Alpha Golf

Coefficient of Restitution (COR) is a physics term for the value representing the ratio of velocities before and after an impact. An object with a COR of 1 collides elastically, bouncing perfectly with no energy loss. While an object with a COR of 0 is said to collide inelastically, effectively “sticking” to the object it collides with. Mathematically, COR is the square root of the ratio of the height of one bounce to that of the preceding bounce.

Golfers paid more attention to physics geeks like me after the USGA started measuring and regulating clubs for COR in 1984. The thinking was that a clubface with a “trampoline” or “spring-like” effect would send balls flying 400+ yards off the tee. So they limited COR to 0.83. (BTW, this rule coincidentally came into play when manufacturers discovered that titanium drivers were much more ideal than steel drivers in creating enormous ball speeds)

Maximizing COR

There are 2 keys to maximizing the COR of a driver:

1) High grade titanium face - SP700 and 15-3-3 titanium are the best choices for elastic collisions

2) Super Thin face - a thin face provides a “spring-like effect” where the face momentarily depresses at initial contact and then “springs” back into shape at launch.

If the face is too thin, the driver can crack at high swing speeds. If the face is too thick, you lose the spring-like effect where the face won’t depress. The right tradeoff of thickness for the particular type of titanium being used is what keeps us golf designers busy in the labs!