At first glance the Birdcage looks like a fairly conventional “aero” style rim, but there is more to it than that. The first clue comes from the name; birds have hollow bones to save weight whilst retaining as much strength as possible, and the Birdcage rim has a hollow bead for the same reason. The rim’s hollow bead is still big and chunky to help reduce the chances of pinch puncturing or flat spotting the rim, but by creating a tiny hollow cavity inside it, GSport was able to to keep the weight down and make the Birdcage their lightest rim available.