Footon-Servetto rider Mathias Braendle was spotted on a brand-new Fuji machine for the opening prologue of this year's Giro d'Italia – only it wasn't a Fuji at all. As it turns out, Braendle was testing a model for Fuji's sister outfit, Kestrel, who acknowledged that it was the latest update of the company's 4000 aero platform.
According to Kestrel brand manager Steven Harad, the 4000 was fully developed – not just tested – in the wind tunnel with the lofty goal of surpassing the aerodynamic performance of Cervélo's P3. And Harad claims the company has well met that goal with the 4000 testing a substantial "20 percent faster".
The most striking feature on the frame is undoubtedly the radically shaped seat tube, which just barely shadows the curve of the rear wheel on the lower half before taking an abrupt bend forward towards the top tube on the teardrop-shaped upper half. In addition, the head tube sports a necked-down center section to reduce frontal area and the non-driveside chain stay is fluted to reportedly direct airflow out and away from the bike. The driveside stay uses a conventional rectangular profile, though, since the fluting was found to be ineffective on account of the chainrings.
Even the front of the BB30-compatible bottom bracket shell – a first for Kestrel – sports a wind-cutting edge and of course, the down tube, fork blades, seat stays, and seatpost all employ aerodynamic profiles.
Kestrel frame designers look to have been careful about the details, too. Sleek center-pull TRP T920 calipers are used front and rear so as not to introduce turbulent housing and brake arms outside of the center plane of the bike, and the rear brake is tucked underneath the bottom bracket where the air is already 'dirty'. According to Harad, the company considered a reverse-mounted front brake at first but found it to actually produce more drag, not less, so it ultimately stuck with a conventional location.
Further back, Kestrel traded in the more common rear-entry horizontal dropouts for sliding vertical drops that still allow for a tight fit between the rear wheel and seat tube but without the usual hassles. Key for pro-level time trial use, the vertical dropouts make for faster wheel changes, too. Plus, the sliding drops maintain proper rear derailleur spacing regardless of wheel position for more consistent shifting – especially important on time trial frames that often have convoluted cable routing.
Speaking of which, the 4000's internal cable routing is fully guided for easy servicing with the housing entering the frame behind the stem to maintain aerodynamically clean frame surfaces. O-ring seals up top are designed to prevent internal corrosion from sweat, energy gels and drinks.
Claimed frame and fork weight is an impressive 1,400g (3.09lb) and Harad says the new 4000 is currently available to the public with complete bike prices ranging from US$4,329-10,829, depending on the build kit
In case you're wondering (as perhaps you should), Harad also confirms that the frame has received explicit UCI approval in spite of its unconventional appearance.
"We submitted our design for approval prior to us doing the final design work," he said. "As you know, the UCI can be tough so we made sure to get approval first!"