UNDERSTABLE – An Understable disc has a highspeed turn that is greater than its fade. For example, a disc with flight numbers 13/5/-3/1 would be considered understable. A short cut method for determining whether this disc is over or under stable is to add the last two numbers in the flight numbers, in this case: -3+1=-2. If the resulting number is positive the disc is said to be overstable, if its negative it is understable, and those resulting in 0 would be considered stable or straight.
The four-number flight designation was developed by INNOVA back in the ‘90s and has pretty much become the standard adopted by most manufacturers today to give players and idea of how their different models fly. The 4 numbers quantify the four aspects of disc flight: Speed/Gide/Highspeed Turn/ and Fade (i.e. 9/5/-2/2).
These numbers describe the flight tendencies of a disc assuming it is thrown flat and at a reasonably fast speed. When the disc is released with an angle or at a low speed the number don’t really apply. Throwing the disc with angle is a means of shaping your shot and you will learn how the disc flies in these circumstances with experience.
Speed is the first number and refers to how fast the disc can fly. Speed is mostly a direct result of the aerodynamics of the discs cross section. Thus, thin sharp-edged discs will fly faster than thick blunt edged models. This number currently ranges from 1 to 15.
Glide is the second number and refers to a disc’s tendency stay aloft as opposed to falling. In general, understable discs have a higher glide than overstable models.
High Speed Turn is the third number and refers to what a disc does shortly after leaving your hand. This early phase of flight is the highest speed the disc will be flying at, since it will start slowing down shortly thereafter.
Fade is the fourth and final number. Fade refers to what happens at the end of the discs flight when the disc has lost most of its speed.
For example, consider a disc with 9/5/-3/1 flight numbers. For a RHBH thrower releasing this disc flat and at a reasonably fast speed, the disc will initially move 3 to the right soon after release and at the end of the flight Fade back 1 to the left.
MORE ABOUT DISC FLIGHT
The first number is mainly due to aerodynamics and the second number is highly related to the last two numbers. But it is the last two that are the most interesting. Disc designers noticed early on that by varying the distribution of weight in the rim and the flight plate caused the disc to rotate differently on its axis. Placing more weight in the rim caused the disc to tilt in the opposite direction of rotation. Thus, for a RHBH thrower (causing a clockwise rotation) the disc would try to tilt left on a disc with a heavier rim making it overstable (9/4/-1/3). The reverse is true for understable discs (9/5/-3/1), less weight in the rim causes it to tilt in the direction of its spin or to the right for a RHBH thrower. And finally, when the distribution of weight reaches a happy medium as with a stable disc (9/5/-2/2), the rotation remains relative flat until the very end of the flight were the disc usually fades ever so slightly.
Speed Getting back to Speed which we previously mentioned ranges from 1 to 15. Generally, the higher the speed the higher the potential for more distance. But speed is s double edged sword. The higher the speed discs require a more precise angle of release or they might not even go as far as slower discs. Speed should be matched to the players experience level. It is generally recommended that new players choose drivers in the 9 speed or less range (until they can consistently throw 300’ with accuracy ).
Weight There are some rules of thumb regarding the appropriate weight for a player’s discs. A heavier disc is potentially more accurate and less affected by the wind. The heavier disc flies better than a lighter disc into a head wind. However, a heavier disc requires more power to accelerate its weight to reach the necessary speed to fly right. A lighter disc on the other hand requires less power to reach proper launch speeds. For this reason, players with lower arm speed, less leverage (shorter arms), or less form can usually get greater distance with lighter discs, but this comes with some costs. The lighter discs are more affected by the wind and don’t do well into head winds. The greater glide achieved through their lighter weight negatively affects their accuracy. The lighter disc has less torque resistance and if thrown too hard may flip over (in the direction of the spin) and speed off out of control.
Disc weights are usually written or stickered on the bottom of the disc by the manufacturer. The PDGA regulates allowable weighs to create a level playing field. And for a brand to print “PDGA Approved” on their discs they must agree to abide by these regulations. The PDGA regulations mainly limit the maximum weight for a disc, limiting it to 8.3 grams per centimeter of diameter. The common weight range is from around 135 grams to 180 grams, but there are discs legal up to 200 grams!
There are no hard and fast rules for determining the right weight range for an individual. This will take some experimentation to determine what’s right for you. Your first rules of thumb will probably change as your game evolves. Our recommendation is to choose putters and midranges near or at max weight (except for the very youngest children), since these discs are thrown for accuracy and the heavier discs perform better in more playing condition than their lighter counter parts. Drivers are a place we encourage you to experiment. Find the weight that goes the farthest and the weight that is most accurate for you. Maybe carry a variety in your bag for different shots and playing conditions.
*All examples are for a right handed backhand or left handed side-arm thrower (RHBH, LHSA), others are the mirror image.