Inside Triathlon Archives: The Cervélo P4

This story originally appeared in the September/October 2011 issue of Inside Triathlon magazine.

The cycling industry seems to have decided nearly unanimously that integrating components into the frame is the best way to design a triathlon bike. The Cervélo P4, which has a retail price of $6,200, has an integrated rear brake, cable routing system and water bottle, but it lacks an integrated aerobar attachment system, which is found on most bikes of similar price. All of the proprietary aerobar attachment systems on other pro-level tri bikes, with the notable exception of the Trek Speed Concept 9 series, offer less fit adjustment than a stem and steerer tube, thus sacrificing adjustability in favor of the aerodynamic performance gained by streamlining the bike’s front end. Instead of an integrated system, the P4 still uses the traditional stem and steerer tube to attach the aerobar. Cervélo, however, claims to have the evidence that the P4 is aerodynamically equal or superior to its more integrated competition and still maintains the functional simplicity of a traditional front-end design.

Aerodynamics

When the other top tri bike makers started designing bikes with integrated front ends, many people assumed that these machines would outperform bikes with standard forks in the wind tunnel. Cervélo asserts otherwise. To prove the point, the company went into the tunnel with its bike and four others, all with integrated aerobar attachment systems, to demonstrate that the Cervélo still matches or exceeds competitively priced bikes that have been released since the P4.

Cervélo positioned the aerobars with the stack height only millimeters different than the position ridden by pro cyclist Dave Zabriskie for the test. The results favor the P4 and show it to be substantially more aerodynamic at shallow yaw angles than the competition. Cervélo paid for the test, after all.

The test conditions were fair and it was monitored by a neutral observer, but the specific fit dimensions chosen optimize the P4’s performance by placing the aerobar directly on top of the head tube without spacers; having spacers can add aerodynamic drag and degrade handling precision. Although Zabriskie is able to hold this position for time trials lasting less than an hour, many triathletes require a taller aerobar position. The impressive results Cervélo generated from this wind tunnel test certainly demonstrate that the P4 has not been left behind by the newer tri bikes, but the test only demonstrates the aerodynamic performance of a P4 when it is ridden without several centimeters of risers.

The horizontal reach value to the aerobars differs between the bikes tested, so they will fit different riders. All bikes were tested with the “fastest aerobar that fits on every bike,” says senior engineer Damon Rinard. The P4 was spec’d with a 3T Ventus, which isn’t standard but can be installed as an upgrade. Yaw angles between 5 and 15 degrees are common for age-group racers.

Function

The only water bottle mount on the P4 is designed to mount Cervélo’s proprietary aero bottle that closes the gap from the downtube to the seat tube. Cervélo’s bottle is more difficult to reach than a standard round bottle simply because it sits low in the frame. To carry more than the integrated bottle’s 20-ounce capacity, the P4 needs an aftermarket bottle mount and the seat post has integrated openings that firmly mount a few specific rear hydration systems.

Unlike many tri bikes priced more than $5,000, the P4 uses a standard front brake caliper instead of an integrated brake. While a few of these integrated front brakes function smoothly, many lack stopping power and are difficult to adjust. The standard Sram Red front brake is both more user-friendly and powerful than many hidden calipers. The rear brake is shielded within a shell behind the bottom bracket, but it lacks stopping power and is difficult to adjust. The rest of the component kit is top-notch, except the wheels. Cervélo specs the P4 with basic training wheels and leaves the race wheel decision to you.

Fit

The P4 is designed to optimize aerodynamic performance, and its geometry forces the rider into an aggressive “long and low” position, for better or worse. The P4 has a long reach value from the saddle to the aerobars and a short stack value to the top of the head tube. Although the standard stem and steerer tube allow the bars to be jacked high above the frame, doing so greatly impairs both lateral stiffness and cornering precision. If you need a tall stack height to ride comfortably, you’re better off riding a frame with a taller stack height, but if you ride this aggressive style, the P4 might be the perfect match. The 3T Aura aerobars stack the pads higher than many other bars, which takes some of the sting off the P4’s demanding position. The length of the extensions can be lengthened or shortened, but the pads cannot be moved fore/aft more than a centimeter.

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