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Center of Gravity
We will start with the Center of Gravity, because it is the easiest to understand. First off, the static weights resulting from CG placement only control about 5-10% of a ball's reaction. This number used to be much greater, however, the dynamics of bowling ball cores and the friction generated by new ball coverstocks have given much more precedence to core positioning and surface than ever before.
The CG is usually marked on the ball with a punchmark, a small punched dot on the ball. Underneath this punch mark, there are a couple of extra ounces of weight to make up for the roughly 2.5 ounces that are removed during drilling. This way, the ball retains its balance and doesn't wobble down the lane because of the top of the ball being lighter than the bottom of the ball. However, over the years bowlers realized that they could drill the holes on other places on the ball thereby shifting the CG to the side. This changes the reaction characteristics because now one side of the ball is heavier than the other side, so the ball will want to lean more in that direction.
There are six (6) types of static weights that result from shifting the location of the CG away from the center of your grip:
  1. Positive Side Weight
  2. Negative Side Weight
  3. Finger Weight
  4. Thumb Weight
  5. Top Weight
  6. Bottom Weight
Positive/Negative Side Weight
Positive side weight means that the CG is shifted towards the side of the ball that is hooking into the pins. If you're right-handed and throw a hook, it's the right side of the ball as you look at your grip with the fingerholes up and thumbhole down. It is also the opposite side of your ball from where your track is. This is the side of the ball where your PAP is located.
Positive and negative side weights have effects on when and how much the ball will hook. A ball with positive side weight will hook later and hook more. A ball with negative side weight will hook sooner and hook less.
USBC regulations place a limit of one ounce of side weight, either positive or negative. This is measured by weighing the ball on a "dodo scale." You compare the weight with the ball facing in one direction to the weight with the ball facing in the other direction. The center of the grip faces up and for one measurement, the fingers are above the thumbhole and for the other measurement, the thumbhole is above the fingerholes (one day I'll get pictures of this and post them).
Finger/Thumb weight
Finger and thumb weight mean the CG is shifted up or down towards the finger or thumb holes. Finger weight will make the ball go longer down the lane and have a snappier backend reaction. Thumb weight makes the ball roll sooner and have more of a smoother arc when it starts to hook.
USBC regulations place a limit of no more than one ounce of finger or thumb weight. Again, this is measured on a dodo scale by comparing two sides of the ball. The center of the grip again faces up, but this time, the finger holes face left on one measurement and right on the other measurement (you're comparing the finger half of the ball with the thumb half of the ball).
Top/Bottom Weight
As mentioned previously, bowling balls come with extra weight placed under the center of gravity punch on the ball to balance out the weight taken out by drilling holes. This weight is called top weight because it is located in the top of the bowling ball. Bowling balls generally are manufactured with anywhere from two to four ounces of top weight although it is possible to find balls that fall outside that range. Lightweight balls are made with less top weight generally for two reasons. Light balls generally are drilled for children so the holes are smaller, meaning there is less weight removed that needs to be balanced out. Also, since the ball has less total weight, an ounce or two of top weight will have more effect on the ball's dynamics and throw them "out of whack."
Top weight has a similar effect as finger weight: the ball will go longer down the lane and snap a bit more on the backend. Likewise, bottom weight is like thumb weight in that it makes the ball roll earlier and arc more.
Unlike other static weights, USBC regulations allow up to 3 ounces of either top or bottom weight. This is measured on the dodo scale by comparing the drilled side of the ball (top) to the non-drilled (bottom) side of the ball.
Top and bottom weight are not necessarily caused by shifting the CG away from the center of your grip. They are more a result of how much extra weight the manufacturer placed in one side of the ball and how much weight is removed from that side during drilling. However, you can alter top weight and bottom weight by shifting the CG. Because top/bottom weight are measured by comparing the grip side of the ball (the top) to the non-grip side (the bottom), if you shift the CG away from the center of the grip, you are moving it around the circumference of the ball towards the bottom. You would be removing top weight (and/or adding bottom weight depending on how you look at it) by shifting the CG. Therefore, the most top weight you can have in any particular ball after drilling (and before drilling any extra holes) would be if the CG is directly in the center of the grip.