# What the Coefficient of Restitution (COR) Did to Driver Specifications

Do you know what Coefficient of Restitution (COR) is?

COR is the ability of an object (the clubhead in this case) to rebound an object – the golf ball.

Drop a golf ball squarely on the the face of a driver that is anchored and immovable. The ball will bounce back at a lower speed than the speed it was going when it struck the face. It is calculated by dividing the resulting speed by the initial speed. If it lost no speed, the COR rating would be 1.00.

The rulemakers in golf – the USGA and the R and A have agreed on a rule that allows any golf club to have a COR of no more thn 0.83. In other words, if a ball is dropped from 12 inches, the ball can not rebound more than

12 inches x 0.83 = 9.96 inches.

If it does rebound more than 9.96 inches, the club is illegal and not allowed in tournaments.

The Results of this Rule

The rule was implemented in order to keep golf courses from becoming obsolete. If the ball could be hit substantially farther, golf courses would be too short.

Golf club scientists working for club manufacturers quickly figured out how to make metal woods with a COR 0.83 on a consistent basis. With all modern drivers having the same COR, there is very little difference in distance a driver can drive the ball due to clubhead characteristics. Just about every driver has the same COR of 0.83.

Now, the only head characteristics I am aware of that change the distance a ball can be hit are:

• clubhead aerodynamics that have less drag in the air
• a slot behind the face on either the crown (top) of sole (bottom) of the clubhead – or both
• various protrusions along the top of the face. Ping has done this with the G30 driver

Why Would Club Companies Advertise That Their New Model Hits Farther?

New drivers are often advertised as hitting farther than previous models. There are several club characteristics which can do that. Keep in mind that we all age.

• The clubhead variations discussed above make only very minor distance increases.
• The newer golf balls spin less and need to be launched higher than the old rubber band wound balls in order to maximize flight in the air where there is less resistance.
• As we get older, a softer or lower bend point shaft will kick the ball to a higher speed and higher trajectory for more carry.
• Higher loft heads will also launch the ball higher so it carries farther.
• Most drivers have a lower marked loft than their actual loft. The lower marked loft doesn’t hurt an aging golfer’s ego, and the higher actual loft increases carry distance. The most extreme example I have seen was a TaylorMade R9 driver marked 12.5 degrees with an actual loft of 17 degrees. Apparently their quality control people missed it before it went out the door.

The Bottom Line

Any good quality driver head with the proper loft, proper head weight, and proper shaft (including correct length) will perform well for you. You won’t be able to buy a club like that off the rack. Visit a good custom clubfitter who can measure your swing with various shafts and heads of various lofts to get a driver that will perform well for you for years.