For my last article of 2016, I would like to spend some time talking about Centre of Gravity or CG.
The Merriam Webster dictionary defines the centre of gravity as the “centre of mass” or “the point at which the entire weight of a body may be considered as concentrated so that if supported at this point the body would remain in equilibrium in any position.” If you think about CG for a moment, it is actually what we are trying to attain every time we swing a club. No matter which club we have in our hands, to get the purest strike, we have to line up the centre of gravity of the clubhead with the centre of gravity of the ball. When we do this we get that wonderfully solid feeling at impact.
It is quite easy to locate the CG on an unassembled iron head by simply balancing the face on the tip of a retracted ball point pen. On hybrids, woods and drivers specialized equipment is needed due to the fact that the CG is located somewhere inside the head. The centre of gravity in any club head can also be referred to as the “sweet spot” The sweet spot really is about the size of a match head, about 1/8 of an inch in diameter. No matter what is done to a clubhead to expand the sweet spot, the CG remains the CG. Designers can help mitigate the effects of an off centre hit but the sweet spot cannot really be expanded.
Whatever the head might be, the center of gravity can be changed only by one of three methods: 1) Weight is moved in a given direction, 2) How far the weight is moved and 3) how much weight is moved. The greater the mass, the greater the effect.
So why is CG so important in clubhead design? The simple answer is that it has a major effect on spin and launch angles. It is important to understand that relocating the CG in a clubhead is not a simple thing to do and also has a significant impact on feel. To alter the CG of a clubhead requires moving weight as far as possible. Given the size of clubheads, it is mainly the driver head where a club designer can play around with the centre of gravity. Even in a driver, it is difficult to move the CG much more than a couple of millimeters. But this is enough to have a significant effect.
Now let’s look at what happens when we move mass in a driver head. First of all, if we move mass toward the face, the initial launch angle will be lower, the spin rate will decrease, the club will be a bit more difficult to square up and the moment of inertia (MOI – resistance to twisting) of the clubhead will decrease. If we move the CG back from the face the initial launch angle increases, the ball spin increases, the clubhead is easier to close and the MOI increases. If the CG is moved up toward the crown, the launch angle will decrease and the spin will increase. If the CG is moved down the launch angle increases and the spin rate decreases.
For any given golfer’s swing there is a CG location that is better suited for his or her swing. For example, if you hit a high ball with too much spin, a driver with a more forward CG may be best for your swing or if you have a tendency to hit toward the toe a driver where the CG is more horizontally oriented toward the toe may be a better fit for you. But let me stress the words “may be”. What has to also be considered in fitting a driver to the golfer’s swing is his clubhead speed, his dynamic loft as well as his angle of attack. These three factors have a huge effect on ball flight and can certainly make driver selection more difficult.
So what can the average golfer do with this information? Quite frankly the answer is not a lot. I think it is important to understand CG and how it affects ball flight but if you have a driver that you think would be better with a lower CG and more toe located CG, for example, there is no way of altering it. No amount of lead tape no matter how carefully placed will affect the original design
That is why it is critical to get professionally fitted for a driver or any other club. It is imperative to know what design parameter(s) are most critical to your swing dynamics. Without having detailed information about what is happening at impact, you have no way of knowing whether the CG , the attack angle or any other parameter is right for you. Clubfitting has become more and more complex as club technology advances, so let your clubfitter sort out what is the best design for you and then you can relax and be confident that the club that you have in your hands is the right one for you.
/ Don Irving, Master Club Fitter, Artisan Golf