Frame builders have a number of materials to choose from when it comes to tubing, but how do the materials differ and what considerations do the builders need to think about when choosing their metal?
Most bike frames are constructed using tubes made from aluminium alloys. These are cheap, corrosion resistant, fairly lightweight and easy to form into frames.
Numbers like 6061, 6063 and 7005 are a code for the additives (chiefly silicon and magnesium) that are mixed with the aluminium to form each alloy.
Every ‘recipe’ has slightly different properties.
Steel is much denser than aluminium and much stronger too. This means frame builders can use smaller-diameter, thinner-walled tubes and maintain the same strength and stiffness.
Weight is higher, but the skinny tubes make it easier to design in a little vertical flex for a comfier ride.
Steel is harder and more expensive to mass-manufacture than alloy though.
3. Carbon fibre
Carbon fibre is a composite of sheets of strong carbon threads bonded together with resin.
The advantage for bike frames is that it’s significantly lighter than metal for a given stiffness.
Carbon fibre can also be moulded into smooth, complex shapes.
It’s pricey though, and expensive moulds make it uneconomic for brands to change their designs regularly.
The main advantage of titanium over aluminium or steel is its fatigue resistance.
Most metals have a defined number of load cycles before they’re likely to fail. Titanium is far more resilient to repeated stresses and strains, and this means skilled frame fabricators can build frames lighter and with more compliance without risk of failure. For a price.