Dangerous Descending: The Truth about Aerodynamics in Cycling

Dangerous Descending: The Truth about Aerodynamics in Cycling

The latest hot topic in the World of Cycling are the new rules brought in by the UCI banning various riding styles that they deem as dangerous in racing and training, with hefty fines for those who disobey the new rules.

It also appears to be the opinion of the UCI representatives that they want to try and prevent amateur riders from emulating some ‘less controlled’ riding styles adopted by the pro-peloton.

Amongst the newest set of guidelines from the UCI, they have outlawed the descent style known as the ‘super-tuck’, along with the Rouleur-classic style of ‘arms on the bars’ - where the rider will tuck down and rest their forearms on the bar tops - a basic iteration of the time trial position, designed to increase aerodynamic efficiency for the rider in the wind on the front of the peloton or breakaway.

Super Tuck Descending Style

The theory behind both these riding techniques being that the rider is reducing their profile and wind resistance, and thus increasing aerodynamic efficiency, and reducing their effort and fatigue.

Although not the first to use it, the super-tuck was largely made famous by Froome in the 2016 Tour, where he was seen on a fast solo breakaway descent, sitting atop the top tube of the bike and hunching forward over the handlebars.   Some riders who adopt this style of descent can also be seen (awkwardly) pedalling their biles in an effort to keep up their speed.  

Although the UCI appears to be making a concerted effort to improve safety across the sport, the new rules have largely been met with derision amongst the cycling community, with some members of the pro-peloton also speaking out.  

The general consensus being that improvements in safety should start with race organisers - for example improving the finish straights, safer barriers, road furniture, and less errant vehicles on the course, as opposed to attacking riding styles and techniques.  

Some voices are concerned that this could be a slippery slope, with more and more rules being implemented that could affect the sport in a negative way.

Does it matter?  Does it work?

Does the super-tuck work?  Does resting your arms on the bars make a difference?  Some riders are convinced that these styles are effective in reducing drag and effort, however some say they don’t believe they make enough of a difference to matter.

Aerodynamics are incredibly important in Cycling (and other sports), and here at Avenir we only know too well how imperative aerodynamic efficiency is.  As a performance cycling brand, all our kit is designed from the first sketch to last stitch to incorporate aerodynamic efficiency as one of our core principles of our design process.

In order to illustrate the theory and research around aerodynamics, and their application to cycling specifically, we've put together the in-depth, comprehensive information, straight from the experts, about the real benefits of aerodynamic riding, and the real reasons riders strive to ride in the most efficient way possible, seemingly taking risks to do so...

Below, aero design experts Nathan Barry & Len Brownlie talk about all things kit, position and aero, and give insight into the importance of aerodynamic efficiency. 

The Definition of Aerodynamic

Of all the forces you have to overcome on your bike, the two greatest watt-sappers are: air resistance, and gravity (e.g. when the road tilts up).

You can obviously avoid the latter by staying on flat ground (but who wants to do that!?). 

Either way, it’s impossible to avoid 'air'.  Even on a perfectly windless day, you create a lot of wind as a cyclist, and the faster you go, the harder it blows.  

At speeds over 15kph, air becomes the dominant force of resistance.  By the time you hit about 48+ kph, a huge 90 percent of your power goes into overcoming air resistance, or what scientists call aerodynamic drag. 

While aerodynamics is the study of the properties of moving air and the interaction between air and solids moving through it, cyclists should also understand drag reduction.

Here’s a quick refresher on the two major types of drag you face as a cyclist...

Pressure Drag

As you ride, you slam into air particles, which get compressed when you hit them and then become spaced out after they flow over you. 

The difference in air pressure from your front to your back creates a drag force.  

Aerodynamic shapes reduce this pressure drag by minimising that difference in pressure and allowing the air to flow more smoothly over your front and reduce the low-pressure wake behind you.

Skin Friction Drag

There is friction between your body and the air particles moving over you, as well as friction between the layers of air around you.  The air over your body is stationary; the air passing over you is fast moving and free. 

The transition between those areas creates friction - which then creates drag (and drag is bad...!).

Skin friction drag can be manipulated to reduce overall drag, as you see with dimples on a golf ball or for instance the textured materials on the shoulders & leg panels of an Avenir Skinsuit or Elite Race JerseyElite Bib-Shorts.

Nathan Barry is an aero design Engineer, with a Ph.D. in applied aerodynamics:

“Surface roughness increases the skin friction by making the air more turbulent near the surface,”

“The benefit is that a turbulent boundary layer has better energy transfer, and this allows the flow to remain attached longer over the round surface, thus actually reducing pressure drag.”

So, who benefits from Aero?

"There’s a common misconception that aero only matters if you’re going fast"

Nathan Barry:

“People will say, ‘I’m not fast enough to need aerodynamic equipment.  But actually, good aerodynamics provides greater time savings to slower riders than faster ones.”

"It’s true that the faster you go, the more aerodynamic drag consumes your total power. Doubling your speed from 30 to 60 kph creates not double the resistance, but closer to eight times the resistance. But even at relatively slow speeds, the majority of your power goes toward overcoming air resistance",

"At 15kph, half of your power is going to overcome air resistance." "At speeds near 50 kph, 90 percent of your power goes into overcoming air resistance."

Barry goes on to say:

“The slower you go, the more time aerodynamics will help you save, because you’re spending more total time on the road.  If you’re out there doing 28-32 kph, you can still save a big proportion of time by reducing your aerodynamic drag.”

Reducing drag can even help you climb faster...

“A bike that is designed to reduce drag will climb faster than a lightweight bike up to about a 6 percent gradient, or even a 7 percent gradient for stronger, elite level riders,”

Barry also says: 

"Above that gradient, you then get some additional savings from weight reduction..."

How aero can you go...?

The argument for the 'Super Tuck' and 'Forearms on Bars'...?

"When you’re looking to minimise drag, the first place to look is in the mirror..."

Len Brownlie, Ph.D., is a aerosports expert who has previously worked with Nike to develop vortex generators (which are kind of like a series of tiny wings) for their competitive athletic wear.

“You, as the rider, are bigger than your bike and, as such, account for 70 to 80 percent of the frontal area of the bike plus the rider”, explains Brownlie.

Unsurprisingly, lowering your torso toward the bike significantly reduces frontal area and drag.  But you hit the point of diminishing returns more quickly than you would think the lower you go. One study by Barry and a team of researchers at Monash University tested riders in a series of hand and body positions as they pedalled against a constant 45 kph wind, chosen to simulate the race speeds in elite road races and triathlons.

The highest drag position was the classic upright riding position with your hands on the hoods, which required 430 watts to overcome air resistance. 

Lowering into the drops with straight arms saved a bit of energy, requiring 417 watts. 

Going even lower in the drops by bending the elbows and hunkering down saved more energy still, requiring only 385 watts.

Best in class

But, the most aerodynamically efficient posture was actually hands on hoods, arms bent with forearms parallel to the ground

In that position, the rider needed to produce 372 watts - a 13.4 percent reduction from the first hands-on-hoods posture.

For a rider churning out 300 watts on a 40K time trial course, that simple adjustment of posture (bending the elbows and lowering the torso) could shave off nearly three minutes from start to finish.

As it turns out, there is such a thing as too aero...

Research shows that altering your position on the bike also affects your breathing and power production.

In one study, 19 trained cyclists performed a series of power tests, starting at a 24-degree torso angle and dropping incrementally to zero (or as close as possible; not everyone could get that low).

Every performance parameter tested, including efficiency, heart rate, cadence, V02 max, and peak power output worsened as the torso angle dropped. Power output fell 14 percent - around 51 watts - from the highest position to the lowest. Of course, the cyclists’ frontal area was also reduced (by up to 14 percent), as they got lower, so they would be more aero in real-world conditions.

However, the researchers concluded the lowest position hindered performance so much that even trained competitive cyclists should avoid it. For the other positions, it’s a trade-off between how many watts you lose to impaired performance versus how many you gain in aerodynamic advantage.

So, there you have it, the argument for increasing the aerodynamic efficiency on the bike.  

However we will add, this is all the science, it does not take into account the safety aspects of the UCI’s decision - and of course, we applaud the UCI for continuing their efforts for a safer sport.

Avenir Cycling specialises in the design and production of high-performance Road & Track cycling apparel.

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