Core Shape Effect
Core Shape determines ball motion.
Bowling balls have a wide variety of Core Shapes. The Core Shape is the "Engine" of the ball and the Coverstock is the "Tires". The Core has its own spin rate, separate from the bowler, and its own Perferred Spin Axis (PSA). The PSA of the core is different then the Positive Axis Point (PAP) of the bowler's release. The PSA is where the PAP is migrating towards when the Core is trying to become stable. There are some general rules that apply to Core Shapes and their effect on ball motion. Ball motion has 3 phases, Skid - Hook - Roll.
The taller and thinner the core shape the later the roll phase starts.
The shorter and fatter the core shape the earlier the roll phase starts.
The smaller the overall size of the core the shorter the length of the roll phase.
The larger the overall size of the core the longer the length of the roll phase.
The smoother the shape of the core, the longer the hook phase, the smoother the ball reaction.
The more angles a core shape has, the shorter the hook phase, the more angular the ball reaction.
Symmetrical core shapes have longer skid phase, longer hook phase, and shorter roll phase.
Asymmetrical core shapes have shorter skid phase, shorter hook phase, and longer roll phase.