When the C Series was originally conceived, there was a general consensus that a focus on comfort was clearly required for an endurance-style bike. At the same time it was identified that the endurance bike market had not kept up to modern road racing frame weights, making ultra low weight a very high priority. So how did this lead to the use of the Squoval shape you see in our C Series bikes?
To understand the answer, we need to look at the Cervélo design team’s motivations during the original Squoval engineering exercise. During this stage in our development, we had completed our ride testing of a strain gauge-equipped bike, and determined what the actual loads exerted on the bike were during riding, and where these loads were concentrated. During this time our team developed a protocol to discretize each tube using its end conditions, and maximize the structural efficiency as an absolute, balancing the weight of the tube with its stiffness in the ways identified by the strain-gauge bikes. This led us to realize that the seatstays could be reduced to their radically small size and still function effectively to take the load while riding. The original Squoval tube shapes represent an absolute commitment to structural efficiency, with no compromises made.
On reflection of the type of rider the C Series would be intended for, we realized that some compromises should be made to this thinking. We then started to look deeper into the definition of comfort. Our pro rider feedback has consistently been that heavier frames with thicker tubes were touted as being the "most comfortable." Through riding our competitors’ products that had very high deflection and were also touted as "comfortable," we knew that some combination thereof was where we needed to be.
We hypothesized that by sticking to regular modulus material, and avoiding the temptation to add UHM carbon, which is so good at helping keep the stiffness up at very low weights, we could capture the damped feeling that we hear again and again correlates with comfort. In addition, we also prioritized vertical compliance during all FEA exercises in an attempt to absorb some of the larger bumps in the road that would surely be encountered by this type of rider.
So, we had our goals laid out: high frequency road buzz was tackled by avoiding the temptation to make ultra thin, ultra high modulus tubes. Low frequency bumps were tackled by prioritizing vertical compliance. But how could we possibly hit our improbably low weight goals (850 grams painted with all small parts!) and get a bike that was stiff enough to ensure that it handled in the confident fashion our customers demand?
Thus was born Squoval IPC (In Plane Compliance). This is the shape you see on the new C Series.
This tube shape maintains the original’s focus on structural efficiency, while flattening the tubes slightly in the plane (vertical) where we need compliance. The broad Squoval shapes allow us to push the material most affecting stiffness as far away from the neutral bending axis as possible, taking maximum advantage of the shape of the tubes. The super wide profiles increase the effectiveness of the materials by an exponential factor, as it gets further away from the centre axis.
All of this combines to provide a frame that is compatible with all major disc systems on the planet, is stiffer than our early-generation Classic Squoval bikes, gives us a highly damped, vertically compliant frame, and offers class demolishing weight.