Background

A balance hole is an extra hole in the bowling ball that is not used for gripping purposes. Balance holes are primarily used to make the ball static weight legal to the current USBC Equipment Specifications and Certifications Manual if they are outside the legal limit after drilling. Once a bowling ball has been drilled, there are still options to fine-tune the reaction for the bowler. This article is going to look at how balance holes can be used to alter the reaction of a bowling ball.

Traditional thinking

Balance holes can influence ball reaction depending on the size and the location of the hole. Before reading this article, take a look at your current equipment. Do any of your bowling balls currently utilize a balance hole? If so, was there any thought put into the location of it, or was it simply to make the ball static weight legal? You may notice that you really like a ball with a certain location and size of balance hole, but it might not be your favorite on a different ball. Why is this? Let’s examine.

Traditionally, balance holes were presented in very simple terms. Historically, the higher the balance hole is in relation to the midline, the more it decreases the flare potential of the bowling ball. The lower the balance hole is in relation to the midline, the more it increases the flare potential of the bowling ball. Figure 1 illustrates this. While this is mostly true, there can definitely be some exceptions. Not all balance holes in the same location are going to have the same effect on the ball. There are other variables that are going to influence how they alter the bowling ball’s performance.

The term “RG” refers to the radius of gyration – a very important bowling term to become familiar with. This basically tells you how much of the mass is located towards the center of the ball.

Low RG’s means more of the mass is centrally located. Higher RG’s mean that more of the mass is located away from the center. Lower RG balls are going to require less energy to change direction. They will transition faster and roll earlier. Higher RG balls require more energy to change direction. They will transition slower and roll later.

Every ball is going to have both a low RG and high RG axis. Take a look at Figure 2. It’s important to note that the pin is the surface designation for the low RG x-axis of the bowling ball. In general, 6 3/4″ from the pin is going to be the high RG y-axis of the bowling ball. The distance from the x-axis to the balance hole is going to be crucial in determining how much and what kind of effect that the balance hole has on the reaction of the bowling ball. Shorter distances (3″ or less) to the x-axis are going to decrease reaction. Longer distances (4″ or more) to the x-axis are going to increase reaction. Distances somewhere in the middle are going to have little to no effect. Why does this occur? Let’s take a look.

the difference in RG’s

Every hole that you introduce to a bowling ball is going to raise the RG of the ball in that particular location of the hole itself. We know that the pin designates the low RG axis on the entire ball. Figure 3 represents a 15lb Torrent. Looking at the numbers, a Torrent in this weight has a low RG of 2.56 and differential of 0.044. This means at the location of the pin, the RG of the bowling ball is going to be 2.56. If we go approximately 6 3/4″ away from the x-axis, we will find the y-axis. The y-axis is the high RG axis of the bowling ball. This is essentially a 90° angle from the top to the side of the core. The difference between these two axes represent the total differential of the ball. Using some simple math, we can calculate what the high RG axis of an undrilled 15lb Torrent is. 2.56 (Low RG) + 0.044 (Differential) = 2.604 (High RG). It is important to note that the RG of the ball is going to change as we move across the surface of the ball. Somewhere in between 0 and 6 3/4″, the RG will be somewhere between 2.56 and 2.604. The shape of the core primarily influences this. Now that we know the RG’s of the Torrent, we can take a look at how balance holes are going to influence them.

 

 

Distance from the x-axis

Let’s start with hole placements with shorter distances from the x-axis. Imagine putting an extra hole directly through the pin as an extreme example. We know that introducing a hole into the ball is going to raise the RG of the ball in that particular spot. The x-axis is the lowest RG spot on the entire ball. If we add a hole to it, we are raising the RG of the lowest RG spot on the ball. This makes the lowest RG spot on the ball higher and closer to the high RG axis. This is lowering the total differential between the two, which makes the ball weaker and respond slower as it transitions down the lane. Think about where the mass is being taken out of the core. The pin is designating the top of the core. If we drill a hole directly through the pin, we are taking more mass out of the top of the core. This essentially makes the core shorter, which lowers the total differential and raises the overall RG.

Now let’s take a look at hole placements with longer distances from the x-axis. Imagine putting an extra hole 6 3/4″ away from the x-axis. As always, when introducing a hole into the ball, that hole is going to raise the RG of the ball in that particular spot. Approximately 6 3/4″ away from the x-axis is the high RG axis. If we put a hole on the high RG axis, we are raising the RG of the already high RG axis of the ball making it even higher. What is this going to do to the overall differential? The low RG axis remains unchanged, but now the high RG axis is even higher. The total differential has increased and the RG has remained lower. Imagine where the mass is being taken out of the core with the hole 6 3/4″ from the pin. All of the mass will be removed from the side of the core. This is going to make it skinnier than it was before compared to its height. This will increase the total differential and keep the overall the RG lower.

Finally, let’s take a look at medium distances. If we put an extra hole at 3 3/8″away from the X-axis, we are precisely between both the low RG axis and high RG axis. This is going to have little effect because we are taking mass out at a 45° angle relative to each axis. We are taking mass out of the top and the side which cancels out the effect. If we get farther than the 3 3/8″ distance, we remove more mass from the side. If we get closer than the 3 3/8″ distance, we remove more mass from the top. Each of these effects have been outlined above and should make sense.

Sizes are pretty self-explanatory. As you can imagine, the larger and deeper the hole, the more effect the hole will have on the reaction of the ball. This is because we are removing more mass out of the core. This means there are a lot of options when it comes to size and depth. I always suggest starting with a smaller hole because you can always increase the size based on what you see from the initial ball reaction.

 

Position on the arc

The final variable to look at is the position of the balance hole on the arc. Let’s imagine that we put an extra hole in the ball 5″ from the pin. There are many different positions on the ball that are 5″. Looking at the Figure 4, we can place a balance hole anywhere on this arc and it will remain 5″ from the pin. The further out we put the hole towards the VAL, the more we are going to smooth out and slow down the reaction. This happens because the holes are further apart. The closer we get the hole towards the thumb, the faster this ball is going to transition. This happens because the holes are closer together creating a larger intermediate differential after drilling. It is important to note that you always need to make sure that tracking issues won’t occur when determining where to place the balance hole. You will always want to throw the ball first and make sure you aren’t placing the balance hole near any track flare. Keep in mind, if you are using a flare increasing hole (4″ or more), the ball is going to flare more after the hole is drilled. You will need to put the hole further away from the flare rings.

 

 

Looking at balance holes like this makes it easier because it gives you consistency from ball to ball. The mass is being taken out of the same spot on the weight block to create a more consistent reaction regardless of the differences in layout. In Figure 5, the ball on the left is drilled 3 x 4 x 1 and the ball on the right is drilled 6 x 4 x 3. If both balls were to have a balance hole located on the PAP, the balance holes are not going to have the same effect on each of the balls. It’s going to increase the total differential and lower the RG on the 6 x 4 x 3 ball because the balance hole is 6″ from the pin. On the 3 x 4 x 1 ball, the balance hole is going to have less of an effect because it is drilled in the neutral zone of 3-4″ from the pin. Keep in mind, all of this information is relative to all of the other pieces of the puzzle. Remember that Pin-to-PAP distance is going to be another variable influencing the reaction. Clearly a ball with a 6″ pin-to-PAP distance is going to be cleaner through the front part of the lane and flare less. The location of the hole is one of the secondary factors that goes into ball reaction.

 

 
symmetrical verses asymmetrical

The last thing we cannot ignore is the effect of hole placement on a symmetrical versus an asymmetrical core. Take a look at Figure 6. Remember that an asymmetrical ball can be fine-tuned even further because of the presence of the PSA, or the preferred spin axis. The closer the balance hole is drilled to the PSA, the higher the intermediate differential is going to become. The ball is going to transition faster because it has a higher intermediate split. The further the balance hole is drilled from the PSA, the more intermediate differential you are drilling out of the ball. Essentially, you are drilling out some of the asymmetry which makes it transition slower as a symmetrical ball would. All the other principals aforementioned are the same regarding balance hole distance from the x-axis.

Essentially, if we put a 1 1/4″  hole 6 3/4″ away from the pin and drill it 3 1/2″ deep, we are going to significantly increase the total differential and lower the RG of the ball. This is going to result in it transitioning much faster and hooking more front to back and right to left overall. If we put a 1 1/4″ hole through the pin drilled 3 1/2″ deep, we are going to significantly decrease the total differential and raise the RG of the ball. This is going to result in the ball transitioning much slower and hooking much less front to back and right to left. If we decrease the size or the depth of these holes, we will reduce the impact that they had in their respective locations.

summary

In summary, you can really see how much of an effect can be created using different balance hole locations and sizes. Hopefully now, you have a better understanding of how balance holes further from the x-axis increase flare potential and balance holes closer to the x-axis decrease flare potential. Keep in mind that there are many pieces to the puzzle that is laying out a bowling ball. Some are more influential than others. This article strictly looks at the effects of balance holes and keeps all other variables constant. Learning more about how these variables work together to create good ball reaction is crucial to understanding what your ball is doing as it transitions down the lane. Knowledge is power – put them all together and you’ve got some serious power.

Always remember: not all balance holes are created equal!