Aerodynamics: Debunking the Myths

legendWhile aerodynamics have been a consideration for road cyclists since the days of Graeme Obree’s washing machine bike and his famous superman position, it has only been recently that bike, wheel, and component manufacturers have really started putting more emphasis on the true effect aerodynamics have on performance. It’s become such a hot button topic among roadies with those valuing aerodynamics placed firmly against the weight weenies still fussing over a few grams of weight on the big climb. Cycling magazines, both online and print, and various blogs and forums are rife with ‘aero vs weight’ debates. More often than not these articles give pride of place to aerodynamics spouting wind tunnel test data and power savings metrics based on complex calculations and formulae while the weight-weenies scoff and vocalize their mistrust.

“Trust me, when I put on a set of light weight wheels, you can really feel the difference.”

“Wind tunnel tests are great but they don’t give an accurate model of real world conditions.”

“Sure aerodyanmics are important in TTs and triathlons, but when you’re riding in a peloton, you get the benefit of a draft, all that gear aero gear doesn’t help in mass start events.”

These are just some of the arguments made in conversations I’ve had with other riders online, in races, and over beers at the pub. Why is there such a deep divide between camps? If one is really better and it is apparent, why do weight weenies still cling to their featherlight wheels while aero junkies prefer fat hoops and strange helmets? In this post I’m going to go over some of the common myths perpetuated among the peloton and illuminate some of the reasons why roadies are so suspicious of aerodynamics and cling to their lightweight bikes.

I must, however, admit that being married to an aerospace engineer gives me a certain bias toward the aero crowd. And yet my commitment to aerodynamics is not because of marital obligations, but because of the many hours spent having the fundamentals of aerodynamics (physics, fluid dynamics, airfoil design etc.) drilled into my head for hours and hours. I, too, was once a weight weenie, even when purchasing a set of wheels only a few months ago I hesitated more than once because of the weight penalty incurred by creating a more aerodynamically sound wheel shape. And every time I brought it up my wife patiently (for the most part) explained to me once again how aerodynamics work and why I shouldn’t be concerned with the weight of the wheels.

But let’s move on and debunk some myths and get inside the brains of the weight-weenies out there.

Myth 1: On big climbs its better to sacrifice aerodynamics for weight.

Reality: Not necessarily. While weight is certainly a factor when going up hill, the amount of weight savings you gain from dropping 500-700g from your wheels by sacrificing aerodynamics won’t make that much difference. The reason why light cyclists are better climbers is because they’re significantly lighter than the rest of the riders around them, not just a few grams, but a few kilograms. If you’re climbing up a 15% grade, the amount of power required to move those extra few grams on the bike or the wheels (even at speeds of 12km/h) weight only starts to outdo aerodynamics after an hour of steady climbing at that grade. But if the race is mostly flat or even rolling for the first 100km and you have 10-20km of climbing at the end, as some big races often do, the power savings of riding on heavier aerodynamic wheels over those 100km will significantly outweigh the weight penalty going up the climb with the heavier wheels. You’ll be climbing on much fresher legs than the climbers on their non-aero wheels.

On anything less than long monstrous mountain climbs, aerodynamics will always trump weight, even on courses with rolling hills and sharp steep climbs. If you race primarily in North America, there likely won’t be any race where your few grams of weight will help you much, if at all (as long your alternative is soundly aerodynamic).

Myth 2: In criteriums with lots of hard accelerations, wheel weight is more important.

Reality: Not by a long shot. The effect of weight on acceleration is a linear increase. Meaning that for every 1km/h you accelerate, you will need to produce 10 more watts of power (the numbers here are made up in order to explain the differences). Aerodynamic forces, however, require an exponential increase in power to overcome. Meaning that the first km/h requires 10 more watts, the second 30 more watts, the third 60 more watts. You get the idea. It because of this that aerodynamic forces are roughly 49 times greater during an acceleration than added mass. Bottom line: you will accelerate faster on more aerodynamic wheels than you will on lighter ones.

Myth 3: There is no benefit to having an aerodynamic frame and/or wheelset while riding in the draft of another rider.

Reality: This myth displays a fundamental misunderstanding of how aerodynamics work. This would only be true if the draft created a vacuum in the which the drafting rider could jump into. This is impossible on planet earth. And if it were, it wouldn’t matter how good the draft was, you’d have no air to breath. The fact is, even in a draft there is still air moving over you and it is still turbulent air. A rider who is more aerodynamic in the draft will work much less than one who isn’t. The next time you’re on the wheel of another rider, try getting down as low as possible, you’ll probably find yourself having to brake more frequently to prevent ramming into the lead rider.

Myth 4: But my lighter wheels feel faster on climbs!

Reality: Physics doesn’t give a shit how you feel.

In all seriousness though, most riders will argue this last fact until they’re red in the face. And there might actually be some truth to it in the metrics. There is a significant problem with bikes and wheels that are supposedly aerodynamic: basically, they’re not. And this is the real reason why weight-weenies have yet to come around. Most of the aero equipment they’ve tried isn’t that aerodynamic. And when you hand someone something that weighs more but doesn’t make up for it in the way of aerodynamics, you’re not going to be convinced because all else being equal, light weight is better than heavy. But when the heavier item is designed properly with regard to aerodynamics, it far outstrips the non-aero lightweight competitor.

So this next statement is probably going to piss off a lot of roadies, particularly those who do believe in aerodynamics and have invested buttloads of money into their aero equipment:

Chances are, my aero minded friend, your bike and wheels aren’t that aerodynamic. Especially if you’re buying Chinese wheel sets and/or frames.

1273257664874-1sx5u9umzx0w8-670-70When it comes to building a lightweight wheel, there is only one criterion that needs to be evaluated in order to deem it a success: is it lightweight? If yes, you have a successful wheel design. The question is much more complicated when designing something that is meant to be aerodynamic. Asking the question, “is it aerodynamic?” doesn’t cut it. Most wheels and bikes built for aero efficiency in the last 10 years are technically speaking aerodynamic. Early aero wheel designs, like the one pictured in this article, are great when cutting through the wind head-on. They’re great wheels on the track because this is always the case. But when riding on the road, the wind is almost never coming from directly ahead. In fact, most testing has shown that around 6-12 degree yaw is the most common direction to encounter the wind from (this would be around 10:30 and 1:30 on the clock). The early style V-shaped rims and many early toroidal shapes actually perform worse in those types of cross winds than a standard box-shaped rim. So naturally you’re not going to notice much improvement. The same goes for bike design. Many aero bikes out there are designed to have great aerodynamics when cutting through a head-on wind, but perform poorly in typical crosswinds.

A note on the Chinese stuff: Chinese wheels and frames are typically built on designs that are not patented or are very cheap to license. The reason they’re cheap is because they do not perform very well and/or are very old designs. Some of the wheels currently being sold on Alibaba and other Chinese sites (and distributors over here) are built using designs that can be up to 15-20 years old. When buying wheels and bikes it’s important to figure out whether your wheels are built on these license-free designs or if the company branding the wheels actually did their own in house R&D.

Is there a solution? Oh yes. Have no fear, Aero is here. Wheel manufacturers like Flo Cycling, and bike manufacturers like Giant have started to design aerodynamic bikes taking into consideration variations in yaw. The new Giant Propel is arguably one of the fastest road bikes on the market because of its aero design, outperforming the Cervelo S3 by far. The science of aerodynamics is sound. It is unequivocally more important than weight in 99% of situations, but the market is lagging behind in application and design. We’ll likely see the end of the weight vs aero debate very soon with aero being donned the king of the realm.

As a final point, if you own a set of wheels that are shaped in a V (like the one pictured) or even a V-ish U shape, you probably wasted good money on something that is not really giving you any advantage whatsoever. Sell your climbing bike. Sell your climbing wheels. Sell your old Vs. Use the money to buy a set of properly and carefully designed aerodynamic wheels and start saving real power on flats and climbs. Because let’s face it, unless you are literally climbing the Alpe D’huez, aerodynamics always trump weight.

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2 thoughts on “Aerodynamics: Debunking the Myths

  1. Agree! It’s all about aero. 😀 Then again read any glossy cycling mag these days and you’d think that you MUST have two bikes; an aero bike and a lightweight climbing bike (I seem to have neither).

    What’s the aerodynamic issue with the V shape?

    1. Basically its an issue with crosswind. The V-shape design was founded on the principle that the tear drop shape is the most aerodynamic shape we know of. If you imagine the V shape cross section in the picture with a tire on it, it’s shaped like a tear drop. The problem, however, is that its aerodynamic properties are only useful when the wind is coming from directly in front. Tear drops are not very aerodynamic when the wind shifts to one side or the other. In addition, while the front end edge of the wheel cutting through the wind is tear drop, the tailing edge is reversed, which is once again not at all an aerodynamic shape. So that V-shape wheel loses is aero advantage in any type of crosswind and creates almost as much drag in the back edge of the wheel as its reduces on the front.

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