Buyer's guide: should you upgrade to carbon fibre wheels?
Got your eye on a new carbon fibre wheelset? Here's everything you need to consider before taking the plunge
Carbon fibre has become one of the most popular materials in the bike industry, and when it comes to wheels, your choice is between that and an alloy construction. There are definite advantages and disadvantages to both materials, but carbon has established itself as the leading performance material for wheels right now.
But why is that, and what are the advantages (and disadvantages) of using carbon over aluminium? We’ve spoken to two experts, Alex Schmitt of powerhouses DT Swiss and Dov Tate of British carbon wheel builders Parcours, to get their insights into carbon wheelsets, and help you arrive at the right wheelset for you.
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.
When did carbon fibre become a popular material to build wheels with?
Carbon fibre wheels first began to emerge in the early nineties, as manufacturers started experimenting with the material that had only a decade previously made its debut in the high-performance arena of Formula One (in a structural capacity fundamental to the strength of the chassis, rather than an appendage), with the McLaren MP4/1 car of 1981.
As we see with aerodynamic development today, the crossover between the crucibles of motorsport, the aerospace and bike industries are clear and present.
“Following on from Greg LeMond’s Tour de France win in 1989, aerodynamics really started to come to the fore in the world of cycling," says Tate. “Track pioneers such as Chris Boardman and the Lotus bike only served to reinforce this."
Of course, gestation on the road took longer – quelle surprise, with roadies notoriously cautious when it comes to adopting new technologies.
“While deeper section wheels became commonplace on the track, in triathlon and at some road races, it took longer for the majority of road racers to adopt the new technology," adds Tate. "In fact, it was only after Fabian Cancellara took the win at Paris Roubaix in 2010 [on Zipp's new 303 carbon aero wheels] that alloy rims were finally consigned to the history books in pro cycling."
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.
What innovations and developments have emerged over the past few years?
Considering how relatively recently carbon wheelsets have emerged on the market compared to their alloy siblings, there have been plenty of jumps in technology that have refined and improved upon the technology, some of which we've already alluded to.
"The use of high-temperature-resistant resins for the rim braking surface has improved the braking performance and safety," says Tate, referring to how some carbon rims could fail under high braking stress in the early days of carbon hoops.
“You wouldn’t use these specific resins across the entire wheel, though, because they tend to be more brittle so would affect impact resistance in a crash.
“Similarly, advances in brake pad compounds have improved braking performance and some wheels now use a textured or treated brake track. Of course,the introduction of disc brakes has also been a game-changer for carbon wheels because building them to accommodate a brake track has become irrelevant."
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.
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...
The rim profile may be designed with a smooth U-shape profile to improve its behaviour in crosswinds, or have a sharper V-profile for ultimate frontal efficiency.
The wider the rim (both internal and external), the wider the tyre you can run on it. For optimum performance, a wide tyre should be paired with a wide rim, not only for safety but to ensure the tyre adopts the preferred profile (by ensuring a smooth transition between tyre and rim, rather than a lightbulb shape).
DT Swiss' carbon wheel range is a good example of how some brands have tailored the rim width in accordance to the ideal tyre width. The latest ARC aero wheels, for example, have a 17mm internal width design for use with a 23mm tyre (to reduce the frontal area), while the PRC hoops, pitched as road all-rounders, increase that to 18mm, intended to be paired with a 25mm tyre. Finally, the ERC endurance hoops have a 19mm internal rim width designed for 28mm tyres, given comfort and versatility (for use on rough roads or off-road) are priorities for those hoops.
Ultimately, tyre width has a knock-on effect on the pressures you can run, as well as the versatility of the entire wheelset. Remember, the wider the tyres, the lower the possible air pressure, and the higher the comfort levels, as well as claimed improvements in rolling resistance, too.
Brake track treatments
Disc brake carbon wheels need no brake track, so if you’re after a disc set of wheels, you can swiftly move on. Those using rim brakes should note any brake track treatments, however – for example, Roval’s ‘glass scrim’ layer or Mavic’s iTgMax laser treatment that are designed to improve performance.
Some wheelsets may use an alloy insert to help disperse brake track heat, while others will rely upon specific high-melting point resins.
Hubs and spokes
No wheelset is complete without these components, so make sure the wheelset you opt for has good hubs and spokes to ensure the quality of the entire build.
Some spokes may be bladed to help with aero efficiency, while hubs can have anything from stainless steel to ceramic bearings, with an inevitable impact on both rolling resistance and cost.
This is another subject that’s rearing its head in the industry, and for a critique of whether tubeless compatibility is right for you, read our guide.
Most high-end wheels are tubeless-ready, come supplied with rim tape, and are designed specifically for a tight seal for the tyre at the rim. You can run tubeless-ready wheels with or without tubes though.
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.