We're used to equipment manufacturers talking up their accolades and where their gear was triumphed, so when Zipp told us that the 303 had won a stage in every race in professional cycling, or the race outright, it sort of washed over us. And then we asked them to prove it, and they did. That's impressive, and it speaks to the versatility of the 303. At 45mm deep, it's deep enough to add serious speed without being so deep that it'll be too affected by crosswinds. It's tough enough for Roubaix, and light enough to crest the Pyrenees. In short, it's all the rim you need, and none of the rim you don't. The Firecrest shape is Zipp's name for their wider, toroidal rim profile that does a better job of shunting wind past the edge of the rim as it moves over the tire. A side benefit is that the same tire effectively becomes wider, giving you a bigger contact patch and better control. In addition to the shape and versatility, Zipp re examined braking on carbon fiber rims it's never been good. To this end, they've built in a silica ceramic fabric at the brake track, which reduces the heat impact on the carbon fiber while providing better grip for your brake pads. You'll have to use Zipp's Tangente Platinum pro or cork brake pads, but they'll work a lot better than they used to.