What is the difference between roof load and the permissible load on roof racks?
September 9, 2026
The roof load is the maximum weight that your car's roof is allowed to carry, including roof racks, roof box, and all contents. The permissible load on roof racks is a separate, often lower limit set by the roof rack manufacturer. You must always use the lower of the two values. In this article, we answer the most frequently asked questions about weight on the car roof, so you can hit the road safely and worry-free.
What exactly does roof load mean for your car?
The roof load is the maximum weight that your car's roof can structurally support. This figure is stated in your car's registration certificate or owner's manual and applies to everything you place on the roof: roof racks, a roof box, a roof tent, bicycle carriers, and their contents combined. The maximum roof load of a car varies by make and model and is generally between 50 and 100 kilograms.
It is important to understand that the roof load is a safety limit determined by the car manufacturer based on the strength of the roof structure and the stability of the vehicle at driving speed. An SUV often has a higher roof load than a small city car, but values can vary significantly even within the same segment. Therefore, always check the specifications of your specific car model before loading anything onto the roof.
A common mistake is that people only consider the weight of the roof box itself, whereas the roof load refers to the total weight of everything mounted on the roof. Roof racks easily weigh two to five kilograms per set, and that counts.
What is the permissible load on roof racks and how does it differ from the roof load?
The permissible load on roof racks is the maximum weight that the roof racks themselves can support, as determined by the manufacturer of the roof racks. This is a different and often lower limit than the roof load of the car. If your car has a roof load of 80 kilograms but your roof racks can only handle 75 kilograms, then 75 kilograms is the limit you must adhere to.
The two limits complement each other but are established independently. The roof load protects the roof structure of the car. The load capacity of the roof racks protects the mounting points, the bars, and the brackets of the racks themselves. Both limits are binding, and you exceed both at your own risk.
When choosing roof racks, it is wise to opt for a set with a maximum load capacity at least equal to your car's roof load. This way, the roof rack is never the weakest link. the Hapro roof boxes page You will also find information about compatible roof racks that match your car's specifications.
How much does a roof box weigh and does that fit within the roof load?
Depending on the model and size, a roof box typically weighs between 10 and 20 kilograms. An entry-level model like the Hapro Roady (300 liters) is relatively light, while a larger box like the Traxer or Zenith carries more gear and therefore more weight. Add the capacity to that, and you quickly reach a total of 40 to 60 kilograms on the roof.
Whether this fits within your car's maximum roof load depends on three factors: the weight of the roof racks, the weight of the roof box, and the weight of the luggage you place inside. Add these three up and compare the total to the lowest of the two limits: that of the car or that of the roof racks.
A practical example: suppose your car has a roof load capacity of 75 kilograms. Your roof racks weigh 4 kilograms. Your roof box weighs 14 kilograms. That leaves you with 57 kilograms for luggage. For most families, that is more than enough for clothing, shoes, and small items for a week's vacation.
What happens if you exceed the roof load?
Exceeding your car's maximum roof load poses immediate safety risks. Too much weight on the roof raises the vehicle's center of gravity, which impairs driving stability, particularly when swerving, cornering, and at higher speeds on the highway. In the worst-case scenario, the roof could collapse or the roof racks could detach.
In addition to the safety risk, there are also legal and financial consequences. If you are involved in an accident and it turns out afterwards that the roof load was exceeded, your insurer may refuse to pay the damages in whole or in part. The overloading is then considered a contributing factor to the accident, which can have unpleasant legal consequences.
Moreover, structural overloading can cause permanent damage to the roof structure, even if no accident occurs. This reduces the value of your car and can cause problems during an MOT inspection or when selling it. In short: the roof load is not a guideline, but a hard limit.
How do you distribute the weight in a roof box as safely as possible?
Distribute the weight in a roof box as low and as centrally as possible. Place heavy items such as shoes, books, and wetsuits at the bottom of the box, as close as possible to the car roof. Light and soft items such as clothing, towels, and pillows go on top. Also ensure that the weight is balanced on the left and right sides so that the car is not loaded unevenly.
Good weight distribution has a direct impact on handling. A roof box that is more heavily loaded at the rear than at the front can make the steering lighter and the car feel less stable, especially at higher speeds. Try to keep the center of gravity as far towards the middle of the box as possible.
Additionally, it is wise to secure loose items properly or place them in bags. During a braking maneuver, loose items slide forward and can hit the front of the suitcase, causing vibrations and noise. A tightly packed suitcase not only rolls more quietly but also more safely.
Are you unsure which roof box best suits your car and your travel needs? Via the Hapro website You will find a handy configurator that lets you quickly check which model and size best suits your situation. Do you have any further questions? Feel free to contact us and we are happy to help you further.
Frequently Asked Questions
Where can I find the maximum roof load of my specific car?
The maximum roof load is listed in your car's owner's manual, often in the chapter on technical specifications or loading. You can also find it on the vehicle registration certificate (part 1B) or via the car manufacturer's website by entering the model year and version. If you can't figure it out, a dealer for your car brand can quickly help you.
Am I allowed to use a roof box if my car does not have factory rails?
Yes, that is possible. There are roof racks that are attached via the door panels or using special clamps on the roof frame, without the need for factory rails. However, it is essential that you choose roof racks that are specifically compatible with the make, model, and year of your car to ensure a secure and stable attachment. Always check the mounting instructions and the maximum load capacity of the chosen racks.
Does a full roof box affect my fuel consumption?
Yes, a roof box increases your car's aerodynamic drag, which leads to higher fuel consumption, even when the box is empty. The heavier and fuller the box, the greater the effect. Driving at a lower speed on the highway and removing the box when you don't need it are the most effective ways to limit the extra consumption.
Is there a maximum speed I must adhere to when driving with a roof box?
Most roof box and roof rack manufacturers recommend a maximum speed of 130 km/h, but some models have a lower recommended speed, such as 120 or even 110 km/h. Always consult the manual for your specific roof box for the applicable speed. Also, keep in mind that at higher speeds, driving stability decreases as the box becomes more heavily loaded.
What do I do if my roof box starts vibrating or making noise while driving?
Vibrations and noise are usually caused by a loose fastening or uneven weight distribution in the trunk. First, check that the trunk is properly locked and that the roof racks are securely fastened. Then, ensure that loose items in the trunk are secured or packed in bags so they cannot slide around. If the problem persists, stop at a safe place and recheck the entire assembly before continuing your journey.
Can I also use a roof box to transport ski equipment or surfboards?
A standard roof box is not suitable for long-distance sports equipment such as skis, snowboards, or surfboards, because they are longer than the depth of the box. Special ski mounts or extended roof boxes with a ski pass-through exist for this purpose, such as certain models in the Hapro range. If you want to transport both luggage and long-distance sports equipment, look for a box with an integrated ski holder or combine a roof box with a separate ski carrier on the same roof racks.
How do I best store my roof box when I am not using it?
Preferably store a roof box lying down or hanging in a dry, frost-free place, such as a garage or storage room. Clean the box of dirt and salt before storage to protect the hinges, locks, and plastic. Leave the box slightly ajar or store it open if possible to prevent moisture or odors from accumulating inside.