There are four main materials that bike frames are made from. In order of price low to high: steel, aluminium, titanium and carbon fibre. Each of these materials have different properties and is manufactured slightly differently which means that the end ride you and I feel will be different.
Why does that matter though?
Well, to put it bluntly, a high end steel frame could be just as good as a low end titanium frame. And similarly, a high end aluminium frame will give a low carbon fibre frame a run for its money.
So if you are looking for a new bike, and asking yourself which is the best material for your new bike frame, don’t just automatically go for carbon fibre! It might actually be worth your while checking the other materials as well.
OK, you’ve caught my attention. So what’s the difference between steel, aluminium, titanium and carbon fibre frames?
We could do a degree on the difference in these materials. No literally, we can actually do a materials science degree to explore the differences. But to cut a long story short, the fact that these four materials have different molecular structures means they will have different properties when riding and also different manufacturing processes.
Poor old aluminium frames, eh?
Lets start with our good friend aluminium. I feel sorry for this guy – people assume its heavier than carbon, less durable than titanium and less comfortable to ride than steel so automatically assume they are looking at an inferior frame than titanium and carbon fibre. But there is light at the end of the tunnel for aluminium – this doesn’t necessarily have to be the case.
Aluminium frames are alloys (a combination of more than one metal) where the exact composition depends on the properties the manufacturer is looking to achieve. Consider the 7000 series T6 aluminium frame in the Bowman Pilgrim – it is triple butted (more on that later) with a high yield strength making it stiffer and more robust, compared to say Bowman Palace or Palace:R, made from 6000 series aluminium which is slightly more pliable. Sure the price is different between the two frames, but they would ride differently as well because of the different alloy composition.
I thought Aluminium bikes are harsher to ride than Carbon Fibre?
Well that certainly was the case in the good old days, but perhaps less so now for the lower end carbon frames. You see, in the old days we used to make aluminium bikes with stiffer and bigger tubes which were the same dimensions in every axis. This means that the properties didn’t change. This is unlike a Carbon Fibre frame where the length can be different from the width for instance. Alas, technology has improved meaning that new manufacturing methods such as hydroforming mean aluminium frames don’t need to just be plain tubes uniform in thickness, they can now vary, giving different properties and therefore different cycling ‘feels.’
To all intents and purposes, aluminium is now softer, but still stiff enough to peddle and steer with. Its metallic properties make it ideal to work with because it is less strong than steel so easier to mould. Its less dense than steel which means it won’t transmit road bumps as much through the frame, giving a more comfortable ride. But don’t get ahead of yourself just yet, it is still less so than carbon fibre.
Oh right, and aluminium is cheaper than Carbon Fibre?
Yep, that’s right. The reason is not so much the cost of the raw material, but the actual manufacturing process. Carbon fibre bike frame manufacturing entails lots of people do lots of repetitive tasks. Even though the tasks are essentially simple, machinery cannot (correct me if I’m wrong here) perform them, and so, these people need to be paid, pushing the price of those carbon bike frames higher. This is compared to steel welding and brazing which, in and of itself is skilled, but can be done relatively easily.
Is aluminium or carbon fibre better for safety?
Again, that pretty much comes down to the properties of the tubes being produced, which in turn comes down to the manufacturing process. But I know what you’re getting at – different materials have different failure and yield points. I could talk about Young’s modulus and the elasticity of different metals, but I don’t want you to run a mile… suffice to say, carbon fibre will snap and break whereas aluminium will dent, bend and then break. That’s why if you’ve ever seen a carbon fibre frame in an acute accident you will see lots of carbon fibre fragments (think Formula1 accident).
Steel and aluminium frames have a little more give to it in this respect, it can be bent before snapping. Does this mean it is safer to ride? I’m not so sure about this. However, it is worth noting that Trek now give a life time warranty on their frames, so maybe they’ve figured out a way of improving manufacturing to avoid this.
Does aluminium corrode?
Steel rusts. We knew this already though. What you might not know is that aluminium does corrode – this is what you see with that white powdery stuff on aluminium frames. But I wouldn’t get yourself worried about this, modern frames are treated to avoid this these days. And as I said, companies like Trek offer lifetime warranties… so chill out! On the subject of corrosion though, this is something you most definitely do not need to worry about with carbon fibre bike frames.
Carbon Fibre frames are good then?
Carbon fibre is what everybody wants. You want it. Your mum wants it. And your dog wants it.
It’s not dense (a good thing), but it is strong. It is mouldable and shapable.
The low density means it doesn’t transmit road shocks through the frame which makes it a more comfortable ride. And because it is mouldable you can build a frame with any characteristic you want. So for instance the top tube might have a larger height than width to make it more stable horizontally than vertically. This again means it will not transmit bumps and lumps on the road whilst maintaining integrity when riding.
If you’re still not convinced, look at the thin seatstays which can again flex for vertical shock absorption.
And just to rub salt on the wound, a bigger downtube holds the crankset in place so that more of the energy you use when peddling gets converted to forward propulsion. And that flexion won’t break it.
We’ve come a long way since the wooden frames in the early 19th century. And now with the improvement of technology we are seeing a resurgence in steel tubing, especially given the influences from motorsport and aviation.
Steel is good for safety – it won’t fail catastrophically. And it can be recycled. In fact it’s so durable that the steel frame you are riding now will probably give you the exact same ride in 50 years time.
Aluminium bike frames come in for more performance orientated cycling. With hydroforming manufacturing techniques, we can now use bigger tubes that have been butted for various thicknesses, changing stiffness properties.
Titanium bikes are light and strong. They have good durability but you have to be very precise with the welding of this material which makes it a slightly more specialist manufacturing process.
And carbon fibre? Well, put it this way, if its good enough for a Formula1 car, its good enough to be your next bike frame!
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