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Bowling Ball RG Numbers
The United States Bowling Congress defines the RG (Radius of Gyration) of a bowling ball as a measurement in inches and is the distance from the axis of rotation at which the total mass of a body might be concentrated without changing its moment of inertia.
Another description for RG is a measurement by some manufacturers in a range from 2.460 to 2.800, but some companies have converted them to a 1-10 scale to help give the consumer a better frame of reference. These numbers describe the distribution of mass in the bowling ball and RG is an account of the location of that mass inside the bowling ball.
High RG numbers indicate that the ball's mass is distributed more toward the cover (cover heavy) which promotes length through the heads of the bowling lane. Low RG numbers indicate that the ball's mass is distributed more toward the center (center heavy) which promotes an earlier roll through the front part of the lane. Medium RG describes sufficient bowling ball skid length to reach the mid-lane before transitioning into the hook phase of overall motion.
Placing RG range measurements into three relative numerical spreads is a means of creating a consistent rating system bridging all of the manufacturers. This placement of RG numbers will help you convert the numbers provided by the manufacturers into three simple categories when evaluating any bowling ball and would be as follows:
Low RG: 2.460 - 2.570
Med. RG: 2.570 - 2.680
High RG: 2.680 - 2.800
The next time you are searching for a new ball, check out the RG specifications to help you select a ball with the appropriate length potential rating. Please be reminded that the core type and shape as engineered by the manufacturer is how the RG numerical rating is achieved.