For us, the most rewarding days come with the toughest challenges that set our quads on fire and get our hearts pounding. They're days when all we're doing is climbing, and all we can manage is to think about the next few minutes or seconds of pedaling. We down our electrolyte-filled water and push forward because there's nowhere else to go but up, and we can't help but think about the rewarding descent that's sure to come. With a lightweight, stiff bike, these climbs are manageable and even enjoyable. With the R5 Ultegra Di2 Road Bike, these climbs are what we look forward to. They're what this bike is made for, and they're what we end up priding ourselves on. The sky is the limit with Cervelo's R5. First, we want to focus on the ridiculously light weight of the R5. This new frame is 130 grams lighter than the previous model, which means there's a 16-percent reduction in the already "stupid light" frame. But, that's not all there is to this road machine. It can do everything from sprinting to precision handling and, while it may not be the most comfortable endurance bike of all time, it is well-suited for distance rides where we navigate multiple mountain passes. The R5 frame captures a professional riding fit and feel with an aerodynamic riding position from the lowest possible frame stack. Drag is reduced with internal cable routing to improve aero gains, and tube shaping is designed to do the same with a wind-slicing feel. A lower bottom bracket and longer wheelbase optimize pedaling efficiency and speed, and the frame is estimated to be 21-percent stiffer at the head tube, making this a road bike that's faster than ever. We would be remiss if we did not mention that the Cervelo R5 is equipped with a Shimano Ultegra Di2 groupset for smooth electronic shifting at the lowest possible price point for this top-of-the-line steed. This is one of few bikes that can handle everything from sprints to climbs to swerving descents, and we love to see it. No matter where ...