Which frame material is best?

Does carbon offer unrivalled properties? Is aluminium merely a "low-cost" option? In this article, we will examine the frame materials of both road and mountain bikes.

It might seem that the topic of bike frame materials is relatively straightforward, and we encounter many stereotypes. Aluminium is cheap but heavy, while carbon is expensive and light. Only connoisseurs ride titanium, and steel? It probably died out with the demise of classic Favorit bikes. 🙂 However, as is often the case, it's not that simple.

Aluminium vs. carbon

The two most common materials we encounter for bicycle frames are aluminium and carbon. The former dominates the 'more affordable' bike segment, while the latter rules the world of racing and performance.

However, not all aluminium is the same, and not all carbon is the same. It's not uncommon to hear the claim that high-quality aluminium can surpass cheap carbon in its properties. A clear flagship among such bikes is undoubtedly the CAAD (Cannondale Advanced Aluminium Design) series. So, what are the pros and cons of these two strong contenders?

Aluminium

Aluminium frames are currently the most widespread and probably the easiest to mass-produce. They are also the most suitable material if you're just starting out with road or mountain cycling, or if you have a lower budget.

It's relatively light, corrosion-resistant, and won't give you a heart attack when paying. Additionally, it's quite stiff for its weight.


However, stiffness also leads to several less appealing characteristics. The first of these primarily concerns road bikes. Let's be honest, roads are what they are, and when I was riding them on an older aluminium road bike, I often thought to myself: "I wish I had carbon already..."

Simply put – because an aluminium frame is stiff, its ability to absorb road vibrations is diminished (side note – even carbon won't perfectly solve the problem of broken roads 🙂).


A more significant drawback, however, is that every aluminium frame will crack sooner or later, and repairs are usually not feasible. For road cycling, these are more of an exception (frames aren't stressed as much there), but if we look at more demanding disciplines like enduro or downhill, cracked frames are a more common occurrence. Especially for heavier riders. 🙂

Pros of aluminium frames

• relatively light,
• relatively easy to work with,
• inexpensive,
• corrosion-resistant,
• and nowadays, even aesthetically pleasing – welds can be smoothed.

Cons of aluminium frames

• don't absorb bumps – therefore less comfortable,
• cracks mean the end of the frame (they cannot be safely repaired).

💡 Did you know…?
Every aluminium alloy has its four-digit designation. The basic raw material for a frame is always (of course) aluminium. However, since it's a relatively soft metal, an admixture of other chemical elements is necessary – magnesium, chromium, copper, iron, and so on.

These additives are represented by the first digit of the four-digit number. For example, if we take a closer look at the most common alloy, 6061, we find that magnesium and silicon were primarily added to the aluminium. The other digits indicate the alloy's specificity or a particular type.

Carbon

Every racer's dream? A carbon bike, of course! It might be surprising, but carbon's strongest asset isn't its lightness. Carbon frames are stiff, yet comfortable. In this, they differ from aluminium, which is relatively light and stiff in most cases, but falls short in terms of comfort. To find out why, we need to take a closer look at how carbon bikes are made and the material itself.


Unlike aluminium, which is shaped thermally, manufacturing a carbon frame requires a mold. Layers of carbon are then placed into it, bound together by a resin binder – thus creating a carbon composite. By varying the layering method, we can achieve the following properties:

• frame stiffness – Carbon frames are often said to be stiff. For simplicity, let's imagine applying a certain force to the frame. If the carbon fibres are not laid in the direction of the applied force, the result is stiffness.
• comfort – Unlike aluminium, carbon is capable of significant flex. A good example is the well-known Ghost Lector. Its seatstays are bent (following the design of leaf springs, commonly found on heavier trucks or pickups) and thus contribute to better damping. If flex is desired in a certain part of the bike, the carbon fibres are laid in the direction of the applied force.

And what's best about this phenomenon- also known as anisotropy? The direction of fibre placement (as well as the number of layers) can be chosen as needed. This means we can achieve stiffness in areas like the bottom bracket, thus maximising power transfer during pedalling.

Conversely, specific areas of the frame can flex with a different fibre lay-up angle, contributing to comfort. Carbon flex is particularly desired in MTB frames with single-pivot linkage kinematics (zero-pivot, or flexpivot), where part of the absorption is handled by the shock absorber and part by the seatstays.


The thought of a carbon frame also warms the heart of many a 'weight-weenie'. And that's not all. Due to the manufacturing process, we can produce any conceivable shape, thus improving, for example, the aerodynamics of a road bike or the damping elements of a mountain bike. Or simply create a bike with a unique design. 🙂


The dark side of carbon is its fragility in specific types of impact. We can see this from time to time even in World Tour races – broken frames, handlebars, seatposts... However, these bikes are stressed in a more extreme way than when a hobbyist 'puts their bike through its paces,' and after all? Cracks in a carbon frame (unlike aluminium) can be repaired. Unless it's a 'total write-off.' 🙂

However, what every cyclist will need to pay attention to is tightening the bolts. Along with a carbon bike, it's definitely worth getting a torque wrench.

Pros of carbon frames

• desirable weight-to-stiffness ratio,
• higher riding comfort,
• customizable shaping,
• material longevity.

Cons of carbon frames

• price,
• susceptibility to damage from specific impacts,
• difficult to recycle.

💡 Did you know…?
The first commercially successful bike with a carbon frame was the Kestrel 4000, as early as 1986. However, the absolute first was the Bowden Spacelander model from 1960, which had a rather daring design for its time – but only a few hundred units were sold. A carbon bike made its debut at Tour de France in 1989 in the form of the Look TVT model, ridden by Greg LeMond.

Steel

My very first road bike was, of course, a steel Favorit. Quite heavy, with rather impractical shifting, but it was mine. I probably don't need to add that I didn't ride thousands of kilometers on it, and soon I switched to aluminium. 🙂 Steel ruled the cycling world 40-50 years ago, only to be later pushed out by aluminium and carbon. The reasons were simple – price and weight.


Steel is characterized primarily by its strength, yet it is surprisingly flexible. I remember at one point considering converting my Favorit to a 10-speed road groupset, and the rear dropout spacing was problematic.

But where force doesn't help, more force does, and if needed, I could relatively easily spread the rear stays... of course, this is quite a 'barbaric' intervention and the components would probably suffer, but it's ideal for illustration. Longevity, strength, and the ease of repairing a damaged frame are also strong advantages.


However, the positives end there. A steel frame = a heavy frame (compared to competition). At the same time, since it's processed iron, steel is the only material susceptible to corrosion. However, it finds its place among more affordable fitness bikes. Or, given its price, in the segment of increasingly popular bikepacking machines.

It also holds its own in the production of trail hardtails, as it can absorb slightly more bumps. Could we be seeing a revival of the phrase "steel is real"?

Pros of steel frames

• strength,
• flexibility (slightly higher comfort compared to aluminium),
• longevity,
• easy to repair.

Cons of steel frames

• higher weight,
• susceptibility to corrosion.

💡 Did you know…?
In 1978, the 1,000,000th Favorit bicycle rolled off the production line in Rokycany. By the company's collapse in 2001, over 2,000,000 of these legendary bicycles had been produced.

Titanium

A bike for life? Definitely titanium. It shares many common characteristics with steel – it's durable, resistant to damage, and relatively easy to repair – at least compared to aluminium. An added bonus is its corrosion resistance. And another bonus is that after buying a titanium bike, you won't eat for at least a month, as you'll have no money left. 🙂

Jokes aside, the truth remains that titanium bikes maintain their reputation as 'those luxury bikes'. This material is popular among 'garage' builders, resulting in unique specimens.


Similar to aluminium, titanium itself requires additives like vanadium or aluminium to achieve perfection. This creates a titanium alloy that has a better strength-to-weight ratio compared to steel, offers many properties similar to carbon, and is almost indestructible. Most titanium frames come with a lifetime warranty.

So why isn't titanium used in professional cycling if it has such appealing characteristics?

It all comes down to the final price. This is also contributed to by the fact that producing a high-quality titanium frame is quite challenging due to the shaping and handling of the material. The welding method is also different – since titanium reacts less favorably with oxygen compared to aluminium or steel, argon is used in the welding process.

Pros of titanium frames

• durability,
• resistance,
• weight-to-strength ratio.

Cons of titanium frames

• price,
• complexity of the processing.

One could continue with other 'exotic' materials, such as magnesium, bamboo, or wood. Recently, 3D printing has also come to the forefront. However, in our region, we most commonly encounter the four materials above. When choosing a specific material, several important questions should ultimately be considered:

• how much I want to invest in the bike,
• how long I plan to ride the bike,
• rider's weight.

These three questions can also provide a better picture of which frame material will be most suitable for a particular cyclist.

Photo source: editorial archive