8-16 vs 8.3-16

[phaser]

What does that first number refer to, and what's the difference between the 8 and 8.3?

 

[North Idaho Wolfman]

Width and height ratio, it's 8" wide but that also effects the height and the RC of the tire.

 

[tiredguy]

What does that first number refer to, and what's the difference between the 8 and 8.3?

Both of those numbers are the section (- overall -) width of the tire. The 8 is 8 inches wide and the 8.3 is 8 and 3/10ths of an inch wide. Some front R1 tires by different manufacturer's make them different sized probably to gain flotation maybe. If you're looking at the difference because you need to replace some tires find out what the rolling circumference is and if it's within 2% you're good to go.
Al