What is the bulge in the middle of the rear seat of a car?
4 Answers
The bulge in the middle of the rear seat of a car is part of the vehicle's floor, designed for the smoothness of the chassis. Since the underside of the car's chassis accommodates the exhaust pipe or drive shaft, rear-wheel-drive vehicles typically require a drive shaft to transmit the engine's power to the rear wheels, necessitating such a structural bulge. The reasons for the bulge in the middle of the rear seat are as follows: 1. Rear-wheel-drive vehicles need to accommodate the drive shaft: Cars with front-engine, rear-wheel-drive layouts require space for the drive shaft in the middle. The front-mounted engine transmits power to the rear wheels via the drive shaft. If the drive shaft is too low, it can easily scrape the ground, affecting the car's ground clearance. Raising the vehicle height would impact the car's center of gravity, hence the need for a locally raised floor to protect the drive shaft and enhance the car's stability, ground clearance, and handling. 2. Front-wheel-drive vehicles need to route the exhaust pipe: If the car's chassis is designed low and the vehicle is front-wheel-drive, the middle bulge is designed to provide space for the exhaust pipe. 3. Increasing chassis resilience: Generally, the raised floor can significantly increase the body's strength several times over. This design enhances the chassis's resilience. Many cars without such a bulge have been observed to break upon impact. The semi-circular bulge in the floor acts like a raised steel beam, reinforcing the structure.
The raised hump in the back seat of a car is commonly referred to as the center tunnel or driveshaft tunnel, and it's particularly prevalent in rear-wheel-drive or all-wheel-drive models. Its primary purpose is to house the drivetrain components running from the engine to the rear axle, preventing the floor from being completely flat and occupying too much underbody space. Through my experience in driving and car maintenance, I've learned that this raised design actually enhances structural rigidity and safety, as it helps distribute impact forces and reduces the risk of deformation during collisions. Of course, it can be quite annoying for passengers—those sitting in the middle rear seat have to awkwardly straddle it, making long trips especially uncomfortable. In electric vehicles, this hump sometimes conceals battery packs or charging cables to ensure safe power transmission. My advice when car shopping is to check reviews carefully and opt for models with a completely flat floor for greater comfort.
When I bought my car before, I also noticed that raised hump in the rear seats. At first, I thought it was a design flaw, but later learned it mainly serves as the transmission shaft tunnel. In gasoline-powered cars, this feature is crucial because the engine needs to transfer power to the rear wheels, requiring this space in the floor for mechanical components to operate. For front-wheel-drive vehicles, the hump might be smaller or less noticeable. As a young car owner who frequently goes on road trips, this design does affect space utilization—whether it's placing luggage or having a child sit in the middle, it feels awkward. However, on the flip side, it enhances the car body's rigidity and resistance to bending. When inspecting a car, don’t overlook this area to avoid issues like aging wiring or debris getting stuck. If possible, opt for models with lower humps to improve daily convenience.
My friend's car has a hump in the rear seats, and the first impression when sitting in is strange. It might be part of the central tunnel, hiding the driveshaft or exhaust system. The height of the hump varies between different car models, more prominent in rear-wheel-drive cars, while front-wheel-drive cars may only have a slight bulge. Some cars are designed with cup holders or air vents here, making it practical in disguise. As a passenger, I always wonder what structure it is when I'm in the car. Later, I heard that this is a compromise made by engineers to save costs and optimize layout, ensuring that mechanical components are not exposed. But having your legs resting on it does affect comfort, especially during long trips sitting in the middle of the back seat.
