When buying a new road bike wheels are typically the weakest stock component in terms of quality and performance. Even high-end bikes come with wheel sets that do not match the quality of the rest of the bike. Because of this wheels are often the first upgrade made by riders. Most serious racers have multiple sets of wheels in their arsenal for a broad range of uses. For most riders, particularly those on a budget, a good set of quality all round wheels is enough to tackle most circumstances. Buying wheels can be a tough process if you don’t know what to look for and what your needs are. Spokes, rims, and hubs are three basic parts of a wheel set and variations in the quality and purpose of each of these components will alter the intended use. There are four basic wheel sets that a rider should consider: aero, climbing, training, and all round. In this post I will go over some of things to look for in order to identify which wheel sets fall into these categories and how to determine which is best for you.
Aero wheel sets have are becoming increasingly more popular as riders realize the significant role aerodynamics play in cycling. The aero wheel has gone through a drastic evolution in the last 20 years and as a result not all aero designs are created equal. As I discussed in a previous post, designing an aerodynamic wheel that is effective in bike racing is no small feat. It takes more than just plopping a tear dropped shape rim into a wind tunnel and then calling it aero. There are so many variables that need to be taken into account in order for a wheel to effectively aerodynamic. In order to be effective an aero wheel has to remain aerodynamic throughout a broad spectrum of wind directions. The angle of the wheel in relation to the wind is referred to as yaw. 90 degrees yaw would be a direct cross wind and 0 degrees yaw would be a direct head wind, for example. Most aero wheels in the past were designed without accounting for variations in yaw. They were simply put in a wind tunnel and tested to see how the air flowed directly over the wheel at 0 degrees yaw. This is why early rim shapes where V-shaped. The principle being that the V-shaped rim with a tire on it would create a tear drop shape, which is commonly held to be the most aerodynamic shape. The problem with these early designs is that the tear drop shape is not very aerodynamic when the wind comes from any direction but directly ahead. Research has shown that the most common direction that cyclists encounter the wind is around 10-15 degrees yaw. Thus an effective aero wheel will be most aerodynamic in this range. A number of wheel manufacturers have begun to take yaw into account when developing wheels and many aero wheels made by larger companies which do their own R&D are coming out with better more aerodynamic wheels.
Rim depth is a prominent factor in aero wheels with deeper often times being more aerodynamic and shallower being less aerodynamic. A deeper rim (60mm or 90mm) has a larger surface for the air to gradually separate and come back together as it travels over the wheel. This means that Separation, the point at which the air no longer flows across the wheel surface happens much later. The point of separation is where drag begins essentially. A shallow rim has less surface so the air has to quickly separate and come back together, the point of Separation happens much earlier and therefore the area of drag created behind the wheel is much larger. AeroVelo has put together an excellent video demonstrating how these principles work.
The construction of aero wheels will vary by manufacturer. Most contain some amount of carbon in the construction. This is true of all aero wheel sets deeper than 45mm. Some are made solely out of carbon while others employ an aluminum rim with a carbon fairing bonded to the rim. There are pros and cons to both. In each case, the deeper the rim, the heavier the wheel will be. A full carbon rim may sound light, but because the braking surface is carbon, heat dissipation becomes a problem in the construction of carbon rims. Wheel manufacturers use more carbon in the rim, thus making it heavier in order to help dissipate heat. In addition, because the braking surface is carbon, special brake pads must be used. Aluminum bonded wheels remove the heat dissipation issue and allow for regular brake pads to be used. Because aluminum is inherently heavier than carbon fibre, there is no weight saving, although there isn’t much penalty either because less material can be used, aluminum conducts heat much better than carbon and so dissipation is not a problem. The primary advantage to aluminum bonded wheels is that they are much more durable and can withstand greater impact forces than carbon. If you crash on a full carbon wheel and the fairing becomes cracked, this can compromise the integrity of the wheel. In an aluminum bonded wheel, the carbon fairing has no structural purpose so can be used even when the carbon is cracked or damaged.
The primary downside to deep aero wheels is crosswind. In higher winds, particularly when there are strong gusts, some wheels become unstable. A good aero wheel set which takes yaw in account will be more stable but there will always be some side to side motion with deep rims. The rear wheel is not affected as much by crosswinds because it is fixed while the opposite is true of the front wheel. A good combination would be a 60mm front with a 60mm rear or a 60mm front and a 90mm rear. Using a 90mm or deeper on the front is really only suitable for races where wind is not a factor; short sheltered criterium courses or time trials, for example.
If weight is a primary concern, keep in mind that you will sustain a weight penalty by using aerodynamic rims. Although the aerodynamic advantage of a good aero wheel will offset weight in most situations. See my other post for more on this.
Not much needs to be said about climbing wheels. If they are light, they are effective. There are some caveats to buying climbing wheels. To make wheels lighter, manufacturers remove material sacrificing strength and durability. Climbing wheels often have weight limits and the lightest wheels out there are probably not suitable for most people who aren’t already lean as toothpicks. The lightest wheels I’ve ever seen were just over 1kg for a set but could only be used by riders 70kg or less. If you’re already very light and looking for ways to shave a few more grams, climbing wheels might the best bet. If you weigh over 80kg, chances are the wheels you’ll be looking at won’t be light enough to make it worth sacrificing aerodynamics for weight. A reasonable set of climbing wheels strong enough to carry a regular sized person (not one of those pro freaks with no body fat) will be in the 1200-1500 gram weight range. A good set of aero wheels weigh in around 1600-1800 grams. Those couple hundred grams won’t make much of a difference on a big climb if you already weigh 75kg or more but you will notice the aero benefits.
If you’re a sprinter, a lightweight set of climbing wheels also may not be right for you. The lack of material means that they cannot sustain the forces put out in a hard sprint, particularly if you are heavy and muscly like a real sprinter. You will be truing your tires constantly if not wrecking them altogether.
Training wheels are often the most overlooked part of a rider’s kit and many use the stock wheels as their training wheels. And by training wheels I don’t mean the little wheels you had on your bike as a kid to help you balance, I mean the wheels you do most of your training on. Training wheels are great to have because while they may not perform as well as your race wheels, in training all that matters is how hard the workout was, not the speed you can ride at. Because you’ll be spending the majority of your time on these wheels, it is worth it to invest in a decent set that will last and take the abuse you put it through during your training rides. A robust aluminum box shaped rim with good spokes and a decent hub is your best bet. Mavic makes some excellent moderately priced wheels that are durable and perform well. Try to get something simple and common. A training wheel with odd length spokes and nipple sizes will be a nuisance to true and repair. You will spend a lot of time on these wheels, you want them to be easily serviceable not just in general but also while out riding (i.e. avoid tubular training wheels). In a race you will have the benefit of neutral support but out on a long century ride by yourself, you’ll want to make sure you can change a tire and adjust the spokes if need be on your own on the side of the road.
For most people who aren’t interested in investing their child’s college fund into bike gear or those on a budget, a good set of all round wheels will be the best option. These will be very similar to training wheels but performance is more of a factor. You want something that is still durable and will hold up, since it will be the only wheel you ride on whether it be a solo training ride, club ride, hill climb, TT, or mass start but you also want it to perform well. You might spend a little more money on these wheels than training wheels but you’ll still be spending much less than you would on a set of deep dish carbon wheels. You want something that will be a good compromise between weight and aerodynamics. Many 30mm-45mm aluminum rims made by a good manufacturer will be both lightweight and still retain some aerodynamic properties. Flo Cycling makes an excellent 30mm aluminum wheel that is both incredibly durable, decent weight, and fairly aerodynamic.
Hubs and Spokes
Hubs and spokes are not as easy to assess visually when determining appropriate use or even recognizing quality. A good hub doesn’t look much different from a bad hub but there are some things you look into before selecting a wheel set with regard to hubs and spokes.
With respect to hubs, you’ll want to know whether the bearings are cup and cone or cartridge style. There are benefits and disadvantages to both. Cup and cone style hubs have a cup built into the hub body which the bearings sit loose inside, the cone screws onto the hub body and seals the bearings in and forces them into their proper place. When repacking bearings, it is imperative that you use the correct torque otherwise the wheel will spin too loose or too tight. You don’t want to have play in the bearings but they should be overtightened either. Over time, dirt will get into the bearing housing and little ruts will form in the bearing surface and the cup and cones themselves. When this happens, the hub will need to be replaced. This is often indicated by spinning the wheel in your hand. If when the hub spins it feels smooth, the bearings are fine, if it feels rough and ‘grindy’ the bearings are probably shot. In cartridge bearings, the bearings are housed in a circular chamber not unlike roller blade bearings or wheel bearings in a car. On some hubs, these cartridges are not replaceable or very difficult to replace.
You also want to determine whether you want standard spokes which lace using a bent j-shaped spoke or straight pull spokes. The former are more common and spokes are more easily available, the latter are easier to replace.
Spoke number is also a factor, less spokes means lighter and often more aerodynamic but this sacrifices strength. Some spokes can be trued using external nipples, as is common on most bikes, while other require a hex wrench and the tire must be removed to access the inside of the rim. These are commonly using on deep dish aero rims where the carbon fairing is non structural. Otherwise, they can use straight pull spokes with tension nipples placed at the hubs.