ARE AERO ROAD BIKES ALWAYS FASTER?
They look divine and are mooted to save watts, boost speed and generally make you a happier human being. But do those aero-roadster claims stack up? And do they provide the versatility a recreational rider needs? Cycling Plus investigates…
Believe the advertising and aero road bikes are the greatest invention since the wheel. The bike industry, however, is just that – an industry. And an industry doesn’t thrive if it’s standing still. Where once weight, or lack of it, ruled, now it’s all about curvaceous carbon and concealed cables. But do they always deliver a faster, watt-saving ride compared to traditional lightweight roadsters? Good question…
CHARACTERISTICS OF SPEED
The performance road-bike market branches o but, in general, it’s divided into two camps: lightweights and aeros. Trek and Specialized have their ultralight Emonda and aero Madone; Giant its TCR and Propel; Specialized its Tarmac and Venge – you get the picture.
Historically, lightweights featured round tubes to aid power transfer and save grams. They don’t strictly adhere to that template now but aero roadbike tubing remains wider. Other aero features include integrated cockpit, hidden cables and concealed brakes (albeit many have now moved to disc brakes). Geometry tends to be more aggressive, too. On paper they look fast. And they perform fast in the lab, too, according to the co-founder of aero wheel builder Swiss Side, Jean-Paul Ballard.
“In 95 per cent of cycling situations, aero road bikes are faster,” explains Ballard. “Aerodynamic drag is the major resistance and consumes around 69 per cent of the power applied to the pedals. Reducing aerodynamic drag has by far the greatest impact on increasing speed.”
Swiss Side might be new to you but they’re not new to slipstreaming. Ballard spent 14 years working in Formula One including as head of concept design at Sauber. He moved into cycling in 2014 and, thanks to Swiss Side’s successful Hadron deep-rim wheel, has rivalled the likes of Enve in a cyclist’s wishlist.
Ballard’s unequivocal assessment comes from hours in the wind tunnel and field testing. Computer modelling’s also key to product development.
As it is to one of the world’s largest cycling manufacturers, Merida. When Merida launched the second iteration of its Reacto aero road bike in 2017, it hammered home the aero credentials by emphasising the importance of weight.
The team revealed that they’d modelled the 21 stages, 56 categorised climbs and 3529km of the previous year’s Tour de France parcours and concluded that not one stage would the likes of Louis Meintjes and Rui Costa of Lampre-Merida have ridden faster on the lightweight Scultura compared to the Reacto.
IT’ S ALL ABOUT THE AIR FOIL
At the heart of this time-saving is the ability of those widened tubes to shrug
“A E ROD Y N A MIC DR A G IS THE MAJOR RESIS TANCE AND CONSUMES AROUND 69 PER CENT OF THE POWER APPLIED TO THE PEDALS” JEAN!PAUL BALLARD " CO!FOUNDER OF SWISS SIDE
o! drag. “Drag is primarily down to two factors,” explains Rob Lewis of CFD (computational fluid dynamics) specialists TotalSim. “One is skin drag, which is the friction of the air rubbing over the surface. The other is pressure drag. That’s more di"cult to explain but, essentially, is why a brick has more drag than the same-sized object but in a more streamlined shape.”
A blunt object disturbs the air flowing around it, forcing the air to separate from the object’s surface. Low-pressure regions from behind the object result in a pressure drag against the object. With high pressure in the front and low pressure behind, the cyclist is being pulled backwards. Rounder tubing’s an aerodynamic tyrant in this respect, chopping up air. Aerodynamic tubing is not.
“And that’s been shown by research all the way back to the 1950s,” adds Lewis. “Professor Ascher Shapiro [one-time professor of mechanical engineering at Massachusetts Institute of Technology] showed that airflow is far more turbulent passing over round objects compared to a smooth airfoil, which is essentially a tapered tube.”
It’s been calculated that the drag of a cylinder is 20 times more than a teardrop shape (highlighting why cable routing’s more than a marginal gain); in other words, you could have a cylinder that’s 10mm wide and it’ll create the same drag as an airfoil shape that’s 200mm wide. Essentially, that teardrop shape keeps what’s termed a laminar boundary attached to its surface longer than a cylindrical tube, whose round shape creates drag-inducing mini vortices.
It’s why aeroplane wings are the shape they are; that said, looking out of EasyJet’s finest, you’ll see a teardrop ratio far greater than aero tubing. “That’s down to the UCI’s tubing rules,” explains Cervélo co-founder and now aerodynamic consultant Phil White. “Historically, it was a 3:1 ratio – namely, the depth of tube couldn’t eclipse more than three times its width – but the UCI has relaxed these regulations recently.”
VIRTUALSLIPSTREAMING
Marginally relaxed. Now the rules state: ‘The maximum height of the elements shall be 8cm and the minimum thickness 2.5cm’. That equates to a ratio of 3.2:1. Arguably, that princess-and-pea change won’t radically shake up design. It might not matter. For years, canny manufacturers have overcome this limiter by creating a phantom slipstream.
“We were the first to utilise Kammtail technology,” says Trek engineer Doug Cusack, who introduced this aerodynamic phenomenon to their Speed Concept range in 2010 and continues to apply it to the 2019 Madone collection. Simply put, the American giants used 5:1 airfoil tubing, before slicing o! the end to create an actual 3:1 shape… but the airflow purportedly still reacts as it would with the 5:1 tubing.
“When air flows over a truncated aerodynamic shape, it fills in the missing tail with a recurring vortex of air that takes the shape of a virtual tail,” continues Cusack. “The virtual tail also changes shape to allow for even more e"cient airflow by allowing the tail to bend to the most e"cient shape as the angle of the wind flow changes. Blunting the end of the tubes also improves handling, especially in crosswinds.”
The physics might be complex. What’s visibly clearer is that innovations like the cutaway seat-tube cradling the rear wheel and a smoother, more integrated cockpit are designed to reduce drag. You don’t see Lewis Hamilton powering his V6 engine around Silverstone in a Mercedes box, for instance. It begs the question: why’s the bike industry developing and heavily marketing aero road bikes now when some of these aero ideas have been around for years? Back to Phil White…
“We actually created the first aero road bike back in 2002 with the Cervelo Soloist, but we couldn’t a!ord to mass produce it in carbon so started in aluminium,” White explains. “We were proud of it but there were legitimate beefs: one, it didn’t handle very well, especially descending; two, it didn’t transmit power very well – it lacked sti!ness. That was despite us adding material on the side to prevent the tubes from flexing. It was called Smartwall technology.”
“PROFESSOR ASCHER SHAPIRO SHOWED THAT AIRFLOW IS FAR MORE TURBULENT PASSING OVER ROUND OBJECTS COMPARED TO A SMOOTH AIR FOIL” ROB LEWIS COMPUTATIONAL FLUID DYNAMICS SPECIALISTS TOTALSIM
Still, the Soloist sold well, meaning the next iteration came in carbon. “Gradually, through changes of geometry, seat stays dimensions and having more control over the carbon lay-up, both handling and sti ness improved.”
EVOLUTION OF AERO
Cervelo’s current aero bike is the S5, complete with oversized frame tubes that purport to be sti er and lighter than ever before, saving 5.5 watts over its previous incarnation – as we discovered from the 32-page technical guide. We are committed. That ‘lighter and sti er’ proclamation’s rolled out by every roadbike manufacturer when it comes to press launch with the wind-tunnel core to both development and marketing.
Specialized has the luxury – and arguably competitive advantage – of designing and refining in their own windtunnel or Win Tunnel. Chris Yu, leader of innovation and engineering at Specialized, tells us that it proved a key tool in the development of the Venge. “We started with a complex and bespoke computer optimisation simulation to create a library of shapes called the FreeFoil Library, which represented an optimum combination of aero performance, sti ness and weight,” explains Yu. “We then used these shapes to create our first prototype frame, which we validated and fine-tuned in the tunnel.”
It might not sound as exciting as riding an aero road bike but scientists are nothing if not precise. And that precision led Specialized to develop the Venge with and without a rider on. And that’s key, says Bert Blocken, aerodynamic expert at Eindhoven University.
“Our research shows that the di erence in drag between time-trial bikes at the 2018 Tour was up to 25 per cent,” Blocken explains. “But that’s without the rider. This drops significantly when the rider is added and changes the flow of air. Although generally the case, the fastest ‘isolated’ bike isn’t always the fastest.”
If you’re about to spend up to ten grand on an aero bike based on claims of X per cent faster than its competition, check where those figures derive from. The wind-tunnel’s important but clearly lacks the dynamic uncontrolled behaviour of the open road. Which is where field testing comes in. Recently, the likes of Leomo and Notio have launched products that measure aerodynamics on the road.
And then there are R&D-only tools like Swiss Side’s pressure rake – a technology adapted from Formula One. What looks like a TV antennae is attached to the rider’s seatpost to measure the pressure drag behind the rider and bike. “In the wind tunnel we can measure the drag force and how it changes with di erent set-ups or positions, but it doesn’t tell us exactly where a change is coming and how the airflow is a ected,” says Ballard. “The rake allows us to measure and visualise the energy lost [the wake] in the airflow behind the bike and rider to better understand the aerodynamic setup. We’ve just finished a two-day session with Team Ineos where the pressure rake measurement system was employed for on-road and wind tunnel measurements.”
“OUR RESEARCH SHOWS THAT THE DIFFERENCE IN DRAG BETWEEN TIME" TRIAL BIKE SAT THE 2018 TOUR WAS UP TO 25 PER CENT” BURT BLOCKEN ! AERODYNAMIC EXPERT, EINDHOVEN UNIVERSITY
AMATEUR BENEFITS
Swiss Side’s innovative tools have confirmed that aero bikes, plus wheels, are quicker both in and out of the tunnel. Which is all very well, but Swiss Side and their contemporaries heavily test with professionals or top-end recreational riders who commonly average between 25-28mph on the flat. That can be double what a sportive rider might generate.
“Even at much lower speeds, aero drag is the biggest resistance that a rider must overcome,” says Specialized’s Yu. “While the power savings may be smaller for a rider at lower speeds, the amount of time saved over a distance is similar because they’re riding longer.” So, if an aero bike’s only saving you five watts compared to 15 watts for a professional, you’ll still enjoy a significant benefit as you could be riding for 10 hours instead of three.
Yaw angle (wind angle) also plays a part. The faster you ride, the lower the range of yaw angles you experience. So while Peter Sagan might slice through a yaw angle of 3-7 degrees, recreational riders are more like 10-12 degrees. Manufacturers will design their aero-bike tubing to maximise speed at this figure. It’s why one aero-bike shape di ers to the other. Specialized designed the Venge based on its vision of the perfect range of yaw, while Trek designed to a di erent range.
If this is all a touch confusing that’s because aerodynamics is. Unlike weight that’s more tangible. It’s clear that stripping excess reduces mass to move, which really pays o on the hills. It’s why amateur hill climbers, not restricted by the UCI’s 6.8kg minimum weight, strip bar tape, remove outside chainrings and even drill holes in the frame to shed weight. Jack Pullar’s 2012 national hill championship triumph, for instance, came aboard a bike that weighed 5.5kg. Still, that lightness hinders on the descent – and we’d certainly not recommend drilling your bike! So where does that leave a more practical, everyday lightweight bike in its battle against aero?
“The point where weight becomes as important as aerodynamic drag only occurs in an uphill time-trial scenario,” says Ballard. “And that’s when the average gradient for the entire course is greater than 4.5 per cent for recreational cyclists or 7.5 per cent for a pro.”
Unless you reside in the Alps those situations are rare. So where are we? The evolution of material technology plus the explosion in analysis and data means aero road bikes are arguably faster for all levels of cyclist. Where once the weight di erence between a lightweight and aero bike was significant, now it’s marginal. (As an example, Orbea’s Orca Aero M10 Team is only 300g heavier than their lightest frame.) Then again, cycling’s more than just numbers and science. Save 20 watts on the flat, cut a few seconds and you’ll feel the same. Shave o a kilogram or two and you’ll feel a million dollars. The conclusion? Convince your better half that two’s always better than one…
“THE POINT WHERE WEIGHT BECOMES AS IMPORTANT AS AERODYNAMIC DRAG ONLY OCCURS IN AN UP HILL TIME! TRIAL SCENARIO” JEAN- PAUL BALLARD " CO -FOUNDER OF SWISS SIDE