars
The design of the thresholds varies depending on the class and purpose of the vehicle. Let's look at the key differences:
| Vehicle type | Features of thresholds | Typical materials | Vulnerabilities |
|---|---|---|---|
| Sedans and hatchbacks | Narrow, low, often with chrome trim | Galvanized steel, aluminum (premium class) | Edges under doors, places where moldings are attached |
| SUVs and crossovers | Wide, with integrated footrests or plastic extensions | Reinforced steel, composites | Lower part (contact with dirt), footrest mounts |
| Minivans and station wagons | Long, often with additional stiffeners | Steel with anti-corrosion coating | Areas under the rear doors (moisture accumulation) |
| Sports cars | Streamlined, can be part of an aerodynamic body kit | Carbon, aluminum, high-strength steel | Body kit fastenings, joints with the body |
U budget models (for example, Lada Granta or Renault Logan) thresholds are often made of ordinary steel without additional protection, which accelerates the appearance of rust. B premium cars (such as Mercedes E-Class or Audi A6) use aluminum or galvanized steel, as well as multi-component coatings that resist corrosion longer.
Interesting fact: some pickups (for example, Ford F-150) thresholds play a role frame strength element, so damage to them may affect the load capacity. And in electric vehicles (like Tesla Model 3) high-voltage cables are often laid in thresholds, which complicates their repair.
If your car has sills with plastic overlays, regularly check the fastenings of the moldings - dirt often accumulates under them, which retains moisture and provokes corrosion.
⚙️ Functions of thresholds: from protection to safety
Many drivers mistakenly believe that thresholds are needed only for beauty or to avoid getting their feet dirty when landing. In fact, they have at least five key functions:
- 🛡️ Protecting the interior from moisture and dirt: thresholds close the gap between the body and the door, preventing water from getting inside.
- 🚗 Strengthening body rigidity: Together with the roof and floor, they form a “box” that prevents deformation when hitting obstacles.
- 🔊 Noise absorption: reduces the level of road noise entering the cabin.
- 💥 Energy absorption during an accident: in modern cars, the sills are crumpled along special “lines”, reducing the force of impact for passengers.
- 🔧 Fastening interior elements: Floor mats, door trim, or even seats (on some models) are often bolted to them.
In cars with passive safety systems (for example, with airbags in the doors), the thresholds may contain impact sensors or squibs that are activated in the event of an accident. Therefore, their deformation after an accident requires mandatory diagnostics at the service station - even if outwardly the damage seems insignificant.
For example, in Volvo XC60 thresholds are integrated into the system SIPS (Side Impact Protection System), which distributes the energy of a side impact. And in BMW 5 Series they are part roll cage, which protects the battery in hybrid versions.
Thresholds are not only a “cosmetic” element, but also part of the passive safety system. Damage to them may reduce the protection of passengers in an accident.
⚠️ Typical damage to thresholds and why they are dangerous
Thresholds suffer from three main types of damage, each of which leads to serious consequences:
- Corrosion - the most common enemy. Starts small "bugs" (spot spots of rust), which over time corrode the metal through and through. Particularly vulnerable places:
- 🔹 Joints with wheel arches (dirt and salt accumulate).
- 🔹 Attaching plastic overlays (moisture stagnates under them).
- 🔹 Bottom edge (constant contact with road reagents).
Why are these injuries dangerous?
- 🚨 Reduced body rigidity: rusty thresholds lose up to 70% of their strength, which increases the risk of deformation in an accident.
- 💸 Fall in car value: when selling, a car with rusty sills loses 15–30% of its price (depending on the degree of corrosion).
- 🚗 Problems with passing maintenance: in some countries (for example, Germany), a car will not pass inspection if the sills are rusted through.
⚠️ Attention: If you notice that the doors become difficult to close or there is a creaking sound when moving, this may be a sign threshold deformations after the blow. In this case, a test on a slipway (a special stand for diagnosing body geometry) is required.
🔧 How to check the condition of the thresholds yourself
Diagnostics of thresholds can be carried out without visiting a service center. You will need:
- 🔦 Flashlight (or flashlight on your phone).
- 🧲 Magnet (to check the presence of putty).
- 👆 Screwdriver or thin metal rod.
Step by step instructions:
☑️ Checking thresholds in 5 steps
Pay special attention to:
- 🔸 The inside of the threshold (from the cabin side). To do this, open the doors and inspect the lower edge of the seal.
- 🔸 Weld seam locations — Corrosion spreads fastest there.
- 🔸 Drainage holes (if they exist). Their clogging leads to the accumulation of water inside the threshold.
If you find:
- 🟠 Small "bugs" (up to 1 cm) - they can be eliminated locally (cleaned, treated with a rust converter and painted).
- 🔴 Through holes or swellings — Part of the threshold will need to be replaced (welding a “patch”).
- ⚫ Deformation after impact — straightening is required on the slipway.
What to do if the threshold is rusted through?
If corrosion has eaten through the metal to holes, temporary measures (like cold welding patches) will not help - moisture will penetrate further. The only reliable way is to cut out the rusty part and weld a new piece. In services, this work is done using spot welding or gas burner, after which the seams are treated with anticorrosive and painted. The cost of such repairs is from 8,000 to 25,000 rubles, depending on the car model.
🛡️ Methods of protecting thresholds: from anti-gravel to “liquid fender liners”
Threshold protection must be comprehensive: A combination of mechanical barriers and chemical treatment gives the best results. Let's look at the most effective ways:
1. Mechanical protection
- 🛡️ Plastic or aluminum trims: Protects against stones and scratches, but requires regular cleaning underneath.
- 🧲 Magnetic moldings: Easy to install and remove, but not suitable for all models.
- 🚗 Footrests-extenders (for SUVs): increase ground clearance and protect the lower edge.
2. Chemical protection
- 🧪 Anti-gravel coating (for example, 3M Scotchgard or Liqui Moly Unterbodenschutz): applied to paintwork and protects against chipping.
- 🔬 Anti-corrosion mastic (for example, Tectyl or Dinitrol): the internal cavities of the thresholds are processed.
- 🎨 Ceramic coating: Expensive, but provides protection for 3–5 years (e.g. Ceramic Pro).
3. Additional measures
- 🧹 Regular washing (especially in winter): removes salt and reagents. Use contactless car wash or steam generatorso as not to damage the paintwork.
- 🔧 Treatment of drainage holes: Clean them every six months to avoid water stagnation.
- 🛡️ Installation of “liquid fender liners” (for example, Rust Stop): creates an elastic protective layer on internal surfaces.
Expert tip: If you do a lot of gravel or off-road driving, mix and match mechanical protection (overlays) with chemical (anti-gravel + mastic). For example, on Toyota Land Cruiser 200 many owners install aluminum thresholds from ARB and further process them Tectyl ML.
⚠️ Attention: Do not use to protect thresholds bitumen mastic water-based - it quickly cracks and begins to let moisture through. Give preference to formulations based on synthetic resins or rubber.
💰 The cost of repairing thresholds and when it’s better not to save
Threshold repair prices depend on the degree of damage and restoration method. Below is an indicative table for cars middle class (for example, Skoda Octavia or Hyundai Tucson):
| Type of repair | Cost (RUB) | Due date | When to use |
|---|---|---|---|
| Local rust removal (cleaning + painting) | 3 000 – 7 000 | 1–2 days | Small “bugs” (up to 2–3 cm) |
| Replacing part of the threshold (welding a “patch”) | 8 000 – 15 000 | 2–3 days | Through corrosion (holes up to 10 cm) |
| Complete replacement of the threshold (with straightening) | 20 000 – 40 000 | 3–5 days | Severe deformation after an accident |
| Anti-corrosion treatment (internal cavities) | 2 500 – 5 000 | 1 day | Prevention or after repair |
| Installation of protective pads (kit) | 5 000 – 12 000 | 1–2 days | Prevention for new cars |
What to look for when choosing a service:
- 🔧 Availability of slipway: For repairs after an accident, a body geometry check is required.
- 🔥 Welding method: spot welding is better than gas welding (less risk of overheating the metal).
- 🎨 Painting warranty: high-quality services provide a guarantee of 1 year.
- 📝 Use of original spare parts: non-original thresholds may not match in shape.
Saving on repairing thresholds is dangerous: cheap welding or low-quality mastic will lead to rust returning in 6–12 months. For example, replacing the threshold with Volkswagen Golf in a “garage” service it can cost 10,000 rubles, but if the master uses cold welding instead of an arc, the seam will quickly come apart.
Repairing thresholds is not a job worth saving on. Cheap materials and poor-quality welding will lead to relapse of corrosion and even greater costs.
FAQ: Frequently asked questions about car thresholds
🔹 Is it possible to drive if the threshold is rusted through?
Technically yes, but it is extremely dangerous. Perforation corrosion weakens the body, which can lead to:
- 🚗 Deterioration in controllability (the body loses rigidity).
- 💥 Failure of safety systems to operate during an accident.
- 🚨 Problems with passing technical inspection.
If the hole is small (up to 5 cm), you can temporarily seal it epoxy resin or aluminum tape, but welding is required in the near future.
🔹 How often should thresholds be treated with anticorrosive?
Recommended frequency:
- 🔹 New cars: first treatment after 2–3 years (or 50,000 km).
- 🔹 Cars older than 5 years: once every 1–2 years.
- 🔹 After renovation: Immediately after welding or painting.
Use oil anticorrosion agents (for example, Noxudol) for internal cavities and wax compositions (for example, Turtle Wax) for external protection.
🔹 Why do thresholds rust even on new cars?
Reasons:
- 🔸 Poor factory processing: Some budget brands (eg. Datsun or Lada) save on anticorrosion.
- 🔸 Microcracks in paintwork: caused by stones or car washes with hard brushes.
- 🔸 Electrochemical corrosion: if moisture has accumulated in the threshold and there is contact with aluminum or copper parts.
Solution: check thresholds after every winter and treat rust converter (for example, Tsinkar) at the first signs of corrosion.
🔹 Is it possible to restore thresholds without welding?
Yes, but only when minor damage:
- 🔹 Fiberglass + epoxy: Suitable for holes up to 3cm.
- 🔹 Cold welding (for example, Poxipol): temporary solution for small cracks.
- 🔹 Putty with reinforcement: For cosmetic repairs only (does not restore strength).
For serious damage (holes larger than 5 cm, deformation), welding is required.
🔹 Which thresholds are better: plastic or metal?
Comparison:
| Threshold type | Pros | Cons |
|---|---|---|
| Metal (steel/aluminum) | ✅ Strong, durable, better protects against impacts | ❌ Heavier, susceptible to corrosion (if not galvanized) |
| Plastic (ABS, polyurethane) | ✅ Lightweight, do not rust, cheaper to repair | ❌ Less durable, may crack if hit hard |
The best option is metal thresholds with plastic overlays (like Toyota RAV4 or Skoda Kodiaq).