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FAQ: Steel vs. Aluminium

One of the most commonly asked questions we get is “Why do you build Steel and not Aluminium frames?”

 

There are many reasons why steel and not aluminium, and we will try to explain from our side. Warning: This might be more technical than you expect.
 

The very first and most important reason is the technology required to work with steel alloys comes from very cheap all the way to highly expensive and sophisticated. The technology to work with aluminium starts at everything but cheap. Once you go touring and ride far away from where you can get everything by touching the "buy now" icon on your smartphone to places where you can barely meet anyone, sometimes, things happen. Frames, frame parts, stays, forks, they can fail. It's a fact. If you have a steel frame, you have a good chance that in every village anywhere in the World, on every continent, there is at least one person who has a welding machine that can weld and repair your frame. Maybe not perfectly, but just well enough so you can continue, or even finish your trip. If your Aluminium, Magnesium or Carbon frame fails on a place like that, you're done with riding. Stuck in one place, waiting to get a replacement part can be frustrating, long lasting and again not cheap.

Of course, we do use Aluminium for some of the parts, where it can be used and not compromise the reliability of the trike.

There are many explanations about technical differences, advantages and disadvantages, but it all gets simplified to a single fact: Steel frames are more reliable, last longer, and cope much better with fatigue...
 

  • Mannesmann ST52BK is a High precision calibrated Cold Drawn thin wall seamless tubing
  • ST52 equivalent is DIN 2391 and EN10025–1994. ST52 pipes are low carbon manganese steel pipes that are easily weldable
  • ST52 pipes have excellent machinability
  • The welding of ST52 pipes can be done by using any of the conventional welding processes
  • With the welding of ST52 pipes, there is no pre-heat treatment or post-heat treatment required
  • ST52 has a Chemical Composition of Phosphorus 0.050% max., Silicon 0.50%, Carbon 0.20%, Sulphur 0.050% max., and Manganese 1.50%
  • ST52 BK DIN 2391 has a Yield Strength of 520 Mpa and Tensile Strength of 600 Mpa

 

ST52BK steel alloy compared to the two most used Aluminium alloys, 6061 and 7075:

6061 is commonly referred to as “structural” aluminium. It is often used in construction and is commonly used to extrude aluminium bars, pipes, rods, and tubes. It is also highly versatile, being used for bicycle frames, electrical fittings, and heat sinks. It has better general characteristics than 7075, with higher corrosion resistance, weldability, and machinability. But it does not have the same high strength that 7075 aluminum has. Although 7075 has high strength, it has lower corrosion resistance than other common aluminium alloys and does not offer the same levels of machinability or weldability. Where strength is the most important consideration, 7075 can be the optimal choice. Still, ST52 is stronger than any of these two and comes with the best features of these two Aluminum alloys in a single material.

 

In direct comparison:

  • Aluminium 6061 has
    • Yield Strength of 276 Mpa
    • Tensile Strength of 310 Mpa
  • Aluminium 7075 is roughly 1.5 times stronger than 6061
    • Yield Strength of 450 Mpa
    • Tensile Strength of 520 Mpa
  • Steel alloy ST52BK we use
    • Yield Strength of 520 Mpa
    • Tensile Strength of 600 Mpa

And that is the main reason why these Aluminum frames usually must be much beefier, and even though lighter per volume unit, they aren’t really lighter for the same end result.