COR question

[neophytea]

Coefficient of Restitution (COR) as stated in Golf Digest, Feb 11, page 99.

“The measurement of spring like effect of a flexing clubface.  The USGA limit is .83, which means that if a balll is projected at a club at 100 miles per hour, it must bounce off at 83 mph or slower to conform.”

My question is: If a certain club is conforming at 100 mph with a rebound velosity of 83 mph, what is the rebound velosity at a swing speed of  120 mph, 140 mph and 80mph?  Must all swing speeds have a COR of -.83?

My hypothesis is that through technology and engineering club makers are making clubs that conform at 100 mph but may have a rebound velosity greater than .83 at high swing speeds which may result in a cor much lower than .83 for someone like me who has a much lower swing speed.

Swing speed 80 mph / rebound velosity ________ mph = _____ COR

Swing speed 100 mph / rebound velosity 82.9999 mph = -.83 COR  makes club legal.

Swing speed 120 mph / rebound velosity _______ mph = _____ COR

Swing speed 140 mph / rebound velosity _______ mph = _____ COR

I am looking for a club that conforms at 100mph and has the highest COR for my swing speed.

[Harmonious]

Sounds like a question that should be asked of club manufacturers.  But, for what it's worth, I think there are many more important things to worry about than what the coefficient of restitution of your driver may be.  Whether it is .83 or .80 doesn't make much difference.

[Stretch]

The USGA actually tests spring-face conformity in a rather more sophisticated way, using a steel ball on a pendulum that swings down to contact the center of the driver face. The "characteristic time" the ball remains on the face is measured by extremely accurate sensors. The current allowable limit (equivalent to 0.83 COR) is 239 microseconds, with a tolerance of 18 microseconds, for a maximum of 257 microseconds.

It is my understanding that the COR would be a constant at any speed over 100mph up until the point where the driver face actually caved in. As far as lower speeds go, I do remember reading in one of Tom Wishon's books that tests of nonconforming (ie. more than 0.83 COR) drivers with average golfers showed little distance gain because they lacked the club head speeds necessary to fully flex the face.

[WUTiger]

A local clubfitter suggests there's a downside to pressing the COR limit and trampoline effect: The thinner clubfaces are less durable.

[596]

I use a non-conforming driver sometimes just for fun.  Its COR is 86 (94 ss)  I might get 10-12 more yards with this driver compared to my Callaway Edge.  Not really a big difference in the grand scheme of a 6300 yard course.  The ad stated an extra 20-40 yards....NOT.  I figured I'd try one just for fun.  Actually I'm having it re-shafted this week with a longer, lower kick and stiffer shaft.....just to see what happens.

A company in Phoenix sells "hot" drivers.  They will not recommend a COR of more then 86 for someone with a swing speed over 90 and will in any case not recommend shaving a driver to a COR of more then 90 (90 COR is for swing speeds under 80mph).  If you have a good swing speed of over 90 and use a COR of 90 you will dent the club face in a short matter of time.  They don't recommend using the club more then a few times on the range to save it for the course.

You can send them your driver and they shave the face thinner for more trampoline effect (COR) or you can buy already shaved.  They advertise/sell on eBay.  There's also a company somewhere in NY that shaves them, too.

[jamo]

Originally Posted by WUTiger

A local clubfitter suggests there's a downside to pressing the COR limit and trampoline effect: The thinner clubfaces are less durable.

One funny/neat thing to note about that is long drive guys will usually use drivers that have thicker faces, and thus a lower COR, than normal. For durability reasons.