Steel or Aluminium

There are a huge range of steels and almost equally huge range of aluminium alloys. They all have different properties and characteristics. It is important that you research which alloy you are looking for and why. They all have specific names, but let's stick to "steel" and "aluminium".

Steel is stronger than aluminium, so it can have smaller section tubes for the same strength and stiffness as aluminium. Because of that they look spindly (in my eyes). It is springier than aluminium which gives it a more lively feel when riding. Or so I'm told, it is so long since I rode a steel framed bike that I can no longer remember.

It is the ride feel of steel framed bikes that makes them popular. It is this quality that I believe makes steel framed hardtails nicer to ride than aluminium ones. But once you get suspension at both ends, how the hell can you tell? (Not a rhetorical question).

But as I said above, I can't comment on that. There are enough people that think it's worth the money to keep the steel framed bike business actually in business.

The downside is that steel rusts. Steel frames come protected in some way, of course they do! But it would remain a concern for me, having seen my own steel bike rot away when I was an early teenager. Steel is also heavier than aluminium. So for the same strength and stiffness, aluminium bikes are lighter. Aluminium does not rust, it will corrode under certain circumstances, but nothing to worry about.

Steel is easy to join, it can be welded, brazed, glued, rivetted, all manner of methods. It is very predictable and is most unlikely to crack or break. Depending upon how exotic the steel, some heat treatment before and after the weld may be necessary. Aluminium is harder to join, it needs welding with care and will probably need some heat treatment immediately afterwards and maybe before too. It is more likely to crack and then break, but this is such a small problem that it hasn't stopped all the major bike brands using aluminium. If you do get a crack or a break, welding can be done, but it tends to destroy the benefit of any post heat treatment that has been performed, ie the bike will be not as strong. New techniques that I am unaware of may have overcome this of course.

Aluminium frames are cheaper to mass produce, steel ones are cheaper to hand make. To keep the weight down, aluminium tube sections need extensive forming of a type that is difficult to do in steel. That basically puts them outside the ability of DIY frame builders, unless they are content to use standard sections.

Overall, aluminium frames are cheaper than steel. Many reasons, but principally because they are mass produced in their tens of thousands, if not in millions. There are rumours that Giant have a fully integrated frame factory in Taiwan that starts with raw materials and produces frames for not just Giant, but many different brands.

There is a good reason why most bikes today are aluminium frames. They are cheap, reliable and light. But does this make them nicer to ride? I don't know because I have never ridden a modern steel framed bike.

The above is a gross oversimplification. Not all Al frames are "harsh" - ask the owners of several generations of Cannondale CAAD bikes. Al tubes are bigger diameter - but thats because as a material its less stiff (has a lower Youngs Modulus by a factor of 3) than steel. So for the same siffness (resistance to bending) Al has to have larger diameter tubes. But... for use off-road, where you have large low pressure (very low these days with tubeless setups) tyres, often suspension and generally softer surfaces, I don't think it makes a jot of difference. So, go with whatever frame material your best choice bike comes with and enjoy it.

Have you considered wood?