The old saying goes that there’s more than one way to skin a cat, and it applies to just about everything in life, including going fast on the bike. You can get your position right, or even buy a fast frame. You might decide that an aero helmet will help you save a few minutes on the bike course, or perhaps cleaning up your profile with aero bottles and BTA setups. Or, you might have done all that, but still have those starter wheels that came with your bike. We can help with that last one in just a little bit.
But for now, you need the basics on just what an aero wheelset is, how it is put together, and what the real-world differences are between an all-carbon setup versus a bonded aluminum rim with a carbon fairing and even a deep-section aluminum set. Let’s get started.
The v-shape above is, more or less, what you got for the last 5-7 years if you wanted fast wheels. A V-sectioned, asymmetric design that, when purchased, looked like everyone else on the market when you removed the stickers. And, generally speaking, that was pretty much the case – there were a limited number of factories in China that could work with carbon fiber to produce wheels so you went down, selected your factory, negotiated your price per container and which logo you wanted on them. No problem. It is worth pointing out that the “V” shape has some distinct advantages. One: it is relatively cheap to produce and thus, cheap to purchase, even as a fully-carbon wheel. Two: At 0 degrees of yaw (that is, you are riding directly into a headwind), the V is actually slightly less drag than a toroidal rim. Three: Because they are typically made by the thousands in Chinese factories, they tend to err on the side of cautionby overbuilding the wheels and thus they can typically (not always, and this is not intended as an endorsement for our Clydesdale readers!) take some measure of punishment.
The downside, however, is that V-sectioned wheels are absolutely murder in anything that isn’t a direct headwind. They steer generally terribly out past 5 degrees of yaw because the wind has significant purchase on the flat sides with no rounding and thus can push the bike, and thus the rider, around as it wishes. While they certainly rank highly on the “affordable” meter, the drawbacks to this style of rim should make even the most penny-pinching rider think seriously.
Standing in stark contrast to the V-shape are toroidal wheels. These will typically appear relatively symmetric with a tire mounted to them, encouraging significantly better handling in the more real-world conditions of 5-20 degrees of yaw. Furthermore, they offer a more consistent, and therefore predictable, performance in those not-quite headwinds, so you don’t accidentally end up in traffic from a gust. The downside is that the toroidal shape is relatively new in terms of bike tech, and as such is more expensive as companies recoup their R&D costs on a per-wheelset basis. Small price to pay for staying in the bike lane, in the opinion of this writer.
Bear in mind, that if you are truly judicious, you can find some wheels that occupy a middle ground (Mavic’s Cosmic SLR comes to mind), and these are generally referred to as a hybrid-toroidal wheel. Where you wish to fall in this sliding scale is up to you, but understand the trade off as you move about it. The other major point of wheel design, and thus purchase, is the materials used to produce your new set of go-fast bits: Carbon, aluminum, or some combination of the two?
Historically speaking, bicycle wheels were aluminum and that was the end of it. Then came the late 90’s and a company called Lew Composites. Lew produced the first widely-available carbon clincher wheel in 1998 and the industry hasn’t looked back, since. Yes, most of the pros still ride tubular, but this is changing and has a lot more to do with things like rolling resistance than it does aerodynamics, and the real-world difference between tubular and modern clinchers is for another article (and perhaps a PhD thesis). Wheel technology since the mid-90s has really taken off and the materials, though having gotten more exotic in terms of carbon blends and resin choices boil down to two options: Carbon fiber or aluminum, with a smattering of hybrids combining the relative merits of both.
At the tippy top of the ladder is the all-carbon rim. Using just carbon fiber has a weight benefit that is not able to be ignored (on the order of a pound over an entire wheelset), where the carbon fairing is bonded to the tire bed and brake track (both carbon), and formulated using a different resin blend to handle the unusually high temperatures from hard braking. This is so extreme, in fact, that Zipp had to not only build a thermal imaging rig to figure out the temperature load, but also had to source aircraft-grade carbon fiber resin to handle it for their wheels. Cheap, this isn’t. Furthermore, the basic fact remains that carbon brake tracks simply do not perform nearly as well as aluminum, and have the potential to deform or blow out a tire under extreme braking (though no one here at AeroGeeks is personally aware of an instance where this has happened) – but when you are out for that speed title, the weight can matter.
At the other end is, predictably, the all-aluminum deep-section wheelsets. These are becoming rarer as the availability of carbon has climbed, but they do still exist. While heavy, they are typically bombproof and bargain-basement priced. Be forewarned, you will not find an all-aluminum toroidal wheel – these are V section only and as such, are both heavy and do not exhibit strong crosswind performance.
The happy medium, from a cost to performance perspective, is the growing number of aluminum rims with a carbon fiber fairing bonded to them. They offer relatively low production cost, significant inherent strength, wholly improved braking performance and aerodynamics that rival the toroidal fairings that can be produced from an all-carbon setup. The catch, here, is that they will weigh more than their more expensive brethren, anywhere from a 1-400g. While this is not insignificant, the typical price for an aluminum/carbon setup is less than half of a toroidal, all-carbon wheelset.
So which material and shape combination are the best? That’s not a question that we can reliably answer. Some days, you simply need the braking ability of an aluminum brake track. Other days, your TT course is long, flat, and you’ll be the only one on it. Perhaps you’ve found yourself at a track cycling day, and there’s no wind to care about at all, so those V sections will work just fine for you. This is why those options exist, and choice is never a bad thing. But neither, in the opinion of AeroGeeks, is knowledge.