Whenever I look on companies websites, I see these 2 terms in a ball's specification. Can someone explain to me what they mean? Does the RG determine how soon a ball revs up, for example a lower RG causes the ball to rev up sooner?

Thanks, Andrew

That's true in general.  Lower RG values mean more weight is concentrated in the center of the ball, higher means a more cover-heavy ball.  Low-RG tends to mean earlier hook, more midlane reaction.

Of course, that's not always true and it depends on surface prep as well.  But two balls with similar surfaces, one lower RG than the other, and the low-RG ball will start up sooner.

Differential measures the difference between the RG as measured through the pin and the RG as measured 90 degrees from the pin.  On a symmetric core ball, that 90 degrees can be anywhere, but on asymmetrical balls, the second RG value will be different due to the asymmetry.

SH