Someone said a few years ago that there was nothing new left to do with BMX rims, yet since then GSport has gone on to do quite a lot of new stuff, and here’s an example of the latest. 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 can also keep the weight right down. The next innovation was to adapt their cross-lacing design to the narrow inner wall of the rim. They managed to squeeze a few extra millimeters of spoke offset out of the design to help increase lateral wheel strength, and by carefully tailoring the rim’s cross-section we managed to match all the angles to the nipple so that the walls of the rim section act like the ribs inside the Ribcage rim, which helps to support the spoke nipples as much as possible. Traditionally, the greatest flaw in “aero” rims has been the valve hole. “Aero” rims position a lot of very efficiently utilized mass in the base of the rim to support the spokes and give the rim good strength, then a huge hole is drilled through it for the valve stem and a massive weak-spot is created. With the Birdcage GSport has offset the valve hole so that this section can retain its strength. A handy side-effect of this is that fitting a pump is now more convenient. Aside from these original features, GSport spent a lot of time “sweating the small stuff”. They’ve ensured that the deep center allows for easy tire removal and fitting, and they've made sure that the sidewalls, while slimmed down, are still suitable for brake use. The end result is one of their 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.