How to Fit a Roof Box on Car? Everything You Need To Know

If you want to go on a trip with your friends or family and want to enjoy a comfortable ride, a roof box is a solution to enjoy the ride with full of comfort by keeping the items in the roof box and not in the passenger seats.

You have to make sure that your roof box is properly and safely attached to your car. But how can you do that?

Here, you will find the way to Fit a roof box on a car quickly, easily, and safely.

Do You Need Roof Bars for a Roof Box?

Roof Bars

Yes, of course. Roof bars are very important for installing a roof box. You cannot do that with the help of a rope. You have to find a place for the box to bolt into on top of your car or van.

Suppose your car does not match the standard size of the roof bars. You can then order a set and have them installed so that you can safely install your roof box.

Installing a roof cargo box on top of your car is the easiest way to increase your car’s storage capacity. But you have to install them correctly. If they are installed incorrectly, then they can be harmful to your car.

Installing a roof box is not a hard task. But you have to keep some important matters in your mind before installing the box, such as the weight capacity of the roof of your car or the roof bars weight capacity.

Do Some Research

Before buying a roof box or a set of roof bars, you should always do some research. It would be best if you did not go for the cheapest roof bar options available on the market. Moreover, you should also choose bars that are compatible with the roof of your car and the roof box you want to buy unless you will not be able to use them for a long time.

Can a Roof Box Overhang?

Roof Box Overhang

There can be some overhang when a roof box is installed on a car, but you should keep it to a minimum amount. Finding the 100% perfect size of the roof cargo box can be difficult, so buying a roof box that is an inch or two inches bigger than the exact size is OK and will not cause you any problem.

But if you choose a roof box bigger than a couple of inches on each side, it can create some problems, including balance issues. So you will not be able to enjoy a clean and quiet ride. A jerky ride is not comfortable at all, and it is very dangerous.

But still, if you can’t avoid the overhang, you should find a longer, not wider, roof rack. You should find the roof bars that are designed to accommodate longer stuff so that more support can be added to the roof box.

It would be best to choose a roof box that will not interfere with any other road users. So you should not install a roof box designed for an Audi Q7 on a Mini Cooper.

You should not accept too much overlap at the back because if you are driving a hatchback or a car with a trunk door that lifts higher than normal, the trunk can get damaged with the roof box.

There is also a possibility of smashing your rearview window, which is not a good thing. So choose the box which is not too much overlap.

A Balancing Act

After all, it would be best if you also were careful about loading the items in your roof box. You should place your luggage perfectly in the box so that the weight can remain balanced and distributed evenly. Choosing the right roof box for your car will help you in this.

It will be a good decision for you if you go on a short drive nearby your house with the loaded roof box so that you can have an idea about how it feels to drive with a loaded roof box on top of your car. You should also check the breaking to see if it create any problems.

It is better to give it a test drive so that you do not need to pull over on the highway to fix anything or make any adjustments to the roof box.

Do Roof Boxes Fit Any Roof Bars?

Thule Atlantis Rooftop Cargo Box

Most of the roof boxes are compatible with most aftermarket roof bars. But roof boxes that are long or designed to carry longer items such as skis, fishing rods will need the extra support of other bars.

Check Your Specifications

Again, if you want to fit a roof box that weighs a little bit more than the roof bar’s weight limit, then you have to add another bar or two to keep the box stable on top of your car. 

Adding the extra roof bars around the original rack or slide will help you evenly distribute the weight of your roof box to your roof bars. The extra bars will ensure safety and security, and they will not interfere with the original rack or bars.

If you want to install a roof rack or roof bars on top of your car by yourself or if you want to replace an old roof rack, you should do some research and make sure that it will fit with your roof box. You have to line up the holes for the bits and bolts.

Roof Cargo Bags as an Alternative to Cargo Box

SUAOKI Roof Top Cargo Bag

If you could not find the perfect roof box for you or have issues fitting a roof box on top of your car, you can go for the cargo bags. It is also a beneficial way of increasing the storage capacity of your car.

Follow Instructions

If you want to install your roof box or roof bars perfectly on the roof of your vehicle, you should install the roof box by following the instructions that come with your roof bars and roof box. If you don’t do that, you can face any problem while you are on the way. 

So if you are confused about anything, go and check the instructions and make sure everything is correct. 

Moreover, it would be best if you studied the combination of roof bars and roof boxes that you have chosen for your car because both your bars and box manufacturers should have some compatible products designed for the product you have brought.

They should also mention the maximum weight capacity that the box and bars can take together. So you should carefully decide which one you should buy so that you can travel safely and prevent the roof of your car from being damaged once the box and bars are mounted.

Will Roof Racks, Bars, and Boxes Damage My Car?

secure in place

If you carefully follow all of the instructions by the manufacturer, you will not face any problem, and the roof box or roof rack will cause no damage to your car.

Mind Your Backs

While packing your roof cargo box, you should load maximum weight at the lower end of the box. The manufacturer also recommends it. So you have to be careful. Moreover, roof boxes are bulky things, and they are hard to handle for just one person.

You need anyone to help you mount your roof box on the bars. It will also keep the car from being dented, scratched, or damaged. Moreover, the manufacturer may have recommended a maximum speed limit when you’re driving with the box.

So you should carefully read the manual. If you drive over the speed limit with the roof box installed, then you may face problems, or you might need to stop and fix it before you cause an accident.

When you are installing the roof box, you should also be careful tightening the screws. If you leave it slack, it will shift on the bars and make noises again, or if you make the screw too tight, then it can damage your roof bars and the box. So you have to keep it in a perfect position.

You also have to be careful that you should not go by under a short bridge or go into a parking garage with the roof box installed on top of your car. Because if you hit a low-hanging beam, your roof box can be damaged.

Moreover, the bars or rack also can be damaged or come off from the roof of your car and can cause costly damage to your vehicle. So be very careful if you do not want to spend a lot of money on a roof box.

How Far Apart Should the Roof Bars Be?

When you are spacing roof bars apart, you have to keep in mind that the further you keep them apart, the harder it will be for them to support your roof cargo box’s weight. Most manufacturers recommend that bars should be spaced at a maximum of twenty-four inches apart. So make sure that this standard applies to any crossbars that might go along with the rack that is currently in place.

You will need extra support if you want to carry heavier items with your roof box. Adding a different bar or two will help the box in distributing the weight of the bulk.

You have to space the bars at an equal distance from one another so that the box can be evenly supported by the bars. Most roof boxes are made out of hard plastic, so if they fall on the roof of your car, then your roof of the car can be get scratched. A cargo bag also can drop and touch the top of the vehicle.


Check your vehicle’s owner’s manual to know the roof of your car’s maximum weight capacity so that you can decide how many bars will be needed to secure the roof box.

You have to determine what you want to carry with the roof rack and make sure that the roof rack is compatible with that thing. You also have to make sure of the safety and add more bars if needed so that the item you are carrying cannot damage the roof of your car.

If you are confused about whether you should stick with what you have or not, then you can look for advice from a professional. He will help you know which combinations are best and even help you prepare your car before attaching the roof box.

What’s the Best Position for Roof Box on Car?

Best Position for a Roof

It would be best if you spread the stuff’s weight as evenly as possible so that the roof box could not shift hard and you do not have to take any emergency break to make any changes to the box.

If your load is too heavy, you should put some weight in the trunk to make the car more aerodynamic and help airflow.

Last but not least, the less drag on the car, the better it will be for your fuel economy.

Safety Considerations

An overhanging roof box at the front can interfere with your front view and make it dangerous to drive your vehicle. Roof boxes are usually designed to place them more to the back.

Moreover, it would be best if you always remembered how far back you had mounted the box so that you can open the trunk door without damaging it with the roof box. You should keep an inch or two space between the back of the roof box and the trunk door.


If you have read the full article, we hope it will be beneficial while installing a roof cargo box on top of your car by yourself.

-our editorial board has reviewed this article and has been approved for publication according to our editorial policy.

Best Seller List of Rooftop Cargo Boxes:

Bestseller No. 1
JEGS Rooftop Cargo Carrier | Hard Car Top Large Luggage Box | Waterproof Storage | Heavy Duty Solid...
  • SECURE & PROTECT YOUR GEAR in this 18 cubic ft. HDPE plastic hard shell car top cargo carrier; high-capacity interior dimensions 57 L x 38 1/2 W x 17 3/4 H inches; aerodynamic design for fuel efficiency
  • WATERPROOF STORAGE FOR YOUR LUGGAGE with a four corner locking system, front latch, and weather-tight seal for ultimate car rooftop protection and security
  • EASY & CONVENIENT LOADING AND UNLOADING from either side of the car make for smooth travel and hassle-free storage
  • NO TOOLS REQUIRED, EASY ASSEMBLY AND INSTALLATION. All mounting hardware and simple instructions are included to get you safely on the road quickly
  • MADE IN USA, LIMITED LIFETIME GUARANTEE. The JEGS Rooftop Cargo Carrier’s high-quality construction and performance give you peace of mind
Bestseller No. 2
Thule Force XT Rooftop Cargo Box, Large, Black
  • A versatile roof-mounted cargo box for everyday use
  • Provides 16 cubic feet of additional packing space
  • Designed to fit a wide range a vehciles with maximum space efficiency
  • Quick-mount system "clicks" when roof box is secure and properly mounted
  • Dual-side opening for easy access to all areas of the box, from either side of the vehicle
Bestseller No. 3
SportRack Vista XL Rear Opening Cargo Box (Black, 18 Cubic Feet)
  • Fits SportRack Roof Rack Systems, square, round and most factory racks (Check fit guide)
  • Tool-free mounting hardware for easy installation and removal included
  • Rear opening for easy access away from traffic includes a key lock to secure contents in the box
  • ABS construction that is durable and UV-resistant; Easy to clean with mild soap and water
  • Min-max crossbars spacing: 23 5/8" - 29 3/4"; Max weight capacity: 100 pounds
Bestseller No. 4
DNA Motoring PT-ZTL-8099-GY Pair Aluminum Roof Rail Cross Bars+Cargo Box Baggage Carrier w/Lock+Keys
  • Cross Bars: Aluminum Bar Construction; Aluminum Mounting Brackets
  • Cargo Box: Heavy Duty ABS Plastic Construction
  • Capacity: 12 cu. ft. / Dimensions: 68" L x 31" W x 16" H
  • Opens to 14. 75" Wide to Store Bulky Items
  • Opens from the Side and Stays Open Till you Close It
Bestseller No. 5
Menabo Quasar Roof Cargo Box 320 Liters with Lock, Matte Black, Made in Italy
  • Menabo model "QUASAR" roof box with elegant profile and equipped with anti-theft lock. Quick and secure mounting via "U" hooks. Right opening side (passenger side)
  • Maximum load: 50 kg / 110.2 Lb.
  • Load capacity: 320 litres - Anti-theft system: Included
  • Colour: rough black
  • External dimensions (LxWxH) 128x90x38 cm - Internal dimensions (WxWxH) 120x82x34 cm.
Bestseller No. 6
Thule Sidekick Rooftop Cargo Box Grey, One Size
  • Compact roofbox, ideal for small loads such as camping gear or golf clubs
  • Sturdy U-bolts with reinforcement plates and adjustable brackets provide a secure fit to rack
  • Compact design leaves room for other roof mounted accessories
  • Passenger side opening for easier loading and unloading
  • External dimensions: 54 x 25 x 15.5 inch
Bestseller No. 7
Thule Motion XT Rooftop Cargo Carrier, XXL
  • External dimensions: 91.5 x 37.5 x 18 inches | Internal dimensions: 84.5 x 33 x 16 inches
  • Roof-mounted cargo box provides 22 cubic feet of additional packing space
  • Fits 5-7 pairs of skis / 3-5 snowboards
  • Load capacity: 165 pounds | Product Weight: 55 pounds
  • Designed for optimal space efficiency, aerodynamics, and vehicle fit
Bestseller No. 8
Thule Vector Rooftop Cargo Box, Medium, Black Metallic
  • Full trunk access with minimal risk of contact with the cargo box, thanks to its forward position on the vehicle roof
  • Easy to mount thanks to the PowerClick quick-mount system. The integrated torque indicator clicks when it’s properly mounted, ensuring fast and secure fitting
  • Reinforced lid makes for a smooth, effortless dual-sided opening and closing
  • An elegant, sporty design with seamless integration of the lid and the base that adds a distinctive look to any car
  • A premium interior with integrated lighting and a felt-lined base for increased gear protection that enhances the user experience
Bestseller No. 9
Waterproof Vehicle Roof Top Mount Travel Storage Box Rooftop Luggage Cargo Carrier w/Lock + Keys 53"...
  • ▶️ Heavy Duty ABS Plastic Construction
  • ▶️ Overall Dimensions: 53" L x 34" W x 15" H
  • ▶️ Opens to 14" Wide to Store Bulky Items
  • ▶️ Capacity: 10 cu. ft.
  • ▶️ Opens from the Side and Stays Open Til you Close It
Bestseller No. 10
DNA MOTORING PT-ZTL-8139-BK Roof Top Cargo Box + Pair Universal Aluminum Side Rail Cross Bar, Black
  • OEM Style Cross Bars: Aluminum Bar Construction; Connects to Factory Roof Rails
  • Cargo Box: Heavy Duty ABS Plastic Construction
  • Overall Dimensions: 67" L x 30" W x 13" H
  • Opens from the Side and Stays Open Til you Close It
  • Includes Mounting Hardware & (2) Keys

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Last Update : 2021-07-10