The Cervelo P5X: Three Years in the Making Part 2

What went into developing the ultimate triathlon bike? In the second of four excerpts from Intervals magazine, Lead Designer, David Killing recalls how the P5X frame took shape around the needs of every athlete


Athletes don’t want to tape nutrition to their bikes, sacrifice aerodynamics for hydration, or jam flat kits under their saddles. It’s just that there have been no other options — until now.

Our field research revealed that most riders have two or three water bottles on board, and that it’s important for them to easily swap out round bottles at aid stations. We also learned that the average age-grouper carries more than 1,600 calories of fuel — gels, bars, chews and so on — during an Ironman bike leg. At the same time, it became clear to us that athletes are setting up their rides their way. The most common configuration we identified was a bento bag behind the stem, a bag behind the saddle, a round bottle on the downtube and an aero bottle between the arms. How many riders used this setup? Just 3.8 per cent! Stunningly few. Clearly, a bike with three accessible round-bottle positions, and plenty of customizable modular storage, would make athletes very happy indeed.

This conclusion called for a battery of new tests. In one memorable and useful case, we filled in the centre of a P5 with a flat mounting surface, and by moving two halves of a bottle around on the surface we were able to come up with a design domain for bottle placement that wouldn’t interfere with an athlete’s legs. We also grafted a 3D print-out of our in-frame storage onto another P5 to test for vibration, noise and latch reliability. It soon became clear that the stealthy shape of the P5X frame would be influenced as much by bottles and storage as by stiffness, aerodynamics and weight. From structural R&D we already knew we wanted to leave access for a round bottle in the downtube area. This led to three frame concepts:

  1. structure behind the bottle
  2. structure beside the bottle
  3. structure above the bottle

Having the structure of the frame surround the bottle laterally posed a manufacturing challenge, and made the system too wide to accommodate a rider’s legs. We tried some interesting designs where the bottle dropped into the frame vertically like a car’s cupholder, and others where it slid in horizontally like a torpedo. All of these ended up being too wide or featured walls that were too thin to be stiff enough. Putting the main structural seat-tube behind the bottle was a strong contender for the final shape, as it provided easy, familiar bottle access. But we came up with something better: By running the toptube above the bottle, we were able to incorporate the Smartpak into the junction of the toptube and headtube — exactly where athletes want it. This set off a design domino effect: The empty space in front of the rear wheel could then be used for a removable case, providing an alternate horizontal bottle position.

Our industrial designer, Stuart Munro, has several Olympic-distance and Ironman triathlons under his belt, and has seen first-hand how willingly athletes make storage sacrifices. Combining his racing experience with our field observations and athlete feedback, he developed a modular storage system that covers the widest-possible range of race requirements while allowing athletes to make it their own. Take the Speedcase on the downtube: It can be packed with extra clothing and other needs for a long training ride, and then removed for an Ironman 70.3 event. Likewise, the Stealthbox in the downtube provides space for larger items like a tubular tire. Not to mention the Smartpak, which features a removable lid for extra in-frame storage and yielding even more flexibility. Personal? Check. Best? You bet it is!