Short answer: The weight you can carry on your vehicle's roof is determined by two separate limits, and the lower one applies. The first is the capacity of the roof bars themselves — with Thunder Carrier roof bars, this is 85 kg while driving, 275 kg while parked (when using a rooftop tent)respectively. The second is the roof load limit stated in your vehicle manufacturer's owner's manual, which is usually lower. The roof bars' own weight also counts toward this limit.
Why isn't there a single weight figure?
There is no single answer to “How much weight can you load onto a vehicle roof?” because three separate parties set the limits:
- The vehicle manufacturer: States in the owner's manual how much weight the roof sheet metal and rail mounting points can support. This depends on the vehicle's body structure and varies from model to model.
- The roof bar manufacturer: Specifies the strength of the crossbars and brackets. For Thunder Carrier TRX1 and TRX2 series, this figure is 85 kg while driving.
- The equipment being carried: If you use an accessory such as a roof basket, roof box, or bike carrier, it has its own capacity too.
The lowest of these three values is your actual limit. Ignoring any one of them is unsafe, even if the other two are higher.
85 kg while driving, 275 kg while parked — why the difference?
The difference between the two figures comes from whether the load is moving or stationary.
While driving (dynamic load): When the vehicle is moving, the load on the roof applies more than just its own weight. Braking, acceleration, cornering, and road imperfections create additional forces on the load; the momentary force on the roof when driving over a speed bump can greatly exceed the load's static weight. For this reason, the limit while moving is kept lower: 85 kg.
While parked (static load): When the vehicle is stationary, these additional forces do not occur and the system supports only vertical weight. A rooftop tent is used in this scenario: the tent is set up, the vehicle is parked, and the occupants' weight is added to the load. Under these conditions, Thunder Carrier roof bars are designed to support up to 275 kg.
Important to note: The 275 kg figure applies only while the vehicle is parked . Do not drive with a rooftop tent set up and loaded; pack it away before setting off, and the dynamic limit of 85 kg applies again.
How to find your vehicle's roof load limit
- Open the owner's manual. It is usually under a section titled “Loading,” “Roof Load,” or “Roof Box.” Some vehicles also display it on a label on the driver's door sill.
- Subtract the weight of the roof bars themselves. The roof limit specified by the manufacturer refers to the total weight — roof bars are included. For example, if your vehicle's limit is 75 kg and the roof bars weigh 5 kg, your net load capacity is 70 kg.
- Include the weight of any additional equipment. If you use a roof basket or roof box, its empty weight also counts toward the limit.
- Use the lowest value. If your vehicle's limit is 50 kg, the roof bars' 85 kg capacity does not increase that figure.
If you cannot find a figure in the manual, ask an authorized service center for your vehicle. Guessing may permanently buckle the roof sheet metal or damage the mounting points.
Distributing the load correctly matters more than the number of kilograms
Staying below the limit is not enough on its own; how the load is positioned also determines safety.
- Distribute the weight evenly across both bars. Putting all the load on one bar overloads it, even if the total weight is below the limit.
- Place heavy items in the center and low down. The lower and more centered the center of gravity is, the less the vehicle is affected by corners and crosswinds.
- Secure long loads against sliding. For long loads such as ladders, lengths of profile, pipes, or canoes, a load stop fitted into the T-track on the roof bars prevents the load from sliding forward under braking or backward during acceleration. Using more than one load stop, at the front and rear, is recommended for long loads.
- Use a ratchet strap. A load stop limits sliding; it does not replace tying the load down. The load must always be secured separately.
- Stop and check within the first 50 km. Connections settle after you set off; recheck all fasteners at your first stop.
How does driving change when there is a load on the roof?
A load on the roof raises the vehicle's center of gravity. This increases sensitivity to crosswinds and sudden steering inputs. When traveling with a load, reduce your speed, enter corners earlier, and increase your following distance. Increased wind resistance also raises fuel consumption; removing the roof bars when you have finished carrying a load reduces both fuel consumption and wind noise. Thunder Carrier roof bars are designed to be easily removed and stored in their own box when not in use.
Frequently Asked Questions
What is the maximum weight that can be carried on a vehicle roof?
There is no single general figure. The limit is whichever is lower: the roof load limit specified in the vehicle manufacturer's owner's manual or the capacity of the roof bars themselves. Thunder Carrier roof bars have a capacity of 85 kg while driving and 275 kg while parked; if your vehicle's limit is lower, your vehicle's limit applies.
Does the weight of the roof bars also count toward the roof limit?
Yes. The roof load limit specified by the vehicle manufacturer refers to the total weight on the roof, including the roof bars themselves. To find your net load capacity, subtract the weight of the roof bars and, if applicable, the roof basket or roof box from the limit.
Can I drive with the 275 kg parked limit?
No. The 275 kg figure applies only while the vehicle is parked, typically when using a rooftop tent. When the vehicle is moving, braking, cornering, and road impacts create much greater forces; that is why the limit while driving is 85 kg, and you must return to this limit before setting off.
Can I pile the load onto a single bar?
No. The capacity is based on the combined carrying capacity of both crossbars. Even if the total weight is below the limit, putting all the load on one bar overloads that bar and its mounting brackets. The load should always be distributed as evenly as possible across both bars.
How do I stop a long load from sliding?
A load stop fitted into the T-track on the roof bar profile limits the load's forward and backward movement. For long loads such as ladders, lengths of profile, pipes, or canoes, using more than one load stop, at the front and rear, is recommended. A load stop does not replace tying the load down; secure it separately with a ratchet strap.
Does a roof basket or roof box increase capacity?
No, it reduces it. A roof basket and roof box organize and protect the load, but their own weight counts toward the roof limit, reducing your net load capacity. They organize the load; they do not increase capacity.
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