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Flash: Cannondale’s 16.6-pound cross-country bike

By Robbie Stout

Cannondale Flash: Without pedals, the bike weighs 16.5 pounds.

Cannondale Flash: Without pedals, the bike weighs 16.5 pounds.

Photo: Robbie Stout

On the last day of the 2010 Cannondale release in Park City, Utah, the research and development team were excited to unveil a new high-end hardtail cross country bike.

The age-old weight gap between mountain and road bikes is now becoming smaller. Of course getting weight down is always a major goal for bike manufacturers, but with the strength and specific performance depends of cross-country racing, ideal weight and actual never seem to finish together.

For the Cannondale research and development team, the last 18 months have been highlighted by the development of the Flash Carbon, a super lightweight cross country race bike. This new rendition of the F-Series, Cannondale’s previous hardtail line, weighs just 16.6 pounds in the medium size, without pedals. The frame weighs 950 grams. The Flash Carbon has made momentous leaps forward in carbon fiber optimization, system integration, and comes at a time when mountain bike components are better than ever.

Cannondale Flash: A complete Flash Carbon is hanging under this scale.

Cannondale Flash: A complete Flash Carbon is hanging under this scale.

Photo: Robbie Stout

The Flash Carbon was co-developed with former Scott bicycles engineer and carbon technologies guru Peter Denk. After a decade of partnership, Denk and Scott Sports parted ways in October of 2008. Together, Cannondale and Denk have created what they are calling the lightest hardtail, ever.

When it comes to frame building, most engineers focus on three attributes: stiffness, strength, and weight. For the Flash Carbon, Cannondale vice president of research and development Chris Peck says that they have added a fourth attribute, and that is vertical compliance. The Flash Carbon is technically a hardtail, as there are no rear suspension pivots or suspension chamber, but through integrating S.A.V.E (synapse active vibration elimination) technology into the bike’s chainstays and seatpost, the rear triangle is said to feel pretty soft.

Stiffness, Strength, and Weight

Cannondale Flash: Notice the generous tire clearance and smooth transition between the top tube and seat stays,

Cannondale Flash: Notice the generous tire clearance and smooth transition between the top tube and seat stays,

Photo: Robbie Stout

Throughout the frame, Cannondale uses a high modulous carbon fiber lay up which they say reduces the weight dramatically yet provides impressive power transfer.

With weight savings in mind, the Flash Carbon uses a direct mount for the front derailleur. The benefits of having a direct mount are that it’s always in perfect alignment, it’s lightweight, and less carbon can be used on the seattube because it doesn’t have to stand up to the forces of a front derailleur clamp. From an engineering standpoint, Peck believes that an ovalized seattube near the bottom bracket is better for stability, but isn’t possible with a front derailleur clamp.

Carbon fibers are said to be strongest when straight. Based on this concept, Cannondale avoid bends in the carbon fiber whenever possible. The toptube and seatstay junction is continuous, creating a smooth transition where they meet. Peck believes that this maximizes carbon fiber’s properties, weighs less, and provides better frame efficiency.

Cannondale Flash:  : Continous carbon fibers run from the toptube through the seatstays.

Cannondale Flash: : Continous carbon fibers run from the toptube through the seatstays.

Photo: Robbie Stout

Some of the carbon technology highlighted by Peck includes a high impact resin and fiber used to protect the frame’s structure from impact. In areas where the frame is drilled, such as the water bottle mounts, Cannondale engineers use a special mesh designed to prevent delamination. This mesh is the alternative to adding carbon layers in the downtube, which would add unwanted weight. When asked if drilling holes for the water bottle cages sacrificed the frame’s integrity, versus rerouting the fibers around the holes, Peck said that drilling holes into straight fibers was better than creating bends. The bottom of the downtube has a lay up that is better for stone-impact protection. Finally, an anti-corrosion mesh is used in areas of the frame that come into contact with other machined parts, such as the seatpost.

Cannondale engineers also found ways to minimize weight in the disc brake mounts, without sacrificing strength. The postmount for the rear disc brake is direct and avoids the addition weight of an adapter. In testing the durability of the rear disc brake mount, Peck said that not only did the Flash Carbon stand up to the standard disc brake load tests, but it also excelled in the testing standards used for tandem disc brakes.

Cannondale Flash: The S.A.V.E. chainstays provide a small amount of flex to provide better ride comfort.

Cannondale Flash: The S.A.V.E. chainstays provide a small amount of flex to provide better ride comfort.

Photo: Robbie Stout

The Flash Carbon uses carbon cable stops all around. As another weight savings method, whenever possible, cables are run internally, without the additional weight of unnecessary cable housing.

Vertical Compliance

The S.A.V.E. chainstays on the Flash Carbon are designed to flex vertically under heavy loads and impacts. In seatpost pull-down lab tests, in which the frame is supported by the headtube and rear dropouts and a 320kg load is applied to the top of the seat tube, Cannondale engineers measured 5mm of deflection.

Cannondale has engineered a new S.A.V.E. seatpost. This 27.2mm seatpost is flattened in its midsection in the same way that the chainstays are flattened, to allow for flex in the vertical plane. In a lab test described by Peck, the Flash Carbon seatpost showed 15mm more deflection than a Thomson alloy post under a 270-pound load at 70mm behind the center of the clamp. The Flash Carbon seattube is compatible with any 27.2mm seatpost.

Putting the Flash Carbon to the test

So what does all this technology mean for the Flash Carbon? Cannondale sent a Flash Carbon frame, which they assured was totally stock, to the German tester Dirk Zedler. Zedler is best known for his rigorous testing for Tour Magazine and is known to manufacturers as a reliable third-party tester for frame integrity.

Cannondale engineers say the Flash Carbon was the highest-scored mountain bike for strength-to-weight that Zedler had ever done. The test procedure goes like this: the frame is held horizontally by the rear dropouts and there is a single support beam under the center of the headtube. A steel bar is then inserted into the headtube and a weight is hung by this bar where the tire patch would normally exist. Measurements are then taken for the flex of the frame. The resulting score was 102 (stiffness to weight). This number is calculated by dividing the force and distance, 97nm/deg by the frame weight in kilograms, 0.95kg.

In the real world, the Flash Carbon has yet be tested for an extended time, but national marathon mountain bike champion Jeremiah Bishop had an initial reaction. “Unbelievable,” he said, ”I was speechless when I first picked it up. It was an amazingly smooth and stable ride for a bike that light.” He went on to say, “It is very maneuverable and is going to be a real treat when the trail goes uphill.” Finally, he said, “I’m looking to ride the Flash Carbon at the national short track championship.”

Cannondale Flash: The 88 needle bearing technology of the Lefty fork provides smooth engagement during heavy braking.

Cannondale Flash: The 88 needle bearing technology of the Lefty fork provides smooth engagement during heavy braking.

Photo: Robbie Stout

Other notes

The Flash Carbon has no rider weight limit and has a lifetime warranty. It uses a BB30 bottom bracket and is shipped built with a Cannondale Hollowgram SL double crankset with SRAM XX chainrings. The wheelwell is large enough to fit up to a 2.35 inch mountain bike tire. The Lefty Speed Carbon SL 110mm fork weighs under three pounds, making what Cannondale calls the lightest hardtail bike in the industry.

The Flash Carbon will be available in a 29er model in December. However, the 29er model will use standard modulus carbon instead of high modulus because it brings it down to a more reasonable price point.

Flash Carbon Component Highlights;

Flash Carbon Ultimate – $9,600 – 16.5 pounds (without pedals)
Lefty Speed Carbon SL 110
DT Swiss XCR 1.2 carbon wheelset
Schwalbe Furious Fred 26 x 2.1 EVO folding
Cannondale Hollowgram SL crank 42/28
SRAM XX groupset
Fi:zi’k Antares Carbon

Flash Carbon 1 – $6,400
Lefty Speed Carbon SL 110
Shimano XTR Lefty wheelset
FSA K-Force Light BB30 crank 44/32/22
Shimano XTR shifters and derailleurs
Shimano XTR disc brakes

Flash Carbon 2 – $3,750
Lefty Speed Carbon with DLR 110
DT Swiss XCR 1.5 wheelset
FSA V-Drive BB30 crank 44/32/22
SRAM X-7 shifters, X-9 rear derailleur
Avid Elixir R disc brakes

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