Well you don't necessarily need more air. You need the amount of air that track conditions dictate. The better the track the less air you can run, conversely the worse the track conditions the more air you need. When the track is poor you need as much contact patch as possible. MOre air will do just that, as the rear end housing is pushed down the tire will flatten out giving you more contact patch. Less air for a tight track will allow the tire to cup in the center and give you less tire on the ground, giving you more wheelspeed. It is chattering cause there is not enough power to overcome that with the full tread making contact. You need to tighten the extension and lower the air pressure to overcome that...