Hot Drivers and COR


Frankly GolfEditor's Note: This is the latest in a new weekly feature from Golf Channel Chief Technical Advisor Frank Thomas. To submit a question for possible use in this column, email
Mr. Thomas,
I have two questions related to COR (Coefficient of Restitution). The USGA ruled that a .83 COR was the maximum they would allow in a driver face for legal tournament play. However, until 2008, the R & A (Royal and Ancient) governing board still allows a driver up to a .86 COR.

1) When a USGA pro plays at St. Andrews, or some other course that is governed by R & A rules, are they allowed to use a driver with a higher COR?

2) Can the COR of a driver vary based on the temperature of the club face? If so, by how much?

Best regards, Chris, IL

There is no limit on the COR for drivers, other than in championship play, in countries under the jurisdiction of the R&A. The R&A does enforce the .830 limit for championship play and recommends that all PGA events adopt the same limit. The maximum COR is governed by the Laws of Physics and the (unachievable) limit is 1.00.
Almost every manufacturer is making drivers for the market outside the USA and these vary between .830 and up to .900 I am told. It is going to be interesting to see what happens on January 1st 2008 when the rules will change for the R&A (Royal and Ancient Golf Club of St. Andrews) to mimic those of the USGA and all drivers must conform to the .830 limit. If the masses of golfers dont give up the clubs they purchased (maybe only six months earlier) then we have open defiance of the rules, which dilutes the authority of the governing body and also makes it so much easier to violate another rule. The problem, as I see it, is that once the club has been in use, without being a violation of the rules, one is inclined to believe that it will be OK forever, especially if it has a benefit perceived or otherwise.
By the way, the perceived increase in distance that .860 will give the golfer over .830 is probably eight to ten times the real achievable increase. Temperature does not have a measurable effect on the COR in the range of normal golf weather. To learn more about COR visit
Why do most pro golfers and others, cover their driver, fairway woods and putter, but not their irons? Is it necessary to cover the golf clubs? What are the advantages or disadvantages?
Thank you, Carlito, California

The only reason why anybody covers (head covers) their clubs is to protect them. Generally the putter and the woods are more likely to get dinged than the irons and this is the only reason for covering (protecting) them, not to keep a hot driver hot. Wood head covers were originally designed for wooden clubs for the same reason i.e. to protect the fine finish and thus prevent them from absorbing moisture. With todays oversize metal heads it is becoming more difficult to find a big enough head cover that is easy to put on and take off. Manufacturers seem to be doing a better job, however, in some cases it looks like the head cover costs almost as much as the club it is covering. You may find some golfers who are very particular about their irons and they have rubberized head covers but this is the exception.
What is the origin of the rule on damaged clubs and how can it possibly benefit a player, such as Kevin Stadler, to have a damaged club in his bag? -- Juliet, CO
The rule requires that a shaft must be straight. If it is accidentally bent in the normal course of play (not in anger) the player may continue to use it for the remainder of the round even though it does not conform, or the club may be repaired without delaying play. However, a club which was damaged during a round and is non conforming due to the damage must be repaired to the point where it conforms before using it in a subsequent round.
In most cases a damaged club is not going to help any way so get it fixed as soon as possible to help your game and stay on the right side of the rules.
My swing speed is right around 90 mph, my back swing is slow and deliberate, but on my downswing I try to rip the balls head off. My drives seem to go rather short and definitely fade; my average drive is around 200 yards with carry and roll. Should I be hitting it around 220 carry and around 230 with any kind of roll? So my question is would I be better off with a senior flex shaft? -- Rick, Kentucky

I think a regular shaft flex is fine and you should be driving the ball farther than 200 yards with a head speed of 90 mph. To correct the fade you may need a slight swing correction. But the distance problem is probably the incorrect launch conditions. You ball speed should be close to 130 mph and a launch angle of about 13 to 14 degrees and the spin rate of about 3,000 rpm.
If you dont have these conditions then see what a different head design would do. Eleven or 12 degree loft would be a good start.
Frank Thomas, inventor of the graphite shaft, is founder of Frankly Golf, a company dedicated to Helping Golfers. Frank is Chief Technical Advisor to The Golf Channel and Golf Digest. He served as Technical Director of the USGA for 26 years and directed the development of the GHIN System and introduced the Stimpmeter to the world of golf. To email a question for possible use in an upcoming Let's Be Frank column, please email