Why Do License Plates Fall Off When Driving Through Water?

[SanJoanna]

License plates tend to fall off when driving through water due to three main factors: installation method, material, and water flow. The details are as follows: 1. Installation Method: Many people prefer adding frames to their license plates, which often prevents the proper installation of the bottom two screws. Typically, license plates are secured with only two screws, primarily because many car bumpers are narrow and protrude forward. The limited width of these bumpers means they often only have two mounting holes for the license plate, leaving the plate in a suspended state with no screws at the bottom. 2. Material: License plates are usually mounted on the bumper, which is commonly made of modified polypropylene. While this material provides cushioning during collisions, is lightweight, and helps reduce fuel consumption, it can deform under external force. When driving through water, the rapid flow can pull the screws out of the deformed bumper, causing the plate to fall off. 3. Water Flow: There is often a gap between the license plate and the bumper. When a vehicle drives through water, the water hitting the bumper is forced upward and into this gap, creating an outward pushing force on the plate. As the vehicle moves through the water, this force causes the plate to wobble back and forth, eventually leading to it being washed away.

[DelMila]

Last time my friend's license plate was washed away by floodwater, and the mechanic later said the key issue was with the mounting method. Nowadays, many cars only use two screws to install the license plate, but the bumper material is relatively soft. After soaking in water, the deformation increases, and the screw holes get pulled loose. Plus, floodwater isn't just water—it's mixed with sand and small stones. When the car drives through, it's like the area under the license plate is repeatedly hit by a high-pressure water jet. I've seen cars with lost plates firsthand—the anti-theft clips were so rusted they snapped with a light twist. These rubber clips expand and become brittle when wet, and after a few soakings, they're useless. Later, the mechanic taught a trick: go to a hardware store and buy a pack of stainless steel screws, then install four screws for both front and rear plates. It's been five years, and the plates haven't fallen off since.

[DeRyan]

As a seasoned driver who has lost license plates three times during typhoons, I know this pain all too well. There's a gap between the back of the license plate and the bumper. When the car rushes into standing water, the flow violently pushes upward through this gap. It's like someone using a crowbar to pry the plate from below – regular screws simply can't withstand that. Those with modified license plate frames suffer even more, as the metal frame acts like a lever when hit by water, directly tearing the screw holes apart. Once, when I retrieved a washed-away plate, I found the plastic screw nuts completely shattered. Now, I regularly apply anti-rust lubricant to the screws and never exceed 8km/h when crossing water puddles – the water impact force is proportional to the square of the vehicle speed. Driving too fast is like hitting your plate with a sledgehammer.

[DiEmiliano]

My auto repair buddy told me that license plates need to withstand wind pressure like billboards, but manufacturers install them carelessly. The factory-provided screws are pitifully short, and the thick plastic bumper can't hold them firmly. I've taken off waterlogged plates before - the mounting claws were all bent. Standing water is actually an accomplice; tire pressure creates vacuum suction from water waves, combined with flow impact, it's like two hands pulling at the plate. Be especially careful with potholes right after rain - muddy water grinds screws worse than clean water. Check the license plate frame's bottom quarterly, replace immediately if cracked. Road puddles with winter de-icer in northern areas are worse, corrosive as sulfuric acid.

[VanRowan]

Last month, I just helped my neighbor retrieve a license plate from the sewer. Upon closer inspection, it turned out that the aging bumper clips were the real culprit. Nowadays, cars mostly use clip-on bumpers. After being soaked in water, the elasticity of the clips decreases, causing the entire bumper to sag and, in turn, pulling the license plate askew. When driving through water at speeds exceeding 30km/h, the water pressure can reach 0.5 kilograms per square centimeter—equivalent to hanging a bucket of water on the front of the car and slamming it against the license plate. Even more absurd is the fact that the rear license plate position on many cars is right in the trajectory of water spray from the wheels, as if being continuously blasted by a high-pressure water gun. It's recommended to apply 3M adhesive tape on the back of the license plate as a buffer during installation and to immediately lift the plate to dry the clip slots after driving through water.

[VanTalia]

Once I saw an auto parts market selling license plate screws at a discount, I realized that the original factory parts were of inferior quality. These iron-containing screws, when soaked in water, undergo an electrochemical reaction with the aluminum plate of the license plate, causing the screws to disintegrate. This is especially important for car owners who have modified their headlights, as high-power light assemblies cause the bumper to heat up over time, leading to premature aging and brittleness of the plastic. When impacted by water, the plastic expands three times faster than metal, causing the screws to pop out of the holes instantly. Having lived in the south for twenty years, I've seen auto repair shops filled with recovered license plates every rainy season. The best solution is to use 304 stainless steel screws with spring washers, and remember to open the hood to check for any wobbling of the license plate after driving through water.