If you’re looking to buy a complete bike or just a frame, you’ll need to think about the comparison between steel vs aluminum bikes, and which would be better for you.
With such diverse choices, it can often be difficult to decide which bike frame material to go for when buying a new bicycle. The material of your frame is one of the most important factors that will affect how your bike feels to ride.
So, it’s essential that you choose the right frame material for your favorite type of riding, your storage options, and your budget. There are so many things to consider; weight, price, strength, ride feel, and many more.
So, given all of the different factors that can affect your decision, what is the most important consideration when choosing a material for your frame?
Well, that’s a difficult question. But in this article, we’ll discuss all of the differing qualities of steel and aluminum and what effect this might have in practice. We’ll be covering:
- Steel Vs Aluminum Bikes: Comparing The Materials
- Aluminum Vs Steel Bikes: Which Should You Go For?
Let’s get started!
Steel Vs Aluminum Bikes: Comparing The Materials
When considering steel vs aluminum bike frames, there’s a lot to consider. Here we’ll break down the comparison between the two in each different category worth thinking about.
Weight
Weight is probably the first thing that most people will think of when deciding between frame materials. When comparing steel and aluminum, there is a really sizeable difference, too.
Steel is the heaviest choice out of the common bike materials, coming in at a rather weighty 7.84 g/cm3. What this means in practice is that a solid cube of steel, 1 cm in each direction, will weigh 7.84g.
Aluminum, on the other hand, is light.
Not quite as light as the lightest frame material options, such as carbon fiber, but considerably lighter than steel. Coming in at just 2.71 g/cm3, that’s under a third the density of steel.
But for bike frames in practice, it’s not quite so simple. It’s extremely unlikely that an aluminum frame will weigh less than a third of a steel one.
Although its density is significantly lower than that of steel, aluminum frames often need thicker tubing in order to remain strong enough to support a rider.
On average, an aluminum frame will be around 1-1.5 kg lighter than an equivalent steel frame.
So, although the density is much lower; when comparing actual bike frames, the difference isn’t quite as significant.
But how much difference does 1-1.5 kg make in practice?
A lighter setup makes it easier to accelerate and decelerate but is less able to maintain speed. This means that when taking on bends or attempting to attack other riders in a race, aluminum will be slightly faster, and steel will be faster on long, straight descents.
This also gives lighter bikes a “nippier”, more agile feel to them, whereas heavier frames can feel a little sluggish in comparison.
Additionally, a lighter bike generally makes climbing easier since there will be a lower resistive force due to gravity. You’re dragging less weight up the hill, so it’s slightly easier.
But, in practice, a difference in weight of 1 kg doesn’t make as big a difference as you might think when climbing.
Assuming the same power output, even over the course of a 45-minute climb, a single kilogram will make only around 30 seconds of difference to your time, as shown in this video.
This isn’t that important for a casual rider, but if you’re a competitive cyclist or an avid hill-climb racer, that 30 seconds becomes much more decisive.
What you have to remember, particularly when climbing, is that the weight that matters is the combined weight of you and the bike, and as a percentage, 1 kg is likely to be under 2% of that total.
So, weight probably isn’t the most important factor for most riders, but if you’re going for the lightest setup possible but don’t have the budget for carbon fiber, aluminum is the one to go for.
strength
Tensile strength refers to the amount of pressure that a material can absorb before deforming or breaking.
Aluminum has just over half the tensile strength of steel, and this is the reason that more material is required for an aluminum frame than a steel one.
However, in practice, since there is more aluminum in the frame, the strength of the two materials as bike frames isn’t as different as this result may suggest.
What does make a bigger difference, however, is the type of deformation that may occur in the event of a crash. An aluminum frame won’t crack like carbon fiber, but due to its inflexibility, if it gets a dent or a buckle, it may snap.
However, steel is the most flexible bike frame material by quite a way and is far more likely to buckle or bend without snapping. Additionally, it’s far easier for a frame builder to fix a buckled steel frame, again due to its flexibility.
In terms of performance, however, this is unlikely to make a huge difference unless you end up in a crash since both materials are pretty strong.
Ride Feel
Except for a few specific types of riders, this is probably the most important factor when choosing a bike material since it makes the most direct difference to your experience on a ride.
“Ride feel” describes how the bike feels underneath you as it goes over a lightly uneven surface, usually described on a scale from “hard” to “soft”.
A soft ride feel means that the material naturally absorbs a considerable amount of vertical vibration as you go over a surface that isn’t super smooth, saving the rider from needing to absorb these vibrations with their body. Generally, this is going to feel more comfortable.
A hard ride feel will absorb very little vibration and can be a little uncomfortable when riding on a surface that isn’t perfect asphalt or if you’re in the saddle for long hours.
Steel is far more flexible than aluminum. In practice, this means that steel flexes when traversing bumpy terrain and absorbs a considerable amount of vibrations internally. At the same time, aluminum stays rigid and will feel less comfortable on an uneven surface.
So, aluminum provides a “hard” ride feel, and steel has a “soft” ride feel.
However, a hard ride feel isn’t all bad. Soft material may absorb vibrations due to the surface underneath you, but it can also absorb some of the power you’re putting out from your legs, making it less efficient, particularly when you’re on smooth asphalt.
This makes aluminum more responsive than steel.
This means that, with all else equal, on a smooth surface you’ll be marginally more efficient on an aluminum frame, and on a bumpy surface you’ll be more efficient on a steel frame.
Reactivity
Reactivity, in the context of a bike frame, refers to the degree of the material’s degradation in response to external conditions, usually rain and cold.
Aluminum is a reactive metal. However, it doesn’t rust or corrode.
This might seem bizarre, but the fact that the element is reactive is precisely why it doesn’t corrode.
When exposed to oxygen (i.e. the air), an aluminum surface reacts with the oxygen to form a new molecule, aluminum oxide, in a thin, hard film that coats the surface. Aluminum oxide is non-reactive and so acts as a protective layer against rust and corrosion for aluminum.
So, rain and cold won’t affect your bike, and you don’t have to worry too much about getting it wet.
However, regardless of the material, you should never store your bike outdoors.
Even if the frame doesn’t corrode, your components, welds, or sometimes lug nuts may render the bike dangerous and inefficient.
Steel is extremely reactive with both air and water.
When exposed to air or, even worse, to water, the surface of steel reacts with it to form rust, which is far less strong than the material itself.
The longer the material is exposed to the elements, the deeper the rust layer becomes, weakening the structural integrity of the bike and resulting in corrosion.
A severely corroded steel frame no longer has the same strength properties, so it is not safe to ride and can’t be fixed. So you have to be much more careful about riding your bike in the rain or in harsh conditions. And, of course, never store your bike outside!
- Got a more mild rust problem? Check out our Guide to Removing Rust From a Bike here!
Environmental Impact
If you cycle instead of drive, this makes a huge difference to your individual environmental impact, and regardless of your bike, this is undoubtedly a good thing to do.
Riding a bike produces fewer greenhouse gas emissions than driving a car. But it’s not emission-free.
Although the bike doesn’t require fuel to move and so doesn’t release carbon dioxide as you’re pedaling, the bike itself still has to be made. The manufacturing process can be responsible for a surprisingly large amount of CO2.
Of all the common bike frame materials, steel releases far less CO2 than any other, at just 1.9 kg per kg of steel made.
Aluminum, on the other hand, is responsible for considerably more. Manufacturing a kilo of aluminum comes at a carbon cost of around 18 kg, which isn’t insignificant.
So, for the environmentally-conscious cyclist, steel is perhaps the better choice.
However, regardless of the material, cycling is still miles better for the environment than driving or even any form of public transport!
Aluminum Vs Steel: Which Should You Get?
Essentially, this completely comes down to your priorities and what type of riding you enjoy.
If you’re a hill-climb racer or you like to enter races on short, tight closed circuits, then the weight difference will make aluminum the obvious choice.
However, if you’re a bikepacker, for example, many choose steel due to the slightly higher strength and enhanced comfort on poorly paved roads and on longer rides.
However, aluminum frames are often paired with carbon fiber forks, which significantly reduces the hardness of the ride. So, if this is the case, then the decision isn’t quite as clear-cut.
If you, for some reason, like to ride in the rain, then aluminum is probably the better choice since it won’t rust or corrode.
Additionally, if you’re buying a bike second-hand, then aluminum is often slightly safer since it won’t be internally corroded, whereas a steel frame could have begun to corrode from the inside without you knowing. Always ask the seller how the bike was stored!
When it comes to price, there’s no clear answer either. Desirable vintage steel frames can often be extremely expensive, but a cheaper vintage frame could come at a very reasonable price. The same can be said for aluminum, to a lesser extent.
However, if you’re on a budget, the cheapest bikes you’re likely to come across will be aluminum or steel. The average price is roughly similar, so it really comes down to a case-by-case basis and what you’re looking for.
Hopefully this guide has helped you on your way to making a decision!
