One of the most common questions among those thinking about buying a roof tent concerns the load on the car roof. The maximum load that car manufacturers state is usually far less than the combined weight of a roof tent with a family in it. So how does it actually work?
Most people who use roof tent tanks have probably asked themselves one of these questions at some point:
- Will my car roof hold the roof tent?
- How much extra weight can my car handle?
- In the car's manual, it says that the maximum load on the car roof is 75 kilos, but the weight of my roof tent and the roof rails is 70 kilos. I weigh 100 kilos, my wife 70 kilos and the children together 60 kilos. How does it work?
It is not so strange that this needs to be explained. It is not part of everyday life to load your car roof with such a heavy load, let alone to be on top of it yourself.
Can I or can't I 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 specified is the so-called dynamic maximum load, it is therefore set for when the car is in motion. That it exists is so that the car's driving characteristics are not adversely affected.
A roof tent with people in it is instead a static stress for the car. Sure, you move up in the roof tent, but not very much compared to the time you lie still. The car stands firmly on its four wheels and the family of four who were previously in the car are now on the roof. The total load for the car has thus not changed. As long as the maximum permissible weight for your car is not exceeded, you do not need to worry.
But how is that possible? Won't the car roof be pushed in under heavy load?
Sure, if you were to climb up and stand in the middle of the car roof, it will leave clear footprints on most car roofs, and depending on the weight and effort, you can definitely manage to push through the roof if you jump on it. But the load from a roof tent is neither at one point nor in the middle of the car roof.
The weight is distributed over the roof racks
A roof tent must always be mounted on roof racks suitable for your car, or a suitable roof basket. For every car there are recommended roof racks, either directly from the manufacturer or from other suppliers.
The roof rails usually consist of a stable aluminum or steel profile fitted with feet at both ends. If your car has railings/rails, the feet enclose these. It is either these or fixed attachment points for the roof rails that we recommend for attaching roof tents. We do not recommend that you use the roof rails that are clamped to the edges of the car.
Now imagine your roof tent lying flat on the roof racks. The weight of the roof tent and the people in it is then spread primarily over the two roof rails, which means that each foot on the roof rail carries 75 of the approximately 300 kilos that the aforementioned family of four weighs together.
Tips for reducing the load on the roof tent on your car
- To spread the load, you can mount your roof tent on 3 or 4 roof racks if you wish.
- Place the roof rails as far apart as possible and preferably so that they sit as close to the rail's connection points to the car body as possible.
- Place the roof tent as evenly as possible over the roof rails, so that it protrudes equally front and back and has the same distance to the long sides of the car up on the roof.
- Check that the roof tent is properly mounted on your roof racks by pressing firmly on your roof tent after installation, the roof tent should not be able to be lifted or moved on the roof rack.
The construction of the car
Regardless of whether you install the roof rails on a car with or without rails, the load is always directed to the vehicle's frame, which is the strongest part of the car body. The frame is a bit like a cage that encloses the passenger cabin.
The car roof is enclosed both by a roof bracket that goes over the car and roof beams that run along the car. They rest on so-called pillars, as you can see in the illustration below.
The body with the pillars consists of multiple folded and reinforced steel profiles that are designed to withstand the dynamic and static forces a car is exposed to. The steel profiles are spread over the body so that the passengers are as protected as possible in the car – even in the event of an accident.
Imagine a car overturning and landing on its roof. The body is made hard so as not to be pushed in and crushed by the car's static weight. For the car to be compressed, more dynamic force would be needed; such as a fall from a great height or external forces such as a scrap press.
Why is there even a maximum weight limit on the car roof?
The permissible roof load is limited by car manufacturers to ensure overall stability and functionality while driving. With a load on the roof, the car's center of gravity is shifted upwards. The roof tent's approximately 60-70 kilos does not only strain the roof racks and the car body. It also affects acceleration, braking distance and cornering. It is therefore important that the weight of your roof tent does not exceed the maximum load for your car's roof.
How much weight can your roof racks support?
It is important that your roof tent does not exceed the maximum load for your roof rails. That maximum load is usually within the range of the car's permitted roof load capacity (between 75 – 150 kilos), which means that they can easily handle a roof tent.
It is important not to exceed the permissible load of the roof rails 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 as in the case of the car roof, the roof racks can withstand 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 entirely certain that this will be covered by your insurance/warranty. In an insurance case, an exceeded ceiling load can lead to a disclaimer. Whether or not 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 do not officially differentiate between dynamic and static roof loads. By doing so, they could void any warranties and are probably not responsible for damage caused by overloading when using the roof tent. The same applies to roof rack manufacturers.
Summary
As long as your roof tent is correctly assembled and the weight falls within the limit of...
- the maximum permissible load for your car roof
- the permissible total weight of the vehicle
- the permissible load capacity of the roof rails
... then you won't 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 .
Keen to start roof tenting? Here you can see our roof tents .
