The main function of the rear bumper of the car
The main body of the rear bumper (often referred to as "lower guard" or "flow guide plate") is an important component of the rear bumper assembly. Its main functions include the following aspects:
Aerodynamic optimization: It guides the airflow at high speeds, reduces rear turbulence, lowers the drag coefficient, improves driving stability, and helps reduce fuel consumption.
Scratch protection: As the outermost plastic component at the bottom of the vehicle, it is resistant to dirt and wear, effectively preventing damage to the vehicle's paint or chassis from scraping against the shoulder of the road, stones, or other obstacles during reversing.
Collision buffering: In low-speed rear-end collisions or scratches, it absorbs and disperses part of the impact force, reducing damage to key components such as the rear bumper body, tail lights, and exhaust pipes.
Decorative and styling function: Through different designs (such as the diffuser shape of sports models, or the anti-scuff strip of SUVs), it enhances the overall visual effect and improves the appearance coordination.
Protecting the chassis components: It blocks flying stones, sand, and other debris on the road surface, preventing them from directly impacting the sensitive components such as the oil lines and circuits at the bottom of the vehicle.
This component is usually made of black plastic (such as polypropylene PP), taking into account durability, low cost, and easy maintenance. If there is severe cracking or deformation, it is recommended to replace it in time to ensure its normal function.
The "lower main body failure" of the car rear bumper usually refers to problems such as deformation, cracking, detachment, subsidence, or failure of fixation in the lower part of the bumper. According to the latest public information as of May 2026, the common causes and handling methods are as follows:
Common failure causes
Loose or broken fasteners or screws: The bumper is fixed to the vehicle with fasteners and screws. Over time or after collisions, they may loosen, causing the bumper to sag or rise.
Material aging or thermal expansion and contraction: Plastic materials (such as PP, ABS) become brittle and deform under repeated high and low temperature cycles. Especially in summer under high-temperature exposure, they contract when cooled, easily causing cracks or dents.
External impact or scraping: Low-speed collisions, scraping against curb stones, or flying stones can cause dents, bulges, cracks, or even fractures.
Improper installation or failure to restore after repair: If during operations such as replacing the guard plate or adding radar, the fasteners or screws are not installed correctly, the force distribution will be uneven.
Vehicle structure deformation: If there has been a severe collision, even if the bumper itself is undamaged, the deformation of the vehicle installation points will cause abnormal positions of the bumper.
Recommended handling steps
Initial inspection
Observe if there are obvious cracks, dents, missing fasteners.
Check if the fasteners on the bottom and both sides are loose.
Simple repair attempt
If it is only a loose fastener, simply tighten it (be careful not to tighten it too much and cause plastic cracking).
If the fastener is damaged, replace it with the same model fastener (low cost, can be purchased online or at auto parts stores).
If there are minor scratches or small areas of paint loss, use a color-matching pen or self-etching paint to handle it.
Professional repair advice
If the crack length exceeds half the width of the bumper, it is recommended to replace the new part and weld to ensure sufficient strength.
Severe deformation or dents, you can try heating with a hot air gun + external force correction (only for PP material), but the operation risk is high, it is recommended to be operated by a professional technician.
If you suspect vehicle structure deformation, it is necessary to go to a professional repair shop for four-wheel alignment or chassis inspection.
Preventive measures
Avoid prolonged exposure to the sun, try to park in a shady place.
Use neutral car wash agents, avoid chemical corrosion.
Regularly check if the gap between the bumper and the vehicle body is uniform, and promptly tighten loose components.
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