this is what us old school bmx'ers refer to as "rake and trail". In a nutshell if you slide the fork tubes down as far as they will go(fork caps even with top of triple clamp) you will raise the front end.This makes the bike slower turning and more stable at higher speeds with less possible headshake. Sliding the fork tubes up into the triple clamps(fork caps hit bottom of handlebar) will make a quicker turning bike ,lower front end, and possiblly more head shake. I'm guessing the stock position from the factory is the best comprimise.(sp) In the tight northeastern woods I tend to quicken the steering a bit....;. headshake can be caused by a bunch of other things too. hope this helps