Cervelo S5 Road Bike - ifixie

Cervelo, the brand arguably responsible for popularizing the modern aero road bike, has pulled back the curtain on a their latest iteration. The S5 will be the weapon of choice for Garmin-Cervelo team riders at the upcoming Tour de France. It’s a faster, stiffer and lighter frame than the S3, says Cervelo. The S3, however, is no slouch as the winner of our Editors' Choice Race Bike award and the platform upon which Thor Hushovd won the 2010 World Championships. The S5 may not win any awards for beauty, but Cervelo thinks it's the world’s fastest frame approved for professional racing.

From the outside, the S5 looks more aerodynamic than the S3, owing particularly the rear-wheels sheltering seat tube cutout and wide seat stays. The overall theme and the key to the S5's improved aerodynamic performance, says Cervelo, was minimizing the number of leading and trailing edges. For example, the S5's downtube was "dropped" so it now tucks behind the fork crown: this turns multiple surfaces – the fork crown and the downtube behind the fork crown – into a single surface and eliminates an area of high turbulence found on other frames, allowing air to slip more efficiently over the frame.

The seat tube cutout has the same goal, routing wind around the seat tube and the tire as a single surface, not two. A seat tube cutout is not a unique feature, lots of Tri and TT bikes have one (and even some other road bikes), but Cervelo improved on the concept. The cutout is optimized for 23mm tires, and the dropouts are vertical (bikes with a large seat tube cutout usually have horizontal dropouts), for no-hassle wheel changes.
According to Cervelo's wind tunnel testing, installing a water bottle on the average road frame adds 5 watts of drag; two bottles add 10 watts. On the S5, Cervelo nests the bottles closely together in an attempt to get the wind to flow more smoothly over the two bottles. That, combined with careful downtube shaping, leads Cervelo to estimate a half-watt saving for each bottle. Still obsessing over water bottle placement, Cervelo added a special feature for professional athletes who often have a follow vehicle and only carry one bottle at a time. For those riders, Cervelo installed an extra set of bottle bosses in a low position on the downtube which it saves 1.4 watts compared to traditional bottle placement.

These aero tricks, along with a shielded rear brake, result in a frame that Cervelo claims saves 9.2 watts compared to the S3, when riding at 25 miles per hour. Measured in time, the S5 is 38.6 seconds faster than an S3 in a 40-kilometer time trial. Compared to the non-aero race bikes that Cervelo tested, the S5 saves up to 32 watts.

(bicycling.com)