Well I learned to 180 first on my bmx, which weighs about 10.9 kg. But after practicing the technique on it for a while I can now pull 180s and 3-taps on my old ticket and even on the mongoose which weighs around 13.5 kg. My point is that it's good to learn it on a light bike, but once you get the hang of the technique, then you suddenly start doing it better on heavier bikes too