Increasing load capacities with the roof rack.
The roof rack is a simple but effective accessory for vehicles with a closed body frame. It can be fitted and removed in a few simple steps.
Structure of a roof rack
A roof rack consists of a frame with fastening elements. The fastening elements are attached to the roof rails or to the intended connection points of the car roof. In addition to a variety of universal roof racks, car manufacturers offer models that are precisely designed for the respective car types. Although the specialised roof racks cannot be remounted on other cars, they offer the best possible performance on the intended vehicle.
The core element of every roof rack is the hollow profile. It is usually made of aluminium. Roof racks made of galvanised sheet steel are rarer. Aluminium racks are convincing because of their low weight and high load-bearing capacity. Steel racks usually have a higher load-bearing capacity, but they are much heavier. In addition, steel girders can corrode despite their galvanised surface.
For the basic construction of bent hollow sections, elliptical or oval cross-sections have proven their worth. They generate particularly robust moments of area, from which interesting bending strengths can be produced with low wall thicknesses using the right material. This contributes to the lightweight construction of the roof rack.
Roof racks are glued, riveted or screwed together via sleeves. The use of glued joints is particularly advantageous because the absence of holes means that the profiles are not weakened. Where there is no other option, riveted and screwed connections are only used in places where the roof rack is subjected to the least load.
Selection of roof racks
Roof racks are manufactured in a wide range. The simplest variant is a single crossbar. It is mounted transversely between the roof rails or on the roof bead. However, mounting it directly on the car roof is not recommended because it can always cause scratches.
A single roof rack can only be used for small loads. A typical use for the single-rack solution is mounting headlights, signal lights or additional exterior speakers. Mounting an additional load requires at least one more crossbar. However, two beams alone are only the minimum requirement for safe transport. This solution is not suitable for fragile goods such as glass plates, laminates or wooden panels.
The greatest transport safety is provided by complete carriers with a lateral structure and a sufficient number of cross ribs. These distribute the weight optimally and offer many possibilities for securely fastening the load.