Kestrel Airfoil Pro SL review£2,699.00

Standout time trial ride

BikeRadar score3/5

American innovators Kestrel were one of the first companies to build bikes and components from carbon fibre, and one of the first aero triathlon brands too. Now they’re back in the UK after a decade and the Airfoil Pro SL is a standout relaunch ride.

It's a proper hard-kicking, hard-driving race bike that rides as distinctively as it looks. It takes no prisoners in comfort, though, and small-scale manufacturing means you're getting adequate rather than astounding kit.

Ride & handling: Impressively stiff and stable speed machine

The missing seat tube dominates the look of the Airfoil, and it also dominates initial expectations of the ride. We were expecting a pliable and comfortable seated sensation from what looks like a very large carbon leaf spring formed by top tube and seat stays.

We couldn’t have been more wrong though, as the Kestrel feels standout stiff in every direction – including vertical compliance. The plus side of this stiffness is obvious when you squeeze your shoulders against the bars, press on the pedals and feel the chain lock against the road.

There’s no dilution of drive anywhere between you and the tarmac, and on smooth roads it’ll turn whatever wattage you’ve got into serious velocity. Even the big powerful riders in our test team came back impressed with its resistance to their frame-twisting, bottom-bracket-bending charms.

The light, low-rimmed wheels give an added edge to the Kestrel kick out of corners, and with a low complete bike weight (17.37lb/7.88kg), it has a clear advantage over its price rivals on extended climb sections.

There’s no twist or yaw between the top and down tubes through the reinforced head tube coming back down the far side, and tracking is as accurate as you could wish for at all speeds. The Kestrel’s geometry is friendly and helpful whether you’re trickling out of transition or carving sweeping turns in a tuck.

There’s plenty of stability for fishing food out of your back pocket or relaxing into the rhythm of the ride. It handled deep-section wheels okay too when we swapped it onto some to explore its full aero potential.

Kestrel airfoil pro sl: kestrel airfoil pro sl
Kestrel airfoil pro sl: kestrel airfoil pro sl

You can feel that big down tube being shunted about in more squally conditions, though. The sheer stiffness of the frame also starts to fatigue you early, and that will only get worse if you upgrade to deeper aero wheels.

The buzz and chatter saps momentum and the ability to keep a smooth pedal spin over longer, rougher sections so its suitability for longer events definitely depends on the quality of the course.

Frame & equipment: Unique-looking, accurate but harsh chassis, plus reasonable spec

The most obvious mark of individuality on the Kestrel is the complete lack of any sort of seat tube. There’s a short wing cantilevering back off the down tube for the front shifter and a back-sloped section between the super-deep bladed seatstays and the angular seat cluster, but there’s nothing joining that to the bottom bracket.

Despite missing one of the three main tubes the frame isn't particularly light (3.51lb/1,594g). This is mainly because the down tube is vast to compensate, extending above and below the conventional bottom bracket bearings in a rectangular section, before tapering away towards the head tube in a teardrop profile.

The head tube is reinforced top and bottom, and the chainstays are oversized as well. Despite the truncated seat cluster there’s still reasonable room for adjustment of the aero seatpost. The Airfoil comes in six different frame sizes, with the smallest two running 650c wheels to keep things in proportion.

At this price, the Kestrel should score highly in terms of kit, and the carbon fibre Profile cockpit (including carbon brake levers) certainly gets things off to a good start. Shimano Ultegra kit is perfectly functional, if not fantastic for the money. A Wipperman chain avoids the only weak link in the Ultegra system too.

The angular rimmed Mavic Ksyrium Elite wheels flatter overall weight and agility compared to deep-dish sets. The bike is definitely gagging for an aero wheelset to drive home the low drag frame advantage at higher speeds though.

The Kestrel own-brand EMS saddle is comfy, however, and the saddle clamp can be shunted back and forward to change the effective seat angle between time trial and triathlon angles.

Ksyrium elite wheels accelerate fast, but aren’t as aero as deeper section rollers on other bikes here: ksyrium elite wheels accelerate fast, but aren’t as aero as deeper section rollers on other bikes here
Ksyrium elite wheels accelerate fast, but aren’t as aero as deeper section rollers on other bikes here: ksyrium elite wheels accelerate fast, but aren’t as aero as deeper section rollers on other bikes here

Guy Kesteven

Freelance Writer, UK
Guy started filling his brain with cycle stats and steaming up bike shop windows back in 1980. He worked the other side of those windows from '89 while getting a degree in “describing broken things covered in mud" (archaeology). Dug historical holes in the ground through the early '90s, then became a pro bike tester in '97. Guy has ridden thousands of bikes and even more components the world over since then and can remember them all in vivid, haunting detail. Can't remember where the car keys are, though.
  • Age: 45
  • Height: 180cm / 5' 11"
  • Weight: 68kg / 150lb
  • Waist: 76cm / 30in
  • Chest: 91cm / 36in
  • Discipline: Strict sadomasochist
  • Preferred Terrain: Technical off-piste singletrack and twisted back roads. Up, down, along — so long as it's faster than the last time he did it he's happy.
  • Current Bikes: An ever changing herd of test machines from Tri bikes to fat bikes and everything in between.
  • Dream Bike: His Nicolai Helius AM custom tandem
  • Beer of Choice: Theakston's Old Peculier (not Peculiar)
  • Location: Yorkshire, UK

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