The fastest aero road bikes
The latest aerodynamic bikes are slipperier than ever
In just a few years aero road bikes have gone from The Next Big Thing to a mainstream bike option. The latest models have been tweaked to be faster than ever, according to the manufacturers, and to alleviate the harsh ride that characterised some early aero bikes.
Aero road bikes essentially draw the aerodynamic features from time trial bikes into a road frame, and balance the demands of weight and stiffness into a package that, on paper, looks to be the ideal all-round choice.
At any decent speed, most of your effort goes into overcoming air resistance, so reducing a bike's drag means you'll go faster, or ride at any given speed with a lower power output. Who doesn't like the sound of that?
Most of your air resistance comes from your body. Wearing non-flappy clothing will help, as will losing weight. But the 20% or so of air resistance from your bike is enough for engineers and designers to focus on making road frames and products more slippery in the air. In the pro peloton aero road bikes have been quickly adopted, where the margins of victory are very slim and there has been a focus on gaining ever smaller performance gains over the years.
Weight, and the lack thereof, used to be the main driving force of frame development. Along with stiffness, these were the two cornerstones of bike design. These days most bikes are light, many well below the UCI’s 6.8kg weight limit (which doesn’t affect non-racers anyway), and come with more stiffness than is sometimes comfortable.
All that has made aerodynamics more important for manufacturers. Specialized has built its own wind tunnel, for example, and most manufacturers are testing in wind tunnels. Nevertheless, aero road bikes haven't converged on a perfect, slippery common shape. Different engineers prioritise different ways of improving aerodynamics but there are shared design trends: skinny, aerofoil-shaped tubes, integrated brakes, and internal cable routing.
Let's take a look at the latest aero offerings.
Long hailed as the fastest aero road bike by people who know a lot about aerodynamics, the Cervelo S5 has received quite a makeover this year. It still looks like an S5 but Cervelo claims to have finessed every tube profile and found significant drag reductions. It’s also increased frame stiffness in the head tube and bottom bracket to improve handling. Another change is the shorter head tube to put the rider in a lower, and more aerodynamic, position. Cervelo has also developed its own aero handlebar which is compatible with a regular stem.
The Noah FAST packs a lot of innovative aero technology, including slotted forks and seat stays, integrated v-brakes and small ridges on the leading edges of the frame surfaces to smooth airflow. It’s still available, but the Belgian company has released the new Noah SL which is lighter than the previous Noah with a 950g claimed frame weight. It still features the innovative F-Splitfork, but there’s no slotted rear stays and the raised ridges have been incorporated into the tube shapes. The integrated brakes are gone, in their place regular caliper brakes in front of the fork and at the seat stay.
Developed in collaboration with Team Sky and Jaguar, the Dogma F8 is the first aero road bike from Pinarello, and it’s just won the 2015 Tour de France, though we reckon Chris Froome could have won on any bike. The F8 uses FlatBack tube profiles, a Kamm Tail sort of shape, with a rounded leading edge and chopped tail. Pinnarello has also lowered the seat tube water bottle cage and it’s further shielded by the down tube. Meanwhile, up front the fork has been derived from the company’s Bollide time trial bike with an aerodynamic shape, and the crown closely nestles into a recess in the down tube.
The second-generation Aeroad CF SLX has been inspired by the work on its futuristic Speedmax time trial bike, with razor sharp aero tube profiles and an optional one-piece handlebar and stem assembly. Much of the company’s focus with the new bike has been in reducing the frontal surface area, so along with the new handlebar there’s a narrower and hour-glass shaped head tube to help reduce drag. Other changes include the new tube profile, a variant of the Trident shape used on the Speedmax, and a seat tube that hugs the curvature of the rear wheel. Unlike some aero road bikes that integrate the brake callipers, Canyon has opted for direct-mount Shimano brakes in the regular positions.
The Venge has had a radical makeover, with an all-new aero frame with the most interesting integrated brakes we’ve ever seen. Manufacturers have been integrating brakes into the frame in an effort to reduce drag, but the Specialized approach, with custom designed brake calipers, is claimed to produce zero drag. Elsewhere, a new aero handlebar and stem provides full internal cable routing, there are almost no visible cables on this bike, a further measure to reduce drag.
The Foil arguably kicked off the whole aero road bike trend, bringing aerodynamic design that was once the preserve of time trial bikes to regular road bikes. This update has been a long time coming but it’s evolution, not revolution that is the news here. Changes to the front-end see the down tube lowered and wrapped around the fork crown, and a smaller rear triangle and new internal seat clamp in the top tube. The rear brake is also positioned underneath the chain stays.
Once an all-round lightweight race bike, the Madone has been given a complete aerodynamic makeover this year. It features a version of the Isospeed decoupler borrowed from the Domane to provide some comfort (aero road bikes have traditionally compromised comfort in the quest for speed) and it’s wrapped up in a frame with Kamm Tail shaped tubes. Like Specialized, Trek has also developed its own brake callipers, and they’re concealed within the fork and seat stays. To keep the cable routing of the centre pull front brake nice and clean, the head tube features flaps that open and close when the fork is turned.
Merida’s Reacto features tube profiles shape in accordance with NACA airfoil principles, and using the popular Kamm tail approach of chopping off the trailing edge, tricking the air into acting as if the trailing edge were there. More than any other bike here, the Reacto looks like a time trail in drag. There’s an aero seat post, internal cable routing and the rear brake is positioned underneath the chain stays. The front brake, meanwhile, is found on the front of the fork.
Not quite aero road bikes
Not strictly an aero road bike as such, but Cannondale has lightly modified its latest SuperSix Evo with new Truncated Aero Profile (TAP) main tubes and lowered the seat tube mounted water bottle to reduce the drag.
In the same vein, Canyon has given its latest Ultimate CF SLX a light touch of aerodynamic influence. It has developed a new D-shaped down tube, seat tube and seatpost, which along with a new internal seat clamp, adds up to a claimed 10% reduction in drag compared to the previous non-aero Ultimate. It doesn’t challenge Canyon’s Aeroad CF SLX for outright slipperiness in the wind tunnel though, but does point to a future where all road bikes might one day be shaped in the wind tunnel.
Launched in 2013, the TimeMachine grew out of the understanding of aerodynamics BMC derived from its TM01 time trial bike project. It uses a truncated wing profile (not unlike a Kamm tail) for the main sections of the frame. To reduce the air turbulence over the frame memebrs BMC puts a smooth groove at the leading edge of forward facing sections, called a Tripwire. This delays flow seperation and keeps the air attached for as long as possible, minimising drag — in essence it's doing the same job as the dimples on a golf ball.
The Propel Advanced SL 3 was Giant's bold entry into the aero road bike fray and gave rise to a whole range of highly-regarded Propel bikes.
Key to the frame is the AeroSystem Shaping technology that is the result of Computational Fluid Dynamics (CFD) research and wind-tunnel tests. Every tube has been carefully shaped, with a teardrop shape in evidence wherever you look. Interestingly, the down tube has been shaped with a water bottle in mind. It’s flattened where the water bottle normally protrudes from the sides of a conventional down tube.
Unlike many aero road bikes, the Alize's tube shapes are surprisingly chunky with nary a teardrop profile in sight. Whereas traditional aero bikes feature aerofoil shaped seat and down tubes that are prone to flex and can perform poorly in cross winds, the tubes on the Alize have been designed to act as a complete package enabling wider, stiffer and lighter tubes to be used.
the lower third of the down tube which features what Neilpryde call an 'Extended Kammtail'. The kamm tail is the latest buzzword in the cycling world. In effect it's an aerofoil with the tail sawn-off, and has been used on cars since the 50s. What Neilpryde have done, however, is extend this concept so that both the down tube and seat tube act as a single kammtail aerofoil enabling them to increase the size of the down tube without damaging aerodynamic performance.
Chris Boardman knows a thing or two about aerodynamics, winning the individual pursuit gold medal at the 1992 Barcelona Olympics and breaking the hour record on three occasions. The AiR in his signature range of road bikes borrows heavily from the stunning AiR TT bike. The frame has a deep section down tube, internal cable routing and a fair amount of melding together at the point where the top, down and head tubes meet. There are flat surfaces on the inner faces of both the fork and rear stays, designed to work with deep section wheels and ensure that airflow smoothed by the wheel isn't disturbed by a more traditional section fork blade.