The Cervélo S5 Ultegra Di2 feels just like a pro bike. A member of Cervélo's Garmin-Sharp pro team would be hard pressed to tell the differences between this bike and what he's given to race in World Tour races. The reason is that the frame is the frame they get, and the Shimano Ultegra Di2 eleven-speed group feels at the fingers just like Dura-Ace.
But what should matter more is that the S5 kills as an aero bike. It gives back 32 watts of effort when riding at 40kph compared to a normal road bike. That's a pretty big savings and something every road racer and triathlete should want. But what is harder to see is that actually offers more benefits to slower riders. Since cyclists create their own wind, they are fighting it so long as they are moving—it might not help you on a trainer, but on the road, it will, and the longer you are out, the more of a benefit it will give. And when it comes to hills, Cervélo's modeling has determined that for most riders, aero benefits outweigh light weight until a hill's gradient goes over five percent.
Not that the S5 isn't light. It is. It is also a road bike. It shares a geometry with Cervélo's R-series bikes, and their advanced modeling, when combined with the data they acquired on how forces affect bicycles, means they were able to design their particular mix of fibers and plies so that the S5 is stiff like a road bike and flexes like a road bike.
You'll see the Rotor 3DF BBright 52/36 semi-compact crank in the middle of the bike. This is important for several reasons. Cervélo partnered with Rotor to create the BBright standard, one that allows for a big 30mm thru-axle on the crank and a wide bearing platform for greater stability and more building options. With the shell so wide, Cervélo can make frame shapes that work with this dimension. They came up with shapes that are lighter and more aero and stiffer because of it.
The crank is mated to an eleven-speed 11-25 cassette. The wide, closely-spaced range allows for easy climbing, superior descending and lots of stops in between. Pushing a Di2 button is easy, so easy, you might finally be accused of shifting too much. For all the ease of shifting, the re-designed brake calipers might be the highlight of the group. By pushing both pivots to the outside, it's easier to work with wide rims and easy to modulate force with a single finger.
Knowing that pulling for electronic and internal cabling can be a limiting proposition, Cervélo has designed their internal routing system to work with any shifting and braking system and can be changed at a moment's notice. Future-proof cabling means that the ports can be plugged and cable stops installed and vice versa, so you can have hydraulic or mechanical braking, electronic or mechanical shifting.
The Cervélo S5 Ultegra Di2 bike does more than go fast. It rides like a racer.