GLOSSARY OF BOWLING BALL TERMS

-BACKEND HOOK POTENTIAL
-CORE TORQUE
-DIFFERENTIAL
-MASS BIAS
-POSITIVE AXIS POINT (P.A.P.)
-RAIDIUS OF GYRATION (R.G.)
-REACTICE RESIN URETHANE
-TRACK FLARE

AXIS TILT
Ranges from 0 to 90 degrees. This is determined by the direction your axis is facing when you release the ball. 0 is parallel to the gutters, 90 is parallel to the foul line. The less axis tilt you have, the sooner the ball will go into a roll. Higher degrees of axis tilt promotes skid.
BACKEND HOOK POTENTIAL
A rating of how much a ball hooks on the backend. Usually on a scale of 1 to 25.
CENTER OF GRAVITY - (CG)
The heaviest spot of a bowling ball. The point where the ball weighs out with no finger, thumb or side weight before drilling.
Top of Page CORE TORQUE
Core torque Internal or core torque refers to the mass distribution within the core and the internal lever arms created by the core. Core torque is an assigned value of the ball's ability to combat rollout, the complete loss of axis tilt. High torque balls are more effective than lower torque balls at delaying rollout. Core torque can also be one indicator of the type of reaction that a bowler can expect at the breakpoint with high torque balls having the propensity to be more "violent" and the lower torque balls tending to display a more even, predictable transition from skid to roll. Top of Page DIFFERENTIAL
The difference in the Radius of Gyration or RG on the x-axis and the y-axis. RG differential indicates the amount of flare potential of a bowling ball. "Once you have a grasp on RG, the differential becomes easy. It is the difference between the lowest and highest RGs. You compute the high and subtract the low from that and you have the differential. The ABC/WIBC have also placed a maximum on differential. It is .080. There is no minimum for differential. What differential tells you: RG Differential is an indicator of track flare POTENTIAL in a bowling ball. Differentials in the .01s to .02s would mean that a ball has a lower track flare potential, .03s to .04s would be the medium range for track flare potential, and the .05s to .080 would indicate a high track flare potential. These ranges above are not based on cardinal rules. They are BTM in-house rules of thumb because there are no published guidelines. 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. A low differential will allow for only a modest variance in length (from shortest drilling to longest) which may translate into as little as a foot or two. An extremely high differential may translate into a length window in the neighborhood of eight feet. Top of Page MASS BIAS
As noted by Larry Detweiller at Faball USA, ..." Simply put, the mass bias in a bowling ball occurs when the mass (weight block or portion of weight block) is bias (more dominant) in one direction inside of an object (in this case a bowling ball). If you took a bulb shaped, single density core and positioned it dead center from side to side inside the ball, there would be no mass bias. You also would have a ball that is a pin in. In order to kick the c.g. away from the pin to create a pin out ball, you have to "tilt" the core inside the ball, or drill the entire core slightly off center. This became a common practice among manufacturers as the demand for pin out balls increased. When this is done however, you create a "dynamic imbalance" inside the ball because the mass is more dominant or "bias" in the direction of the "tilt" or "offset". That is the most important factor when discussing the mass bias, it is a DYNAMIC POINT ON THE BALL. Positioning the mass bias in different positions when laying out a ball will have a great impact on the "motion" the ball will make as it is going down the lane. (even arc, hook/set, skid/flip and so on) There are people who will argue that static imbalances (finger weight, side weight etc.) are more important than dynamic imbalances. My reply to that, is that a dynamic imbalance is a real point in the ball, it is constant and does not change unless you alter it by drilling into it with a drill bit. A static imbalance or the c.g., will change as soon as you put one hole in the ball. It will change again with each additional hole you put in the ball as well. While static weights can be used to "fine tune" the reaction of the ball at the break point, it is the dynamic lay out that dictates the roll of the ball. If a pro shop operator truly understands the principals of the mass bias and how to apply them, they can greatly increase your overall satisfaction with the ball you purchase. Top of Page POSITIVE AXIS POINT (P.A.P.)
This is the axis of the ball during the first few revolutions that is created totally by the bowler's release. The point on the ball that is equidistant from all points of the release ball track. Top of Page RAIDIUS OF GYRATION (R.G.)
The measurement that tells us the core's impact on the skid potential of the ball. "Identifies how fast a ball begins to rotate once it leaves the bowler's hand. Three designations for RG balls are low, medium, and high. A high RG ball goes longer because it takes longer to begin rotating and stores its energy on dryer conditions. A low RG ball revs up early and is a more evenly arcing ball used on wetter conditions. There are three axes on a bowling ball used to measure RG (radius of gyration). The lowest RG axis (usually denoted by the letter Z) is the axis through the pin. The highest RG axis (usually denoted by the letter X) is located 6-3/4 inches from the pin through the center of gravity (CG or heavy spot). The intermediate RG axis (usually denoted by the letter Y) is located 6-3/4 inches from both the low and high RG axes.
Even though all bowling balls of a given weight are about the same size (minimum diameter of 8.500 inches to 8.595 inches), these balls are constructed differently. Some use two materials (one shell and one core), others use three or four or five or more pieces to construct the shell(s) and core(s)
Each of the materials used has a density (which roughly translates intop weight per unit of volume). Zirmonite (as used in the Columbia pin) is denser (heavier by volume) than Bismuth Graphite (used in the core of the Brunswick Zones) which is denser (heavier by volume) than the fired ceramic that is used in the Columbia and Track cores. These and the other dense-material cores used by other manufacturers are all heavier by volume than the material used in the main cores. The main core material is denser than the foam-like material used as outer cores or inner shells, the purpose of which is to keep some balls in compliance with the ABC/WIBC weight limitation and to help pinpoint a certain RG value. Then there is the urethane used for the outer shell of the ball which by density fits in between the core materials.
Even though you may have a bowling ball with as few as two parts or as many as five or more, all balls have one characteristic. They will act as if all of their weight is located at a point some distance away from the rotational axis. This distance is the radius of gyration (RG). For example, a bowling ball has a maximum allowable diameter of 8.595 inches (maximum radius = 4.2975 inches). Theoretically, the RG could be any distance from just over 0 inches--by placing ultra-dense materials in the center of the ball and extremely lightweight filler beyond--to just under 4.2975 inches by placing ultra-dense materials near the outer shell and filling the inner areas of the ball with lightweight foam.
In the first example, the ball would be as center heavy as possible. In the second, it would be as shell heavy as possible. The problem with unlimited RG is that the two extremes would produce variations in ball performance that would be enormous. One would roll immediately and the other would "lope" all the way through the pindeck.
The ABC/WIBC, in an attempt to limit the amount of variation in ball performance that could be achieved through construction, placed minimums and maximums on RG. The rule states that the minimum RG can be no lower than 2.430 inches and no greater than 2.800 inches. This means that every ball must act as if its entire weight (mass) is rotating at a distance of not less than 2.430 inches or more than 2.800 inches from the axis. Since the total span of RGs ranges from 0 to 4.2975 inches, technically all bowling balls fall within the overall medium RG range. However, when anyone in bowling talks about RG, they are not referring to the total range of possible RGs, but instead only to the RG range allowed for the sport--2.430 to 2.800.
In the At a Glance chart and in ball reviews and comparisons in BTM, the following scale is used for low flare potential balls:

Low RG = 2.430 to 2.540
Med RG = 2.541 to 2.690
High RG = 2.691 to 2.80

There is a slight upward adjustment for high flare potential balls. Determining the RG: For BTM fellow ball geeks, the formula for finding the radius of gyration (usually denoted by the letter k) is: the square root of the ball's moment of inertia divided by its mass (k-squared = I / m)."* What RG tells you: Like with everything else in bowling, RG--in and of itself--tells you very little. It is ONE indicator of length. The characteristics of the three types of balls are as follows:
A low RG ball will be easier to "rev up" and it will rev faster quicker because most of the mass is located relatively close to the center of the ball. Since it revs faster sooner, it also wants to hook sooner. Medium RG balls are intermediate-length balls. They are a little more difficult to spin (takes more power) so most bowlers will see a slight loping characteristic through the heads and early midlane followed by a faster revving action and later hook--than you would get with the low RG ball. High RG balls are the hardest to rev up since the mass is concentrated farthest from the center and therefore bowlers will see longer lope, much later revving up, and the latest hook from these balls.
Top of Page REACTICE RESIN URETHANE
A polymer that is a cousin to traditional urethane; used as the coverstock on most modern balls; it is generally a surface that grabs the lane sooner, resulting in more and earlier hook than other coverstock surfaces. They can feel "tacky/sticky" when warm. They tend to "react" much more to differing lane surfaces, hooking more on drier lanes and skidding more in oil. Top of Page TRACK FLARE
"In simple terms, track flare is the migration of the ball track from the bowler's initial axis (the axis upon release) to the final axis (the axis at the moment of impact with the pins), thus a new ball surface from the bowler's initial axis (the axis upon release) to the final axis (the axis at the moment of impact with the pins), thus a new ball surface touches the lane upon every revolution. Increased track flare gains greater rotational energy and hitting power. Decreased track flare creates greater ball skid. No track flare will have a ball rolling on an oily surface each revolution.
A flaring ball always rolls on a new surface. All bowlers who rotate the axis will see some migration (track flare) using any ball with any drilling with two exceptions. There is no track flare if the pin is placed on the bowler's positive axis point (axis drilling), and there is no track flare if the pin is placed 6-3/4 inches from the bowler's positive axis point (in their ball track). Track flare is evident as the side-by-side rings that encircle the ball. The ball's first rotation is the ring farthest from the middle finger hole and the last is the one above the finger holes closest to the ring finger. Track flare for full rollers is often reversed. Flare potential is the maximum amount that the axis of the ball can migrate given the construction of the ball AND provided that the bowler has a maximum power release. Maximum actual track flare for any ball in the hands of any bowler can be obtained by placing the pin in leverage position for that bowler. Only a small percentage of bowlers can make a ball flare to its potential.
Track flare is a length modifier. Large flare means that the ball is presenting a fresh, dry surface on all successive revolutions. While on oil, this means little to the performance of the ball, but when the ball crosses from the oil to the dry, the dry ball surface bonds with the dry lane surface to increase the coefficient of friction which causes earlier hook and greater total hook. That is, earlier and greater hook when it is compared to a smaller flaring ball that is tracking over the same area of the ball and presents an oil covered surface when it crosses from the oil to the dry which reduces friction and promotes additional skid causing a later and more defined hook. Track flare potential also provides one indicator of which balls will be better suited to oil (large flaring ones) and which will be better suited to dry (small flaring ones)." Track Flare Potential - The amount of "Flare" described in inches.
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