Technical Comments on the OEM Driver Models That Claim Performance Changes from Movement of the Center of Gravity

From the desk of Tom Wishon:

A number of clubmakers have recently asked TWGT to comment technically on the trend among some OEM companies to offer driver models that claim performance changes from a movable weight on the head intended to change the position of the Center of Gravity (CG) inside the clubhead. We’re always happy to use our depth of understanding of the relationship of the science of head design parameters to practical shot performance to help clubmakers gain the knowledge to be able to be armed with the best information to discuss such matters with golfers who may ask about such trends.
With the introduction of their SLDR driver, Taylor Made Golf Company launched a marketing campaign advising golfers to “Loft Up” when using this club. In TM’s explanation, because the SLDR head is designed with its CG closer to the face, ball flight will be lower with less spin. Thus to achieve the optimal launch and spin performance with the model, the company is advising golfers to use more loft than what the golfer may have used with his previous driver.

It is true that a more forward CG can slightly lower the launch angle and spin of the shot – but ONLY for golfers who have a later and later to very late unhinging of the wrist cock angle (release) on the downswing. For golfers with an early to midway to even slightly later than midway release, a more forward CG will not lower flight and spin, nor will a more rear located CG increase launch and spin.
In addition, TM’s manner of changing loft is through the adjustable hosel device on the SLDR. With all such devices, only if the golfer manually holds the face square to the target line when starting the swing will the hosel device adjustments change the loft. If the golfer soles the driver to address the ball to hit the shot, no adjustable hosel device on the market will change loft. If the golfer soles the driver to address the ball the adjustment said to be done to change loft instead changes the face angle of the head with no change in loft.

Thus for the SLDR driver to perform as claimed and for the Loft Up advice to work for a golfer, the golfer first must have a later to very late release, and second, has to have the habit of always holding the face square to the target line with the driver when he hits the shot. No statistics exist which indicate how many golfers have an early/midway vs later/late release. Nor is there any way of knowing how many golfers have the habit of manually squaring the face of their driver vs soling the driver before hitting the shot. Common sense estimates would say that there are far more golfers with an early to midway release than there are golfers with a later to very late release.

Another driver model now on the market that has brought questions from clubmakers to TWGT is the new Big Bertha driver from Callaway. Designed with a rod with 9g of weight on one end and 1g on the other that is positioned vertically inside the head, golfers can reverse the position of the rod to put the 9g weight on the top of the head to raise the CG to achieve a lower launch angle with less spin, or to put the 9g weight on the bottom of the head to lower the CG to gain a little higher launch with more spin.

Does this driver do what the company claims? Let’s use an example of moving weight on a driver head to get an idea of how much weight it takes to move the CG a specific distance. First of all, a basic rule concerning weight movement vs CG movement. The farther you pl
ace a specific mass of weight from the CG, the greater the distance the CG will move toward the weight. Conversely, the closer you place a specific mass of weight to the CG, the less distance the CG will move toward the weight.
The center of the hosel weight bore on the 919THI driver is 50mm from the CG inside the 919THI head. Placing a 9 gram weight in the hosel weight bore on the 919THI drivers will move the CG a distance of 3/32” horizontally toward the weight bore. Thousands of clubmakers who have built the 919 driver have discovered this 3/32” movement of the CG toward the heel does not change the performance of the 919THI driver at all.

Regarding the movement of 9 grams to the top or bottom of a driver head, its maximum distance above or below the head’s original CG is far less than the 50mm distance from the weight bore of the 919THI driver to its CG. Every driver head ever made has its vertical CG located approximately 2/3’s of the face height up from the bottom of the leading edge. This is because the top crown of the driver is much larger than the sole, thus weighing more to pull the CG above the center of the face.
A typical 450-460cc size driver head has a face height of 53-55mm, with a sole to crown height of 60-64mm, depending on the curvature of the top crown of the head. That means most 450-460cc driver heads have their vertical CG position located on average 36mm up from the sole or 26mm down from the top of the crown.

When the 9g weight is placed on the top of the driver head, at the most that weight is 26mm above the head’s original CG. When the 9g weight is placed on the bottom of the driver head, that weight is not more than 36mm above the head’s original CG. Keep in mind that the closer you place a specific mass of weight to the CG, the less distance the CG will move toward the weight. Now remember that a 9g weight placed 50mm from the CG in the weight bore of the 919THI driver moved the CG 3/32” toward the weight bore. Hence the 9g weight placed either 26mm above the CG is going to move the CG up around 3/64”, while the 9g weight reversed to be positioned 36mm below the CG is going to lower the CG around 1/16”.

Bottom line: a 3/64” and 1/16” movement of the CG down or up in a driver head is quite an insignificant distance when it comes to having a visible effect on launch angle, spin or trajectory.