In The Know Cycling

What matters most in choosing between wheelsets? In some ways, this is much like choosing a car. Depending on who you talk to, there are a lot of different factors to consider. Depending on how you intend to use the wheels, some of these factors are more important than others.

Let me try to simplify and organize the many selection criteria into four groups: performance, design, quality, and cost.

Here are the selection criteria that make up each of the groups mentioned above:

Performance: Versatility, specificity, aero drag, sidewind stability, lateral stiffness, vertical compliance (aka comfort), responsiveness, durability, and for rim brake wheels, braking are the key measures I’ve used to assess wheelset performance, to a greater or lesser degree depending on its intended use.

The most desirable all-around wheels will provide the versatility to ride all the different types of terrain (hills, flats, false flats, straights, corners, sprints, mountains, fast downhills, windy roads) that you’ll experience and a range of training and many events (club races, centuries, club, charity, group rides) you’ll do, without compromise.

With the growing popularity of cyclocross and gravel or dirt riding, you can add a wheelset’s ability to ride road and these off-road situations to the versatility consideration.

Specificity is a measure of how well a wheelset performs for its intended terrain, surface, or event. A wheelset intended to perform its best in a flat aero time trial should be evaluated in that situation and would perform differently than one intended for steep road climbs or gravel events.

Detecting how much aero drag there is in your wheels is next to impossible on the road. The best surrogate of this and the way I and my fellow testers attempt to determine wheelset aero drag is to notice your ability to hold your momentum at different aero speeds ranging from 20mph/32kph to 25mph/40kph without putting out additional effort or power.

Many promoting mid-depth and deep section ‘aero’ wheels will correctly tell you that 70-85% of your energy goes into overcoming wind resistance but won’t tell you that aero wheels won’t make you any faster until you get going at speeds of 20mph (or 32kph).

For those of us measuring our power output, recognize that independent tests show you will reduce your drag (and improve your aerodynamics) somewhere between 10-15 watts going from shallow depth aluminum wheels to mid-depth carbon ones at aero speeds. Very roughly and unscientifically speaking, that could yield a 5% to 7.5% wattage improvement for the cycling enthusiast putting out an average of 200 watts during his or her ride.  Sounds like the bump you’d get riding every day with ‘good legs’ or ‘good sensations’, non?

Note also that your choice of inner tubes and tires, rolling on tires that are slightly narrower than your rims, and setting your tire inflation pressure right can reduce your rolling resistance to create an additional 5-10 watts of benefit. So, there are lots of ways to improve your aero performance (see here for how to position yourself right and here for other gear that will make you more aerodynamic).

The flip side of going faster with a deeper, more aerodynamic wheelset is that taller rims often have less sidewind stability out on the road when the wind is blowing more than 10mph/16mh or when you catch gusts of wind. A great deal of product development in recent years has focused on creating rim profiles that keep your wheels stable in these side winds to maintain your ability to steer the bike when winds come at you from different angles.

Lateral stiffness tells you how stout and precise a wheelset is as you transfer your power through it to do a hard acceleration, go up a steep pitch, or lean into a corner. A stiff wheel will do a great job of transferring your energy and power when you really step on it to sprint, throw in a dig, close a gap or when you get out of the saddle to charge up a hill. Stiffness comes from the combination of rim, hub, and spokes working together rather than being dependent more so on any one of those three.

Your comfort is an outcome of a wheelset’s vertical compliance, what tires you use, and how much you inflate them. You can make a wheel more or less comfortable by running it tubeless, using better tires, and lowering the pressure.

But, you can only do so much to make a wheelset comfortable given its compliance. Vertical compliance is determined by the wheel’s rim, spoke, and hub materials and how they are aligned and assembled.

Responsiveness is a measure of how quickly a wheelset accelerates from a stop or when you attempt to accelerate while underway from one speed to a much faster one. You accelerate most often after slowing at a stoplight or sign or after making a turn. If you race or group ride, you might accelerate to start a breakaway, move past someone slowing in front of you, kick it in on a hill, or when doing a sprint for the town line or finish line.

A wheelset’s durability is a measure of how well it remains intact after hard impacts and over it’s lifetime.

For rim brake wheels, braking is a critical performance criterion. When first introduced, wheels with carbon brake tracks were clearly inferior to aluminum ones, some say dangerously so. The joke went that brakes would only slow but never stop a carbon wheel, that is until the heat generated from braking either blew out the tube or warped the rim.

Here again, technology and design advanced considerably before disc brake wheelsets became the focus of the industry and R&D budgets, improving carbon wheel braking performance through the use of new resins, weaves, brake track finishes, and brake pad compounds.

Optimizing the performance of some of these criteria can compromise the performance level of others.

For example:

• Versatile road bike wheels that perform well across many riding situations usually aren’t the best performers in specific cycling disciplines like climbing, time trials, or criteriums.
• Carbon wheel rim shapes optimized to reduce aero drag usually aren’t among the most stable in strong side winds and vice versa.
• Some laterally stiff wheels can be quite harsh even with wide tires and at low inflation pressures.
• Making carbon wheels exceptionally light can also make them prone to cracking while building them to endure hard impacts can make them heavier.

Typically, the more expensive the wheelset, the more these trade-offs are reduced or balanced. The best wheelsets deliver the highest performance levels of each of these criteria without making trade-offs.

Design: Design defines how manufacturers want their wheelsets to perform. Sometimes they perform as designed, sometimes not. The key design criteria are wheel weight and material, rim depth, width and profile, hub and spoke selection, and brake track and wheel finish.

The best performing wheels will usually be among the lightest, principally to enable quick acceleration each time you shift gears on the flats, increase your cadence or head up a climb. Weight is determined primarily by choosing between carbon or alloy rim material, the hub and number of spokes on each wheel, a hooked or hookless rim design, the lay-up and resin choices, and the rim depth, width, and profile (which in turn determine the amount of material used in the wheel).

At the end of the day, rim depth and width of wheels selling in the same price range will determine weight differences more than the other factors.

If you ride a lot of different wheelsets in different conditions as I and my fellow testers do, you’ll notice performance differences starting at about 100 grams (or 3.5 ounces) of weight difference. For most, it’s more likely that you can really feel something at around 150 to 200 grams of difference, typically the weight you can cut going from the stock wheels that came with your bike to a good pair of carbon wheels you can upgrade to. That said, lighter is always better but below about 100 grams, the difference provides more of a marketing advantage than a real performance one.

Wheelset weight is a surprisingly hard number to pin down. Why? There’s no standard for what should be weighed and companies measure and market it differently. Some publish the rim weight alone knowing that the difference between the rims is the weight that matters most. Many publish the weight without tape or valve stems and with the lightest free-hub option which together can drop 50-60 grams or so off the actual wheel weight.

Further, the weight published by the wheelset manufacturers is often not the same as the wheelset’s actual weight. The actual weight of many wheelsets I’ve measured over the years is often 40-50 grams and sometimes considerably more than the “claimed weight,” a term used by many reviewers and retailers to apparently absolve them of responsibility for actually measuring and reporting a weight different from what has been marketed.

I’ve studied the claimed weight and actual weight measured by reviewers for many of these wheelsets and weighed them myself. The bottom line is that most of the better wheelsets within a category (e.g. value-carbon all-around, performance-carbon all-around, climbing, aero, or all-road) wheelsets I’ve evaluated are within 100-150g of each other, whether on the basis of claimed or actual weight. That’s a difference I think you could certainly brag about but most of us aren’t going to be able to notice on the road.

The rim’s outside width, the width of the rim across the brake track, has increased significantly in recent generations of carbon wheel design. Tests have shown that a wider tire enabled by a wider rim reduces a tire’s rolling resistance and also improves both comfort and handling. A couple of generations ago, most carbon wheel outside rim widths measured across the brake track increased from 19-20mm to 22-23mm. The most advanced current generation of carbon rim wheels have outside widths of 28mm to 32mmm.

Rim inside widths, or the width across the bead hooks that grab the tire inside the rim, have increased from 15mm to 17mm to 19mm (rim) and 21mm (disc) and now to between 23mm and 25mm over the last few generations.

With rims that are wider on the inside and outside and with wider tires, you can put a greater volume of air into the tires, yet still have them support your same weight at a lower tire pressure. This softens the ride, making it more comfortable and giving you better handling. Running a lower pressure also puts less stress on the wheel structure and extends its life. Running it at the same pressure lowers your rolling resistance by creating less vibration and forward direction when come raise up even slightly off the road and return over and over again, especially on warn paved roads.

As mentioned earlier, crosswinds can affect your ability to steer a bike with a set of 40mm and deeper rim wheels.  Using carbon allows wheel designers to shape the profile of rims to offset this effect. Traditionally rims had a ‘V’ profile, with the rim linearly increasing in width out from the narrower inner or leading edge, where the rim meets the wind and spokes, to the outer one, where it meets the tire and the wind exits.

To deflect crosswinds, the newer design wheels have focused on making the leading edge wider and more rounded (somewhat like a ‘U’ ) and in some cases by also curving the rim wall from inner to outer edge like an oval or what designers call a toroid (or ‘0’ shape), instead of it running without any width variation. Some have made other adjustments along the inner edge in an attempt to deflect crosswinds like Reynolds swirl lip generator (SLG) design or Zipp’s sawtooth rim that varies in depth.

Finally, spoke and hub choice and rim finish are clear design choices, though I think they are more about personal preference and performance more than actual performance. Most quality wheels come with spokes and hubs made from one of the two or three major manufacturers.

The larger, integrated cycling product companies typically make or design and have hubs to put on their wheels. Still others use the same, top-end DT Swiss 240 hub either branded as such or with the wheel maker’s brand on the hub shells and the 240’s mechanical component ‘internals’ underneath the shells.

Spoke number, alignment, and shape (round, elliptical or bladed, butted or not noting thickness changes along the length of the spokes) do vary considerably from wheel to wheel. The number of spokes used and how they are aligned or ‘laced’ is part of the overall design used to create a wheel’s strength and stiffness. They have a minor effect on weight (we’re talking a few grams here and there) and their shape has minimal influence on aerodynamics though some wheel makers market the heck out of their bladed spokes.

While having fewer spokes, having them laced in a unique pattern or having flat ones may set the look of certain wheels apart for the rest of the crowd, focusing on spokes in isolation really doesn’t get you any closer to choosing between one wheelset or another. If you true your own wheels, it may be more important to you whether the spoke nipples are accessed outside or inside the rim, but that may be something to know rather than use to make a choice.

Hubs used on the best wheels are generally very good and, as mentioned above, many come from the leading manufacturer DT Swiss. Most use bearings made of stainless steel and come in a sealed package while others are ceramic and move more freely.

These choices largely affect durability and maintenance, which shouldn’t be issues if you own good wheels. At the extremes, hub choice can affect weight and acceleration but in a minimal and hardly discernible way. Hub flange diameter and placement can also affect wheel stiffness when considered in combination with the rim, spoke and assembly of those components and the hubs.

Hubs use different mechanisms and have ‘pawls’ and slots the pawls engage to get the rear wheel spinning when you begin pedaling. This affects how quickly the wheel engages when you first start rolling or increase your cadence. Much of the differences in the number of pawls or points or degrees of engagement from one good hub to another are hard for cyclists to notice on the road.

More importantly to most of us, some hubs may roll smoother when you are going down the road or freewheel quieter than others when you are coasting, though these are often subjective differences and only affect performance if the rolling isn’t smooth at all or the noise of the freehub annoys you so much that it affects the enjoyment of your ride. There are a couple of manufacturers that make truly excellent hubs but distinguish themselves by creating identifiably unique sounds coming from their hubs and offering them with shells in a wide range of colors.

In simple terms, the latest generations of carbon rims for rim brake bikes from the best wheel makers use resins and manufacturing processes that make carbon clinchers more durable than alloy ones and their rims resistant to overheating. Better brake track finishes and brake pads have greatly reduced and in most cases eliminated brake squealing typical of earlier generation carbon wheels. They also contribute to dissipating heat created at the rims.

New brake track finishes have brought the dry weather braking performance of carbon clinchers nearly on par with alloy wheels and wet weather braking within range. These finishes vary in detail but are typically textured or etched surfaces or have added materials on top of the smooth resin making up the rest of the rim, both creating more friction and wicking more water during dry and wet braking. Other companies still have braking surfaces that are smooth and essentially unchanged from the rest of the rim and perform less well than the newer finishes.

Rim finish – everything from matt to glossy rims with bold white or ‘blacked out’ lettering – is a personal choice. While it has no effect on performance, I understand that looks and brand will matter to some road cycling enthusiasts, especially if it makes you think you are going faster or are more excited about riding your wheels and bike with some of these distinctive design touches.

At the end of the day, evaluating and comparing wheelset performance is very subjective. Wheelset aerodynamic performance, for example, is probably one of the most marketed characteristics and provides an example of why you need to be careful buying into the hype. While aerodynamics is one of the most important and distinguishing criteria for racers in a wheelset’s overall performance, it is also one of the hardest characteristics for the cycling enthusiast to objectively assess and compare and is far less important to your speed than your position on the bike and your fitness.

Here’s why. Most companies selling wheels based on their performance rather than their price have done extensive wind tunnel testing in a controlled environment on their own wheel designs and against competitors’ wheels to help develop the current generation of carbon wheels. Very few publish the results and when they do they are often selective, on incompletely labeled charts and with little detail about their testing protocol.

While most tests look to see how much drag the wheels produce at different angles to the wind (‘yaw’), there is no common approach to testing the wheels, for example, either on and off a bike or on specific brands and types of bikes and tires. Of course, some bikes and tires are themselves more or less aerodynamic.

You are really only getting a true measure of the front wheel’s aerodynamic effect. On the road, the airflow over your rear wheel is disturbed by the ‘wake’ created from the front wheel and the down and seat tubes in front of the rear wheel. You are also creating a good deal of turbulence at the intersection of the rim and spokes as your legs pedal like egg beaters. Go ahead and try to model the aerodynamics of that situation!

With wind tunnel testing in hand, wheel manufacturers market the most flattering parts of this incomplete, non-comparable wind tunnel aero information and often market the qualifications of the engineer who led the aero design and supervised the wind tunnel analysis along with a combination of “unique” technological breakthroughs available only in their wheels.

I understand that companies must have some tools like CFD (computer fluid dynamics) around which to design and that wind tunnels provide necessary baseline measures, (and that all of this makes for good marketing), but how well these tests relate to the real world of on-the-road cycling with varying road, wind, bike and rider conditions seems very hard to correlate.

While most people will say aerodynamics and weight are two of the most important measures of a wheel’s performance, as you can see, neither of them are conclusive based on numbers alone. You really have to take what the wheel manufacturers and their retailers tell you about these performance and design features with a great deal of skepticism.

In place of their claims, which the buyer guides and some bike shop salesmen repeat back with great enthusiasm, I’ve drawn from the experience of independent reviewers and enthusiasts who have ridden many different wheels in different conditions on the road over many miles and that of my own experience with specific wheelsets.

Quality: Durability, warranties, and service/support are the selection criteria that define wheelset quality.

Rim, spoke, and hub durability all matter though rims and especially carbon rims are usually the weakest link and most expensive to deal with. Most hubs put on all-around wheels sold in the performance all-around category are very durable and easily serviced as part of an annual bike check-up or if there is a problem. Modern-day spokes are strong and relatively easy and inexpensive to replace, something you rarely need to do as a result of normal riding.

Carbon rims are far more durable than they used to be and most are stronger than alloy rims. While I’m not aware of any tests that compare alloy and carbon wheel lifetimes, anecdotally most service shops will tell you that carbon wheels will last longer than alloy wheels under normal conditions. Wheels with fewer spokes will reduce the weight some but increase the stress on a wheel.

At the end of the day, it really comes down to the rim manufacturing quality and how well the company stands behind its product if something goes wrong. Most major manufacturers make very durable wheelsets in this all-around category and offer competitive 2-year or longer warranties that cover materials and workmanship.

Some companies are just more responsive than others to issues that require direct service or support. Online forums are filled with stories about company service, both good and bad, and most companies have established their reputation.  Fortunately, most are good.

Most local bike stores and online retailers that are certified dealers of specific wheel brands stand behind the products they sell. It’s pretty easy for them to do so; they send the wheelset back to the manufacturer in most cases.

Ultimately, the manufacturer determines the service response to a damaged wheel – repair time, replacement, cost if any, etc.  I’ve tried to sort through both the durability ratings and warranties offered by manufacturers but also listened closely to what shops and other enthusiasts say about the durability and service/support response to different wheelsets.

Current generation carbon wheels don’t have issues on typical flat and hilly terrain. For carbon rim brake wheels, the biggest issue continues to be overheating and deforming during extended braking, for example coming down a long mountain pass and dragging the brakes or holding them for long periods of time like you would do with an alloy wheel.  Manufacturers do not warranty damaged carbon wheels caused by overheating, but as mentioned above, the latest generation carbon wheelsets will not get damaged in this way unless you drag the brakes.

I’ve written more about the quality of carbon wheels today and the best technique for braking a carbon rim brake wheel on mountain descents in a post reviewing carbon clinchers designed for mountain climbing and descending here.  If you only feel comfortable being able to use the constant braking or dragging technique and want the best braking surface short of going to disc brakes, I recommend you choose an alloy wheelset.

Cost: While you often get what you pay for, some wheels cost a lot more than others with only a tenuous relationship between cost and performance, design, or quality. Wheelsets north of $2000 appear to be priced based on their brand name, business model, product and market strategy, and product volume more than any other factors.

Some companies spend a lot to advertise and sponsor professional cycling teams to create a distinctive wheel-focused brand appeal and purposely sell low volumes. Others look to be ubiquitous with a broad range of cycling products including wheels and use their large distribution networks to achieve more profit through higher volume sales on lower priced wheels and a range of other cycling products. For us, cycling is a sport, a past-time, a passion.  For them, it’s a business.

Some manufacturers also dictate selling prices to retailers and threaten their distribution agreements if they stray from those prices. In some countries it’s legal, in others it isn’t and the market pricing reflects this.

For example, many online retailers based in the UK often sell high-performance wheels at 20% off the manufacturer’s recommended price and occasionally discount these up to twice that amount. You will seldom see this on a current model year wheelset sold in a US local bike shop or US-based online retailer. Because of what’s known as Minimum Advertised Price or MAP agreement, the retailer has to agree to price it at the MAP if they want to sell the company’s product. And, the courts have ruled that it’s legal.