Every disc has a four number rating system: Speed, Glide, Turn, and Fade. These four numbers represent a flight rating that helps you understand the flight path or characteristics of a disc golf disc as it flies through the air. Or in other words, how a disc is supposed to fly with a proper throw. A disc for example could have a rating of (7,4,-2,2). This means the disc is a Speed 7, a Glide of 4, a Turn of -2, and Fade of 2. Lets explain what each number will do to better help you understand the physics.
Speed 1 to 14
Speed describes the discs distance potential or the rate at which a disc can travel through the air. A speed of 1 is the slowest and 14 the fastest. A disc must be thrown at the proper speed to achieve the discs distance potential. It requires more power, or arm speed, the higher the number gets in order to get the proper flight path. For beginners, it is best to throw discs of lower speeds (1-5) first and work on achieving the correct flight path before advancing to discs of higher speed (6-9). This requires a lot of practice to correctly throw a disc with enough arm speed, but be patient it will come. High speed discs are not recommended for beginners.
Glide 1 to 7
Describes how much the disc wants to stay airborne. Discs with higher glide fight to stay in the air longer, were as discs with lower glide fight to get to the ground faster. When you are wanting distance it is best to have a disc with higher glide, when you are wanting accuracy and placement it is best to use lower glide. Beginners trying to maximize distance should choose discs with more glide. When throwing into wind though you would want a disc with lower glide because the wind already lifts the disc, and the opposite is true when throwing with the wind, you could use a disc with higher glide as a tail wind is pushing the disc down. We will talk more about wind when we talk about turn next.
Turn +1 to -5
Speed and glide help the disc move straight forward but turn and fade are all about the left to right movement of a disc. Turn is affecting the flight at the beginning of the throw. The number represents how much the disc will naturally want to turn the opposite of how it is spinning or rotating when thrown. When a disc is turning clockwise the disc naturally wants to go left with the rotations, but a more negative turn will help the disc fight the natural turning direction. The opposite is true for a counter-clockwise turning disc. For example, if I throw right handed backhand (RHBH) the disc will be spinning clockwise and will want to turn left so in order to help negate that I might want to throw a disc with a turn of -3. If I want the disc to negate the left movement even more I would throw a disc that is more negative, ie. -4 or -5. In order for beginners to maximize their distance they will want to throw -4 or -5 turn discs.
Fade: 0 to 5
As turn affected the beginning flight of the throw fade affects the flight at the end of the throw. All discs will fade at the end of their flight, but the higher the fade number the more the disc craves the fade. For example, a disc spinning clockwise will naturally move left, if I wanted the disc to go further left then I would want a fade of 4 or 5. In order for beginners to maximize their distance they will want to throw discs with low fade.