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Triathlete senior editor Aaron Hersh reviews the brand new Kestrel 4000 Pro SL-Ultegra, which retails for $4,000.
The Kestrel Airfoil has been the brand’s marquee bike for well over a decade and every version of it has shared one key feature—no seat tube. This unique characteristic reduced the Airfoil’s aerodynamic drag and allowed the bike to absorb road vibration instead of sending it up to the rider. At first glance, the Kestrel 4000 looks a lot like an Airfoil with a seat tube, but it is built around an entirely different design philosophy and its ride experience—not to mention aerodynamic characteristics—reflects the next step in Kestrel’s evolution.
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The biggest consequence of Kestrel’s decision to build its newest flagship bike with a seat tube is increased stiffness in all directions. The Airfoil doesn’t bob incessantly like a beam bike, but it has significantly more lateral and vertical give than traditional bikes. The 4000’s thin, arching seat tube bolsters the frame enough to drastically increase its responsiveness compared to an Airfoil but still preserves some of that silky ride feeling. There are stiffer triathlon bikes than the 4000, but there might not be one that is smoother.
The Kestrel 4000 fits a short person much differently than it fits a tall person. The small frames are a good match for riders who prefer an upright position, but the tall bikes are better for riders who need to get low. This trend is more extreme at the smallest and largest sizes. Although this geometric quirk prevents bike fitters from categorizing the 4000 as aggressive or conservative, all sizes are built around sound triathlon-specific geometry. Every 4000 comes with a seat post that creates an effective seat tube angle of 79 degrees or steeper. Just make sure your particular size matches your fit preferences because a small 4000 is appropriate for a rider who requires a more upright position and a large 4000 is best for a rider who prefers a “long and low” position.
Other than the addition of a seat tube, the aerodynamic details on the 4000 form the most significant difference between the Airfoil and Kestrel’s new flagship. The Kestrel 4000 doesn’t have an integrated aerobar attachment system, such as those on the Trek Speed Concept 9 Series and the Scott Plasma Premium, but it has wind tunnel-proven aero features that allow it to bang heads with every other bike in the transition area. The shift housing is routed into the frame in the space behind the stem to shield the housing behind the aerobars. The front brake cable routes straight down the head tube and never strays into clean air. Combine the efficient cable routing with the 4000’s slender downtube, streamlined head tube and narrow seatstays and it’s obvious why Kestrel says, “The 4000 records better drag numbers than the Airfoil at all yaw angles, without a rider.”
The vast majority of tri bikes have a flashy rear derailleur but budget parts everywhere else. Although the rear derailleur is perhaps the most noticed component on a bike, it minimally impacts a bike’s functionality. The 4000 Pro SL-Ultegra is not equipped with a cheap mix of components masquerading as high end; it is a true Shimano Ultegra component kit and it executes crisp front and rear shifts because of high-quality parts—such as the Ultegra crank and cassette—that often go unnoticed.
The 4000 Pro SL-Ultegra faces very stiff competition at the $4,000 price point, such as the Cervelo P3, Felt B12 and Scott Plasma 20. All three of these bikes have been proven to be aerodynamically efficient, although certainly not identical, and are spec’d with excellent components, similar to the 4000 Pro SL-Ultegra. The Kestrel rides smoother than the P3 and B12 and is a worthy competitor for these other outstanding bikes, although it rings the register a few hundred dollars higher than the three incumbents.