Ava Romero
COR, or Coefficient of Restitution, is a term from the world of science and physics that has made its way into the golf industry. It is a measurement of the energy transfer between a golf club and a golf ball, and it is important because it determines how far a golf ball will travel. The COR of a golf club can be measured by firing a golf ball from an air cannon at a club head and measuring the velocity at which the ball bounces off. The COR value is expressed as a number between 0 and 1, with 0 indicating no energy transfer and 1 indicating a perfect energy transfer. While the USGA and R&A no longer use COR to measure drivers, it is still used to measure fairways, hybrids, and irons, and it continues to be a relevant factor in the distance a golf ball will travel.
| Characteristics | Values |
|---|---|
| What does COR stand for? | Coefficient of Restitution |
| What does COR mean in a golf context? | The energy transference between a golf club and a golf ball |
| How is COR measured? | By firing a golf ball from an air cannon at a club head and measuring the velocity at which the ball bounced off different areas on the face |
| What is the COR scale? | 0.000–1.000 |
| What does a COR of 0 mean? | All energy is lost in the collision |
| What does a COR of 1 mean? | All energy is transferred from one object to the other |
| What is the current COR limit? | 0.830 |
| What does a COR of 0.830 mean? | 83% of the energy from the club face can be transferred into the ball |
| What happens if a COR is above 0.830? | It is ruled non-conforming under the rules of golf |
| Who regulates COR? | The USGA and R&A |
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What You'll Learn
COR and ball speed
The acronym COR is short for "Coefficient of Restitution". It is a scientific term used to describe the energy transference between two objects. In the context of golf, the COR of a club measures its ability to transfer energy to the ball when the two collide. A higher COR means less energy is lost at impact, resulting in more distance.
The COR measurement is expressed as a number between 0.000 and 1.000. A COR of 0.000 would mean that all the energy is lost in the collision, whereas a COR of 1.000 would mean that all the energy is transferred from one object to the other, with no energy loss. In golf, a COR of 1.000 is impossible because the club and ball are made from different materials and have different masses.
The USGA and R&A regulate the COR of golf clubs to prevent manufacturers from creating clubs that can hit the ball too far. The current COR limit for clubs is 0.830. A COR higher than 0.830 is ruled non-conforming.
The COR of a club can be measured by firing a golf ball from an air cannon at the club head and measuring the velocity at which the ball bounces off different areas of the club face. This is known as the COR test. However, the COR test is time-consuming and has been replaced by the CT (Characteristic Time) test, which uses a small, portable pendulum system that strikes the club face with a steel ball. Sensors then measure the amount of time the two objects are in contact.
The COR of a club affects the ball speed, which is one of the factors that determine how far the ball travels. A higher COR will generally result in a higher ball speed due to increased energy transfer. Additionally, the swing speed or clubhead speed also affects ball speed. A faster swing speed will result in a higher ball speed, assuming all other factors are equal.
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COR and energy transfer
The acronym COR stands for "Coefficient of Restitution", a term from the world of science and physics. In golf, it is used to measure the energy transfer between the clubface and the golf ball. The coefficient of restitution of Object A is a measurement of Object A's ability to transfer energy to Object B when the two objects collide. In a golf context, Object A is the golf club, and Object B is the golf ball.
A COR of 0.000 would mean all energy is lost in the collision, whereas a COR of 1.000 would mean a perfect, elastic collision where all energy is transferred from one object to the other. A COR of 1.000 is impossible in a golf club-golf ball collision because the clubface and the golf ball are made from different materials and have different weights or masses. Therefore, there will always be some energy loss at the moment of impact in golf.
A higher COR means more distance, or how far you hit your golf ball. In other words, the higher the COR, the farther a player will be able to hit the ball. A COR of 0.830 means that a maximum of 83% of the energy from the club face can be transferred into the ball. The USGA imposes a COR performance restriction at 0.830 to ensure all clubmakers are working toward the same maximum limit.
The COR of a golf club can be measured by firing a golf ball from an air cannon at a clubhead and measuring the velocity at which the ball bounces off different areas on the face. Sensors can also be used to measure the amount of time the club face and the ball stay in contact with each other. This is known as the CT or "characteristic time" test.
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COR testing methods
COR, or Coefficient of Restitution, is a scientific term used to describe the energy transfer between two objects. In the context of golf, it is used to measure the energy transfer between a golf club and the ball. The COR of a golf club is measured by firing a golf ball from an air cannon at a club head and recording the velocity at which the ball bounces off different areas of the club face. The velocity of the ball before and after it hits the club face is used to calculate the COR, which is a numerical value between 0.000 and 1.000. A COR of 0.000 would indicate that all energy was lost at impact, whereas a COR of 1.000 would indicate that all energy was transferred from the club to the ball, resulting in the ball rebounding at the same speed it hit the club.
The USGA and R&A regulate COR in golf clubs to prevent manufacturers from creating clubs that can hit the ball too far, which could overwhelm golf courses. The current COR limit for golf clubs is 0.830, meaning that a maximum of 83% of the energy from the club face can be transferred into the ball. Any club with a COR higher than 0.830 is deemed non-conforming.
While COR testing provides an accurate representation of the physics of a golf club hitting a ball, it is time-consuming, taking around 45 minutes to map each club head. As a result, the USGA and R&A moved to a different test called the CT (Characteristic Time) test in 2004. The CT test also measures the spring-like effect of a club face, but it uses a small, portable pendulum system that strikes the face with a steel ball. Sensors then measure the time the two objects stay in contact with each other. The CT test is quicker and easier to use than the COR test, but it is not considered a perfect replacement due to differences in how the tests are set up and measured.
It is worth noting that while COR is no longer used to measure drivers, it is still used to regulate fairway woods, hybrids, and irons. Additionally, club manufacturers are constantly exploring new ways to improve the energy transfer from the club to the ball, which directly impacts the COR.
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COR limits
The acronym COR stands for "Coefficient of Restitution", a term from the world of science and physics. In a golf context, it describes the energy transference between a golf club and the ball it strikes. The COR measurement is expressed as a number between 0.000 (meaning all energy is lost in the collision) and 1.000 (which means a perfect, elastic collision in which all energy is transferred from one object to the other).
The COR limit in golf clubs is currently 0.830. This means that a maximum of 83% of the energy from the club face can be transferred into the ball. Any club with a COR measuring higher than 0.830 is ruled non-conforming under the rules of golf.
The USGA and R&A regulate COR in golf clubs to prevent manufacturers from making clubs that give players too much distance. Before 2004, the R&A and the USGA tested drivers using a COR test, which measured the spring-like effect of a club head. This was done by firing a golf ball from an air cannon at a club head and measuring the velocity at which the ball bounced off different areas of the face.
While the COR test was accurate to the physics of a golf club hitting a golf ball, it was time-consuming, taking about 45 minutes to map each club head. In 2004, the USGA moved to a different test, called the CT test, which uses a small, portable pendulum system that strikes the club face with a steel ball. Sensors then read the amount of time the two objects stay in contact with each other. The limit of time placed on golf clubs is 239 milliseconds with a tolerance of 18 milliseconds. Therefore, any golf club that measures higher than 257 milliseconds on the CT test is deemed illegal.
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COR and club face materials
The acronym COR stands for "Coefficient of Restitution" and is a term from the world of science and physics. In a golf context, it is a measure of energy transfer between the club and the ball. The COR measurement is expressed as a number between 0.000 (meaning all energy is lost in the collision) and 1.000 (which means a perfect, elastic collision in which all energy is transferred from one object to the other). The perfect 1.000 figure is impossible to achieve in golf because the club and ball are made from different materials and have different mass properties.
The USGA and R&A regulate COR in golf clubs to prevent manufacturers from making clubs that give players unfair advantages in terms of distance. The current COR limit in golf clubs is 0.830. Any club with a COR measuring higher than 0.830 is ruled non-conforming.
COR is influenced by the materials used in the club face and the design of the club face. For example, ultra-thin-faced drivers can exhibit a "'spring-like effect" or ""trampoline effect", where the face of the driver depresses and then rebounds when striking the ball, providing extra speed and distance. This effect is enhanced by materials such as Super Hardened Beta Titanium, which increases the spring effect and durability of the club.
The design of the club face can also impact COR. For instance, the ""Bulge and Roll" curvature of the driver face can enhance the "Gear Effect", bringing off-centre hits back to the fairway. Additionally, a 100% Cupped Face Forged design increases the size of the sweet spot, resulting in greater forgiveness and more consistent ball flight.
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Frequently asked questions
COR stands for Coefficient of Restitution.
COR is measured by firing a golf ball from an air cannon at a club head and recording the velocity at which the ball bounces off different areas on the face.
A higher COR value is generally better as it means there is less energy loss at impact with the golf ball. The maximum COR value allowed by the USGA is 0.830.
COR affects how far you hit your golf ball. A higher COR equates to more ball speed due to higher energy transfer.
CT stands for Characteristic Time and is the test that replaced COR in 2004. CT uses a small, portable pendulum system that strikes the face with a steel ball. Sensors then read the amount of time the two objects stay in contact with each other.
