Every disc golf disc is described by four “flight numbers”. For example, the TeeBird’s flight numbers are 7 / 5 / 0 / 2. What does that mean?
These numbers correspond to Speed, Glide, Turn, and Fade. They are not objectively-defined and vary from manufacturer to manufacturer, but are useful for giving a general sense of how a disc flies.
Glide is the least important, so let’s get it out of the way first.1 Glide ranges from 0 to 7 and describes how the disc “floats” or generates lift. A high Glide (like the 5 on the TeeBird) means that the disc will float farther but be more subject to wind. If you’re a beginner, you usually want discs with high Glide.
To understand Speed, Turn, and Fade, you first have to understand how discs fly. Let’s assume you are throwing a right-handed backhand throw.2
The most basic axiom of disc golf physics is that when a disc is thrown right-handed backhand:
- at sufficiently high speed (the start of the throw) the disc will bank right (turn)
- at sufficiently low speed (the end of the throw) the disc will bank left (fade)
Viewed from above, the flight path will look like this (from Disc Golf Puttheads):
A disc’s Turn and Fade flight numbers, therefore, describe how much a disc is going to bank right at the start of the throw and how much it will bank left at the end of the throw.
Turn, sometimes called high-speed stability, ranges from 1 to -5. A disc with 1 Turn is extremely difficult to turn: it will not bank right even if thrown very fast. A disc with -5 Turn will be very easy to turn: even if thrown relatively slowly, it will bank right, and indeed, if thrown with any reasonable power, it will bank so hard right that the disc will go perpendicular. The TeeBird has a Turn of 0, which means that it is probably not going to bank right unless thrown ludicrously fast.
Fade, sometimes called low-speed stability, ranges from 0 to 5. A disc with 0 Fade finishes very straight: even as it slows down, it’s not going to bank too far left. A disc with 5 Fade will bank very far left as it finishes, likely going perpendicular to the ground. The TeeBird has a Fade of 2, which means that while the disc is probably not going to go perpendicular, it will very noticeably fade and bank left as it is finishing.
Sometimes you hear people refer to discs as “overstable” or “understable”. In general, overstable usually refers to discs with more Fade than Turn, while understable usually refers to discs that have more Turn than Fade. The TeeBird is overstable (Turn 0 Fade 2), while a Meteor is understable (Turn -3 Fade 1).3
Finally, all of this is tied together by the first number, Speed, which ranges from 1 to 14. Speed does not refer to how fast the disc flies!4 Instead, Speed refers to how fast the disc must fly in order to achieve its Turn and Fade numbers:
- If the disc is thrown too slow for its Speed, it will be more overstable (less Turn and more Fade) than claimed
- If the disc is thrown too fast for its Speed, it will be more understable (more Turn and less Fade) than claimed.
That is to say, think of Speed as a requirement, not an outcome.5
So for example, if you throw a right-handed backhand flat and straight:
- A Meteor (4 / 5 / -3 / 1) thrown at Speed 4 will bank right because of the -3 Turn, then bank left very gently from the 1 Fade as it slows down. If thrown at Speed 7, however, it will bank right very sharply, and may run out of altitude before it starts to bank left.
- A TeeBird (7 / 5 / 0 / 2) thrown at Speed 7 will fly very straight at first because of the 0 Turn, and then reliably bank left from the 2 Fade as it slows down. If thrown at Speed 4, however, it will begin banking left much earlier in the flight.
This is incidentally one of the reasons people recommend beginners start with putters, which have Speed ratings of 2 or 3 and relatively neutral Turn and Fade numbers. The average beginner is simply incapable of generating the arm speed to throw discs with higher Speed ratings, causing them to quickly fade out and fall short.
After putters, beginners will benefit from initially trying slightly understable discs, which will compensate for the overstability introduced by throwing too slow: that is to say, discs with:
- Speed of 7 or less
- Glide of 4 or more
- Turn of -1 or more
- Fade of 2 or less
You will notice this pattern in nearly every manufacturer’s “beginner” discs:
Finally, flight numbers are far from the only factor in a disc’s flight path. Continue reading here to read how flight path is shaped by four factors: throw type, disc stability, release angle, and environmental variables.
It’s the least important because while none of the flight numbers are objectively defined, Glide is especially not objectively defined. ↩︎
Right-handed backhand and left-handed forehand throws behave the same. However, a left-handed backhand, or a right-handed forehand throw, will be mirrored: that is, the disc will bank left during the turn, and bank right during the fade. ↩︎
I don’t like these terms because sometimes people use “stable” to refer to a neutral, straight flight, which then causes all sorts of problems when you try to extrapolate that to “understable” and “overstable”. And just to make it even more confusing, discs with very low Turn are high-speed stable, but discs with very high Fade are considered low-speed stable. ↩︎
To be precise, higher Speed discs are in fact more aerodynamic and in the hands of a skilled thrower, will travel farther when thrown with the same power. But for an unskilled thrower, the excessive fade introduced by throwing under the disc’s Speed rating grossly outweighs any aerodynamic advantage the disc has. ↩︎
As a rule of thumb, you can estimate your throwing Speed by dividing your drive distance in feet by 35 (or meters, by 10) - if you can throw 250 feet, for example, that’s about Speed 7. ↩︎