Golf Club, Golf Ball Collision: What happens?

One of the biggest differences between professionals and amateurs is the ability to control the distance of any given shot. The main reason for this is where the golf ball is being struck on the clubface. Professionals have the singular ability to strike the center of the face far more often than the average player. This is something Trackman refers to as the smashfactor, better understood as the efficiency of the hit. For example, if the driver strikes the golf ball “perfectly” with 100 MPH clubhead speed, the ball speed should be 150 MPH. A 3 to 2 ratio. This is seen at the elite level only! If the ball speed is less, something was indirect in the contact, or missed on the face of the club. Recreational players hit the toe of the clubface, maybe the heel, high or low at various times.  This makes it impossible to gauge how far, how high or low, or how much spin the golf ball may have, thereby being unable to control the flight.

The collision of the golf club and the golf ball lasts .0004 seconds. During this infinitesimal amount of time, the golf ball gets its marching order. Every characteristic of flight is determined during this time. Knowing what might have caused any given shot is nothing more than knowing the reality of what we call the impact interval. Here is the reality of the strike:

Golf ball hit high on the face: Adds loft to the face, creates high launch, low spin.  

Low on the face: Delofts the face, creating low launch, high spin. 

Toe hits: Face opens - Irons start right, stay right. Great loss of distance. The driver will start right, bend left (gear effect explained below).

Heel hits: Face closes - Irons may shank; Driver will start left, curve right.  

Why the difference in the driver? The golf club is built differently. It has something known as the gear effect. If you look closely at the face of the driver, you’ll notice that it is curved from both toe to heel (known as bulge) and crown to sole (known as roll). For example, a driver of 10 degrees loft in the center might have 13 degrees near the crown and as little as seven degrees near the sole. This configuration helps straighten mishits off the driver, fairway metals, and hybrids.  Even some long irons can have a little bulge. Gear effect can best be described as a shot’s starting direction counteracted by “reverse spin.” Think of gears meshing - as they engage, they go in opposite directions (for lack of a better description). So, a golf ball struck near the toe of the driver will start right and curve left, and one struck near the heel will start left and curve right. However, if the contact is in the middle of the face, and the face is open, the ball starts right and stays right. Confused? Sorry, that’s what happened!

This all has to do with Moment of Inertia (MOI). For us non-physicists, that simply means the higher MOI a driver has, the less it twists on off-center hits…which is what we want; we DO NOT want the face to twist. But there is never NO twisting! And that’s where Gear Effect helps. It would be a tough task to drive with a straight face or no bulge driver! Clubmakers are remarkably adept at manufacturing precision equipment now, but we still have the challenge of centeredness of contact facing us on every shot. If this is the case, why would anyone want low MOI! Well, it gets involved but I’ll explain as best I can.

Professionals and highly qualified amateurs who consistently hit the sweet spot may prefer a lower MOI. The reason is a high MOI raises the center of gravity, and a lower MOI lowers the center of gravity. Professionals prefer a lower center of gravity that enables them to hit the golf ball on or above the sweet spot to create high launch, low spin conditions that many of them prefer.  Remember, this is only for elite-level ball strikers who want to work the ball and can consistently hit the sweet spot. In other words, perhaps .01% of golfers in the world! High MOI clubs are harder to twist in the release and therefore have a rightward bias ball flight - this is not something amateurs want! The elite ball strikers prefer low CG because it makes it easier for them to work the ball. This is why they prefer blades - they are easier to twist.

It is a whole other world, one in which I, as a swing coach, do not get involved. I send my students to professional club fitters who, if they are on top of their trade, will take all these factors into consideration. Good luck. Don’t forget to leave comments in e-edition!