COR is a measure of the efficiency of the transfer of energy between two colliding bodies. To better understand the concept of COR imagine that a ball is fired at a ridged steel plate at 100 mph and it bounces back at 75mph the COR is 75/100 = 0.75 .

It is not possible to get a COR of 1.00 (100/100) as this would mean that there was no energy loss during impact.

Taking into account the weight of the ball and the club head and the speeds of these two colliding bodies, before and after impact one can calculate the COR.

Wooden Clubs

Calculation

It has been found that the COR of the collision between the club head, which does not exhibit any Spring Like Effect (SLE) and a standard ball is about 0.78.

If the face of the club deforms and recovers during impact (like a trampoline), taking up some of the deformation that would have otherwise been in the ball, the COR would increase as there are fewer losses in the deformation and recovery of the club face than in the ball.

In 1998 The USGA has set the COR limit for woods (metal woods) at 0.822 with a test tolerance of .008 effectively taking the limit up to 0.830. This is about 0.05 above no SLE and equivalent to about 10-15 yards in distance based on the resulting increased ball velocity and change in launch conditions.

There is a limit that is governed by the Laws of Physics. From a practical point of view this is approximately 0.930. We all intuitively know that a ball will not bounce higher from whence it was dropped, no matter how resilient the ball or how "springy" the surface. No matter how technology advances or new materials developed the resilience of impact is limited.

Looking at the History of this rule may help:

This rule is essentially unchanged today; however there seems to be some divergence from the literal translation of the rule and the way it is being interpreted and enforced.

The distance Tour players are hitting the ball and how to harness this has been an ongoing concern for many years. In spite of this the USGA in 1998, permitted some SLE which together with the change in launch conditions has added approximately 15 yards to the average driving distance on the PGA Tour.

The method of measuring the SLE in a clubface, recently developed by the USGA is to use a pendulum on the end of which is a metal hemisphere which bounces against the clubface and the contact time relates directly to the SLE.

This is portable but must never be used as a radar gun to police the clubs in players bags. If, however, the player is in doubt as to the conformity of his club, this pendulum device should be available for his convenience. Golfers call infractions of the rules on themselves which includes equipment and so it should be.

FOR MORE ON FRANK'S VIEWS AND ARTICLES ON THE SPRINGLIKE EFFECT AND RULES, CHECK OUT FRANKLY SPEAKING AND LOOK UNDER THE DISTANCE SECTION. YOU CAN ALSO READ FRANK'S ANSWERS TO INTERESTING QUESTIONS ON SPRINGLIKE EFFECT IN THE DRIVER AREA OF THE QUESTION AND ANSWER SECTION.