The diff is the difference from the low rg to the high rg a bowling ball can have. The diff is an indicator of how much track flare a ball will produce. USBC just put an upper limit on diff of .060. A ball with a diff of .025 will have significantly less track flare than a ball at the upper limit. This also has an indication of how much a ball can hook. The larger the flare, the more the ball is trying to turn over, and vice versa.
For example, right now I will compare the Track Heat (.037 diff) vs the Rule GP2 (.052 diff). If you look at the oil rings after you throw a shot, you will notice how much closer together they are on the Heat than the GP2. The balls with less distance between rings have a lower rg, ie, the Heat.
Clint
--------------------
Clint Daley-Owner
Lets Go Bowling Daley
Salem, Ohio 44460
TRACK ADVISORY PRO SHOP STAFF