REVIEW: Diamondback's First Superbike, the Serios AF

Written by
Michael Nystrom
Diamondback's Serios line of triathlon/TT bikes was released at the 2014 IRONMAN World Championships in Kona, HI. The release was relatively quiet, and almost a year later, the triathlon world has remained largely uninterested. With such a deep history in the road-racing scene, Diamondback has the on-paper credentials to back up an endeavor into the tri scene, and its partnership with HED Cycling and engineer Kevin Quan (designer of the successful Cervelo P3) give this bike even more street cred. But how does Diamondback's superbike stack up? Why is it not more popular? ACTIVE got its hands on one--here's what we discovered.
Aesthetics
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The first thing we noticed about the Serios AF was its aesthetics--namely, its sweeping lines, stocky profile and thick tubing. With its sloping top tube and aero fork, the bike looks fast and distinctly individual. With a Shimano Dura-Ace build and HED Jet 6 and Jet 9 wheels, the Serios AF looks like a triathlon bike we could be seen in public with.
Groupset
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For its first triathlon/TT specific model, Diamondback did things right. The bike is outfitted head-to-toe with an 11-speed Shimano Dura-Ace 9000 groupset. The shifting experience is crisp and snappy, as expected from Shimano's top-shelf offering.
Cassette
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As previously mentioned, an 11-speed Shimano Dura-Ace 9000 cassette (11-25T) and chain comes standard. The bike features a vertical rear dropout, which makes changing wheels easier but eliminates the option to move the wheel closer to the frame seat tube. This is a small aero penalty, but we'll take it for convenience.
Rear Derailleur
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The Serios AF comes outfitted with a Dura-Ace 9000 rear derailleur. Gold standard.
Junction
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The Serios AF has an interesting aerodynamic junction between the seat stays and seat tube worth noting. Whether or not this reduces wheel drag is up for debate.
Kammback Design
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Rounded edges and kammback design give the Serios an aerodynamic advantage. While it is less competitive in headwinds, the Serios holds the advantage at +/- 15 degrees yaw. We found this to be true on the roads, as the bike excelled in crosswinds.
Wheelset and Fork
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The Serios AF is built with HED Jet 9 (rear) and HED Jet 6 (front, shown) wheels. The 25mm wide rims handled flawlessly, and the deep carbon faring (not structural) provided a great aerodynamic advantage. The aluminum braking track meant stopping wasn't an issue. We did, however, wish the ride were stiffer.

The fork features a unidirectional carbon build that is both aerodynamic and stiff. Plus, we think the hard edges look cool.
Head Tube/ Down Tube
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Diamondback approached the Serios frame with a "thinner isn't better" attitude, and this mindset is present in the head tube design. The thick head tube transitions into a thinner down tube to improve aerodynamic efficiency. The "airfoil" allows the bike to become more efficient in the 15- to 20-degree yaw range.
Brakes
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The Serios AF includes Shimano Dura Ace BR-9010 Direct Mount brakes. The rear brake is mounted below the bottom bracket, and the dual pivot design ensures maximum stopping power. Although the brakes aren't as aerodynamic as others on the market, they stop better and are easier to work on. Again, this is a practical aero penalty we'll take for increased peace of mind.
Cockpit
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The Serios AF's cockpit is built around the HED Corsair full aero bar. It features an integrated design, and the Corsair is paired to a standard 31.8 mm stem clamp that is easy to adjust. A faring-like cover conceals the bracket and increases the bike's aerodynamics.

The base bar and extensions are entirely carbon, and the Corsair is HED's lightest offering. Unfortunately, there is no internal cable routing and the owner will need to cut the carbon to adjust the extension length. This makes the bike less accessible to many people, and there's no turning back once the carbon is cut.
Armrests
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The armrests on the HED Corsair cockpit flip up for access to the base bar while climbing. At first we thought this was a novelty, but it was really useful on an incline (especially due to its narrow wing). The armrests are the only adjustable component on the Corsair, allowing the rider to move the pads forward, backward or slightly inward. We found the center position to be most comfortable, but the option was a nice feature.
Hand Placement/Brake Lever
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The HED Corsair includes carbon-integrated brake levers. While the levers were light and aerodynamic, we felt they were almost too thin when putting pressure on them. The grips were the appropriate diameter, but we wished for a slightly longer profile--especially while cornering and braking.
Risers
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To adjust the stack height of the cockpit, remove or add a 10 mm or 15 mm aero headset spacer. While in theory this is a convenient feature, there's a catch: You'll have to cut the carbon steerer tube--similar to the aero bar extensions. That's a risky move, unless you know the fit will be just right.
Saddle
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Due to everyone's personal preferences, most triathlon bikes come with a low-quality saddle that will be immediately replaced. The Serios AF comes stock with a tri-approved ISM Road saddle with Cromo rails, perfect for full distance events. The aero seat post is highly adjustable and allows the rider to sit as far forward (or back) as he/she pleases. We preferred a more aggressive, forward position--especially paired with the long (uncut) aerobar extensions.
Parting Thoughts
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The Serios AF is an interesting bike. We like it. It's awesome. And once dialed-in, it's undeniably fast and looks great--and the top-notch components leave little to upgrade. Why then, has it not captured more of the triathlon market? Fit is an issue with the Serios AF--in order to make any real adjustments, you have to permanently cut carbon components. Unless the owner is 100-percent sure, or has tried a different geometry, this is a risky move. Additionally, this is Diamondback's first triathlon/TT specific bike. While it does sponsor the Optum-Kelly Benefits pro cycling team, it has little reach in the professional triathlon market (aside from Rachel McBride). If you're an experienced triathlete and have access to a test bike (the Serios series is mostly offered online, direct-to-consumer), the Serios AF is a superbike with a great value. Personally, we'd prefer to "downgrade" to the Serios F for a build with a shallower wheelset and Ultegra Di2--but the same fit issues apply.

Serios AF, $8,500
Diamondback.com
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