Why is the hood of a car so heavy? (Explained)

The hood of a car can be unbearably heavy. Most hoods are typically made using aluminum or steel. Aftermarket bonnets may be made from dry carbon, carbon fiber, fiberglass, or a combination of these materials.

The main job of a car’s hood is to protect and conceal some of the most important parts of your vehicle. This includes the engine. It also provides access for maintenance and repairs. But seriously, why is the hood of a car normally so heavy?

I went digging and found several suggestions that could explain why. Here’s what I found.

Why car hoods are so heavy

Heat shield

A car’s engine produces a lot of heat during normal operations. The hottest part is the combustion chamber where the fuel and air mixture burn. The temperature of burning gases inside the combustion chamber averages 2,8000 F.

It can get to as high as 4,5000F depending on how fast a car is being driven. One of the main reasons why the hood of a car is so heavy could be to protect the engine from excess external heat. This keeps it from overheating.

Some hoods have a special fabric attached to them that melts over the engine in case of a fire. It provides a cooling effect and acts as an extinguisher to control the spread of the fire. This protects the engine components and gives occupants enough time to exit.

The hood also acts as an insulator during winter. Extremely low temperatures can impact engine performance. The engine takes longer to reach its optimum operating temperature, hence, affecting fuel efficiency. The hood helps to preserve some of the heat.

Downforce

Some people argue that another reason why the hood is so heavy is to provide downforce. Having the car tilting down at the front gives it better grip and allows it to push less air for faster movement and better fuel mileage.

A car that is low stays stable at high speed and when taking corners. The lower ground clearance helps to lower the center of gravity which translates to better handling. The car is able to stick closer to the ground more strongly, reducing the chance of toppling or rolling over at sharp turns.

However, other people argue that for downforce, car manufacturers have better options on areas they can add weight. The hood doesn’t seem like a viable option. Most manufacturers would rather produce a car with lower ground clearance instead to lower the center of gravity.

Pedestrian protection standard

A car’s design plays an important role in protecting cyclists and pedestrians in the event of a front-end collision. It has a huge impact on the severity and scope of injury in crashes.

In Europe, the Euro NCAP assesses how cars protect their occupants and other road users during an accident. It takes a look at the potential risk of injury to the pedestrian’s head, pelvis, upper and lower leg.

In the US, this is done by the Department of Transportation (DOT). Cars must adhere to certain safety criteria that provide protecting during a crash. The front, for example, should act like a crumple zone that deforms to absorb the force of an impact while protecting the occupants.

The idea is that hoods should be strong enough to handle the impact, perhaps making it necessary to use heavy material. The material should also be able to crumple and absorb the shock. An active structure that can also push away from the engine components is also necessary.

Also, weight has an effect on how much impact the people inside a car experience. A lighter vehicle will be pushed backward during a collision while the heavier vehicle stays put. The people inside the heavier car experience less force and if lucky, less risk of injury. The additional weight from the hood might help.

Weight distribution

Another argument is that hoods are made heavy to balance the car’s weight distribution. A perfect balance would be 50/50 front and rear. Weight distribution affects how fast a car accelerates and decelerates as well as how good it handles when cornering.

While driving, it improves steering ability, allows for better braking, better ride quality, and minimizes driving fatigue by helping the driver to stay focused. The weight is usually measured front vs rear.

The argument here is that car manufacturers install heavy bonnets to help balance the car. However, this doesn’t seem like the best place to add mass. The polar moment of inertia is high and the hood itself is located above the vehicle’s center of gravity.

But, it may come as no surprise. In the 80s, BMW ran an “Ultimate Driving Machine” campaign that touted a perfect 50/50 weight balance in its cars. Turns out that underneath the rear trunk carpet was a hidden factory-installed weight weighing about 30 pounds.

So it might be possible for car manufacturers to add weight to a car in odd areas to balance it out.

Final Thoughts

The reasons listed above provide somewhere to start when trying to figure out why car hoods are so heavy. It’s good to note that not all vehicles come with a heavy bonnet. Some feature covers that are light and manageable for most car owners. If you have a car with a heavy hood, ensure that you stay safe whenever you’re working under it.

FAQs

What holds a car hood down?

A vehicle’s hood is held down by a hood latch system. This latch connects to the inside of the car, on the driver’s side. A hood release handle can be found on the left-hand lower corner side of the dashboard. It attaches to a cable that routes all the way to the front. Pulling the release detaches the latch and allows you to open the hood.

What holds the car hood up?

On some cars, the hood is held up by support struts. These allow you to gain access to the engine bay without having to hold the cover up with your hand. Many cars have a prop rod instead that you can use to support the hood as you work on the car.

How much are hoods for cars?

The replacement cost of a hood ranges between $100 and $250 for the part alone. Labor costs range about the same. It’s good to note that this varies widely depending on the brand, material, and type of vehicle. Labor rates also vary between locations.

What’s the point of a carbon fiber hood?

The main reason why car manufacturers use carbon fiber to make different parts of a car is because it reduces the overall weight. It is very popular and can be found on the hood, various parts of the engine, and body panels. It also adds an amazing aesthetic appeal to the car.