Just to add my .02. Anyone trail riding, as opposed to racing, who is thinking of changing their helix should stick with a progressive cut. As Deanm mentioned some helixes are stepped and the result is diminished smoothness during upshift as you can imagine. Just to reiterate as well - steeper angles (larger numbers) = faster upshift at the expense of slower backshift while shallow angles = slower upshift and faster backshifts. If anyone has purchased a clutch kit you'll typically find a steep initial angle to improve low to mid range acceleration that progresses to a shallower angle as speed increases to allow for full shift out.