Efficiency through balance may sound like some dubious cult mantra, but it’s also the key to the design process behind Cannondale’s new SuperSix EVO. The premise is simple enough; find that perfect balance between strength, stiffness, drag reduction, weight and, er, compliance and you’ll have the most efficient – and hence fastest – machine possible.
Each of those five performance factors affects performance in several ways and it may be assumed that building in too much of any one of them will be to its detriment; excessive attention to reducing air drag, for example, would result in excess weight, airfoil-shaped tubes tending to weigh more than round-section ones.
Too stiff and the bike might lack ride comfort; too comfortable and it might soak up too much of the rider’s energy in flex. Too heavy and – er – no; too light and, again, the bike might flex too much, this time laterally and again wasting energy. It’s the Goldilocks zone on two wheels; neither too hot nor too cold, but just right. That’s the idea, anyway. Making it happen is a different matter, but that’s exactly what Cannondale claim to have done, and they’re happy to explain how.
Starting with the information accumulated over three decades of data acquisition via techniques from laboratory testing to sticking strain gauges to frame spars, ‘Dale’s design team, led by Director of Technology Peter Denk, generate ‘force maps’ showing how loads are fed through the frame. These allow them to determine how best to position the CNC-cut plies of carbon fibre that go to make up the frame.
Arguably the least important of the five factors, in that there’s usually enough of it to do the job, is strength. There is, of course, more to “strength” than simply being strong enough to support the rider and resist dynamic loads. The EVO is constructed using ‘Dale’s “Ballistec” technology, which employs high-strength, high-elongation carbon fibres for the basic structure and makes it more fatigue- and crash-resistant than the CAAD10 aluminium frame.
In search of stiffness, high-modulus carbon fibre is applied to the sides of the tubes only; here, it increases lateral and torsional stiffness while leaving the frame relatively flexible in the vertical plane, contributing to the fabled “compliance” of which US cycle engineers are so fond. The fibres at a particular area of the seat tube and fork blades are orientated at a shallow angle that reduces their effective “pulling power” or ability to resist applied loads, thereby making the tube and blades more flexible in the fore and aft plane so they bend as the bike travels over rough surfaces, smoothing them out. The effect is enhanced in the fork by the use of an offset dropout, which increases the amount of curve on the blade for a given rake.
This inbuilt flex in the frame and fork is labelled Speed Save, acts as a sort of micro-suspension and is intended not just to enhance rider comfort but to do the other job of effective vehicle suspension. By allowing the wheels to follow the contours of the road surface without transmitting imperfections to the rider, bump-induced losses are reduced and the whole plot travels faster.
Back to lateral and torsional stiffness, which affect power transfer, stability, handling and steering precision. As stated, the really stiff high-modulus fibres are saved for where they do the most good, on the sides of the frame tubes and fork blades. EVO design takes the fibres down the sides of the seat tube, looping underneath the bottom bracket shell and back up to form a secure, unbroken and laterally-stiff cradle for the bracket shell.
The stays on each side are moulded in one piece with no metal insert required for the dropout. Instead, fibres run continuously from seatstay to chainstay. Cannondale’s expandable core moulding technology is so precise that the profile of the inside of the stays tapers smoothly as it squashes down to the solid carbon dropout. Lacking that aluminium insert, each dropout is said to be 17g lighter than the lightest competitor, the stays being cut at the same distance from dropout centre.
Once bonded to the one-piece seat tube and bottom bracket moulding using a flat butt joint, the chain stays are reinforced with high-modulus fibres that run continuously from the downtube, around the bottom bracket and along the sides of the stays.
While all this lot sits invisible under the skin, the EVO’s take on aerodynamics is readily appreciated from the saddle. The bike is designed to be narrow – “skinny” in Cannondale parlance – to minimize frontal area for both machine and rider. The latter enjoys a top tube that narrows down in the middle for improved knee clearance, allowing a “knees-in” pedaling style. The use of a 1 ¼” lower head bearing shaves some 11percent from the frontal area of the head tube, while the fork blades are around 15percent thinner than previously.
Round or “modified-round” tubes are chosen for the main triangle on the grounds that they outperform a rectangle on air drag and torsional stiffness and a teardrop on both as well as on weight. Here, perhaps, is the outcome of the search for balance – between aerodynamics, stiffness and weight – most evident.
And, of course, topping off the whole assemblage is the fitment of Cannondale’s Hollowgram crankset running in BB30 bearings. The Bedford firm stoutly maintains it is the stiffest available and has the figures to back the claim. It’s certainly impressive to ride.
So, some stats: weight for the 57cm-equivalent frame, as tested by Germany’s independent Zedler Fahrradtechnik laboratory, is the lightest-ever at a stunning 695g; the prototype was even lighter but takes, according to ’Dale, too much time to make. More telling is the specific stiffness, defined as Newton metres of applied torque per degree of twist per kilgramme. 142.3 of them, to be precise. This, too, is the best figure ever seen by the lab. In fact, compared to leading competitors, this leaves the EVO marginally less stiff torsionally than either the Specialized S-Works Tarmac SL3 Race and Storck Fascenario 0.7, but with much lower weight. It’s actually stiffer than Canyon’s Ultimate CF SLX EVO despite being 250g lighter.
So, it’s light and stiff. How does it compare on ride quality? Only a ride will tell. More on that soon.