What is the difference between aluminum and steel roof bars?

Short answer: Aluminum roof bars are lighter and corrosion-resistant; steel offers the same strength at a lower cost, but it is heavier and corrosion starts wherever it is scratched. Since the roof bars' weight reduces the remaining roof load capacity, aluminum has a clear advantage here. The load-bearing profiles on Thunder Carrier roof bars are made from 6061-T6 aluminum; the plastic parts are made from 30% glass-fiber-reinforced polyamide (PA6), and the metal fasteners are Geomet-coated.

Why Does Weight Matter So Much?

Your vehicle manufacturer specifies a maximum total weight for the roof, and the roof bars' own weight counts toward this limit. The heavier the roof bars, the less net cargo you can carry. A material that provides the same strength at a lower weight directly increases your carrying capacity.

Weight also affects installation, removal, and storage: at the end of the season, you may want to lift the roof bars on and off by yourself.

Corrosion: This Is the Key Difference

Roof bars spend most of the year outdoors—in rain, snow, road salt, and sun. The two materials behave differently in these conditions:

• Aluminum naturally forms a thin oxide layer on its surface that protects the metal underneath. If scratched, the protective layer regenerates.
• Steel relies on a surface coating for protection (galvanizing or paint). Once the coating is scratched, the protection is gone and rust starts at that spot and spreads. The points where roof bar brackets are tightened are especially prone to scratches.

That is why aluminum is preferred for load-bearing parts exposed to the elements. By the same logic, smaller parts that need to remain steel, such as bolts and nuts, are protected with a coating—Thunder Carrier fasteners are Geomet-coated.

Is “Aluminum Is Weaker” True?

Not when comparing equal weights. Aluminum itself has lower strength than steel, but this property can be changed through alloying and heat treatment. 6061-T6is aluminum heat-treated to achieve a high strength level, which is why it is used in the aerospace and automotive industries. The load-bearing profile is not a solid bar but a hollow profile with a cross-section designed for strength; durability comes from geometry as well as the material.

The practical measure is not the material's name, but the capacity specified by the manufacturer. Thunder Carrier roof bar crossbars are designed to carry 85 kg while driving and 275 kg when parked.

Are Plastic Parts the Weak Link?

Brackets and fittings on most roof bars are made of plastic, and the type matters. Ordinary plastic becomes brittle in the sun and cracks on impact. Thunder Carrier uses 30% glass-fiber-reinforced polyamide (PA6) for all plastic parts; the glass-fiber reinforcement provides structural rigidity and impact resistance. When assessing a product, ask “which plastic?” rather than “plastic or metal?”

Which Should You Choose?

For vehicle roof applications, aluminum stands out because of its weight and corrosion resistance. Steel makes sense for fixed applications where weight is not an issue and cost is a priority—but the coating must still be maintained. When making your choice, look at these three factors rather than the material's name: the manufacturer's stated load capacity,, the product's own weight, and corrosion protection for the fasteners..

Frequently Asked Questions

What is the difference between aluminum and steel roof bars?

Aluminum is lighter and does not rust thanks to the self-renewing oxide layer on its surface. Steel offers the same strength at a lower cost, but it is heavier and relies on a surface coating for protection, so rust starts wherever it is scratched. Since the roof bars' own weight reduces the available roof load capacity, aluminum has a clear advantage on a vehicle roof.

What Does 6061-T6 Aluminum Mean?

6061 is an aluminum alloy; T6 indicates that it has been heat-treated to achieve a high strength level. This is why it is used in the aerospace and automotive industries. The load-bearing profiles that form the main frame of Thunder Carrier roof bars are made from this material.

Are Aluminum Roof Bars Weaker Than Steel Ones?

In practice, no. Aluminum itself has lower strength than steel, but alloying and heat treatment can change that; strength also comes from the profile's cross-sectional geometry, not just the material. The practical measure is the capacity specified by the manufacturer—not the material's name. For Thunder Carrier, the rated capacity is 85 kg while driving and 275 kg when parked.

Why Does the Roof Bar's Weight Matter?

The vehicle manufacturer's roof load limit refers to the total weight on the roof, including the roof bars themselves. The heavier the roof bars, the less net cargo you can carry. Weight also affects how easy the bars are to install, remove, and store.

Are Plastic Brackets Durable?

It depends on the type of plastic. Ordinary plastic becomes brittle in the sun and cracks on impact. Thunder Carrier makes all plastic parts from 30% glass-fiber-reinforced polyamide (PA6); the glass fibers provide structural rigidity and high impact resistance. When assessing a product, ask “which plastic?” rather than “plastic or metal?”

Will the Bolts and Nuts Rust?

Metal fasteners are among the parts most exposed to corrosion because their surfaces are stressed during tightening. On Thunder Carrier products, bolts, nuts, and all other metal fasteners are protected with the internationally recognized Geomet coating.

Related product: DACIA DUSTER 2010-2013 TRX1 Thunder Carrier Locking Roof Bars