Carbon road bike: what makes good quality carbon and five bikes to consider
'Good aluminium can be better than bad carbon' - it's a phrase we've all heard said - but what is good carbon and how is it made?
Carbon fibre is often seen as the dream material of cycling – when well produced it’s light and stiff, and it can be moulded into any shape.
People often refer to ‘good carbon’ and ‘bad carbon’ – usually as a pre-requisite to saying that quality aluminum is better than the latter.
However, the vast majority of the raw carbon fibre actually comes from just six companies, and often goes on to be used in the aerospace industry. It’s how the material is manipulated by the bike brand which influences the ride quality and strength.
The dream combination is high stiffness, low weight and at an affordable price: usually at least one of the three has to be sacrificed in order to achieve greatness elsewhere.
How are carbon road bikes made?
Raw carbon fibre due to be used for sports equipment (‘Pitch’ type carbon fibre is used elsewhere) is usually made from polyacrylanitrile (PAN) fibre which is heat treated to take on the shape of long and thin fibres. The greater the treatment, the stronger the carbon will be – stronger carbon requires the use of less material which drops the weight.
Though bike brands can use any description they like, the Japan Carbon Fiber Manufacturers Association (JCMA) grades carbon from ‘Low Modulus’ to ‘Ultra-High Modulus’. The level of carbon awarded is based upon the Tensile elastic modulus (stiffness) and Tensile strength (durability).
That’s not to say that the Ultra-High Modulus carbon should be used everywhere. A good carbon fibre frame uses varying grades of carbon across the construction – whilst stiffness is optimum in some areas (bottom bracket shell, down tube), a little flex elsewhere (seat tubes, chainstays) is an asset.
Raw carbon is mixed with other magical ingredients to create a composite. Carbon on its own is too brittle, so it’s mixed with epoxy resin which moulds the fibres together and makes it more able to deflect impact. Once the resin is added the material is called pre-preg carbon. Dassi bikes has also experimented with using Graphene mixed into the material to offer better weight to strength ratio.
When it comes to constructing a bike frame, there are two popular methods used. Most major brands will layer the sheets of carbon fibre, to varying levels of thickness depending upon the quality required.
Decisions as to how the carbon layup should be distributed are usually made by experienced engineers, or with the use computer software. It’s usually then tested in the real world and refined to perfection. The more investment the bike builder or brand can invest, the more sophisticated you can expect computer software used to be.
The direction in which the carbon fibres face has an influence, too – unidirectional (all facing one way) fibres offer the best stiffness to weight ratio. But they’re brittle – so woven carbon is much more common – it copes with impact better and is easier to mould, particularly at complex junctions.
Often, several sections are created and then bonded together. It is possible to bond individual tubes together, and this is more popular among custom frame builders.
Since carbon can be moulded into more aerodynamic shapes, this is also a factor taken into consideration and tested with more computer and wind tunnel analysis.
Carbon road bikes to consider
Carbon is pretty much the number one material of choice when it comes to mainstream frame construction. That means there are an awful lot of carbon bike frames out there and there’s no one ‘best’.
Whilst the frame material is at the heart of the bike, there are other elements to consider when choosing a new steed – the geometry, specification and value for money being key points.
We’ve listed some of the most well renowned carbon frames which have fared well in our reviews below. But for ultimate bike guides looking at every element of the bike, check out some of our other guides.
Carbon road bike on a budget: Boardman Team Carbon
Boardman’s Road Team Carbon is a long-standing entry level carbon road bike, priced at £1,000 with a Shimano Tiagra gropset.
It is constructed from what Boardman calls ‘C7’ carbon, which uses Toray T700 fibres. C7 is Boardman’s entry level choice of carbon, but our reviewer found it more than adequate – stating “Boardman say that this frame provides ‘unparalleled power transfer, comfort and handling’ and for the most part I agree with that statement (for the price).”
Aero carbon road bike: Trek Madone Race Shop Ltd
Another benefit of opting for carbon is that it is very malleable and can be moulded into any shape – which means it can be easily optimised for aerodynamics. When we pitted aero road bikes head to head, using aero testing, we found the Trek Madone Ltd tied with the Specialized Venge. However, the Madone features the brands IsoSpeed decoupler which makes it a much more forgiving and comfortable ride.
To construct the frame, Trek uses its own 700 Series OCLV carbon. OCLV stands for Optimum Compaction Low Void and refers to the process of placing sheets into the mould, applying the ideal combination of heat and pressure to compress them, and limiting voids or gaps between the layers which could compromise strength and durability.
Endurance carbon road bike: Giant Defy Advanced
As mentioned elsewhere, most frame manufacturers work with sheet carbon. Just a few brands have the capacity to work with raw carbon, and Giant is one of them.
Giant’s carbon frames use ‘high performance grade raw carbon fibre’, which is transformed into composite in its own factory. The resin used minimises voids whist staying strong and helps to absorb road shock.
Carbon is a particularly popular material of choice for endurance bikes because it absorbs shocks and vibration from the road much more than any other. The Giant Defy model – available in a range of spec with varying levels of carbon quality (Advanced Grade SL – Super Light being the uppermost) – is an endurance beast with a relaxed but still punchy geometry and disc brakes.
Lightweight carbon road bike: Cannondale SuperSix Evo
The most oft-stated benefit of carbon is that it’s lightweight – but obviously there are varying degrees of this. Going too light can result in a floppy, power sucking ride and finding the ultimate balance is quite a task.
To obtain the perfect balance, Cannondale uses its own ‘BallisTec’ carbon, adjusting the layup to offer stiffness where needed whilst using less material elsewhere. There are also Hi-Mod versions, which use a newer weave of high and ultra modulus fibres for greater rigidity.
Carbon super science bike: Bianchi Oltre XR4
Bianchi is the only bike brand using ‘countervail technology’. Developed for the “extreme conditions of NASA aerospace operations”, countervail tech involves a unique carbon fibre architecture in which a layer of countervail viscoelastic material is embedded across the frame.
The goal of this is to create a more comfortable ride – Bianchi claims vibration is reduced by 80 per cent.
The carbon geekery doesn’t just involve increasing comfort, either. The Oltre XR4 is an aggressive racing machine, with an aero construction to boot.
Of course, there’s a wide range of carbon road bike choices on the market – browse our reviews section for more product suggestions.