What's at the core of my bicycle?

At the very core of every bicycle, there is a frame. The material that frame is made out of has a dramatic effect on the way it rides, its durability, and cost. Every frame tells a story, some of it created right here in NZ.

Bicycle frames have to be extremely strong, while being as light as possible. 

That is a challenge for the metallurgists who create the metal alloys that go into the frames; and the engineers who design the frames and how to make them.

Carbon steel was historically the industry standard for bicycle frames. Steel is broadly an alloy of iron with as much as 2% carbon; the more carbon, the stronger and more brittle the steel becomes. High-tensile steel has no more than 0.25% carbon, for ease of forming into a shape, for example, the thin-walled tubes of a bike frame, and of welding. This is a strong, long-lasting steel.

In New Zealand, steel is made from ironsands mined at Taharoa and North Head, and Waikato coal, at Glenbrook in a two-stage process, first to smelt iron from the titanomagnetite ore, and then, to add carbon to produce steel.

Chromium-molybdenum steel is a light, strong steel alloy, and is increasingly popular in bicycle frame manufacture. “Chromoly” flexes well while retaining its shape.

Cr and Mo are light transition metals, whose presence been recorded in New Zealand; however, no mining of either metal is envisaged at this time.

Aluminium alloys (with minor amounts of silicon and magnesium, and/or with scandium) were developed in the aerospace industry. Aluminium frames are light, strong, stiff, and relatively inexpensive.

In New Zealand, aerospace-quality aluminium is smelted at Tiwai Pt in Southland, from Australian bauxite, with the input of cost-effective hydro-electricity from the Manapouri scheme.

Titanium is very strong for its weight, can flex while retaining shape, and is highly resistant to corrosion. The titanium in bike frames is typically alloyed with aluminium and vanadium, using technology developed for the aerospace industry. The chief drawback is expense; the use of Ti is limited to specialised bikes, at the top end of the market.

In New Zealand, titanium is a by-product of the ironsands industry, which as an oxide (TiO2) makes a high-quality white pigment for use in dyes and paints. Westland Titanium is exploiting the possibility of manufacturing titanium white from ilmenite deposits near Barrytown, on the West Coast of the South Island. 

Carbon fibre is a light, strong, corrosion-resistant, non-metallic material, composed of laminated sheets of carbon fibre glued together. It can be formed into almost any shape (e.g., to reduce aerodynamic resistance for indoor racers). The physical characteristics of carbon fibre can be varied from one part of the frame to another, e.g., stiff where the pedals are attached, and flexible elsewhere for the comfort of the cyclist. The disadvantage is lower impact resistance than metal frames, with a greater risk of cracking and other damage to the frame. It is an expensive material.

Carbon fibre is made from coal, and is one of a number of coal-related smart materials, e.g., activated carbon used to remove impurities in food processing, the carbon filters used in dialysis machines, silicones including an ingredient of toothpaste, and silicon nitride, a light, high-strength, heat-resistant material, invented by CRL Energy.