A steerer tube is the portion of the fork that interfaces with the frame. Steerers come in steel, aluminum, and carbon fiber. Over the years there have been recalls on headsets that "cut" carbon steerer tubes. Carbon fails with no warning, it can be catastrophic. I am a bigger rider, so I insist on aluminum or steel steerer tubes.

Aluminum has proven extremely resilient, and light. However steel is stronger and gives the rider an early warning of "problems", while aluminum fails with no warning.

We have used steel steerer tubes for safety on all folding bicycles for the past 19 years. It seems to be a good choice to minimize problems. However aluminum is an excellent choice for an upgrade.