Does a Roof Rack Really Affect Gas Mileage? Here's the Science and How Much MPG You Lose

In This Article

• The Science Behind the Loss: Aerodynamics and Added Weight
• Key Factors Determining Your MPG Loss
• More Fuel Consumption on Highways
• Different Roof Racks Have Different Impacts
• Practical Strategies to Minimize Fuel Consumption
• Final Words

Key Highlights

• Yes, roof racks reduce gas mileage: This is due to increased aerodynamic drag and added weight, forcing the engine to work harder.
• MPG loss varies significantly: An empty roof rack can cause a 1-2 MPG drop, while a cargo box can reduce fuel economy by up to 25%, and bikes/kayaks by around 28% at highway speeds.
• Higher speeds worsen MPG loss: Aerodynamic drag increases with the square of velocity, meaning fuel consumption is much higher on highways.
• Rack type and loading matter: Factory-installed bars and aerodynamic designs are generally better. Rear cargo carriers are more fuel-efficient than roof boxes.
• Minimize fuel loss: Remove the rack when not in use, drive slower, load cargo smartly for better aerodynamics, and choose fuel-efficient rack designs.

Overview

Does a Roof Rack Really Affect Gas Mileage, or is it a myth? Did you ever wonder why, whenever you strap something on your car's roof, you constantly have to stop at a gas station to get the gas tank filled? Upon investigating, I discovered that many travellers, including me, face the same problem daily.

There is no doubt that roof tops are amazing traveling gear that carry heavy luggage, cycles, and other loaded traveling gear easily. But the convenience of loading things like a roof rack on a car’s roof comes with a cost: more fuel consumption! 

But worry no more, as this guide is here to help you out. We will take you through an in-depth journey of why and how you lose MPG, how to minimize it, and what type of roof racks are suggested to minimize mileage. 

Let’s get right into it.

The Science Behind the Loss: Aerodynamics and Added Weight

To understand the loss of MPG, we first need to know about aerodynamics. To put it in words, when the car is moving, the air pushes it back. To overcome this resistance, especially when the car is moving fast, the car engine has to work harder. 

Now, imagine a roof rack strapped on the rooftop, with or without luggage. Now, more energy will be required to push against the air flow, hence, the fuel consumption increases. 

This statement is not just words but has been proven a numerous tests and studies to show that the greater the mass on the rooftop, the lower the fuel efficiency. 

Key Factors Determining Your MPG Loss:

Several factors contribute to the loss of MPG. Have a look at the following:

• Empty Roof Rack:

Even when the roof rack is empty, it costs you more fuel. A 1-2 mpg reduction in fuel economy is recorded with an empty roof rack attached to the rooftop.

• Cargo or Box:

When a box is added to the top of the car roof, a 25% reduction is recorded in the fuel economy. A sedan driving with a large box on the top is reported with a reduction of 53 mpg to 25 mpg in the fuel economy. It makes up to a 19% loss in fuel.

• Kayaks or Bikes:

Kayaks or bikes strapped on the roof rack are more disruptive to airflow. When the car is driving at 65mph, fuel economy decreases by 28%.

Expert Tip: Reduce your speed, especially on highways, as aerodynamic drag increases exponentially with speed.

More Fuel Consumption on Highways:

This loss in fuel economy is recorded less in a city than on a highway. The reason is that when you go faster, the air resistance increases. This resistance increases with the square of velocity. Hence, double the speed, four times, is the aerodynamic drag.

When the same car is strapped with the same cargo, but one is driving at 30 mph and the other at 60 mph, the fuel consumption of the second car is higher than the first one. That is why the fuel tank empties quickly when you are on a road trip with luggage on the rooftop.

Different Roof Racks Have Different Impacts:

Yes, you read right! Shape, sizes and material (aluminum vs steel) of the roof racks determine the MPG loss of your vehicle. 

• Factory-Installed Bars:

These are straight, flat bars attached on both, left and right, sides of the rooftop. Their shape causes less disruption, hence less MPG loss.

• Market-Bought Racks:

These are on bulkier and heavier sizes. They are bigger than the factory-installed ones and cost more MPG.

• Rear Cargo Carriers or Roof Boxes:

Boxes strapped on the roof cost more fuel than the rear cargo carriers. A rear cargo carrier is a good choice for loading and travelling with luggage as it uses less fuel.

Practical Strategies to Minimize Fuel Consumption:

Though loading luggage will cost you more fuel, but following are some tips to minimize it.

1. Removing Roof Rack When Not in Use:

This tip may seem an obvious one, but many people leave their roof racks attached to the roof the whole year. A wastage of 100 million gallons of fuel is recorded in the US for this very reason. Removing the rack will improve your car’s mpg.

2. Using Rear Cargo Carrier:

Opting for a rear and hitch-mounted carrier has a significant impact on improving a car’s mpg. It is not only good for fuel economy but also makes it easy to load and unload. 

3. Drive Slow:

The speed has a direct impact on the fuel consumption. To minimize mpg, it is best recommended to drive slower as the pressure of air decreases with the decrease in speed, even when the roof is loaded.

4. Load Smartly:

Even when you need to load luggage, make it aerodynamics-friendly. Use low profile boxes and cargos to reduce the pressure of air. Load the heavier luggage inside the car when possible.

5. Opt for a Good Roof Rack Design:

There are many options of roof racks in the market that offer designs made to deflect wind. These sleek designs also help in reducing air resistance and lessening noise.

Final Words:

Hope you enjoyed reading this article and got your answer about Does a Roof Rack Really Affect Gas Mileage? Besides providing ample space and being super helpful to carry heavy and extra stuff while traveling, they might charge you extra fuel, especially at high speeds. But don’t worry, as this issue can be fixed if you use this essential traveling gear wisely. 

For a traveller or people who move continuously, a roof rack is life lifesaver. Whether you want to load a rooftop tent or carry bikes and skis for a summer getaway, roof racks are always there to help. You can make them fuel-friendly by driving slowly, unloading the roof rack when not in use, and opting for fuel-friendly roof rack designs. 

You just need to choose the right rack, load smartly, and drive fuel-efficiently to enjoy all the benefits without sacrificing your MPG. Happy traveling!