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Leftside-drive bike could give Team USA winning edge

The U.S. Olympic team and Felt unveil a radical new pursuit bike with left-side drive and aerodynamic features to address yaw.

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Sarah Hammer and the world champion U.S. women’s team pursuit squad head to the Rio Olympics knowing anything less than gold will be a disappointment. If they do win it, they’ll do so on a bike unlike any other in Olympic history — a radical design with a lefthand drivetrain and asymmetrical frame geared toward the specific aerodynamic conditions of track racing.

Tentatively dubbed the TA/FRD (Track Aero/Felt Racing Development), the pursuit-specific bike has been in development for years. It features an ultra-narrow frame and Hed wheels specially designed to work within those spacing constraints. But most jarring of all is the fact that the drivetrain was moved to the lefthand side of the bike to account for the yaw angles riders encounter in the velodrome. Felt’s designers also claim that this helps with handling, since it moves weight inboard of the turns.

“We started the initial discussions in 2012 after [the] London [Olympics],” says Jim Miller, Vice President of Athletics at USA Cycling. “ I was sitting with the marketing director of Felt Bicycles, and we were talking about what’s next, and I said, ‘we need to figure out how to go one step higher.’”

Felt’s first step was to reassess the way bicycles behave on tracks, which led the company away from some longstanding notions that had dictated track bike design.“The thought process had been, on the track, you don’t really have any wind at yaw,” Miller says. “One of the engineers at Felt who races track, Anton Petrov, wasn’t convinced of that.

So Petrov and team measured airflow on bikes going around the track and found that riders do indeed encounter winds at yaw. “It became fairly obvious that, through the turns and when you exit at one and two, you’re actually at some yaw,” Miller says. “About halfway down the straightaway, you’re at some degree of yaw again.”

What the researchers discovered was that, due to the curves of the velodrome walls and the motion of the riders going past them, wind is a factor on even closed tracks. After repeated tests, Felt’s engineers determined that riders experience winds at 2.5 to 5 degrees of yaw for up to 80 percent of the track’s length. So they set about designing a bike specifically for that.

The TA/FRD doesn’t have the lateral stiffness required for mass starts or sprint finishes; it’s just stiff enough to get the riders going. That allows the carbon frame to be lighter and narrower. Where track bikes typically have 100-millimeter spacing up front and 120 millimeters in the rear (this can vary), Felt’s new bike boasts dimensions of just 70 and 95 millimeters, respectively. “Consequently, the wheels are narrower,” Miller says. “The rear wheel is more of a lenticular disc, but much flatter. So when it fits in the frame, it fits really tight around the fork, and the rear stays are really tight around the wheel. If you were to try to put another wheel in there, it wouldn’t even go in the frame.”

Each airfoil frame section is also designed around those yaw numbers of 2.5 to 5 degrees. The frame is asymmetrical in order to address the wind coming from the left side of the bicycle, and the drivetrain is on the left side of the bike because the drive-side crank arm tends to be more aerodynamic than the non-drive arm. Felt is using an FSA Vision time trial crank on the FA/FRD. “We spent a lot of time in wind tunnels,” Miller says, “and any time you’re testing bikes and you spin the bike at yaw, and when the wind’s hitting the crank, there’s always lower drag on that side than if you spin it to the non-drive side. It’s been pretty consistent that the non-drive side is less aerodynamic. If we know the wind’s coming from the left side, why not take advantage of the aerodynamics of the chainring to reduce the drag?”

The mock-up of each tube was 3D-printed in-house at Felt after engineers drew the initial shapes they thought would work to address the yaw issues. The tubes were then assembled and the 3D-printed mock-up was taken to the wind tunnel for testing. After testing and tweaking, carbon molds were built off the final 3D-printed model.

The finished product is radical for yet another reason. It’s a sport-altering design that was built 100 percent from the ground up for female racers — with the women’s team getting unprecedented financial and technical support. If male pursuit riders ever end up on bikes like this, they’ll be following the women’s lead.

“It was always about women’s team pursuit,” Miller says.