By Lennard Zinn
Ivan Basso was eager to prove at the Giro del Trentino that he is back on form and must be considered the favorite for the Giro d’Italia. He did just that, and his efforts were assisted by having the right tool, namely his new, all-carbon Cannondale SuperSix.
The SuperSix has taken a big jump in frame design since it was introduced in 2008, and its performance was a surprise to me. Being 6-foot-5, off-the-shelf bikes are rarely big enough for me to ride comfortably. Even if they are, the tallest size often tends to shimmy at high speeds or with the hands off the bars.
But at Cannondale’s launch of the bike in northeastern Italy, I had none of those problems when I rode a 63cm 2010 SuperSix on a high-speed, five-hour ride incorporating lots of climbing and descending in the Dolomites.
Design and Construction
The SuperSix is entirely carbon (using only unidirectional fibers crossing each other at angles — no woven fibers for cosmetics). The only exceptions are thin aluminum sleeves in the ends of the bottom bracket shell, aluminum plates on the dropout faces and an aluminum rear derailleur hanger.
Starting from the front, a key to the SuperSix’s stiffness and low weight is the head tube. It’s considerably bigger in cross section than before, and it is deeper (extends back further) as well, creating a huge, hollow, lightweight, very stiff anchor for the fork that greatly increases the lateral and torsional stiffness of the front triangle. Continuous fibers run from the top tube through the head tube and down the down tube, knitting those tubes together into an integrated, high-strength structure. The fibers from the sides of the down tube and top tube run straight, and hence at their strongest, to the sides of the head tube (i.e., at 90 degrees to its axis) and around its ends.
The fork has a tapered steerer, with a 1.5-inch bearing at the fork crown, which explains the large dimension of the bottom of the head tube. There is no aluminum in either the head tube or the fork; the head tube has carbon cable stops and headset bearing seats, and the headset crown race fits right down over the flared steering tube onto a platform formed by layers of carbon wrapped around it. The fork’s underlying structural fibers run with gentle curves all of the way up from the fork blades into the steerer, under those surrounding layers added to form a crown platform that blends seamlessly with the bottom of the large head tube. Rather than being either machined or molded to form a 90-degree corner where the steerer meets the crown in order to seat the crown race, either of which would weaken the fibers, the fibers are net-molded, forming a gently radiused intersection there requiring no machining to mate with the headset crown race (whose inner bottom edge is also curved).
The SuperSix seat tube is now fully carbon, but unlike so many carbon seat tubes, it is round and accepts a clamp-on front derailleur, making the bike compatible with any chainring size. The base of the seat tube flares to meet the huge bottom bracket for BB30 bottom bracket bearings and the 30mm-diameter bottom bracket spindle standard Cannondale pioneered. The inner layers at the top of the seat tube are fiberglass, so that when it is reamed (to fit a 31.6mm seatpost), no carbon layers are cut.
The down tube is tall to wrap around the huge BB shell and is as wide laterally as it can be within
the constraints of the 68mm-wide shell. The top tube slopes slightly up to the front at 2-to-5 degrees, depending on size, and flares toward the front, optimizing its contribution to the lateral and torsional stiffness of the front end. I’m certain that it plays a critical role in the shimmy-free performance I experienced on the 63cm.
The front triangle is molded in a single (monocoque) piece, but without stubs for the seatstays and chainstays to slip over and be glued onto. Instead, the seatstays and chainstays end at a large curved surface to wrap around either the back of the bottom bracket shell or the back of the seat tube. To oppose the different forces on the two chainstays, the right one is wider and the left one is taller. The seatstays are thin and continue to the seat tube as separate tubes to build in vertical compliance and hence ride comfort. Using a test with a 600-pound load on the frame, Cannondale claims to have demonstrated 25 percent more vertical movement than the same test shows with Trek’s, Scott’s or Cervélo’s top models.
Cannondale also claims higher bottom bracket stiffness and head tube stiffness in its tests than its competitors’ comparable models.
All of this hand laying-up of layers into molds is labor-intensive, and Cannondale has abandoned its lifelong commitment to domestic frame production. The frame is made in China with lower labor costs.
Sizes and Other Details
The frame is offered in eight sizes and there is one additional custom mold, made at great expense for Daniele Bennati, Liquigas’ sprinter whose requires a 4cm longer top tube than stock — his frame is a 54cm with a 58.5 cm top tube. The rest of the Liquigas-Doimo riders are on standard stock sizes (Ivan Basso rides a 58cm). The team rode this bike already in the 2008 Tour de France, and Cannondale has been making running changes ever since base on feedback from its lime green and blue-clad riders.
The nude-finish SuperSix, with only a stripe of white and decals on it, saves 60-70 grams over a painted model. The four bike models incorporating the SuperSix High Modulus Ultimate frame and fork (there are less expensive SuperSixes made in the same mold with lower modulus carbon fibers) all have claimed weights in the 14.5 to 15-pound range. Parts options include Shimano Dura-Ace 7970 electronic, Dura-Ace 7900 mechanical, Campagnolo Super Record 11-speed or SRAM Red version.
The electronic Dura-Ace version has a different frame from the others, since the electric wires are run internally. At the drilling points on the down tube, seat tube and right chainstay, there are layers of woven carbon on the inner wall, so that when the drill comes through, it does not split and delaminate structural unidirectional fibers. The electronic cables meet at a junction inside the down tube at the bottom bracket.