Aero Wheels - A Buyer's Guide

Aero wheels look great, sound great on the road, and most importantly make you faster. If you’ve arrived here asking yourself the question “should I buy some” then we’ll help you with a very simple answer – yes!

Page through any more than a couple of cycling or triathlon magazines or web sites and the chances are you will come across wheel reviews. They tend to include terms such as “aero”, “smooth” and “well behaved” but in many cases these are highly subjective claims made by reviewers who have little data to work with. On the other hand some of the better wheel reviews, such as appear from time to time in more technically rigorous publications such as Tour Magazine go far further, incorporating independent wind tunnel test data. These are the kind of reviews we can really learn from.

The purpose of this article is to review the important technical considerations when choosing aerodynamic wheels while directing the reader to relevant analytical resources on this site, resources which should help inform the decision to choose a particular wheel set. These include models we have developed to help you understand the impact of aerodynamic claims on the road - in terms of real watts and time-on-course effects – plus power-speed calculators which reinforce the impact of tyre choice and bearing quality.

Aerodynamic Drag

Clearly the primary consideration when investing in "aero" wheels is aerodynamic quality. Look for wheels for which manufactuers are providing wind tunnel test data or better still wheels for which data is available from independent wind tunnel tests. This data is routinely provided as "grams of drag at 30mph" through a range of yaw angles spanning +/-20 degrees. If you're unsure what is meant by yaw and why it's important in bike racing read our primer Yaw, Drag & Component Choice . Grams of drag doesn't mean a lot to many people, the "at 30mph" part means even less to most amateur riders, so we have developed what we call an Aero Components Evaluator to help you translate that data into real power and time effects on the road. This features public domain wind tunnel data plus manufacturer data contributions for a large range of wheelsets available today.

Clinchers, Carbon Clinchers or Tubulars?

On opting for a particular wheelset there are typically two major configuration options to consider. 1) Shimano/SRAM or Campagnolo - your groupset will determine the tyre of freehub body required on the rear wheel - and 2) Clinchers or Tubulars? Historicaly tubular tyres - which must be glued to the rim and present real headaches in the event of a puncture - have offered lower rolling resistance and represented the obvious choice for elite racing. But in recent times high quality, high tread count clincher tyres - particularly when used in conjunction with latex inner tubes - have achieved similarly low levels of rolling resistance. We provide a Tyre Decision Model featuring lots of rolling resistance test data to help people consider the speed impact of tyre options.

Deep section carbon wheels for clinchers have until recently tended to feature aluminium hoops at the outermost part of the rim and braking surface. This has been a technical requirement linked to structural strength and heat dissipation during braking. To be frank this characteristic has always spoiled the appearance of carbon wheels and frequently has a negative impact on aerodynamics. We highly recommend choosing "(Full) Carbon Clinchers" which tend to be visually and aerodynamically superior.

Deep Section or Disc? Rim Depth?

On the road there is a decision to be made between a wheelset consisting 2 deep section wheels or else 1 deep section wheel at the front and a disc at the rear. Discs are invariably aerodynamically superior to deep section wheels but they are also typically heavier. A perennial question asked by riders is "all things conisidered, which will be faster on course X?" This is a tough question to answer well which requires some level of course modelling to arrive at a scientifically sound answer. We offer Performance Modelling analytics for riders who want to answer this question objectively.

Weight & Inertia

Not into downhill mountain biking? - Then there is no siutation we can think of in which a heavier bike is faster. Lighter wheels will always be preferable to heavy wheels, but we must put the question of weight in context. On many couurses the savings available due to a few grams of weight are miniscule when compared to aerodynamic factors. By all means seek a light wheelset but - unless you're objective is hill climb's or uphill time trials (such as the ITU Triathlon bike leg in Kitzbühel) - focus first on aerodynamics.

Weight carried in a wheelset is more costly than weight carried anywhere else on the bike. Why? Because it adds inertia and higher inertia wheels require more power to accelerate. Inertia is a subject in itself which has limited relevance to riders participating in "steady state" cycling events on non-technical courses such as time trials and triathlon bike legs. Nevertheless you might like to play with our Power Components Calculator to study the impact of inertia on the wattage required to achieve a particular acceleration on the bike.

Bearings

You've done everything you can to choose an aerodynamically optimal, lightweight wheelset - now let's not give away unecessary power to friction in the hubs. While we don't necessarily advocate cracking open your brand new wheels to retro fit ceramic bearings - in many cases the manufacturers stock bearing are amply good enough considering the miniscule gains which might be made if you or someone do a good job of making the switch - our message here is to view what you are buying as a wheel system. It may be that a little known manufacturer in the Far East can perfectly copy the aerodnamic profile of a premium manufactuers rims but do you trust the quality of the hubs and bearings? Faith here is important because there is still a void of data out there on hub bearing friction.

Strength, Durability & Weight Limits

Objectives of aerodynamic optimisation and weight minimisation are pushing wheel manufacturers to create wheels with ever finer tolerances. Keeping in mind that high end racing wheels are aimed at high end racers - elite cyclists and triathletes who would seldom benefit from losing a few pounds - some wheels systems will come with a weight limit. Nobody is saying that a wheelset will be unsafe and simply crumple underneath you if that limit isn't respected but be honest with yourself here and dont make the mistake of buying a wheelset you may damage.

Stability

Deep section and disc wheels can sometimes be a challenge to control under side wind conditions. We're not aware of any research suggesting that the control problem significantly impacts a riders energy expenditure - short of the need to pick oneself out of a hedgerow - and for this reason couldn't recommend forgoing aerodynamic benefit for stability. On the other hand if you can have stabiliy at no aerodynamic cost then why not? We notice a recent trend among manufactuers such as Zipp and ENVE to comment on the stability properties of their wheel designs. What they refer to is insights gained from Computational Fluid Dynamics (CFD) which can be used to design a wheel's centre of pressure towards the hub, thereby improving it's stability. For the meantime we leave this potential benefit to the buyers faith and intution.

Cost & Distribution Channel

Cost becomes a technical consideration in wheel choice the day it limits one's ability to buy performance. Most amateur riders aren't lucky enough to benefit from sponsorship deals which provide unlimited free wheelsets (this is a "Buyer's" guide) and cost is therefore a real consideration for many riders when choosing aero wheels. But it isn't necessarily the case that lower prices equal poorer wheels. We notice a recent trend among some wheel manufactuers - e.g. FLO & Williams Cycling - to provide high end wheels "direct to consumer". It's pretty logical that a manufacturer who isn't feeding a wholesale and retail network can pass on cost savings to the end consumer plus there may be real advantages to a direct link with the manufacturer in the event of any problem. In closing we feel that cost conscious or simply smart riders could do a lot worse than consider accessing a high end wheelset through this option.


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