Tonneau Vs Cap Gas Mileage: Which One Is Cost-Effective?

To protect both your truck bed and the cargo in it from harsh weather, water, or other external factors, there are two things that you can use: a tonneau cover or a truck cap. Both a tonneau cover and a truck cap plays the same role for your truck bed – it covers and protects your cargo.

However, it is also considered an important job for tonneau covers and truck caps to make your truck more fuel efficient, i.e. they might help your truck to consume slightly less fuel when on the run when you’re using them to keep your truck bed covered. 

In this article, I will talk about gas mileage between Tonneau vs. Cap when you install them in your mini trucks like Thuren or Carli.

On average, using a tonneau cover on your truck bed is known to lead to at least 1.5 – 1.8 percent less consumption of fuel per hour. A truck cap can also be thought to do the same but the truth is, there is no direct link or proven theories about a truck cap improving your truck’s gas mileage. 

Although a tonneau cover and a truck cap are both the same things with the same function, it may be possible to save a little truck fuel by using a tonneau cover, but nothing with a truck cap. 

Tonneau Covers Vs Truck Caps: How Do They Work? 

Tonneau covers and truck caps, as well as camper shells or truck shells – are basically all the same thing when it comes to purpose and use. However, the differences can be seen in their materials, shapes, uses, and how they affect the gas mileage of a truck. 

What Is Tonneau Covers? 

As the name suggests, tonneau covers are extra covers that are attached to the truck bed of the vehicle, primarily to keep the cargo – and the truck bed, when the vehicle is empty – covered and protected. They can be both hard and soft, based on what material has been used to manufacture them and how they are used. 

What is Tonneau Covers? 

We generally use two types of tonneau covers in our truck beds: hard tonneau covers and soft tonneau covers. The hard tonneau covers are usually made from aluminum, fiberglass, or hard plastic and they need to be folded into halves or three parts to open up the truck bed.

Soft tonneau covers, on the other hand, are softer, foldable, and lightweight. They can be rolled over or folded over to create space on the truck bed for putting in cargo. 

Soft tonneau covers that can be rolled into a side are the most popular choice, since they are lightweight, less expensive, and can be installed on the truck bed without any professional help. 

What Are Truck Caps? 

Truck caps are also known as camper shells, and they are actually similar in purpose to tonneau covers. The only difference is that while tonneau covers only cover the truck beds, truck caps actually create a larger space and increase the height of your truck bed.

What Are Truck Caps

Attaching a truck cap is like creating an extra room at the back of your truck, a space you can get into and even live in when camping or traveling extensively. Truck caps are made from aluminum, fiberglass, or hard plastic, and they sit atop the truck bed to create a room-like feel.

A truck cap is also attached firmly to the bed and will protect everything inside it from water, wind, dust, or dirt, as well as give protection against theft and break-ins. 

Tonneau Covers Vs Truck Caps: Comparison 

Both are different in looks and shapes, there are some key differences between tonneau covers and truck caps when it comes to their functions. 



A tonneau cover only covers the top of the truck bed and creates just enough space that the walls of the truck bed allow it to. Truck caps create a lot more height inside, just like creating a room over your truck bed. 


A tonneau cover is basically used to cover the cargo inside the truck bed and keep them protected from harsh weather and water.

On the other hand, a truck cap creates a much larger room on top that’s big enough for people to live comfortably inside, as well as much more cargo. 


Air Circulation  

Tonneau covers do not allow air circulation inside the truck bed when it is completely covering the bed unless the cover is folded into halves or a little part of it is rolled up.

Truck caps come with little windows on the sides that can be opened, which allows air circulation. It also means that the truck can be used to carry live animals and even people inside it. 


Although a hard tonneau cover and a truck cap are both made from the same materials, the latter is more expensive and heavier because of its size and shape. 

Gas Mileage 

It is often considered a fact that using a tonneau cover on your truck bed can make your vehicle more fuel efficient, i.e. it can increase the gas mileage of your truck. This is not possible with a truck cap. In fact, gas mileage is reduced when a truck cap is installed on the truck bed. 

Tonneau Covers Trucks Caps 
Space Not much extra space Lots of extra space above 
Use Cover Cargo and truck bed Cover cargo and truck bed, and create overhead room-like space 
Air Circulation No or very little air circulation Adequate air circulation inside because of windows 
Expense Affordable Very Expensive 
Weight Lightweight and easy to carry around Heavyweight 
Gas Mileage Affects gas mileage positively Decreases gas mileage because of additional weight 
Installation Easy to fold and unfold, install and uninstall Difficult to install and uninstall, impossible to fold or remove temporarily 

Tonneau Covers Vs Truck Caps Gas Mileage 

According to truck manufacturers and experienced users, using a tonneau cover can lead to reducing the drag of your vehicle when it’s on the road. If a tonneau cover isn’t used, the open space of the truck bed will capture the flow of air and create the drag, especially at high speed.

This problem can be solved by using a tonneau cover, which will ultimately make the truck more aerodynamic and reduce the rate of dragging. This will ultimately lead to better gas mileage and a significant amount saved at the pump station, depending on how much you use your truck. 

Truck beds, or camper shells, as they are more commonly known – don’t contribute to the reduction of gas mileage. In fact, because they are much heavier, they actually lower the mph because of the extra weight.

Truck caps are also large and take up a lot of space, and they do not improve the aerodynamics of your vehicle in any way. Remember that you don’t need to take off the truck tailgate or even replace the tonneau, Bestop, and Softopper for better fuel economy.

Therefore, if the reduction of gas mileage is your main concern, a tonneau cover is a much better option than a truck cap on your truck bed. 

Frequently Asked Questions (FAQs)

Can Truck Cap Affect Mileage? 

Yes, a truck cap used on a truck bed does affect mileage, but in a negative way. Because they are heavy and take up a lot of time, they reduce fuel efficiency in a truck bed and use more fuel. 

What Happens if I drive Around Without a Gas Cap? 

Driving without a gas cap isn’t really considered dangerous, but it is certainly not recommended. If this happens regularly and continuously, over time, it will cause a significant decrease in your vehicle’s fuel efficiency, as well as damage to the engine and the overall environment.

How Long Does a Gas Cap Last? 

A gas cap usually needs to be replaced every 50,000 miles, but also earlier if they get damaged for some reason. 

What Can I Use if I don’t have a Gas Cap? 

If you’ve lost your gas cap or if you didn’t have one, an acceptable and temporary option would be aluminum foil. Any regular foil used in the kitchen can be used to cover the opening to the gas tank, but it needs to be secured with wire or a rubber band. 

Do Truck Bed Covers Save Gas Mileage? 

Tonneau covers for truck beds are known to save gas mileage but truck caps, or camper shells, do not. Rather, they are known to decrease fuel efficiency.


People do a lot of crazy things to improve their truck mileage. However, semi truck owners like Mack or Peterbilt and Freightliner or International are different as their vehicles are fuel-economical from the factory.

If you are worried about gas mileage and want to reduce your fuel use, either for the sake of the environment or if you want to save money, the best option would be to use a tonneau cover on your truck bed. A simple tonneau cover wouldn’t just protect your truck bed and your cargo, but also save your gas money by increasing gas mileage. 

Even though a truck cap is much better for protecting your cargo and giving you overhead space inside the truck bed, it is heavy and doesn’t really help with fuel efficiency, which makes a tonneau cover the best choice for gas mileage.

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