Why Are License Plates Easily Washed Away by Water?

[DiEliza]

When a vehicle passes through water, the front bumper lifts the water, creating an external force that impacts the license plate, bending it. When this force exceeds the maximum load-bearing capacity of the nut base, the nut is forcibly pulled out of the plastic, ultimately causing the front license plate to fall off. Below is relevant information about license plates: Introduction: License plates, commonly known as tags, also referred to as vehicle number plates, are plates hung on the front and rear of a vehicle. They are typically made of aluminum, sheet metal, plastic, or paper, and bear the vehicle's registration number, registration region, or other relevant information. Function: License plates serve as a numbering and information registration system for vehicles. Their primary purpose is to identify the vehicle's region of registration and to enable the tracing of the vehicle's owner and registration details based on the license plate.

[Lopes]

I've thought about this too. The main issue is that the fixed position of the license plate is too weak. Most cars use just two screws to secure the plate, leaving a large gap behind it. When driving through waterlogged areas, the water flows from the front to the back of the car at a very high speed. When it hits the license plate, it splits into two streams: one flows down along the plate, while the other enters the gap between the plate and the car body. The water entering the gap accelerates, creating a low-pressure area behind the plate that sucks on it like a vacuum cleaner. Additionally, the sharp edges of the plate cause the water flow to lift it upward, making the screws unable to withstand the pulling force. From my experience in car repairs, older cars are especially prone to losing their plates because the plastic clips have aged and loosened. My suggestion is to drive slowly through waterlogged areas during rain and, ideally, use four anti-theft screws for reinforcement.

[GiaLee]

I've seen too many unlucky car owners searching for their license plates after the rain. The key issue lies in the angle of the water flow working against the license plate. Typically, license plates are installed with a slight forward tilt, making them act like a small slope when the car is moving. When a large volume of water rushes over the front of the car, it directly hits this slope, generating an impact force dozens of times stronger than normal driving. The sharp edges along the top and bottom of the license plate create a cutting force in the water flow, while the screw holes are thin and lack any cushioning. The worst part is the plastic license plate frame, which softens and deforms when soaked, causing the clips to loosen directly. Some car owners, trying to save effort, only install two screws, and when the accumulated water rushes over, the entire license plate flies off like a piece of paper. Once, at an auto repair shop, I counted seven or eight license plates collected in just one morning after a heavy rain, all brought in by other drivers who found them.

[JuneLee]

It's quite interesting when you think about it—license plates are like tiny airfoils. The moment a car drives into standing water, water rushes over the top of the plate at high speed while the flow beneath moves slower, creating a pressure differential that lifts the plate upward. At the same time, the water, carrying sand and debris, impacts the screw holes, quickly loosening the fasteners. The design of the front bumper also plays a role; some models have particularly large recesses behind the bumper, where water can create vortex suction. I once tested this at a car wash with a high-pressure hose—just 2 kg of pressure was enough to rip off a plate secured with only two screws. Since then, I've insisted on using four stainless steel screws for my plates, and even in the heaviest rains over three years, none have come loose.

[Sá]

Many car owners often ask me about this. The principle is actually similar to a range hood, where water flowing over the surface of the license plate creates a low-pressure vortex area. If the suction force on the back cavity of the license plate reaches over ten kilograms, ordinary self-tapping screws simply can't hold. The gaps during license plate installation are the root cause—the flatter the plate, the safer it is. I've seen people reinforce the edges with 3M double-sided tape, which really works, but you need to pay attention to the water resistance of the adhesive. Modified cars are even more dangerous, as added front lips can cause water to hit the license plate more violently. During heavy rain, if the speed exceeds 30 km/h, the impact force of the water can reach hundreds of kilograms—enough to tear off the entire license plate. It's recommended to check the aging condition of the license plate frame more often during maintenance.

[LaElisa]

This issue is particularly common in rainy southern regions. The core problem lies in the fact that license plates are designed with four mounting holes, but only two screws are typically used for fixation, and their positions are too high. When water accumulates and flows against the plate, it mainly impacts the lower half, creating a lever effect that can pry the entire plate off. A car wash attendant told me that the plastic-threaded snap screws are the most prone to falling off, while iron expansion screws are much more secure. Once, while helping a friend retrieve his lost license plate, I noticed that the screw holes on his plate had developed green rust and broke with a slight twist. Nowadays, new cars generally come with four screws for plate installation, but owners of older vehicles modifying their cars need to be cautious. When driving through deep water, avoid sudden braking—the abrupt increase in impact force can cause 90% of license plates to disintegrate on the spot.