Best carbon road bike 2023: what makes good quality carbon and five bikes to consider

Carbon is pretty much the number one material of choice when it comes to mainstream frame construction and as such there are an awful lot of carbon bike frames out there and there's no one 'best carbon bike'.

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.

• Best road bikes under £1,000/$1,500
• Best road bikes under £2,000/$2500
• Best aero road bikes
• Best lightweight bikes

Five top carbon road bikes

At just over £1,000, the SLR 8.9 offers excellent value. Sticking with rim brakes, while most brands have switched to discs, saves weight and is also a little cheaper, enabling more money to be invested into the quality of the frame.

And the frame is a real highlight. We found it more forgiving than most aluminium frames around this price point, and also in being significantly lighter it was a real pleasure on the hills. Unlike some other budget-oriented bikes, the frame of this one is of a standard that it’s worth upgrading the individual components around it – a set of deep section wheels, down the line, would breathe extra life into an already zippy bike. 

Although rim brakes are becoming a bit more of a rarity these days, their performance is not to be sniffed at. In a four-way group test, the Boardman SLR 8.9 actually stopped the fastest compared against three cable-actuated disc brake bikes. This test was in the dry, but although rim brakes are a lot more adversely affected by wet conditions, it does show that the technology is certainly still capable.

The rim brakes do mean that the tyre clearance is limited to 28mm, which is a little tight if you're looking to all-day epics on roads of questionable quality. But for the speed oriented, this should be mostly sufficient.

Quite the contrast to the value optimised Boardman SLR 8.9 is the Trek Madone SLR 9 Disc. This bike spares zero expensive and is dripping in top of the range components, such as SRAM's top tier Red eTap groupset and the Bontrager Aeolus OCLV Carbon wheels.

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 brand's IsoSpeed decoupler which really does make for a much more forgiving and comfortable ride.

At 7.5kg, it is a little heavier than some other aero bikes around this price point, but with the Madone's combination of aerodynamic efficiency and shock absorbing qualities, it was more than good enough to make it into our 2019 Editor's Choice awards.   

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.

As an endurance bike, the Defy is designed to be comfortable to ride over long durations, but still efficient enough so that you can cover long distances. As such, the carbon frame features a complex mix of tubing shapes, so as to deliver stiffness where it’s needed – such as around the head tube and bottom bracket – and flexibility where it’s not, such as at the seat stays.

We found the handling felt somewhere between a gravel and a road bike, which was a pretty perfect balance for retaining a lively feeling ride, but also incorporating a degree of stability, providing a confident feel.

Coming with an 11–34 tooth 11-speed cassette, there aren’t actually any single tooth jumps and this does result in sometimes being stuck between two gears – one too hard and the other too easy. If you’re planning on riding this more like a gravel bike, that may not be an issue. But if you’re putting a large number of miles in on the roads, you’ll likely want to swap this out for a tighter spaced option

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. Their 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 Pro being the uppermost) - is an endurance beast with a relaxed but still punchy geometry and disc brakes.

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. The Cannondale SuperSix Evo is renowned for being a bike which strikes the balance to perfection. A disc brake model, in a size 56, has a claimed frame weight of 866g and 389g for the fork.

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 that use a newer weave of high and ultra modulus fibres for greater rigidity.

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 and 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.

How are carbon road bikes made?

Most brands come up with fancy sounding titles for their own carbon construction– FACT (Specialized), OCLV (Trek) Advanced Composite (Giant) are all examples.

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 for the best carbon bikes 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. Cheap Chinese carbon imports might seem as though they tick all the boxes, but you can read our investigation into whether they are worth the risk here (the short answer is probably not).

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).

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 – although that's not something which is ubiquitous amongst the best carbon bikes. 

That said, Ultra-High Modulus carbon shouldn't be used everywhere. A good carbon fibre frame uses varying grades of carbon across the construction, and while stiffness is optimum in some areas (bottom bracket shell, down tube), a little flex elsewhere (seat tubes, chainstays) is an asset.

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 of 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 - woven carbon is much more common - so 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.