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Tour de France tech: Carlos Sastre’s Cervélo R5

  • By Zack Vestal
  • Published Jul. 15, 2010
  • Updated Jan. 28, 2011 at 5:13 PM EDT

Sastre's Cervelo R5, ready to go

Carlos Sastre still has a chance for a stage win when the Tour turns southwest and heads for the Pyrenees next week. His Cervélo R5 is ready to meet the challenge.

A few weeks ago, before the Tour began in Rotterdam, we stopped at the Cervélo TestTeam hotel and talked to engineer Damon Rinard about Sastre’s bike. His new R5 frame is lighter than the R3sl that he’s raced up to now. When we saw the bike, Sastre was still carefully transitioning from his old steed to the new one, ensuring that the position was perfect. But in the high mountains, he’s certain to appreciate the light weight and added stiffness of the new frame.

Rinard described the process of designing the bike. “What we’ve done as engineers is automated what a good engineer would do anyway, which is to iterate using FEA (finite element analysis),” he said. “So we’ve written a software program called CTOP and we use that inside Vroomen White Design to set parameters and instruct FEA to optimize for stiffness and weight. We get done in a week or two what would normally take two or three years,” said Rinard. Basically the computer program builds a frame virtually and analyzes it for strength and stiffness, over and over and over again until the optimal shapes and material distribution are found.

From all the computer-aided engineering work, Cervélo discovered that bottom bracket width was key to adding rigidity to a lightweight frame. “We found that to really pump up the stiffness to weight ratio of the frame, it would help us if the bottom bracket were a little wider,” said Rinard.

So the designers went to work, adding 11mm to the width of the R5 bottom bracket shell. All the growth in width happens on the non-drive side, so the crankset, drive-side bearing location, and right chainstay are unaffected. “What that gives us in the frame is space to make the down tube wider, seat tube wider, and left chainstay wider,” said Rinard. “All this makes the bottom bracket laterally stiffer. In fact, it makes a bigger improvement with less weight than switching from a normal crank to the BB30 crank.”

The system does in fact use a 30mm bottom bracket spindle, but it’s not technically a BB30 crank because of the extra spindle width on the left. Cervélo calls it BBright (say, “BB right”), and it sort of amalgamates the standards of a wide BB shell (like Trek’s BB90) and the oversized crank spindle of BB30. It uses a SRAM PressFit30 BB on the 79mm shell, and Sastre’s Rotor cranks have an additional 11mm of spindle length.

“The main benefit is that we’ve analyzed the bike as a system,” said Rinard. “We’ve done system analysis on it in order to optimize not just the crank like the crank makers have done, and not just the frame like some of the other wider ones have done, but both, so they work together that way.”

Cervelo's R5 bottom bracket is wider by 11mm.

Other design features are more traditional. For example, Cervélo is sticking with a round, 27.2mm seatpost. “We’ve got plenty of stiffness in the frame. And the seatpost, because it’s not triangulated, is a good source of comfort for the riders,” said Rinard. “A smaller diameter there weighs less, is more aerodynamic, and most of all it’s a little more flexible so the riders can have more comfort. Especially Carlos, that’s the main reason he prefers the R-series bikes.” Many of the Cervélo TestTeam riders, including sprinter Thor Hushovd, favor the aerodynamic S3 frames, but the larger frame tubes and aero seatposts on those bikes render them much more rigid on the road.

In another revision from the R3sl that Sastre rode up to this point, the R5ca uses seatstays that are even smaller than the existing R3 and R3sl. In another nod to rider comfort, they’re about 10 percent smaller for additional vibration attenuation.

The fork is a new Cervélo design with less depth in the fork blades. The blades offer a little more flex front to back and thus more comfort, but their thickness laterally is increased to maintain torsional stiffness. The steerer tube is conical, with an oversized 1- 3/8th-inch lower bearing. “The (fork steerers with) 1.5-inch lower bearings are quite rigid, almost so rigid the fork has to be made stronger because it’s brittle,” said Rinard. “It’s too high stiffness that doesn’t absorb enough energy. To reduce the stiffness just enough, we went down to inch and three-eighths so now the fork’s just flexible enough to absorb the energy throughout the fork and it doesn’t need to have that extra material to be super, super strong, but it still makes it more rigid,” said Rinard. “So we found the sweet spot.”

Cable stops on the R5 are co-molded carbon fiber.

Details on the Cervélo extend to the carefully radiused bottom bracket cable guide. Vroomen White Designs actually built a device to measure cable friction and thus built a specific BB cable guide to have minimum friction for the most accurate shifting possible. Rinard said that the lab measured and quantified cable friction, then went about reducing it. In the classic analytical approach of an engineer, Rinard said, “When you put a number on it, argument stops.”

It’s the numbers- and performance-based approach adopted by the entire TestTeam, and with any luck, they’ll capitalize in Paris with Hushovd in the green jersey and a high placing or stage win for former yellow jersey wearer Sastre.

Click here for Complete Video Coverage of 2010 Tour

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