The Affect of a Smooth Driver

About eight years ago I walked into a golf shop called Hickory Sticks in St. Andrews, Scotland.  They build replicas of some of the old hickory shafted clubs found in the British Golf Museum.  They included the Forgan grassed driver, the McEwan playclub, and the Hugh Philp baffing spoon to name a few.  Their work was quite good.  They also build clubs of their own design, and while looking at one of their drivers I noticed it had no grooves on the face.  The head was made of persimmon and the face was absolutely smooth.  I asked the gentleman why they had made it that way and his reply was, “Those grooves don’t have any purpose on a driver.  They don’t do a bloody thing.”  I did not buy one, but it did get me thinking about the reason for grooves on a driver, and are they really necessary?  Are they needed for spin or not?

Most golfers are well aware of how the spin of a golf ball affects their game.  Spin not only effects how high and far the ball travels, but also helps determine how far the ball rolls after landing.  More knowledgeable players are aware of how to tailor their spin for different parts of their game; less spin off the tee for increased roll and more spin around the greens for improved control.  However, most of us are unfamiliar with just how this spin is created.

What was two years later while at a conference in Northern Ireland, I attended a session titled “Can a Smooth Clubface Increase Spin?  The leader of the session was Art Chou of Chou Golf Design Labs.  He and Deshou Liang of Drexel University had done a study where they found a smooth faced club at low loft angles produces more back spin than a rough surface.

To explain this I am going to quote Art, “For lofts under 20 degrees, the period of contact between the ball and the club face can be divided into two stages.  During the first stage of contact the ball is compressed on the club face, making the ball stick to the club surface.  As it compresses, the ball experiences some deformation as the loft of the club causes the ball’s center of gravity to move up the club face.  As the ball tends to move upwards, the club exerts a downward frictional force on the ball surface, creating the ball rotation that becomes backspin.  Due to the large normal force at impact resulting from the relatively low loft angle, this frictional force is independent of the surface roughness of the club face.  This backspin increases until, at the end of the period, the ball experiences such a large backspin that its surface in contact with the club actually starts to move downward.”

Art went on to explain, “During the second contact period, while the ball surface is moving downward, the club exerts an upward frictional force on the ball.  This upward force acts against the direction of the ball’s backspin, reducing the overall spin with which the ball leaves the club face.  Where the downward force experienced during the first stage was independent of the surface properties of the club face, the upward force during the second stage is entirely related to the roughness of the face material.  This is because the forces acting on the ball at this time cause it to slide along the club face instead of sticking.”

This means that the face roughness, or coefficient of friction, does not contribute to the backspin produced during stage 1 but contributes significantly to the forces acting against backspin in stage 2.  So, a rough surface, such as rough steel, retards the overall spin of the ball more than a lower friction material such as Teflon.  Therefore the smoother surface generates greater backspin. 

At higher lofts, such as over 40 degrees, the nature of the contact period changes.  The ball experiences only the first stage of  contact, except this time the increased loft means that the ball never sticks to the club face.  Instead, it only experiences a sliding up the club surface.  This means that the downward frictional force exerted on the ball is proportional to the surface roughness; a rougher club face creates a larger downward force, resulting in increased backspin.

Many individuals attending the seminar questioned the study stating the results were questionable at best and the study needed to be replicated.  That is when Frank Thomas, Technical Director for the USGA stated it had been replicated and was absolutely true.  After his comments the attitude in the room changed from disbelief to trying to understand the research better.

Understand, this is only true of clubs lofted at 20 degrees or under.  So, what does this mean to the average golfer?  The application would be this, if you want more back spin with your driver, fairway driver, or low lofted irons, buff the faces smooth.  There is no USGA rule against a smooth face.  The USGA is only concerned with how rough the face may be.  If you do not want as much backspin created with your low lofted clubs be sure the face does not become worn smooth. If they are worn have them sand blasted so they are cosmetically rough again.  I say cosmetically rough, because the USGA states that the roughness of a face can only be for cosmetic purposes and not to impart spin.

Today with the thin Beta-Titanium faces if grooves were cut into the face it would create a weak spot and break.  You will rarely see grooves cut in the middle of titanium heads now and if they are there they are not cut deep due to the thin face.