What Makes a Disc Understable or Overstable?

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Whether you are a veteran or novice disc golfer, understanding the factors that control your disc’s path through the air is super important.  Sure, your technique matters, but even with identical throws, different discs will behave differently. 

This article will explain how the physical characteristics of a disc come together to affect its flight path, so the next time you choose which disc to use, you’ll have a good idea of how it’ll behave.  You will also read about the 4 ratings on each disc and how they relate to stability.  In the end, whether you need to drive a straight shot or curve around an obstacle, you’ll be able to pick the right disc for the job. 

What is Stability?

What is Stability

Stability is the term disc golfers use to describe a disc’s behavior, given a fast, even throw with no wind.  When discussing stability, most people will assume a right-handed, backhand thrower (RHBH).  For this type of thrower, the disc leaves their hand spinning clockwise, or to the right.

A disc that is stable will continue straight until it loses significant speed, then veer in the direction away from its spin; to the left, for an RHBH thrower.  An overstable disc will turn away from its spin for the whole flight, getting more and more pronounced as it loses speed.  Finally, an understable disc will start turning in the direction of its spin before straightening out and veering off to the left as it decelerates.  But what contributes to disc stability?  To understand how the physical construction of a disc determines its stability, you first have to know about the 4 ratings of a golf disc and what attributes they describe.

Why Do Discs Become Understable?

The stability of a disc is fundamentally determined by its manufacture.  Different shapes interact differently with the air as they spin and change speed.  Since stability is not a perfect science, figuring out which physical characteristics influence it has been based mostly on observation. 

Most understable discs share several qualities.  Having a curved edge and narrow rim, coupled with a domed top, heavily contributes to understandability.  The type of plastic also seems connected, and discs made from softer, less rigid material are generally understable.  Regular wear and tear are also factors, and discs that have taken a beating tend to become less stable over time, regardless of where they started.  More durable materials will hold off this process for longer.  Finally, understable discs typically have a low parting line; the seam produced where the 2 parts of the mold came together during manufacture.      

The 4 Ratings of a Disc

The 4 Ratings of a Disc

Innova, the disc manufacturing company, applies 4 ratings to their discs, and most other producers follow suit.  These ratings denote the 4 major performance aspects of a disc in flight.  When you understand the ratings and what they represent, it is much easier to know and explain the stability of any given disc.  For consistency, most ratings are printed on the top of a disc from left to right in this order: Speed, Glide, Turn, and Fade.

The Speed rating of a disc denotes the speed required to throw it properly; that is, throw it, so it achieves the performance suggested by the other 3 ratings.  Speed is rated on a scale of 1 – 15, with 15 being used for discs with the highest requirement, such as drivers.  The main contributor to a disc’s Speed rating is the aerodynamics of its cross-section – a sharper edge means a faster disc.

Glide is a disc’s tendency to ride the air.  Measured on a 1 – 7 scale, discs with a higher rating tend to ride the air currents for longer.  This makes it easier for players who cannot generate a lot of speed to throw greater distances.  However, high Glide discs are easily disrupted by crosswinds and headwinds.  Low Glide discs, on the other hand, are less easily moved but require significant speed to remain in the air.

A disc’s behavior upon release, when it’s traveling at top speed, is measured by its Turn rating.  The scale goes from +1 to -5, with the lower-rated discs turning more in the direction of their spin – to the right for an RHBH.  The higher-rated discs follow a path farther to the left.  Since Turn represents a disc’s behavior at peak speed, it is sometimes called high-speed stability, and discs with low Turn ratings start their flight as understable.

Fade describes a disc’s behavior after it loses significant speed.  Sometimes called, low-speed stability, the ratings go from 1 to 5, and measure a disc’s tendency to move opposite the direction of its spin – to the left for an RHBH thrower.  Discs with a rating of 5 will veer sharply to the left as they lose speed, becoming very overstable as they near the end of their flight path.

How Do I Know if My Disc is Overstable or Understable?

The best way to tell if a disc is understable or overstable is to throw it; of course, this doesn’t help you in the middle of a tournament.  Instead, there is a shortcut that might give you a good estimate as you rummage through your bag.  Add the Turn and Fade ratings together.  If the number is negative, your disc should be understable.  Positive scores are overstable, and a 0 would be stable.  Of course, you need to account for age and wear and tear, but this method is a great way to get a quick estimate.

How Does it Work?

Adding Turn and Fade together to predict stability accounts for a disc’s behavior at both high and low speeds.  A lower Turn rating shows that a disc will start its flight understable, following the direction of its spin.  However, a higher Fade rating suggests it will veer away from the direction of its spin sharply as it decelerates. 

These two behaviors can cancel each other out, making a disc that turns back and forth, even drastically, end up hitting a target directly ahead of where it was launched.  Understanding the interplay of Turn and Fade, and how they contribute to overall stability can help you choose the right disc for your needs, whether it’s a straight shot or dodging in and among the trees.


While knowing that overstable golf discs turn to the left and understable discs turn right then fade left is a great start, being able to recognize the physical characteristics of overstable and understable discs is even better. 

However, once you know how the ratings on your disc interact with each other to determine overall stability, you can start to up your game with more accurate and complicated throws.  The next time you need to go looking for the right disc, take a look at the ratings, so you’ll know how it behaves at each part of its journey towards the basket.