The S3 fits in the aero road bike category. You can see as much from the huge wing-like downtube, the way the head tube extends like a shaped gusset between the downtube and top tube, the way the seat tube is both aero, and cut away to shroud the rear wheel. The fork is shaped with legs that are long front-to-rear to keep air flow as smooth as possible. The cable routing is internal, and Cervélo worked hard on making sure that mechanical shift cables would have a straight line and minimal friction between the shifter and the derailleur. At the same time, they designed the routing to also work with electronic shifting. The bike comes with both plugs and stops. The battery, if you choose to go electronic, sits under the downtube by the bottom bracket. This is more aero.
At the same time, Cervélo designed in some comfort. The top tube is flattened vertically, both for lateral stiffness and vertical compliance. The spindly seat stays and dramatically-tapering chainstays minimize the upward thudding of riding over rough roads. And the frame has room for tires up to 25mm in width. Wider tires roll better, and with modern wide rims, they’re more aero, too.
Cervélo sticks with conventional brake placement and brakes because they’re easier to work with and work better than internal and hidden brakes. You also get to choose. At the same time, they’re not afraid of proprietary designs. They’re pretty much unique in offering a tapered steerer that has a 1 3/8” lower race. They also favor their own BBright bottom bracket design because it affords the best of BB30 while still allowing for a stronger, lighter stay design and bottom bracket juncture. They use their proprietary seatpost because of the aerodynamics and how they can tune the ride, but they offer a super-adjustable one-key seat clamp so you can really dial in the seat position.
While Cervélo is known for their engineering of frame tubes, they should also get mega props for their efforts engineering their frame geometries. Looking at seat tube lengths proved pointless with the advent of compact frames. Top tube lengths are better, but vary the seat angle, head angle, or head tube length and the top tube suddenly is not such a fixed number. While Cervélo uses the top tube length to name the frame size, and they stick with a 73-degree seat angle, they really focused on making sure there was an even progression in terms of stack and reach numbers. With the sloping top tube they run, the biggest issue for you is to figure out what reach you want.
When you get this as a frameset, it comes with FSA headset, Rotor bottom bracket, and Cervélo’s own aero seatpost.
The Cervélo S3 is the do-it-all frame that happens to be wicked fast when compared to most aero road bikes.
The S3 is probably the greatest hero of Cervélo’s entire road bike line. The Bigla women’s cycling team chose this as their main steed, even in cobbled classics, as did MTN-Qhubeka’s Tyler Farrar, and it’s easy to see why. It’s light, it’s stiff, it’s aero, it’s crash-resistant, and does it all at a reasonable price. It’s a bike high on value no matter what kind of rider you are.