Gone are the days of awkwardly piecing together components that span from road to mountain bike disciplines and tossing them on your off-road drop-bar bike like Frankenstein crafting a living, breathing monster. Instead, we have a groupset of our own with Shimano's GRX system launching earlier this year -- and now you can elevate that group beyond your usual cables with the GRX ST-RX815 Di2 Shifter & Disc Brake Caliper that bring GRX into the electronic scene. At first glance, it's not all that different from Ultegra Di2, well, on the inside at least. Its actuation is the same, and offers the same benefits of program-ability, but on the outside you'll find that the hoods are a whole new beast. They feature a much more drastic slope, and gripping traction designed to keep you securely supported in the cockpit, so an unexpected bump doesn't have your mitts sliding off, plus a re-positioned lever built for easier access whether on the hoods or in the drops, so you can comfortably brake on rough terrain without risking it all. The shift buttons are designed for easy reach from the hoods as well as in the drops, and offer a distinguishable click between upshifts and downshifts for a little extra peace of mind when you're 160-miles deep in a gravel race, and each deliberate move matters. Like its Ultegra road counterpart, the feel of shifting is much like clicking a mouse, requiring just 2-millimeters of movement on your end, so you don't have to put nearly as much focus into shifts, enabling you to pay more attention to the terrain ahead. On the back end of things, Shimano utilizes its BR-RX810 flat-mount calipers for reliable stopping power of ServoWave, and cooling properties of IceTech brake pads. The calipers operate with similar modulation to standard Ultegra, but ServoWave adds in improved feel right out of the gates, as the pads move together more quickly at first, before slowing for better control as you brake. This technology has been popular on the mount...