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 we can also keep the weight right down. 
Aside from these original features, G-Sport spent a lot of time “sweating the small stuff”, ensuring that the deep center allows for easy tyre removal and fitting, and made sure that the sidewalls, while slimmed down, are still suitable for brake use. 
The end result is one of the most high tech rims to date. With a weight of just 408g (14.4oz) it outperforms most rims weighing 20-30% more, and the weight saving from the rotational mass of the wheel feels fantastic.