Does A Roof Rack Decrease Gas Mileage?

Updated on

I was researching around the web to find a good roof bike rack and it got me thinking…

Does a roof rack decrease gas mileage?

What I found surprised me!:

Unfortunately, adding a roof rack to your car will hurt the gas mileage you get. So I decided how and why this happens and if there is a way to help.

Keep reading and I’ll give you some tips that should help!

Why Does A Roof Rack Decrease Gas Mileage?

Unfortunately, anything you add to your vehicle will affect gas mileage. This includes a roof rack, bike rack, luggage rack, pair of bikes, or anything else you may strap to your vehicle.

The more aerodynamic a car is, the better the gas mileage it will have.

Aerodynamics is the study of force and how an object moves through the air. Over the years, cars have become more and more aerodynamic.

This means they are designed to move through the air as easily as possible.

More aerodynamic cars have better airflow and need less effort to speed up. This helps to achieve a better fuel economy because the car has to spend less effort to move.

Fuel economy refers to how much distance a car can travel on its fuel. Better aerodynamics means better fuel economy and better gas mileage.

How does a roof rack affect your car?

Adding a roof rack to a car creates more drag. Drag is a force that moves parallel to the airflow. Creating more drag creates more work for the car.

The drag coefficient is often used to measure this for a car. The drag coefficient is a measure of how easily the car moves through the air.

Carmakers design vehicles with shapes to reduce drag and improve the drag coefficient.

Sleek vehicles have a better drag coefficient than vehicles like pick up trucks, and SUVs.

It’s All About The Design

Does an empty roof rack affect mileage

Carmakers create cars with airflow in mind to improve aerodynamics.

Aerodynamics improve by rounding the car’s corners. Designers also make sure air can flow around the entire car.

The more aerodynamic a car is, the lower the drag coefficient is. The coefficient of drag is often referred to as the Cd.

Most modern cars achieve a Cd of .30, while SUVs vary between .30 and .40. Pick up trucks start at a Cd of .40.

Pick up trucks have a more box-like shape, which makes it more difficult for air to flow around the truck.

Adding a roof rack to a car adds a boxier shape to the top of the vehicle.

This inhibits air flow from running over the car as smoothly. This raises the Cd and thus impacts the gas mileage as well.

Generally, adding a loaded roof rack to your car will lower your gas mileage by at least 10 percent.

Some drivers may see their gas mileage drop by as much as 20 percent depending on vehicle type and type of roof rack.

So if your car usually gets 30 mpg on the highway and you add a full roof rack, your highway gas mileage will drop to 24-27 mpg.

If you must travel with a loaded roof rack, try to choose the most aerodynamic roof rack you can. Do some comparison shopping to find a lightweight roof rack that is also aerodynamic.

When adding load to the roof rack, be sure you don’t have items hanging off or creating a bulge.

Does an empty roof rack affect mileage?

There is no way an empty roof rack can affect gas mileage…


Unfortunately, even an empty roof rack will affect mileage.

Adding an empty roof rack to a vehicle can drop the gas mileage by about 7 percent!

This means that adding an empty roof rack to a car that usually gets 35 mpg will drop the gas mileage to 32.5 mpg.

A drop of 7 percent may not sound like much, but it adds up over time. Say you drive your car 200 miles in a week, which is easy to do with even a short work commute.  

You’ll find yourself having to fuel up more often if you also have empty roof rack. You may make it only 2 and a half weeks before needing to fuel up instead of your usual 3.

Since the empty roof rack does affect gas mileage, it’s important that you remove it when you’re not using it.

This may sound like a obvious solution. But while you’re out driving today, count how many cars you see with empty roof racks.

I bet you’ll notice quite a few!

The extra few minutes of effort may save you quite a few dollars by improving your daily gas mileage.

How does a bike rack affect mileage?

How does a bike rack affect mileage

A hitch mounted bike rack may only slightly affect gas mileage. Adding a bike or two to a hitch at the back of the car does not affect the aerodynamics of the car very much.

This means you may notice a tiny drop in gas mileage like 1 mpg less than without the bike rack.

But, it may depend on the size of your bike and type of bike rack.
You want to do everything in your power to keep your car as aerodynamic and streamlined as possible.

That’s why it’s better for gas mileage to use a hitch or trunk mounted bike rack instead of a roof rack.

But if your bikes stick out very far on either side, you may start to lose some of your aerodynamic abilities.

 You may start to see a drop in gas mileage up to 5 percent. So be careful in choosing what type of hitch mounted bike rack and how you mount your bike.

How much does a bike roof rack affect gas mileage?

A bike roof rack with bikes may make the largest impact on gas mileage.

A roof rack with bikes attached greatly decreases gas mileage.

Gas mileage may drop by as much as 30 percent!

That’s a lot:

If you’re traveling with your bikes attached to your roof, you’ll have to stop more often for gas.

Losing 30 percent of your gas mileage for a vehicle that gets 24 mpg means you’ll only get 16.8 mpg.

Consider a 500 mile trip with a standard gas tank holding 18 gallons. You’ll have to stop for gas over halfway through the trip and then refuel again at the end.

Without the bike roof rack, you’d have nearly made it the entire 500 miles before needing to refuel.

If you have to attach your bikes to a roof rack for an activity then go for it. But if it’s not necessary, then remove the bikes and rack.

Even removing the bikes from the roof rack would help to reduce drag and help improve your gas mileage.

If you’re taking your bikes on a camping trip, remove them from your vehicle and park them when you arrive.

Don’t drive around town with them still attached. This will save you a great deal on gas in the long run.


A bike rack is a great way to take your bikes with you wherever you go. But, they will greatly decrease your gas mileage.

Choosing the most aerodynamic roof rack can really save you on gas money. And never ever driver with an empty rack.

I know this can be a hassle but in the long run it’s worth the extra time and not the extra money.

If you follow these tips you will get more miles out of your car on your road trips!

Photo of author
Bryan Ray is the Co-Founder of The Biking Apex. He's a cyclist and a trainer who loves fitness and loves to teach people how to ride and maintain their bikes and bike accessories.

1 thought on “Does A Roof Rack Decrease Gas Mileage?”

  1. Wow, it’s amazing to know that using roof rack baskets on my vehicle affects its aerodynamics and ultimately lessens gas mileage. I’m planning to have one installed on my car so that I can use it for extra baggage space for when I go on a camping trip with my friends later this year. Lessening my gas expenses for major trips like that would be very helpful.

Comments are closed.

The Biking Apex

Copy and paste this code to display the image on your site