Expected to arrive in the UK by the end of 2011 ( just in time for the next Big Freeze, then), Cervelo’s new S5 represents the Canadian firm’s next step in the development of the “aerodynamic” road bike. Which is to say the road bike designed to optimise aero efficiency rather than to cut weight to the minimum, the distinctive teardrop shape of aero tubing generally requiring more material and hence adding more weight than the roundish tubes of a conventional machine.
But, as Cervelo says; “Aero is always on.” Whatever aero advantage a bicycle may offer over its competitors is there to be enjoyed whenever air drag is a performance-affecting factor. For sure, “always” is pushing it a bit; there’s not much advantage to be had on a steep climb… That said, the S5 weighs an impressive 990g for size 54cm frame, shaving 80g from its predecessor, the S3, which Cervelo previously claimed was the lightest aero frame in the world.
So the S5 is light; it is also, according to Cervelo’s figures, very fast through the air. Essentially it takes features developed on the company’s triathlon and time trial bikes and applies them to road geometry. So, it features a “dropped” down tube, which sits closer to the front tyre and fills the gap behind the fork crown, which normally collects turbulent air. The new shape also reduces air pressure on the underside of the tube.
The back of the downtube is reshaped to improve airflow when riding with one or more bottles and, along with the seat tube, provides a total of three cage mounting positions. The lower of the downtube placements is used when one cage only is fitted, placing the bottle close to the seat tube to keep airflow clean. With a cage fitted to the seat tube, the upper of the two downtube options is used to put both bottles in line with airflow for minimal frontal area.
Seat stays shaped to shield the brake caliper reduce the aerodynamic drag of that component, while the rear wheel sits within what Cervelo calls a Extended Seat Tube Cutout, which more or less envelopes the circumference of the rear tyre from bottom bracket to beyond the seat stays, smoothing airflow on to the rear wheel.
The S5 also features a BBright bottom bracket shell, which adds support to the left-hand bracket bearing and massively increases axle stiffness compared to a standard bracket with oversized external bearings.
All in all, it adds up to a cycle that, compared to the old S3, will save a constant 9W at 25mph and shortend a 60 mile training ride by up to one and a half minutes. Expected savings could be much greater compared to a non-aero road bike.
OK, so the S5 is not the prettiest thing ever to leave the Cervelo design studio but, if it is as effective as claimed, how many owners will worry?
Cervelo S5 frame and fork £2499.99; sizes 48 – 58cm in 2cm increments, 61cm
