could anybody give me a crash course or direct me to one, in the subject of tires.  i have no idea what any of those numbers and measurements mean. please help

The first number, 130, 140, etc., is the section width in millimeters. That's not necessarily the tread width, but the width of the tire at its widest point. The second number, after the "slash," 60, 80, etc., is the height of the sidewall expressed as a percentage of the section width. In other words, a 160/50 tire would, theoretically, have a sidewall height of 80 mm, (50% of 160). The third number is the rim diameter in inches. Except for the rim diameter, these numbers are somewhat subjective. You could measure 5 identically size labelled tires and get 5 different widths and sidewall heights. If I tried, I don't think I could devise a more confusing system of telling a consumer what size tire I was selling.

thanks for the input

Or you could check out, hes got tons of info.  

http://pantablo500.tripod.com

Tire specific

http://pantablo500.tripod.com/pablosgs500page/id24.html