Calculating Load capacity Aluminum Frame

Posted by GimmiGiddi@reddit | overlanding | View on Reddit | 4 comments

I want to build a frame for my roof rack out of aluminum extrusions because ready-made ones start at around €800.

Can someone explain how to calculate the maximum load capacity / payload it can safely carry? I’d like to know how to determine the weight limits before building it.

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dva_mechanics@reddit

The short answer depends on three things: profile cross-section, span between mounting feet, and static vs dynamic load. Dynamic load rating is roughly 50-60% of static capacity. Joint design matters more than the rail itself. T-slot extrusions are strong in bending but connection hardware is the weak point. The vehicle's roof rating is almost always the limiting factor, not the rack.

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cocaine_badger@reddit

There's a deflection calculator on line for 8020, look it up. Usually, your extrusion roof rack will likely have much higher load rating than your actual roof. I'd investigate that first.

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GimmiGiddi@reddit (OP)

Thanks. Yes, my roof got 68kg load rating. I already thought that the roof rack will carry more than that it is just a nice to Know for me what it could handle.

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DepartmentNatural@reddit

So the 8020 site has lots of information on this. You just need to plug in numbers and do some work on it