COR stands for "coefficient of restitution." The USGA wants to know how fast the ball comes off your clubs, and especially your driver. For every victory on the PGA tour, they request the winner to submit his driver for analysis. They test it similar to the way we did it at the Hogan test center. We used a machine called the Stryker, which can shoot a ball up to 120 miles per hour. The club is placed as a stationary device. It is not swung. Then the ball is shot like a cannon at 100 mph off the face. It must not rebound more than 85 mph. If it exceeds that, it is labeled as “non-conforming” and would be subject for disqualification of the winner.
Those two words, “non-conforming,” used to mean the club was illegal. Not so anymore, since many clubs are not sent to the USGA for testing. It might be a club that you as an amateur would purchase. You may purchase a non-conforming club and not even know it. Unless you are playing a USGA-sanctioned event, it really does not matter.
Spring effect means essentially the same as COR. Callaway used the title VFT on their clubs at one time. VFT stands for variable face thickness. The sweet spot on the face had thicker metal and the outer layer was thinner, thus producing a spring effect.
Current technology has advanced a great deal. Manufacturers are working on making the whole face react as if it were the sweet spot. Taylormade has come out with the twist face, which seems to work for off-center strikes. Callaway comes close to making a total sweet spot face with their Epic driver.
I have known about some companies that make and advertized non-conforming drivers. The face is very thin. I would not recommend it if you are a heavy hitter, since the face might crack and cave in. In addition, they are expensive. I personally have some drivers in stock which are non-conforming, but just barely.
I am still a huge proponent of finding the correct shaft that fits you. I know this will give you the best result for distance and how straight you hit the ball.
If you have questions or comments please contact me at Dcharn1@sbcglobal.net. I would enjoy hearing from you.
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