Roof racks are a great way to transport large, bulky items that take up too much space inside your vehicle. However, they are not designed to carry heavy weights, and if you do, you will likely damage your vehicle and risk a serious accident. Most four wheel drive vehicles will only carry a maximum of 100kg on the roof racks. Some full-length steel racks weigh around 50kg and as a result their load-bearing capacity is drastically reduced. A few drums and you’re already looking over the limit. It is important to make sure that the total weight on your roof does not exceed what the manufacturer states as a maximum.
Not all racks weigh 50 kg; many do not weigh more than 15 kg. However, it depends on the design and materials used. What is just as important as checking the maximum load the roof is designed for, is seeing what the roof racks will carry. Some roof racks are only designed to carry 30kg each and again can easily become overloaded. Take note of the conditions the racks are designed to operate in as well. I have seen numerous roof racks that say “not for off-road use”. If you get a set like this, put a few jerrycans on top, and then drive over gravel, sand, or other bumpy roads, you risk damaging the racks, losing your cargo, or damaging your vehicle’s roof.
It is very common to see people loading their roof racks with more gear than should be carried, or loading the roof with more than should be carried. Again, keep heavy things inside your vehicle and big, bulky things on the shelves. By doing this you ensure that the center of gravity stays low and this makes the car more stable. When driving on all four wheels, this is of the utmost importance. Even when you’re on the road, it’s much safer to have a lower center of gravity.
The main reason roof racks are rated for different weights is their design and the material that is used. You’ll find that plastic racks generally won’t be able to hold as much weight as steel or aluminum. Aluminum is lighter than steel, which is helpful if you want to carry heavier loads on top (again, I don’t recommend!)