What is the “balance point” of a cue, and does it affect shot performance?
A cue’s balance point is its center of gravity, which is the point at which you can balance the cue (e.g., if you support it on a finger). Obviously, if using an open bridge, the balance point needs to be in front of the grip hand; otherwise, the cue would lift off the bridge. Other than that, the balance point is mostly unimportant … except for personal preference based on “feel.” The balance point certainly does not impact shot effectiveness; although, weight distribution can affect a cue’s moment of inertia (see below). Also, a shaft that is heavy on the tip end (moving the balance point forward) will affect CB deflection, which does affect shots with sidespin. For more info, see effects of endmass on CB deflection.
Concerning the effects of cue weight, see optimal cue weight.
What is “moment of inertia,” and how does it affect shot performance?
A cue’s “moment of inertia” (or “rotary inertia”) is its effective resistance to pivoting. It increases with cue length and weight, and it changes with weight distribution. If the weight is distributed more in the back (away from the bridge pivot) and less in the front (close to the bridge pivot), the moment of inertia will be greater. This will make the cue more resistant to pivoting (intentional or not). So if you have a piston stroke, the cue will be more likely to stay in line during the stroking motion. However, if the stroking motion is slightly non-straight, the cue will also require more effort to bring it back into line during the stroke. With a pendulum stroke, a larger moment of inertia will require more up/down force on the cue during motion, which might be noticeable to some people.
If you have a very straight piston stroke, there might be a slight benefit to having a cue with a larger moment of inertia since the cue will be more resistant to off-line motion during the stroke. However, if your stroke is consistently straight to begin with, moment of inertia differences should have little or no effect.
from Bob Jewett (via e-mail):
I’d say that any reasonable increase in the moment of inertia would have a “very slight” effect on the effort required to take the cue off-line. I think if a player has a crooked stroke and they are used to a certain balance (and to a lesser extent, moment of inertia) changing that could cause problems even for straight shots.
The balance point will be affected by the type of joint (metal or not) as well as the positioning of the weight bolt. Some cues may allow you to move the weight bolt and some cues have been sold with round weight rings that you can position at two or three points along the multi-section butt.