Bowling Ball RG and Differential Chart

RG and differential are the two numbers every manufacturer publishes about a ball's core. The chart plots one against the other for every ball at the weight you pick, as they change a little from weight to weight. Lines through the middle of the balls shown split it into four core types, so you can see at a glance which balls rev up early or late and which flare hard or stay controlled.

RG (radius of gyration)

How far from the center the core's mass sits, in inches. A lower RG revs up sooner and starts its roll earlier; a higher RG saves its energy for further down the lane.

Differential

The gap between the core's highest and lowest RG, which sets how far the ball's track can flare. A higher differential flares more for a stronger hook; a lower one is more controlled.

PSA (preferred spin axis)

Also called intermediate differential: how asymmetric the core is. Higher is a sharper, more angular move at the breakpoint, lower a smoother arc. Symmetrical cores have none.

Core types

The chart's four corners: early, strong flare (low RG, high differential), late, strong flare, early, controlled, and late, controlled (high RG, low differential).

These describe the core only; the coverstock and its surface matter as much to how a ball reacts. For that, see the reaction chart.