By Tom Demerly.
Remember the Kestrel 4000? It was the first widely marketed, molded, aerodynamic carbon fiber bike. It was the Bicycling Magazine “Bike of the Year” when introduced in the 1980’s, was ridden by Lance Armstrong, Mark Allen, Greg LeMond and won the Race Across AMerica (RAAM) in 1987 under ultra-distance specialist Michael Secrest. The all-carbon fiber, molded (not bonded) aerodynamic frame used parallel 73 degree head tube and seat tube angles designed for Kestrel Bicycles by frame master builder Tom Kellogg. In every way the original Kestrel 4000 sent shock waves through the bike industry that reverberate to this day. What is the current state of the art in triathlon cycling? It is still the molded carbon fiber aerodynamic frame.
Unfortunately for Kestrel they were missing one thing: The brain of Dan Empfield. Empfield and Ralph Ray were working with frame builders at almost exactly the same time as the Kestrel 4000’s release to build a frame geometry designed “from the aerobars back”. It benefitted triathletes and “biathletes” that were running off the bike. A few seasons after the initial release of the Kestrel 4000 a steep-seat tube angle bike with 650c wheels (de rigueur for triathletes at the time) called the Kestrel KM40 was released using the same construction techniques as the original Kestrel 4000. Kestrel had become the aero brand, one of the very first bike brands triathletes identified with.
Kestrel called upon that heritage with the new Kestrel 4000, a bike similar to the original 4000 in name only. The new Kestrel 4000 is a molded carbon aero bike of an entirely new generation. Of course, the design has completely changed, and the new Kestrel 4000 shed its 650c wheels for 700c’s and retained a steep-ish seat angle bias as a tri-specific design. It has also brought some new lessons from Kestrel’s seat-tubeless design, the Airfoil PRO.
Starting at the front Kestrel begins the new 4000 with a robust and capable fork. A fork performs myriad duties: It steers, maintains stability and absorbs road shock. The fork design on the new Kestrel 4000 is a straight bladed affair that partially integrates into the down tube. The result of the robust fork blades and crown on a full carbon fiber steer tube is a responsive front end. Add to that a 73 degree head angle and this bike has a road bike front end pulling a tri bike rear end. If you are descending off the Col de Vence at Ironman France or on the technical descents in the Maritime Alps of the Monaco 70.3 bike course this is what you want. If you are fighting boredom in the third hour of riding a straight line on the Queen K while arm-wrestling the Mumuku Crosswinds on Highway 19 then this steering is a bit of a handful.
Head tube height on this bike is moderately low with only 20 millimeters of change over five sizes that roll on 700c wheels. The miniscule 47cm version turns a pair of 650c’s and is a great problem solver bike for small athletes who can’t find anything other than a custom geometry order form.
Our primary test pilot for the Kestrel 4000 is TriSports.com Founder Seton Claggett. Claggett is entering the meat of his Ironman “build” phase for a fall Ironman campaign at Ironman Arizona. He is putting in 5-7 hour days on his Kestrel 4000 on brutal training evolutions that combine the largest ascents in the Tucson area. One thing Seton discovered early on about the front end of the Kestrel 4000 is the annoying propensity for the cable routing cover to pop off. The cable routing on this bike is good- it enters the top tube behind the head tube in a manner similar to other brands like Felt, but unlike Felt, the entry to the frame isn’t elegant. It’s a minor but conspicuous nick.
The down tube and top tube are aero-styled and provide gutsy enough performance for Claggett to report solid stiffness under pedal load at the bottom bracket. A valid criticism Seton voiced was a lack of options for carrying bottles: there is one bottle mount on the down tube. Claggett has gone to a Profile Design aerobar mount for his Zipp horizontal bottle cage to carry a second bottle on his aerobars. On very long rides he wears a Camelbak hydration pack.
The bike becomes truly interesting at the seat tube and rear triangle. This area appears to combine design themes from the curved seat tube genre of the Cervelo P3 and the graceful arch of the seat-tubeless Airfoil Pro. A benefit is a very small rear triangle. The small rear triangle assists drivetrain performance by being stiffer and snaps-up the ride quality in the back. A pair of massive seat stays shores up the seat tube area. The seatpost is clamped with a replaceable, albeit proprietary, alloy collar and may require trimming depending on how low you need your saddle. An adjustable saddle clamp sits on top of the seatpost and most triathletes will have this in the forward orientation since the Kestrel 4000 sits at about 76 degree seat angle- not quite a total tri bike but somewhat moderated perhaps in concert with the 73 degree head angle. Seton uses a 30cm Fizik Arione Tri saddle on his Kestrel 4000, an excellent choice since it provides that useful extra 3cm of saddle length (and effective seat tube angle) over a standard 27 cm saddle.
The brakes on the Kestrel 4000 are TRP T-920 Aeros, a center pull brake we’ve seen on other aero bike applications. It works fairly well with careful initial setup. The brake can be fussy about adjustments if you aren’t familiar with it, but becomes easy to work with after practice.
At the back of the bike a pair of replaceable alloy dropouts bolt to the frame but restrict quick removal of the rear wheel with an Ultegra derailleur and a full-sized quick release skewer. This necessitated the removal of the skewer end on the drive side to get the rear wheel off. I tried a smaller Zipp quick release skewer and it was better but still not easy to remove from the rear triangle. It simply takes a little extra work to remove and replace the rear wheel on this bike. That could have implications if you flatted during a race.
Considering the influence and legacy of the original Kestrel 4000 from the 1980’s this new version of the Kestrel 4000 is a worthy tribute if not a similarly ground-breaking successor. It does provide a viable other option in Kestrel’s livery of unique and credible designs. Considering a few interesting fit characteristics this remains a relevant bike in the sport.