Gallery: New Two-Wheeled Professional Tool Slices Through Air
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Just days before the start of the 2011 Tour de France, bike manufacturer Cervélo has announced its newest model, the S5. Though aggressively aerodynamic, the carbon-fiber S5 is not a triathlon bike. It’s made for road racing, and it will be under the riders of team Garmin-Cervelo when they line up on July 2 at Passage du Gois for the start of the three-week, 2,132-mile race. Wired was the first media outlet of any kind to get a look at the S5, let alone ride it, which we did this spring. Our access included behind-the-scenes time with Cervélo engineers in the wind tunnel at the University of Washington and our exclusive test ride in Marin County, California, just north of San Francisco. Following are our photos from the wind tunnel sessions, along with shots and impressions from our test ride. __Above:__ A prototype of Cervelo's new aero-road bike frame, the S5, at the Kirsten Wind Tunnel on the campus of the University of Washington in Seattle. Engineers at the wind tunnel compared the S5 with older Cervelo designs and with competitor's bicycles. *Photo: Mike Kane/Wired.com*
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The S5 is an aero-road bike. That category has exploded in popularity over the past few years, with manufacturers like Cervélo, Scott and Specialized all pushing bikes that match the stable handling of traditional bikes with the swoopy tube shapes of triathlon bikes. Once they’re up to speed and moving in a straight line, tri bikes are considerably faster than road bikes. But the aggressive positioning and other factors of tri designs make those bikes far too unstable for riding in tight packs and on twisty roads like those of professional cycling. Additionally, the narrow, airfoil-like tube shapes of triathlon bikes can be notoriously flexy from side to side. That bending absorbs energy from the rider’s pedaling efforts—energy that would otherwise be going to the back wheel. This is less important when holding steady speeds on flat roads, but for climbing and sprinting, which is what road racing is all about, such lateral flex is unacceptable. So the task for Cervélo, and anyone making an aero-road bike, is to find a way to cheat the wind while creating a frame that’s stiff and light enough to be raced at the top levels of the sport. __Above:__ Robert Pike, a mechanical design engineer with Vroomen.White.Design, readies a Cervelo S2 for testing at the Wind Tunnel. *Photo: Mike Kane/Wired.com*
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Cervélo engineers had two design phases to go through before they even got to the wind tunnel to start testing prototypes. The first was computational fluid dynamics (CFD), in which they used software to test the aerodynamic performance of different shapes and designs. It was in this phase that the bike got its distinctive looks. The second was finite element analysis (FEA), in which the engineers used computers to test material properties to find the best way to layer and orient the carbon cloth for maximum stiffness and minimal weight. After months of back and forth and countless iterations between the CFD and FEA phases, the engineers had prototypes they could begin testing. That began a series of trips from Cervélo’s Toronto headquarters out to Seattle and the Kirsten Wind Tunnel at the University of Washington. __Above:__ Mechanical analyst Ivan Sidorvich records results during aerodynamics testing. *Photo: Mike Kane/Wired.com*
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While wind tunnels for testing automotive and aerospace designs are relatively plentiful, the Kirsten facility is one of the few in the country capable of low-speed testing and, thus, ideal for analyzing bicycle performance. __Above:__ Facilities manager Jake Ross, left, and Cervelo/Vroomen.White.Design co-founder and CEO Phil White, walk through one of the Wind Tunnel propellers. *Photo: Mike Kane/Wired.com*
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One of Cervélo’s star riders is American Dave Zabriskie, who is one of the best time-trial riders in the world, thanks largely to his ability to get into an exceptionally aerodynamic tuck. So Cervélo made a flexible model of his body for the wind tunnel. *Photo: Mike Kane/Wired.com*
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Cervélo’s three-year-old S3 has been the benchmark for aero-road designs, literally; marketing literature from rival manufacturers often boasts about how close their bikes’ aero numbers are to the S3. __Above:__ Mechanical engineers Damon Rinard, left, and Robert Pike, both with Vroomen.White.Design, ready the prototype for testing. *Photo: Mike Kane/Wired.com*
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About those numbers: A rider pedaling an S3 at 25 miles per hour would need to produce around 20 fewer watts (approximately 270 vs 250) to hold that speed than a similar-sized rider on a standard frame. Cervélo claims that its wind-tunnel tests showed that the S5 saves an additional nine watts at the same speed, which means that rider on the standard road bike would have to work more than 10 percent harder just to go at the same speed as someone on an S5. *Photo: Mike Kane/Wired.com*
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Mechanical engineer Damon Rinard, one of the main architects of the S5, says one of the bike’s key innovations is the way the tubes come together at the fork. Here, the frame actually has two walls, an external one and an internal one. Between the CFD and FEA phases, Rinard and his team found that the ideal aerodynamic shapes couldn’t handle the physical stresses of riding. So they created a second internal wall—something very difficult to pull off in a carbon mold—to handle the loads, leaving the outer skin to cheat the wind. Additionally, the brake and shifter cables all enter the frame directly behind the handlebar stem, to stay out of the wind. “Cables really screw up aerodynamics a lot more than people realize,” says Rinard. “They’re small, but they’re not at all aerodynamic. And when you’ve got them sitting out in front of the bike, they create this parasitic drag and also mess up the airflow before it even gets to the frame.” *Photo: Jon Snyder/Wired.com*
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In an ideal world, all the tubes would be as narrow as possible to slice through the wind. But in the real world, cyclists ride with water bottles, which drastically disrupt airflow—adding about 50 grams of drag on a typical bike. So the downtube on the S5 flares out at the bottom to direct the wind around the bottle and saving about 14 grams of drag. The bottom bracket—the frame junction where the cranks mount on the bike—is strikingly fat and asymmetrical on the S5. Where a standard bottom bracket is 68mm wide, the S5’s is 79mm wide. The extra 11mm all come on the left side, where the frame extends out to cover the crank bearings. This creates a wider and, therefore, stiffer pedaling platform and also shrouds the bearings from the wind. But because the design merely covers the bearings, rather than move them, it doesn’t change the position of the cranks. Why not do the same on the right side? Because the chainrings and other drivetrain components won’t allow for it. *Photo: Jon Snyder/Wired.com*
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The S5’s seat stays—the two frame sections that extend up from the rear wheel to underneath the saddle—are designed to direct the wind out and around the rear brake, for a further aero boost. Additionally, the stays bow out at the top to provide a bit of vertical flex. This mutes vibrations for a more comfortable ride. *Photo: Jon Snyder/Wired.com*
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Also key to the S5’s aero performance is the way the seat tube wraps around the rear wheel to keep it out of the wind. Rinard says Cervélo went through numerous permutations of this design before finding one that covered as much wheel as possible without compromising fit or performance. “When you set out to make a new bike,” says Rinard, “you fix the rider position and you fix the components in your CAD drawing, then you have to find the best way to connect the dots.” *Photo: Jon Snyder/Wired.com*
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It would take more than one three-hour ride to get a complete understanding of any bike, but we got a pretty good sense of what it can do (haul ass). It was startling to see just how stiff the S5 really is. We stood up on the pedals and accelerated on pitches exceeding 15 percent (steep enough that even walking is a struggle) and saw no appreciable flex. The handling also seemed to be dialed. Aero designs can be a little loose in the front end. But we took the S5 down a long, twisting decent that required frequent braking through dangerously tight turns and always ended up exactly where we wanted to go—and this despite a road surface that was more obstacle course than pavement. But it’s in the flats that the S5 really springs to life. It’s stiff and light—just over 15 lbs for our complete test bike—which means it accelerates with the best of them. And once it’s up to speed, it stays there. There’s a sensation almost of the bike moving out ahead of you. Again, we would need a lot more than just the one ride to give a full review. But our first impression is that this is one of the fastest road bikes around. The S5 will actually be in bike shops on Friday, July 1, so eager buyers will actually be able to get on one even before the start of the Tour de France. Be prepared to pay, though. Complete bikes will start at $3800, but pro-level models will approach $10,000. *Photo: Jon Snyder/Wired.com*
