What does bias ply mean on a tire? Does it mean 2 ply (henceing the "bi"), or does it mean something else. Just wondering.

 

Bias ply quad tires, which are the vast majority of OEM tires, consist of plies, either 2, 4, or 6,run at an angle to the radius of the tire circumference, whereas radial plies run directly at 90 degrees from the circumference of the tire. Some riders prefer radials for their stability and adhesion which tend to reduce sliding in cornering. Other riders dislike the tendancy to break loose with less warning in those situations. On the Raptor, which comes with radials as OEM, I never had a problem in getting them to break loose in corners, but it does take some getting used to the feel before doing so.
I now run Pure Sport Bandit XC's which I have used exclusively for years when replacing OEM tires. They are one of the few sport tires that are real 4 plies rather than "4 ply rated", which are actually 2 plies.
Also radial tires are claimed to give better wear characteristics due to their more rigid construction which allows less squirming & flexing.
More than you really wanted to know?