The Cervélo S3 with Shimano Ultegra Di2 is the ultimate self-sponsored aero bike. It has all the pro features, but scaled to a nicer price. The frameset is great for road racers looking for an aero edge and triathletes who are reluctant to pull for a full-on time trial bike.
Electronic shifting is all the rage these days. Shimano was the first to go big with it, and by producing it at the Ultegra level, they did the world a big service. It's functionally the same as the Dura-Ace Di2, but at a much more accessible price. Push-button shifting at your brake levers means that Shimano could build the lever bodies smaller, which can mean added comfort when holding the hoods, and reach is a plus for those with short fingers. It also makes cabling a snap: your only worry will be keeping the battery charged, and with the help of a long burn time and a warning light, that's a piece of cake, too.
The Ultegra levers activate Ultegra derailleurs, which sweep the chain across the eleven cogs on the 11-25 Ultegra cassette and the two chain rings of the Rotor 3DF BBright 52/36 semi-compact crankset. The battery is stowed at the bottom of the down tube.
The S3 has the geometry of a classic road racing bike and the frame tubes of a time trial bike. It was born out of the Cervélo Soloist, which redefined the aero road bike. And this one is much, much faster, the fruits of Cervélo's relentless pursuit of improvement. The S3 barely resembles the old Soloist, because what Cervélo learned in the intervening time, from their S5 was so profound. The fork has been designed to smooth out airflow behind the front brake. The down tube has been shaped to respond to the different zones engineers found on close study of airflow. The head tube shields the tubes behind it, so they were made narrow. Because the top tube stays in the shadow, it was kept narrow. Because the down tube sees more air as it goes down and water bottles are added behind, the shape changes to reflect both the air coming toward it and the essential cargo behind it. The seat tube was re-shaped to reflect better shielding of the rear wheel and to give enough room for 25mm tires.
The aero shaping is only part of the story. They also re-worked the lay-up and tube shapes to improve the ride. The tapered 1 1/8" to 1 3/8" steerer improves torsional rigidity at the fork for easier and more confident turning without affecting ride quality. The bottom bracket is stiffer for better power transfer. And the seat stays have been dramatically slimmed to improve shock absorption at the rear end. So not only will you be faster on the new S3, but you'll also be more comfortable.
With the S3, as with all Cervélos, you'll also have an easy time finding one that fits. That's because rather than rely mysterious frame sizing templates, they analyzed huge body dimension databases to determine what proportions people have. The result is a linear progression in frame sizes, with each larger frame having more stack and more reach. Thanks to the sloping top tube, people can choose a bike based on how they sit on a bike.
The Cervélo S3 Ultegra Di2 is the aero racer for people looking for a pro-quality edge on the competition at an amateur's price.