Technical Papers by UST Mamiya

UST Mamiya Proforce HMOI

High balance point makes shaft easier to swing for more power, control

MOI (moment of inertia) is the current buzzword in the golf equipment industry. New driver heads, as well as other club heads, claim to have 'high MOI,' making them easier for players to hit straight.

A club head with high MOI is designed to correct off-center shots. By yielding less twisting of the head, MOI heads produce less sidespin. A 'Moment of Inertia' is technically defined as a body’s resistance to angular acceleration about an axis. As an object gets larger, or heavier, or as the weight is distributed farther away from the center of gravity (CG), the MOI increases. When used to describe a golf club head, the MOI is measured about the vertical axis through the CG of the head.

Perhaps a better illustration of MOI is an ice skater spinning in a circle. If the skater’s arms are pulled close to her body, she has a low MOI. Because there is little resistance to rotation, her rotational speed is fast. When the skater’s arms are extended, she has a high MOI. Her balance is improved while slowing her rotational speed.

As MOI is increasing in golf club heads, it is placing more and more load on the golf shafts. Driver heads have traditionally weighed around 198-200gm, regardless of how big they are. The first metal drivers were about 145 cubic centimeters (cc). With this small size, the CG of these heads was quite close to the shaft axis, and the MOI was low. As the heads started to grow in size, even though the weight of the heads remained the same (198-200 gm), the CG of the heads moved farther away from the shaft axis, and the MOI of these heads increased.

Now that driver sizes are maxing out at the USGA-stipulated limit of 460cc, traditionally shaped driver heads have an MOI of up to 5000 gm-cm2. Since the USGA has set a maximum MOI limit of 5900 gm-cm2, however, head manufacturers are still trying to increase the head MOI by using different shapes to reposition the weight. These changes increase shaft loading, thereby affecting shaft performance. in three important directions: 1) torsion (twisting around the shaft axis), 2) bending in the swing plane (the effective loft of the club), and 3) the drooping plane (where on-the-face the impact occurs). It is therefore imperative that a shaft be designed to handle this increased load.

The engineers at UST Mamiya recognize that for players to reap all the benefits from these new heads, they need a shaft designed to work in harmony. The new UST Mamiya Proforce HMOI shafts are designed specifically for the added rigors of 'high MOI' heads.

The Proforce HMOI uses a unique flex profile to handle the extra loading of these MOI heads. The tip section is exceptionally stable in both torque and flexure to minimize the effects of twisting, lag, and droop, providing solid impact for improved control and shot dispersion.

The Proforce HMOI shaft’s higher balance point reduces the heft of the club. This shift in CG of the shaft up closer to the hands, allows the club to be played at a lighter swing weight. When the CG of the club is shifted closer to the grip, it lowers the club's MOI about the grip end and makes the club easier to swing. For example, a 73-gram HMOI shaft swings like a 60-gram shaft, while still allowing a strong, aggressive swing at the ball.

The test results (lower numbers are better):

Proforce V2 75 @ 45 inches D-3 = 2889

Proforce V2 HL @ 45 inches D-3 = 2855

Proforce HMOI 73 @ 45 inches D-1 = 2844

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