Knowing whether you need a symmetrical ball or an asymmetrical ball for the next piece of your arsenal is more important than you may think. Understanding the difference between the two can be a daunting task even for the seasoned professional, but once you have familiarized yourself with the main factors engineered into the ball construction process the sport becomes much clearer and adjustments become easier. Please keep in mind, however, that the information which follows may lead you to your nearest bottle of aspirin! It can be quite technical in nature, so don’t be alarmed if you need to re-read this article a few times before it starts to make sense.

The term differential is the common nomenclature for the difference between the maximum and minimum RG values. The larger the number, the greater the flare potential becomes for the bowling ball.

The radius of gyration, or RG as commonly known, is a measurement in inches from the axis of rotation at which the total mass of a body might be concentrated without changing its moment of inertia. Low RG balls rev up faster and more easily, creating more ball motion, or change of direction.

Total differential (flare potential) can be described as the difference between the X (low RG) and Y (high RG) axes of any bowling ball, symmetrical or asymmetrical.

Intermediate differential is typically only expressed on asymmetrical balls and is the difference in the RG between Y (high RG) and Z (intermediate RG). Intermediate differentials exist on most symmetrical balls, but is not large enough to make a significant impact on the ball’s overall motion.

Differential ratios mandate how asymmetrical a ball is and can be found by dividing the intermediate differential by the total differential. Balls with a larger ratio have a higher degree of asymmetry. Symmetrical balls have the lowest differential ratios in the industry.

There’s a Time and Place

A symmetrical core has an RG (radius of gyration) values of the Y (high RG) and Z (intermediate RG) axes of the ball do not differ by more than 5% of the total differential of the ball. An asymmetrical core is a ball where the RG values of the Y and Z axes of the ball differ by more than 5%. It’s generally accepted that symmetrical drilled balls have a smooth, controllable motion. Asymmetrical balls have a defined, angular shape downlane that respond to friction quicker than symmetrical balls, given the same coverstock composition and preparation. All balls, symmetrical or asymmetrical, become asymmetrical after drilling. Simply put, asymmetrical cores are not in equal proportion top to bottom like a symmetrical core is.

Asymmetrical balls can exhibit large amounts of track flare even with long pin-to-PAP (positive axis point) distances. A 6″ pin-to-PAP distance layout on a symmetrical ball will typically result in a very low-flaring ball. In a strong asymmetrical, however, a 6″ pin-to-PAP distance layout might result in a very high-flaring ball. This is the critical difference between symmetrical balls and asymmetrical balls. This leads to another interesting conclusion: asymmetrical balls can, in general, provide a ball driller with more reaction options than symmetrical balls. Symmetrical balls have only two ball motion “tuning parameters”: pin-to-PAP distance and pin buffer. Asymmetrical balls add a third variable to the equation in the placement of the PSA (preferred spin axis) in relationship to the bowler’s PAP. The higher the undrilled intermediate differential is, the more significant the PSA position becomes.

Bowlers who favor the use of an asymmetric core need a little extra help curving the ball. These balls rev up fast and finish strong with a more aggressive movement downlane. Asymmetrical balls are great for heavy amounts of oil or longer patterns which don’t provide a lot of friction while symmetrical balls are typically smoother and yield a benchmark type of reaction that are more controllable. Symmetricals have two principal moments of inertia (X and Y axes) and asymmetricals have three (X, Y, and Z.) This greater degree of asymmetry is responsible for the highly dynamic moves asymmetrical balls can create.

And finally, don’t forget that there has to be a proper marriage between cover, core, and layout for the ball to react optimally, but we will save that for a later discussion.