The secret of driver head performance? From a design standpoint, it is all about maximizing how “hot” the face is and making sure that they are manufactured consistently to that level of performance. Having worked with a lot of players with swing speeds from 50 mph to 145 mph (yes, 145 mph) I can tell you that driver heads designed for slower speeds have much different characteristics than those for higher swing speeds like our Long Drivers (Krank Golf). I have included a couple of videos courtesy of Krank Golf that explain a couple of these concepts as well.
The first secret is having a high COR (coefficient of restitution) or CT (characteristic time). Both of these measure how fast a ball rebounds off the face of the driver. The highest COR allowable by the USGA is .830. This is tested by firing a golf ball out of an air cannon at a driver head. The velocity of the ball hitting the head is 100 mph and the rebound velocity cannot be more than 83 mph. A similar test is for CT or the time a steel ball stays in contact with a driver head. If the CT is over 257 microseconds, the head is deemed to be non-conforming and cannot be used in USGA sanctioned events. Most driver heads are actually manufactured to slightly lower performance standards than the maximum allowed so as not to run the risk of having a random test by the USGA deem their clubs non-conforming and have to do a recall of all of their drivers. I actually saw that happen in 2007 with the Cleveland Launcher 460 10.5 degree driver!
The second secret is to make sure the driver you have is up to typical . The challenge for the manufacturers is to make their heads consistent so they do not end up with a batch of “hot” or “dead” heads. When we fit golfers, we measure the smash factor (ball speed divided by club head speed) to dial a golfer into the head, shaft and grip that give them the most distance and accuracy. The smash factor is a good measurement as long as we are using a ball flight monitor like TrackMan or FlightScope which measures both club head speed and ball speed accurately. Every year we measure these factors for our customer’s existing equipment as well as our demo clubs. If a golfer is hitting their driver on the sweet spot and the smash factor is still appreciably below the theoretical maximum of 1.50, that driver head is dead. It is not uncommon to find hot and dead heads in our golfer’s bags.
The third secret is making sure your driver head is not flattened, cracked or has gone dead. Every driver has a certain degree of curvature called bulge and roll that allows that head to create the spring-like effect and maximize COR. There is typically 10 degrees of bulge (curvature from heel to toe) and 10 degrees of roll (curvature from sole to crown). Hitting the ball repeatedly on the sweet spot can actually cause the face to “cave in” or lose its curvature. This will cause the club to lose its rebound properties and the club will feel dead. The higher your swing speed and more consistently you hit the ball on the sweet spot, the greater the chance the club face will go dead. The loss of bulge and roll cna be measure simply by sliding a credit card on edge across the face and being sure to see light on either side of the center. A better way is to get a simple 10 degree bulge and roll measuring device from Golf Works and sliding it across the face. A head that has gone dead can also cause erratic shot patterns.
So, make sure your fitter checks your driver to make sure the club you have is performing up to its performance standards. It is quite simple to do and can help you decide if you need a new driver or just a new shaft.