Cannondale road bikes have a long history of breaking the mold of what a "normal" road bike should be. At first, the tubes seemed clunky, and the frames were not incredibly light. Each successive iteration showed improvement over the last as they started using different tube sizes and then added shaping. Eventually, Cannondale expanded its lineup and embraced carbon fiber. Over the years, Cannondale has shown they know what it takes to build great-riding bikes out of aluminum and carbon fiber.
The Synapse has been part of Cannondale’s road lineup since 2002. It has always been more of an endurance ride than a traditional road racer, though the carbon-fiber Synapse has been deployed by Cannondale-sponsored pro riders at cobblestone classics. What makes it an endurance bike is that it has a bit more stack and less reach than their racing bikes. As the Synapse has evolved, it has benefited from increased vertical deflection and tire clearance. The 2018 iteration has room for 32mm tires, and the updated 2022 model has room for 35mm, meaning it could double as a gravel bike if you choose.
The SuperSix is Cannondale’s do-it-all road racing platform. It’s been in their lineup as the carbon-fiber road racing frame since Cannondale has had a full carbon road frame. The current version received updated aero-shaped tubes while still being super-light and stiff. The SuperSix is the default bike for Cannondale's WorldTour racers. For people who want increased aero performance and are less concerned with weight, the SystemSix is a worthy option.
Cannondale’s aluminum road race bikes are a favorite amongst the privateer set. Light and stiff, with solid road-racing geometry, these bikes compete with carbon and even out-perform many more expensive bikes. The latest iteration is the CAAD13, which shares geometry with their top-flight SuperSix. In many respects, the CAAD13 is the SuperSix’s equal, just made budget-friendly and in recyclable aluminum.