Carbon fibre in wheels

The use of carbon in frames is widespread, and is regarded as the go-to performance choice for bike frames in the industry. However, like frames and other components, carbon is also used in performance wheelsets too. But why?

Alex Schmitt explains that the limitations of using alloy for deeper, aerodynamic hoops means carbon has become the go-to material for this kind of wheel.

“It’s not possible to build 45mm-plus deep rims from alloy safely,” he says. “A carbon wheel is also lighter than an equivalent alloy rim, while you also get a great stiffness-to-weight ratio.”

Dov Tate agrees, pointing out that carbon can be produced in more complex shapes, helping to produce an optimised rim for better performance – and at a significantly lower weight.

“This allows full freedom on the part of the designer to optimise the rim shape and profile without being constrained by the limitations of the manufacturing processes. This opens up the possibility for an optimised design fit for purpose,” he says.

What are the benefits and drawbacks of manufacturing carbon wheels?

Clearly, carbon has secured a foothold as the high-end material of choice for performance wheel manufacturing. As Tate mentioned before, there are clear benefits for wheel designers in achieving increased stiffness and reduced weight, as well as bushing the boundaries of aerodynamic engineering, but that comes at a cost.

“The layup process, which involves lining the mould with sheets of carbon fibre in order to be cured, is still a very manual process in many cases which increases the time and cost of manufacturing.”

However, Schmitt points out that once a rim design has been developed, it’s easy to produce high quantities of that wheel with repeatable and high quality levels.

The downside, he says in agreement with Tate, is “the high production costs associated with carbon manufacture and layup,” so even with the good reliability of producing carbon rims, it comes at a cost ultimately passed on to the consumer.

What are the benefits and drawbacks of using carbon wheels for the rider?

For the rider – and for you, the reader,, this will probably be the most important aspect – the benefits of using carbon for wheels are numerous, which is just as well considering the well-recognised costs of producing (and often, buying) them.

Schmitt reinforces the key points of improved aerodynamic efficiency through being able to create a deeper and more intricately shaped rim than would otherwise be possible with an alloy construction, as well as the aforementioned stiffness-to-weight ratio. Carbon rims can be made significantly wider, too.

“Anyone who has ridden a carbon wheel will be able to relate to the benefit of a lighter, more aerodynamic wheel,” adds Tate.

Ultimately, carbon significantly broadens the horizons of wheel engineers. Just look at the undulating profile of Ziip’s 454 NSW wheelset, designed to apparently improve crosswind stability, to see how radical they can get. Or to DT Swiss’ ERC 1100 Dicut wheelset, which combines a 47mm-deep rim with a fat internal width of 27mm while still keeping the weight low at 1,513g.

There’s also the aesthetics to consider. Of course, performance is paramount, but there’s no denying just how good a set of carbon wheels looks in a bike.

However, it’s not all good. As well as being more expensive, stopping power can suffer when it comes to carbon fibre wheels. “Braking performance has historically been the Achilles’ heel of full-carbon wheels,” says Tate.

“However, new technologies and manufacturing techniques [such as Mavic’s laser treatment] have helped close the gap to alloy braking performance, however there is still a perceptible difference.”

Schmitt also recognises the impact of carbon on braking performance, particularly in the wet – although, like many manufacturers, it’s something DT Swiss has spent significant time working on with the use of more advanced construction methods and improved resins.

“In the dry, rim brake performance these days is excellent,” adds Schmitt, “while in the wet it’s still not as good as the alloy equivalent.”

Given that carbon fibre is typically used for aerodynamic wheels, the handling of deeper rims has been another historic drawback of carbon hoops, according to Tate. That, however, is something which has also been addressed in recent years, with the move towards blunter rim profiles.

“Older V-shaped rims would become very twitchy in crosswinds, making for a more hair-raising ride,” says Tate. “However, there are now smoother and more rounded profiles to allow rims to be less susceptible to crosswinds.”

As Tate alluded to in the previous section, carbon fibre wheels are significantly more expensive to manufacture than aluminium wheels – and that, ultimately, is one of the main drawbacks of upgrading.

Just as carbon fibre wheels have advanced in recent years (and we’ll come on to that), so have alloy hoops, and while you won’t be pushing the absolute boundaries of aerodynamics or low weight, a sub-1,500g aluminium wheelset with an up-to-date (wide) rim profile can be found for less than £500.

Additionally, Tate explains that the precision with which carbon rims are laid up and moulded has improved markedly over the years, which has had a knock-on result of improved reliability as well as reducing the weight of rims further.

This has also led to the possibility of creating carbon rims with much smaller tolerances, allowing for the adoption of tubeless technology.

On top of that, and as we’ve already alluded to, the rim profile of aerodynamic wheels has also evolved, from a sharp V-shape to a blunt-nosed U-shape design, to improve aerodynamic performance and handling.

“Fundamentally, this allows the airflow to remain attached to the rim for longer, reducing the force from crosswinds and improving how the wheel feels in blustery conditions,” says Tate.

The industry also borrows concepts from other relevant areas, including the often-cited National Advisory Committee for Aeronautics (NACA) research into optimum (rim) shapes for aerodynamic performance.

Schmitt adds: “Aerodynamic development at the rim has moved forwards a long way in the past few years. Now simulations in the form of CFD (computation fluid dynamics) allow more scenarios to be investigated to arrive at a more efficient rim in real world conditions.”

The key point Schmitt makes, however, is that standards are always moving forwards in ‘all of the areas in which carbon rims are being developed, from brake track heat dissipation and weight savings, to improved stiffness and carbon-resin makeups’.

What about the rest of the wheel?

Of course, while the rim is the most publicised aspect of carbon wheel design, it’s clear that a wheel is more than just this, from spokes and nipples to hubs.

“We know that there is much more to an outstanding wheel than ‘just’ the rim,” says Schmitt. “That’s why we (DT Swiss) have the highest priority on the development of our components – spokes, nipples and hubs – as well.

“Carbon makes sense for the hubshell, but it definitely doesn’t make sense for spokes and nipples or the interior of our hubs. Therefore we combine stainless steel for the spokes, brass and alloy for the nipples and carbon for the rims to get the perfect wheelset and an ideal combination of all components.”

Tate corroborates this view; while carbon construction of a rim is fundamental to a wheel’s behaviour and performance, you need to consider the whole system.

“It will only perform as well as the weakest link,” he says. “So the most advanced rim design in the world will be heavily let down by a poor quality spoke choice, for example.

“Similarly, a low quality hub will offset the benefit of a high quality rim. Often overlooked too is the build quality of the wheel. It’s essential that a wheel is not just tested for lateral and radial trueness, but also that the spoke tension is balanced.

“A wheel can start off perfectly true, but if the spoke tension is all over the place, it will simply pull itself out of true as it’s ridden.”

So what are your options?

There are, literally, hundreds of carbon wheel options on the market. However, these can often be broken down into three broad categories when talking about road wheels: shallow, mid and deep-section. On top of that, you now have the choice of rim and disc brake wheels.

In short, shallow rims afford the lightest weight and maximum stiffness due to the compact, minimalist construction. They’re also the least susceptible to crosswinds due to the reduced surface area.

Deep-section rims use much more material, and are therefore heavier and less responsive when climbing – but the upside is that they’ll cut through the air with greater efficiency.

– Buyer’s guide: should you buy lightweight or aero wheels? –

Sometimes this can be offset when you’re riding in crosswinds, when the more slab-sided nature of the rim catches the air and can destabilise your ride. This is where mid-section rims come in, offering a compromise between aero performance, weight and handling characteristics.

Once you’ve picked a depth range that’s right for you (read our buyer’s guide on the lightweight and aero wheel dilemma for more essential reading), you can then look at specific wheelsets. Consider the following characteristics to arrive at the optimum carbon wheelset for you…

Price

Price will also be a key consideration, but price does not always square with value. For example, where at one end of the spectrum of the mid-section range you can opt for ENVE SES 4.5s specced with Chris King Ceramic Speed hubs for £3,300, you can also buy the excellent £1,850 Roval Rapide CLX50s, do-it-all DT Swiss PRC 1400 Spline 35s for £1,674.99, or value-packed Cosine 55mm carbon clinchers at £600, representing a huge range of cost outlay, depending on the brand, technology and R&D.

Of course, those wheels aren’t neccessarily all created equally, but the bottom line is carbon fibre wheels have become more affordable. The launch of Bontrager’s Aeolus Pro TLR wheels earlier this year is also testament to that.

While undoubtedly there’s a pecking order in the ultimate performance each wheelset will provide (depending on what exactly you want from your wheels), only you can decide if the extra money is worth the incremental performance gains.