Actually, its near impossible to find a ball with both Medium-High RG and Medium-High Differential. Its either one is high, or the other. Or both medium. but rarely both.
Low RG is anything below 2.53ish, usually nothing lower then 2.47.
Medium RG ranges from 2.54-2.56ish, With the higher RG being anything over that.
The differential is as follows... "The difference of the radius of gyration of a bowling ball’s X axis (the weight block vertical) compared to the radius of gyration of the same ball’s Y or Z axis (the weight block horizontal). Differential is an indicator of a bowling ball’s track flare potential. Bowling balls with lower differentials are more stable, therefore generating less track flare potential. Bowling balls with higher differentials are unstable, therefore generating a much larger track flare potential. Also, differential is a guide to the internal versatility of a ball. It can indicate just how much of a length adjustment can be made through drilling. Balls with lower differential will allow only modest length adjustments whereas balls with higher differential may translate into a length window of up to 5-times that of low differential balls. "
Direct from
http://www.stormbowling.com/glossary/glossary.asp
The Radiud of Gyration explantion is here as well... "An account of the location of the mass inside a bowling ball. Rg tells us whether the ball has the mass toward the center of the ball (low rg), toward the cover of the ball (high rg) or somewhere in between (medium rg). 1. Low rg balls rev up quickly. 2. Medium rg balls rev up slightly later. 3. High rg balls lope down the lane saving the energy until later."
Since your mate is looking for something that is gonna give him Big hook, but gets down the lane. You should be looking for something with a Pearl reactive or pearl particle Coverstock, with a Low/ Low-Medium RG. The cover will help the ball get down the lane before making it's move. While the Low RG will give the Ball a big hook. A few balls that come to mind are the Storm Paradigm, or the Track Rule. Both will get you decent length, with lots of hook.
Later Da Cowman!
