The Role of the CG
In an earlier tip we covered pin positions. Other than the surface composition and texture, it’s location in relation to the PAP is the major decision you need to make concerning your ball reaction. However, we have another tool to use when we layout a symmetric core ball. Symmetric core refers to a ball with no built-in mass bias. Essentially, if you cut the core vertically through the pin in any direction, you would have a mirror image.
The CG (center of gravity) is the spot where there is no imbalance, other than topweight. Static weights (finger, thumb, positive, negative, top, and bottom weights) are measured using a balance beam scale called the DODO scale. Manufacturers mark this CG on the ball’s surface. By shifting the CG to the right of the center of span you create a positive weight imbalance (lefthanders shift to the left), by shifting the CG to the left of the center of span you create negative side weight (lefthanders shift to the right). Moving the CG above the center of span, toward the fingers, will create finger weight, moving it toward the thumb will create thumbweight. By creating static weights, we are creating a dynamic imbalance in the ball. However, this imbalance only has a very minor influence because of the small tolerance level set by the ABC. Maximum imbalance for positive or negative side weight, and finger or thumb weight is established at 1 ounce. Maximum imbalance for top or bottom weight is set at 3 ounces.
Effects of static weights are as follows:
- Positive Side Weight - Increase amount of hook
- Negative Side Weight - Decrease amount of hook
- Finger Weight - Delays breakpoint
- Thumb Weight - Causes an earlier breakpoint
- Higher Topweight - Delays breakpoint, creates sharper backend
- Lower Topweight - Causes an earlier breakpoint, creates smoother backend
The minimal effects of static weights stem from their limited leverage. One ounce of static weight equals 1/64th of an inch from the geometric center of the ball. The furthest that the center of gravity can be from the center of the ball at maximum ABC limits is 3/64th of an inch.
Now compare this to the radius of gyration limits. On the low side of ABC limits is 2.43. This means that the mass displacement is 2.43 inches from the geometric center of the ball. The upper limit is 2.80 inches. Sounds to me like a bigger lever arm compared to 3/64th of an inch. You can alter your ball motion much greater by changing RG’s than static weights.
As the core’s RG differential gets larger (ABC maximum is .080), the effects of static weights lessen. Lower differential cores, like 3 piece pancake cores (Maxims and Gyros), are affected greater by static weights. I have met precious few bowlers that can tell the difference between a ball with 1-ounce negative side weight versus 1 ounce of positive side, especially with today’s modern core dynamics and constructions. We have done CATS testing on the ball’s overall reaction with different static weights and the results showed no measurable difference of ball reaction. There were far greater reaction differences involved by the bowler’s inconsistency of ball speed, rev rate, axis rotation and tilt. The greatest reaction differences came when altering the surface friction of the coverstock
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