One of the most common questions among those considering buying a roof tent concerns the load on the car roof. The maximum load specified by car manufacturers is often much less than the combined weight of a roof tent with a family inside. So how does it really work?
Most people thinking about roof tents have probably asked themselves one of these questions at some point:
- Can my car roof support the roof tent?
- How much extra weight can my car handle?
- The car manual states that the maximum load on the roof is 75 kilos but the weight of my roof tent and roof racks is 70 kilos. I weigh 100 kilos, my wife 70 kilos and the children together 60 kilos. How does this work?
It is not surprising that this needs to be explained. It is not everyday that you load your car roof with such a heavy load, let alone that you yourself are up there.
Can I or can I not have a roof tent on my car?
The short answer is – you can. It is no problem to load your car roof with much more weight than the specified maximum load. The maximum load given is the so-called dynamic maximum load, meaning it is set for when the car is in motion. It exists so that the car's driving characteristics are not negatively affected.
A roof tent with people inside is instead a static stress for the car. Sure, you move around inside the roof tent, but not much compared to the time you lie still. The car stands firmly on its four wheels and the family of four who previously sat in the car now lie on the roof. The total load on the car has therefore not changed. As long as the allowed maximum weight for your car is not exceeded, you do not need to worry.
But how is that possible? Won't the car roof be pressed in under high load?
Sure, if you climb up and stand in the middle of the car roof it will leave clear footprints on most car roofs, and depending on weight and effort it is definitely possible to push through the roof if you jump on it. But the load from a roof tent is neither at a point nor in the middle of the car roof.
The weight is distributed over the roof racks
A roof tent should always be mounted on roof racks suitable for your car, or a suitable roof basket. For each car there are recommended roof racks, either directly from the manufacturer or from other suppliers.
Roof racks usually consist of a sturdy aluminum or steel profile equipped with feet at both ends. If your car has rails, the feet surround these. It is either these or fixed attachment points for roof racks that we recommend for attaching roof tents. We do not recommend using roof racks that clamp onto the edges of the car.
Now imagine that your roof tent lies flat on the roof racks. The weight of the roof tent and the people inside is then primarily spread over the two roof racks which means that each foot on the roof rack carries 75 of the approximately 300 kilos that the aforementioned family of four weighs together.
Here you can read more about which roof racks fit roof tents and which you should avoid.
Tips for reducing the load of the roof tent on your car
- To spread the load, you can if you want mount your roof tent on 3 or 4 roof racks.
- Place the roof racks as far apart as possible and preferably so that they sit as close as possible to the rail connection points to the car body.
- Place the roof tent as evenly as possible over the roof racks, so that it protrudes equally front and back and has the same distance to the car's long sides on the roof.
- Check that the roof tent is properly mounted on your roof racks by pressing firmly on your roof tent after mounting, the roof tent should not be able to be lifted or moved on the roof rack.
The car's construction
Whether you install roof racks on a car with or without rails, the load is always directed towards the vehicle's frame, which is the strongest part of the car body. The frame is a bit like a cage that surrounds the passenger cabin.
The car roof is enclosed both by a roof console that goes over the car and roof beams that run along the car. They rest on so-called pillars, which you can see in the illustration below.
The body with the pillars consists of multiple folded and reinforced steel profiles designed to withstand the dynamic and static forces a car is subjected to. The steel profiles are spread over the body so that the passengers are as protected as possible in the car – even in an accident.
Imagine a car rolling over and landing on its roof. The body is made hard so it is not pressed in and crushed by the car's static weight. For the car to be crushed more dynamic force would be needed; like a fall from a great height or external forces like a scrap press.
Why is there even a maximum weight limit on the car roof?
The allowed roof load is limited by car manufacturers to ensure overall stability and functionality during driving. With load on the roof, the car's center of gravity is raised. The roof tent's approximately 60-70 kilos not only load the roof racks and car body. It also affects acceleration, braking distance and cornering. It is therefore important that your roof tent's weight does not exceed the maximum load for your car's roof.
How much weight can your roof racks handle?
It is important that your roof tent does not exceed the maximum load for your roof racks. That maximum load usually lies within the range of the car's allowed roof load capacity (between 75 – 150 kilos) which means they easily handle a roof tent.
It is important not to exceed the allowed load of the roof racks when driving. This is because it affects the car's driving characteristics. Every extra kilo also means that the forces on the fittings and clamps increase.
Just like with the car roof, the roof racks can handle much more weight when the car is stationary.
Worth considering
If damage occurs to your car as a result of using a roof tent, it is not certain that this will be covered by your insurance/warranty. In an insurance case, an exceeded roof load can lead to a disclaimer of liability. Whether any damage to your car is covered by your insurance depends on what your insurance company says, different insurance companies have different rules.
Car manufacturers officially do not distinguish between dynamic and static roof load. Therefore, they could disclaim any warranties and are probably not responsible for damage caused by overloading when using the roof tent. The same applies to manufacturers of roof racks.
Summary
As long as your roof tent is correctly mounted and the weight falls within the limit for...
- the allowed maximum load for your car roof
- the vehicle's allowed total weight
- the roof racks' allowed load capacity
... you will not have any problems with the weight of your roof tent on the roof.
This text is a free translation of a text first published here.
Want to start roof tenting? Here you can see our roof tents.
