Buyer’s guide: should you buy lightweight or aero wheels?
Aero, lightweight, or something in between? We ask the experts to find out how you can choose the best wheels for you
It’s a conundrum that vexes so many road riders: what kind of road wheelset should you buy? With so many options out there, it’s often difficult to pin down exactly what kind of wheel is right for you if you want to upgrade the hoops on your bike.
Broadly speaking, if you’re upgrading your wheels then we can categorise the options into lightweight or aero. You’re either trying to reduce the weight of your bike or help it cut through the wind.
Naturally, not every wheelset fits neatly into a particular category and the lines are often blurred. Take, for example, the rise of the mid-section rim that purports to give an optimum balance of aero efficiency and low weight. An all-in-one, if you like. Still, you may yet be better off with a set of wheels that leans more towards one extreme or the other given your goals.
On your behalf, we’ve tried to get the lay of the land so that you can make the wisest decision possible when it comes to parting with your cash. And, we’ve gone to some of the best in the business for the latest expert advice: Smart Aero Technology, which has had a key role in developing some of the most cutting-edge aero wheels from Enve Composites since 2011, as well as long-term Team Sky wheel suppliers Shimano.
So, aero or lightweight? That is the question.
The case for aerodynamic wheels
Let’s get the basics of aerodynamics nailed down right from the off. As Simon Smart, founder and aerodynamic guru of Smart Aero Technology, says, the forces that slow cyclists down on a flat road come down to two key components: rolling resistance and aerodynamic drag.
“At very low speeds the tire rolling resistance is most significant, but as speed increases aerodynamic drag quickly becomes the dominant force,” he says. “If we take a rider in an average road position with reasonable tyres, we can expect there to be a 50/50 split in tyre and aero resistive force at 12.5mph.”
Even at that relatively low speed, aerodynamics still have a crucial part to play – and, from there, Smart points out the ratio leans towards aero drag much more heavily. “At a more realistic speed on the flat of 20mph, for example, 75 per cent of your effort will be tasked with overcoming aerodynamic drag,” he says.
A deeper aero rim will therefore have a positive impact in reducing the aerodynamic drag the whole bike-rider package presents to the wind. Given that aerodynamic drag is the primary resistance the riders is required to overcome, it follows that an aerodynamic wheelset offers the genuine potential for ‘free speed’. Add other aero gains into the mix and the argument begins to look compelling, says Smart.
“If our average rider gets a better position, clothing, efficient helmet and bike – it would not be difficult to reduce aerodynamic drag by 15 per cent, which works out at 25 watts at 20mph,” he says. “This means 20mph is 11 per cent easier to achieve – a percentage that rises with higher speeds.”
However, Smart is at pains to point out that, before going in search of wheel-based gains, the rider that can make a real difference to aerodynamic efficiency for relatively low cost.
“Costs to improve aerodynamics start off relatively low with position tweaking and clothing changes, but like anything will become more expensive when the low-lying fruit has been dealt with.”
Smart also says that aero wheels specifically can be expensive, while there’s also a small increase in weight to consider given the extra material that’s used in making them. You also need to consider that the greater the rim depth, the more susceptible the wheel will be to catching crosswinds.
The case for lightweight wheels
While Enve are arguably most famous for their aero-optimised wheelsets, Smart also recognises the benefits of going more towards the lightweight end of the spectrum – particularly when it comes to climbing and acceleration. Bike manufacturers will often spec machines with relatively heavy wheels, so many riders will look to upgrade those hoops for something lighter – and it can have a genuine impact on the ‘feel’ of the bike
“When accelerating and climbing, weight comes into play,” Smart says. “For our average 75kg rider on a ten per cent climb, around 90 per cent of effort will be consumed in overcoming gravity.
“To sustain 10mph on this gradient, this 75kg rider would need to produce roughly 415 watts. Each kilogram in weight equates to a saving of around five watts of effort,” he adds.
However, it’s also worth noting it’s very rare that a wheelset marketed as lightweight versus an equivalent aero option will offer a saving anywhere near a kilogram. For example, if you compare Enve’s SES 2.2 climbing wheel with the SES 7.8 aero-specific wheels, there’s actually only 332g of claimed weight difference between the two (1,110g against 1,442g respectively).
While the reduced rotational weight of a lightweight wheelset has a greater effect, pound-for-pound, than static weight in terms of resistance, it also remains true that much bigger differences can be made within the rider themselves, as long as a rider doesn’t adversely reduce their power output by losing weight.
Ultimately, while weight trumps aerodynamics when climbing, if you’re riding on largely flat roads, rolling terrain or even a mountainous course with long valley roads, aerodynamics may well be more important over the course of the ride. It’s about balancing the demands of your riding with your choice of wheelset, but we’ll come on to that.
When it comes to lightweight wheels specifically, and as Smart alluded to when talking about aero wheels, while relatively affordable lightweight hoops are available, you will soon reach a point when you have to dig deep to make further gains. “The cost tends to go up exponentially as you look to shave off more weight to save watts,” says Smart.
Mid-section: an optimal compromise?
So, the lighter or more aero a wheelset is, the more you’re going to have to spend. That won’t come as any great surprise, but it makes buying specific wheelsets even more prohibitively expensive.
With that in mind, should you consider a mid-depth wheelset that aims to address both weight and aerodynamics? As Smart points out, while it’s a compromise of ultimate lightweight or aero performance, there are benefits to avoiding extremes.
“A mid-depth rim gives the best compromise between weight, inertia, responsiveness and drag reduction,” he says. “Our development at Enve has shown us that you need a minimum 35mm rim depth to start to control and improve the flow of the air, while at higher depths it’s all about trading weight for aero.”
“We find that in general, a 45-55mm wheelset is perfect for an average rider of 75kg”
Smart says that at Enve, the focus has been on developing a “sweet spot” wheel, although each rider realistically has a different sweet spot. “It depends on your weight, riding style and where you ride. We find that in general, a 45-55mm wheelset is perfect for our 75kg average rider; it’s deep enough to really feel the aero benefits, but light enough that a 75kg rider wouldn’t notice the weight when climbing,” he says.
“As an example, the majority of the Team Dimension Data riders see the Enve 4.5 (45/55mm) as their go-to all day wheel. But on flatter/rolling stages someone like Mark Cavendish will opt for the deeper 7.8 (70/80mm) wheelset for the full aero benefits,” adds Smart. “It’s only when there is a lot of climbing that the heavier riders will go to the Enve 3.4 (38/42mm).”
At this point, let’s bring in Shimano’s Ben Hillsdon on the discussion. He points out that Shimano engineers designed the latest Dura-Ace wheels, specifically the C40s, as the best compromise between ultimate aero performance and lightweight.
“Going for a mid-section wheel is anything but settling for ‘middle-of-the-road’,” says Hillsdon “But yes, compromise is necessary when it comes to design. Bike racing (and riding in general) is done in a dynamic environment. We can develop wheels that are perfect in a wind tunnel, but don’t give that level of performance in real world scenarios.
Hillsdon expands on Smart’s points, once again looking at the pro peloton. “If a rider is only concerned with sprinting the last 200m then they may choose the C60 (Dura-Ace’s pure-aero wheelset), though a domestique will be working hard throughout the stage so will need something more suited to multiple conditions. Essentially, you’re choosing the best balance of weight, aerodynamics, stiffness and durability.”
The right wheel for the job
Right now, you’re probably thinking ‘this is all well and good, but I’m not a pro’. The same idea applies, however, and you need to carefully consider the type of riding you do to narrow down your options.
“We are left with the fundamental question of where you do most of your riding,” says Smart. “If you only climb, then you’re best advised to go lightweight. However, if you intend to descend quickly down the other side or ride rolling and flat terrain then a mid-depth wheel is a no-brainer.”
“We find that the aero benefits from increasing the rim depth between 30-50mm will far outweigh the small increase in weight and, invariably, the wheels are more stable too.”
Most wheel manufacturers will offer a range of rim depths to suit the needs of all riders. We saw that with DT Swiss’ new range of ARC aero wheels, available in 48mm, 62mm and 80mm depths, and, returning to Shimano’s Dura-Ace line-up, Hillsdon says there are three options to cater for different riders – C24, C40 (selected for the 2017 RCUK 100) and C60s, all of which have specific characteristics designed to best suit the type of riding you do.
“Which wheel is best for you fully depends on the type of rider you are and the kind of riding you’re doing”
“Which wheel is best for you fully depends on the type of rider you are and the kind of riding you’re doing,” Hillsdon says. “Are you just training or are you looking to win a race? Are you a lightweight climber or a punchy rouleur with a diesel engine? How’s the weather, are you likely to suffer in the crosswinds? What’s your bike handling like? What does your typical route profile and the terrain look like?”
“All these questions can have an impact and when choosing which wheel to opt for you should think about all these factors with the goal of getting you from A to B as fast as possible.”
Alloy or carbon rims?
Whichever way you choose to go in terms of aero versus lightweight performance, you’ll then be faced with actually choosing a wheelset. One of the main questions that remains is whether to opt for an alloy or carbon rim construction, which can have a significant impact on the look and performance of the wheel. While advances in aluminium mean alloy represents excellent value for riders who want a set of lightweight wheels which won’t break the bank, high-end aero wheels are typically made from carbon fibre.
“Alloy rims present great value, and certainly HED have done an excellent job of making an alloy rim work well aerodynamically with a carbon fairing,” says Smart. “Until recently, alloy rims have had better braking performance. It’s only some of the latest carbon rims that are able to match alloy braking performance.
Smart says carbon fibre comes into its own in not only enabling engineers to manipulate the rim to boost aerodynamics, but to do so without adversely affecting other areas which impact on performance.
“While the aerodynamic advantage of a carbon wheel may not always be huge, it’s the whole package that brings the carbon aero wheel into a world of its own,” he says. “Reduced weight, increased stiffness whilst retaining ride quality and responsiveness are all factors that will transform any bike.”
Hillsdon also throws the strength of the wheel into the mix. Shimano’s Dura-Ace clincher wheels are constructed as a carbon laminate around an alloy core – the intention being to increase strength and heat resistance. Aluminium has it’s drawbacks, though, and Shimano’s race-ready tubular wheels use a full-carbon construction.
“Gram for gram, carbon is lighter than alloy but it’s not as strong, so an alloy wheel is going to be more resilient than a carbon wheel, but potentially heavier too,” he says. “As a result there comes a point where the increase in material needed to make an aero rim is negated by the weight of making it from alloy materials.
“Dura-Ace tubular wheels [used by the likes of Team Sky], on the other hand, have a full carbon construction for out-and-out, gram-for-gram aero performance.”
Consider the whole product
As Smart alluded to earlier, rolling resistance is an important factor, so points out that rim width is an important consideration too.
“Wider rims that fit wider tires in the range of 25-27mm are a must for better rolling resistance, ride comfort, general grip levels,” he says. “It’s also worth saying that tubeless looks like the future, as we’re seeing more tyres coming on the market. So it’s worth getting tubeless compatibility if you can.”
It’s testament to the influence of tyres on rim design in general that both Smart and Hillsdon agree that aero (and lightweight) rims have evolved significantly in recent years because of the rubber they’re designed for.
“When I started developing wheels with Enve in 2009, we were quite limited by the smaller width tyres generally used,” says Smart. “This meant that we couldn’t put as much width and camber into the rim shapes as we were limited by the 21–23mm tyres.
“As wider tyres have come on the market we have focussed on making rims that work well with the fastest tyres and being able to move away from the more slab-sided rim shapes. Using more cambered profiles has enabled us to improve the dynamic response and stability, which ultimately means that a rider can handle more depth from a stability viewpoint.”
Hillsdon expands on this stability point, using the new ‘D2’ rim profile of the most aerodynamic C60 Dura-Ace wheel as an example. “After extensive prototype testing in the wind tunnel and on the road, we proved that a wide rim shape with a deep tire bed performs best across a wide range of real world conditions,” he says.
Taking the plunge
When it comes to upgrading your wheelset, the most fundamental issue to consider is the kind of riding you’re going to be doing on your new hoops.
That will give you a starting point to make a shortlist, but you also need to consider other factors including how often and when you plan to use the wheels, typical weather conditions, your bike handling skills and general strengths as a rider, plus a multitude of other design considerations, from rim width to tubeless compatibility. Naturally, budget will be a key consideration, too, as well as the wheels you’re upgrading from. For example, if that means a relatively heavy set of down-spec wheels on an off-the-shelf bike, then reducing the weight of your machine may be more of a priority.
Ultimately, as our conversations with Smart and Hillsdon have confirmed, both lightweight and aero wheels have their advantages – it’s why both Enve and Shimano offer a range of wheels to suit. However, as Smart stressed at the start, aerodynamics have a huge part to play for any cyclist.
And, unless you have specific demands for your wheelset (for example, you’re a lightweight climber heading to the hills or a time triallist looking for every aero advantage), or the option of choosing an individual set of hoops each time you ride – and, chances are, that’s unlikely – then it’s about balance. While a mid-section wheel may be seen as a compromise, we’ve learned that medium depth rims are considered closer to a “sweetspot” by offering an aerodynamic advantage while keeping weight under control, and are favoured by many pros as a result.
“It’s about finding the exact balance between watts lost and gained in different circumstances and different types riding. But don’t worry, mid-section is anything but middle of the road,” says Shimano’s Hillsdon. “You only need to take a look at the pro peloton in an average stage and you’ll see how many riders choose this to get the best of both worlds.”
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