How Does COR Affect Your Golf Game?

[GolfSpy WD]

http://wishongolf.com/how-does-cor-affect-your-golf-game/

 

Companies, organizations and industries love to use acronyms because these abbreviations of longer terms can so easily roll off the tongue. One that has been a buzz-acronym in the golf equipment industry since 1998 is COR – short for Coefficient of Restitution.

 

Experienced golfers know the COR is a number which represents how “hot” the face of their clubhead(s) is made – or rather how much distance they can get out of the shot for their swing speed. COR made its way into the golf industry's vernacular back in 1998 when the United States Golf Association got freaked out at the distance the pros were hitting the ball. Acting before ever doing any testing, the USGA blamed the pros' distance increase on the use of the relatively new (at that time) titanium drivers and enacted a rule that placed a limit on the COR of all driver faces.

 

COR is actually a measurement of the energy transfer in a collision of two objects. It can be expressed in a number between 0 and 1. For example, when the USGA put a COR limit of 0.830 on driver faces, that meant no driver would be deemed to be conforming to the rules if more than 83% of the energy in the collision of the driver head with a golf ball were transferred from the head to the ball.

 

The COR rule also became known as the “spring face rule.” This was a little unfortunate because in fact, a higher COR clubface does not really act like a spring. When you think of spring face, it is easy to think that the ball causes the clubface to flex inward, and upon flexing back out the ball is propelled as in the manner of a trampoline sling shotting a gymnast up.

 

Actually, higher COR faces work like this. In the collision of the clubface and the ball, there is always some energy lost. This is because the face flexes inward and the ball is compressed against the face. Both actions result in a loss of energy. Of the two, the ball loses by far the most energy when a shot is hit because it can squash as much as 30% of its diameter against the face of the driver. In a normal shot hit with an old thick face stainless steel metal wood, scientists estimate that 80% of the energy loss in such an impact came from the ball while the balance of 20% came from the clubhead.

 

The idea of a higher COR face design, whether done for a driver or any other clubhead, is to allow the face to flex inward a little more so that the ball is not compressed as much against the face. When that happens, the face loses a tiny bit more energy because of its increase in face flexing. But the ball then loses a lot less energy than before because it is compressed so much less because of the slight increase in face flexing.

 

The net result? The ball takes off at a higher velocity and flies farther for the same clubhead speed and same loft angle on the clubface. Hence high COR means more distance regardless of your clubhead speed.

 

And that's how that acronym really works in the design and performance of a golf clubhead.

[GolfSpy WD]

I saw a few questions about the COR limit recently and we've debated ad nauseum how ball compression effects distance. This seemed to explain both.

[Shambles]

I'd like the premise restated please. As presented, it seems to imply compressing the ball is a bad thing for distance. That's contrary to what I think of as common wisdom.

 

 

Shambles

[GolfSpy WD]

I'd like the premise restated please. As presented, it seems to imply compressing the ball is a bad thing for distance. That's contrary to what I think of as common wisdom.

 

 

Shambles

 

Compressing the ball creates energy loss, as does flexing the club face. However, you need to compress the ball to generate spin. Without spin the ball would drop out of the air sooner. Thus, you need the right amount of compression to generate maximum distance so you get the amount of spin desired without loosing too much energy. I'm assuming loss of energy is not linear to amount of compression here because of the various cores in the ball and the fact that the more something is compressed, the harder it is to compress more.

[JBones]

The makes me understand how I lose so much distance off the driver with balls such as the RX.

[Shambles]

Compressing the ball creates energy loss, as does flexing the club face. However, you need to compress the ball to generate spin. Without spin the ball would drop out of the air sooner. Thus, you need the right amount of compression to generate maximum distance so you get the amount of spin desired without loosing too much energy. I'm assuming loss of energy is not linear to amount of compression here because of the various cores in the ball and the fact that the more something is compressed, the harder it is to compress more.

 

I'll take exception to the description as energy loss. Whereas I do agree that compression is needed to help create backspin, compression also stores energy that, if released at the right moment, becomes greater distance. The same is true, in my opinion, with COR in a club face. Thus a ball can be sent farther if properly compressed and there is a full follow through to also give it a launch pad at release.

 

Knowing that the face compressing and releasing equates to greater distance is what fueled the effort to find the thinnest face possible in practical terms and also the right degree of brittle for the ball. The player's job is to find a way to take advantage of these characteristics to his benefit. Of course, a fair degree of skill is needed to take advantage of this potential. The idea of having a very hard ball and a very hard face proved bankrupt only a couple of decades ago. That's why the 100 compression ball was, for a short period of time, replaced by a run on ladies or 80 compression balls for a short period of time. Skill is needed to take advantage of these . The inability to take advantage can leave the player with the idea that new clubs designed for this are just a marketing ploy to make you change your old clubs for new.

 

New clubs built to take advantage of this theory are presumed potentially longer but the player needs better skill to benefit. Most players have difficulty meeting this requirement and may not even be aware of how much skill is needed to make their ball and club perform well.

 

 

Shambles

[GolfSpy WD]

I'll take exception to the description as energy loss. Whereas I do agree that compression is needed to help create backspin, compression also stores energy that, if released at the right moment, becomes greater distance. The same is true, in my opinion, with COR in a club face. Thus a ball can be sent farther if properly compressed and there is a full follow through to also give it a launch pad at release.

 

Knowing that the face compressing and releasing equates to greater distance is what fueled the effort to find the thinnest face possible in practical terms and also the right degree of brittle for the ball. The player's job is to find a way to take advantage of these characteristics to his benefit. Of course, a fair degree of skill is needed to take advantage of this potential. The idea of having a very hard ball and a very hard face proved bankrupt only a couple of decades ago. That's why the 100 compression ball was, for a short period of time, replaced by a run on ladies or 80 compression balls for a short period of time. Skill is needed to take advantage of these . The inability to take advantage can leave the player with the idea that new clubs designed for this are just a marketing ploy to make you change your old clubs for new.

 

New clubs built to take advantage of this theory are presumed potentially longer but the player needs better skill to benefit. Most players have difficulty meeting this requirement and may not even be aware of how much skill is needed to make their ball and club perform well.

 

 

Shambles

 

That's the point of COR though, how much energy is released during decompression. For the .83 limit, 83% of stored energy is released, meaning 17% of energy was lost due to compression of the club face. Lower COR means less energy transfer.

 

From what I read, higher COR means more flex of the club face so the energy loss is in the club face rather than the ball, so the total release energy is higher and thus the ball travels farther.

 

Here's an article that goes into even more detail: http://www.tutelman.com/golf/swing/golfSwingPhysics4.php

[Shambles]

That's the point of COR though, how much energy is released during decompression. For the .83 limit, 83% of stored energy is released, meaning 17% of energy was lost due to compression of the club face. Lower COR means less energy transfer.

 

From what I read, higher COR means more flex of the club face so the energy loss is in the club face rather than the ball, so the total release energy is higher and thus the ball travels farther.

 

Here's an article that goes into even more detail: http://www.tutelman.com/golf/swing/golfSwingPhysics4.php

 

 

Seems we are not necessarily in disagreement. You are looking at the 17% potential loss and I am looking at the 83% potential gain.

 

Frankly, if I could consistently get even just 80% of the potential 83% I would be a deliriously happy man for a week and then probably be working hard to get the additional 3% all the while cursing the rules makers for limiting my horizon.

 

 

Shambles