A detailed look at Cannondale’s SuperSix Evo
TORINO, Italy (VN) — Yesterday I promised that I would tell you why I think Peter Denk’s latest creation, the new Cannondale SuperSix Evo, is unique. After two rides on it through the lush green hills surrounding Torino and after much discussion with its designers, I can now tell you in considerable detail. I should add that it rides great, and I could fully appreciate that, given the existence of a real 63cm size.
As I said yesterday, Denk saw his mission, once moving from Scott to Cannondale, was to, “first make the best hardtail, then the best full suspension, and then the best road bike.” The SuperSix Evo follows the successful introduction last summer of the Flash Carbon hardtail and the Jekyll (and Scarlet and Claymore) “overmountain” full suspension bikes.
“It’s subject to interpretation,” says Denk, “but I think we did it.”
SuperSix Evo frames are made primarily of the same “BallisTec” carbon as the Jekyll and Flash. The fabric is made in Japan for military applications requiring extreme toughness. It is held together with a hot-melt resin developed for carbon-fiber baseball bats. The fiber has double the elongation (how far it can be stretched before breaking) of high-modulus (HM) carbon, and combined with that resin, it can go beyond the maximum design load of the frame and take tremendous impacts without cracking the way other carbon frames are otherwise prone to, once their maximum design load is exceeded.
Cannondale’s test lab is known to be among the industry’s toughest, if not the toughest, in terms of standards required to pass. One test in particular Denk found to be over the top, and when asked if it goes beyond EN or other industry norms, replied, “Pfaaa! Way beyond! It was originally created 12 years ago when Cannondale had some problems with some tandems. Then they decided to make all of their bikes pass it. It is a really tough test. But we sure know that we have a very safe bike because of it!”
And using computer-generated “force maps” obtained through 30 years of cumulative data acquisition in Cannondale’s test lab, Denk’s team could figure out exactly how to orient fibers in every section of the frame to oppose the forces in every area with a minimum amount of carbon.
While the BallisTec fibers make the frame extremely tough — indeed, Cannondale claims that the EVO is even stronger (does better in destructive and fatigue tests) than its own super-tough aluminum CAAD frames — they alone do not provide the required stiffness to be a world-beater. So Denk and his team add some super-stiff high-modulus (HM) carbon fibers in key places to tune the stiffness. They claim that the net result sets a record for the highest stiffness-to-weight ratio of a frame of 142.3 Newton-meters per degree of deflection per kilogram, as tested by Zedler Fahrradtechnik , the renowned German independent bike-testing lab. In Cannondale-supplied Zedler data, the Cervelo R5 CA (California-built, as opposed to Asian-built) is almost on par, while other major brands taper off well below.
In order to come up with the above stiffness-to-weight ratios, Zedler first produces an accurate measurement of the frame weight done in a consistent method with all frames. As I said yesterday, Dirk Zedler does things like adding 15 grams if a frame has no front-derailleur boss, since that’s the extra the band clamp would add, adding weight for the extra seatpost length demanded by a sloping-top-tube frame, subtracting weight for an integrated headset, since press-in cups are not required, and adding and subtracting weight for variations in top tube and seat tube length from the 57cm norm.
Even though the frame is molded in sections and bonded together, HM fibers connect and ring the entire frame. How? After the frame is bonded together and the joints have been sanded smooth, HM fibers are added on top, with an aerospace adhesive film between that causes the layers to bond together better than if they’d originally been laid up wet together. Using this method, continuous HM fibers come down the seat tube, wrap around the bottom bracket shell, and loop back up to the seat tube. The chainstays are butt-joined to the back of the bottom bracket shell and then linear HM fibers are overlaid on the adhesive film in a staggered fashion to taper the fiber stack depth and width toward the back and smooth the flex transition.
Original prototypes of the frame weighed 570 grams (Denk goes to Asia and builds the first frame himself, in the mold that has already been cut); pre-production prototypes weighed 630 grams; and final production frames, with the minimal finish on the Ultimate model, weigh 695 grams.
Amazingly, the Liquigas team paint job adds 20 percent to the frame weight, bringing it to around 850 grams! Oh well; Cannondale still provides the team with 400-gram plastic-coated steel slugs to drop into the seat tube and bring the bikes up to the UCI-mandated minimum weight. Complete-bike weight of the Evo Ultimate bike, with every component passing Cannondale’s stringent test standards, is 4.95kg (10.89 pounds), as sold, in a 56cm size. I weighed one, and it came out at that! Dura-Ace equipped bikes with a more standard parts selection weigh 14 pounds.
The biggest frame-weight savings came in the rear dropouts. Cutting the dropout section (dropout plus 5cm of seatstay and of chainstay) away from the lightest competitors’ bikes, Denk discovered that the lightest dropout/seatstay/chainstay piece was 34 grams (each). While carbon, those competitors’ dropouts were bonded into separate chainstays and seatstays. Denk managed to cut that weight in half, saving 17 grams per side, by instead making the dropouts hollow all of the way back to the wheel-clamp flats. This combined 34-gram saving is a lot, considering that weight reduction in frames at this level requires chasing individual grams here and there. The downside is that the hollow dropouts required a much bigger, costlier, size-specific mold of the entire seatstay/dropout/chainstay structure than the small chainstay and seatstay molds most companies use, which can be used on a number of different frame sizes.
Additional weight savings came by narrowing (in a manner very unlike Canondale’s heritage) the seatstays, seat tube, top tube midsection, and steerer and head tube base (the tapered steering tube is now 1-1/4-inch, rather than 1-1/2-inch, tapering to 1-1/8-inch).
Weighing in at a Zedler-certified 695 grams in a 57cm size in Cannondale-provided Zedler data, the SuperSix Evo comes in at a mere gram less than the Cervelo R5 CA, and considerably less than all other production frames measured by Zedler, which includes frames of all of the major players. According to Zedler, however, the 315-gram SuperSix Evo fork is bested by over 20 grams by both the Cervelo R5 CA fork (293g) and the Storck Fascenario 0.7 fork (295g).
Speaking of the fork, that is the first line of suspension in the SuperSix Evo frame/fork’s “Speed Save micro-suspension technology” designed to take the edge off of harsh impacts on the road and allow the rider to go faster with more control. Divided into two “zones of vertical compliance,” this system consists of a Zone 1 at the bottom of the fork and the tail end of the seatstays and chainstays, and a Zone 2 at the seatpost and mid-to-upper seat tube.
Fibers on the front and back at the tips of the fork blades, chainstays and seatstays, and at the front upper section of the seat tube are oriented at low crossing angles to each other, which allow them to move with bumps like the casing of a tire. Additionally, the fork is curved more and the blades come further forward, with the dropouts extending back to achieve the desired offset, rather than sticking out forward. And the crossing fibers at the front of the seat tube allow the bottom of the seatpost to push the front of the seat tube forward on impacts, thus adding to the flex in the seatpost that is already an important component of reducing the jarring at the saddle. Finally, the midsection of the chainstays is flattened on the top and bottom to allow the stays to flex vertically, but they are wider side-to-side, thus stiffening the rear end laterally.
“Speed Saver” isn’t suspension; it does not eliminate bumps, but it does take a bit of the edge off, perhaps similar to removing 5psi from your tires. I rode the Evo on many sections of quite rough road over two days, and it is a subtle but noticeable difference. It is also a critical component of improved descending performance that Cannondale claims by virtue of the bike keeping its wheels in contact with the road just a bit better. Super-descender and 2010 Vuelta champion Vincenzo Nibali of Liquigas took the pink jersey in the 2010 Giro by dropping all of his competitors, including his teammate and eventual Giro overall winner Ivan Basso, by a number of minutes on the descent of Monte Grappa. He reportedly was pissed this past fall when Basso, riding on a prototype Evo, was able to keep up with him on a long, serpentine descent on his 2010 SuperSix. Nibali is now riding the Evo and says he is faster descending with it, but that he “has not yet found its limits.” He went on to note that he’d found the descending limits of the SuperSix by breaking his collarbone in a crash on it!
Though the Evo frame has little or no aerodynamic shaping of the tubes, Denk, who tested the bike extensively in the wind tunnel, chose to concentrate on frontal area rather than the shaping most designers of aero frames focus on.
To understand this, consider a number of frames being compared in a wind tunnel at a given wind speed. The formula for drag force is:
Fd = A X cd X ρv2
A = frontal area (surface area facing the wind)
cd = drag coefficient for the object. This is altered by changing the shape or surface texture of the object.
(X is a multiplication sign only)
However, we can ignore the quantity ρv2, because it will be the same for all of the bikes, since ρ is the mass density of the fluid (air, in this case), and v2 is the speed of any of the bikes relative to the wind.
That leaves us with:
Fd = A X cd
(times a constant, for the sticklers).
It is very common for bike designers to focus on the shaping of the frame, in other words, to try to reduce cd, the bike’s drag coefficient. But if the tubes are large, they can still end up with a high drag force slowing the bike, because the drag force equals the bike’s drag coefficient cd multiplied by the bike’s frontal area A.
Denk has done very little shaping of the tubes on the Evo, but he has made the tubes narrower (he’s reduced A but not cd). By going from a 1.5-inch lower headset bearing to a 1.25-inch one, he reduced the head tube diameter by 11 percent. He made the fork blades 15 percent thinner. He made the down tube 20 percent less wide. Also, the narrow midsection of the top tube allows the rider’s knees to come in closer, thus reducing drag.
By sticking with a round down tube, which is the stiffest shape there is when opposing torsion (twisting), the most important force the down tube deals with, Denk eliminated the problems of forces going around corners in non-round tubes, which create forces pushing the walls in or out. And a round shape, especially when it’s cutting through the air at an angle the way the down tube does, is not bad aerodynamically; it’s far better than a rectangular tube, which creates a large low-pressure area behind it pulling it back, as well as whose walls pop inward and outward under torsion. Denk further stiffened the down tube by using the carbon lug it slips over (the lug is part of the bottom bracket shell, molded in a single piece with the seat tube) to stabilize the shape of the very thin down tube so it won’t beer-can under torsion or lateral forces.
As promised, the SuperSix Evo rode very nicely. It took a bit of the edge off of bumps, it handled corners well, and it descended great, taking sharp switchbacks, even rough ones, quite nicely. It also had nary a shake when descending fast with no hands, something you don’t take for granted in a 63cm bike, particularly a superlight one. It also was very easy to lift and hang up on tall road signs! Cannondale has notched up Giro wins under five different riders in the past (Basso, DiLuca, Cunego, Simoni, Gotti); we’ll see if an Evo equipped one comes through this time!