How Do Bowling Ball Cores Affect Performance?

A bowling ball core is what is inside a bowling ball and it is the heaviest part of the ball. It is often called a weight block. A bowling ball core is made of powdered metal oxides mixed with resin and a catalyst.
Atomic Asymmetrical

The core of a bowling ball and its shape—whether it is symmetric like a sphere, or asymmetric like a lightbulb—influence how the ball rotates down the lane. This influence can determine a bowler’s performance.

The Bowling Ball Core

LED symmetrical

At the heart of a bowling ball is a core that determines how a ball will roll and rotate down the lane. While the lane surface and oil pattern will also contribute to ball motion, the core is probably the most significant factor to consider when purchasing a new bowling ball.

Main Types of Cores

There are various types, shapes, and sizes of cores for bowling balls. We’ll group them into three categories. The first type is the low-performance pancake core. Then there is the symmetrical core and the asymmetrical core.

Pancake-type cores

pancake core

Pancake cores are found in polyester bowling balls, beginner urethane balls and reactive resin bowling balls. Pancake cores are usually shaped like “pancakes” or “puddles”, but sometimes they are shaped more like small pucks.

Ebonite International polyester balls typically contain a traditional pancake-shaped core, whereas Brunswick’s polyester balls currently contain a shape that is smaller and more puck-like.

Gravity Marker

Another significant feature of these kinds of cores is that balls that use them usually have little if any separation between the location of the low RG axis (or pin) and the center of gravity marker. In more common terms, they are what we generally call “pin-in” balls.

High RG – Low Differential

Pancake-type cores have similar performance characteristics, regardless of their shape. This includes having a high RG and low RG differential, which means they create very little track flare.

Pin-in Bowling balls

Another main defining characteristic of this type of core is that bowling balls that use it typically have little or no separation between the location of the low RG axis (or “pin”) and the center of gravity marker. In other words, they result in what are commonly referred to as “pin-in” bowling balls.

Most people put the “label” (usually the CG or pin) near the center of their grip when they use a pin-in ball. This is called the traditional layout strategy. There are a few other ways to do it, but they are not used as often.

Symmetrical Core Bowling Balls

Meditate Symmetric

Symmetrical cores are the most advanced type of core technology. Pancake cores are symmetrical cores, but most people think of them as being different from traditional symmetrical cores.

Traditional Cores

When we talk about symmetrical cores, we’re talking about the type of large cores found in two-piece bowling balls that don’t have three different masses. In bowling terminology, this means those cores which don’t have a significantly high intermediate differential.

Most ball drillers and manufacturers believe that bowling balls with small intermediate differentials (for example, less than 0.008”) should be treated as if they are symmetrical.

Axisymmetric vs Non-axisymmetric Bowling balls

Generally speaking, there are two types of symmetrical cores: those that have axisymmetric geometry and those that have non-axisymmetric geometry. A bowling ball core with an axisymmetric geometry can be created by revolving a two-dimensional profile around a central axis.

One popular example of an axisymmetric core shape is the light bulb core. This type of shape has been popular for many years.

Light Bulb

Capacitor Core symmetrical

The classic light bulb core has a symmetrical shape. The yellow two-dimensional profile is rotated about the red axis to create the three-dimensional light bulb shape.

The other type of symmetrical core, the non-axisymmetric symmetrical, has more complicated geometry than the axisymmetric symmetrical, but it is still mathematically symmetrical because of the values of its principal mass moments of inertia.

One example of a core that falls into this class is the Resurgence Symmetric core that is found in the Columbia 300 Eruption line of bowling balls. It has a mostly axisymmetric shape, but it also has a few small non-axisymmetric features.

Not So Simple

This example core shape is mathematically symmetrical, but it does not have an axisymmetric geometry. Note that there is no simple two-dimensional profile that could be rotated about the red axis to produce the final three-dimensional geometry.

Most people don’t need to worry about the difference between an axisymmetric symmetrical core and a non-axisymmetric symmetrical core. The gripping holes and balance hole can hit or miss a core’s non-axisymmetric features depending on how it is drilled, but this usually doesn’t have a big impact on the mass properties of the drilled ball.

The main reason for mentioning the axisymmetric vs. non-axisymmetric distinction is to point out that you can’t necessarily tell if a core is symmetrical just by looking at it. Some bowling balls that look asymmetrical are actually symmetrical mathematically (and that’s what really matters).

Check The Specs

You can tell if a ball is symmetrical or not by looking at the manufacturer’s specifications. If a ball has a low intermediate differential (which is the difference between the ball’s high RG and intermediate RG), then it is most likely symmetrical.

There are a lot of symmetrical cores available for bowling balls. People think that they roll more smoothly than asymmetrical cores, but this isn’t always true.

Asymmetrical Cores

Asymmetrical cores have three different principal mass moments of inertia. This means that they are not symmetrical. In bowling terminology, this refers to cores that have both a differential and a significantly high intermediate differential.

Generally, you should treat bowling balls with very low intermediate differentials (less than 0.008″, for example) as symmetrical cores and the rest as asymmetrical cores. An example of a simple asymmetrical core is shown below.

Sidewinder Asymmetrical

This is an example of an asymmetrical core. It is a rectangular prism with three different edge lengths (and rounded edges).

There are many different shapes and sizes of asymmetrical cores. Bowling balls that use asymmetrical cores come in a variety of weights, hook potentials, and backend reactions.

Disturbance Asymmetric

There is a lot of variation between different types of bowling balls. The simplest balls are symmetrical, like in the image above. More complex balls have a higher degree of asymmetry, which is measured by their intermediate differential.

The difference in size between different bowling balls can range from approximately 0.008″ to 0.025″. This difference is usually not very big, but there are some exceptions. In recent years, extremely large differences in size (of more than 0.030″) have become less common.

People often say that asymmetrical bowling balls produce a more angular ball motion than symmetrical balls. This is true, but the relationship between angularity and level of asymmetry is actually quite weak.

Gas Mask Asymmetrical

There is a key difference between symmetrical and asymmetrical bowling balls. For symmetrical bowling balls, the weight block is put in a certain way and the holes are drilled based on where the person’s hand goes and where they want the ball to go. Asymmetrical bowling balls have the weight block put in a different way so it reacts differently.

Asymmetrical bowling balls are different from symmetrical bowling balls. They use the pin and the “mass bias” marker (which marks where the high RG axis is on the ball). Additionally, some layouts behave differently on highly asymmetrical bowling balls than they do on symmetrical balls.

For example, a 6″ pin-to-PAP distance layout on a symmetrical ball will typically result in a low-flaring ball. On a strong asymmetrical ball, however, a 6″ pin-to-PAP distance layout might result in a high-flaring ball, depending on the positioning of the high RG axis.

Just be aware that when it comes to layouts, asymmetrical bowling balls should not be treated the same as symmetrical balls.

Why are the Cores Named Like This?

Just like with the coverstocks of bowling balls, most manufacturers now give the names of the cores. But unlike with coverstocks, the names given to cores don’t really mean anything to bowlers. The only thing that they can use it for is to identify how the bowling ball will perform on the lane.

Sometimes, when companies make bowling balls, they will put a word in the name of the ball that describes one of its mass properties. This can sometimes be helpful, but it is usually better to use the actual published RGs and differentials to characterize a core.

The Shape of the Core

There are many different shapes of bowling ball cores. A designer must think about many things when they are designing a bowling ball. Some of these factors are how the ball will roll, how it will feel, and how it will look.

Undrilled Mass Properties

Designers often have a target for the mass properties of a core when they are designing it. The low RG, total differential, and intermediate differential are all important to them.

Different shapes of the core affect the mass properties of an object. For example, a spherical core will have lower differentials than a tall and cylindrical core.

As-Drilled Mass Properties

When you put holes in a ball, its mass properties change. The shape of the core inside the ball affects how much the mass properties change when you drill into it.

Some bowling balls are designed so that their mass properties don’t change much when you drill them. Other bowling balls are designed so that the ball driller can change the mass properties a lot with different layouts. The rest of the balls (which is most of them) aren’t really designed for this factor.

Manufacturing Efficiency

Designing a product so that it can be manufactured efficiently is important. This means that the design will be easy to produce and won’t require too many steps or extra materials. It’s also important to make sure that all of the parts of the product fit together properly and work well together.

A bowling ball has to be manufactured. The manufacturer needs to make the bowling balls the same way and with minimal waste.

A core might have features that help the casting process or make it easier to assemble the finished product. For example, a core might be designed so that the liquid core material flows more easily during casting. Additionally, a core might have features that make it easier to assemble multiple products using the same core, such as flat regions that can be used to hold the product in place.

Complicated design features on a core can have a big impact on how the ball behaves. This is because just a small shift in the position of the core can create a lot of static imbalance. When you are looking at a core shape, remember that some of those complex features might be there for a reason- to make it easier to manufacture.

Marketing Aspects

Manufacturers want their cores to look good in marketing materials so that people will buy the bowling balls. The cores are what people see most in marketing and they want them to be appealing.

Factors Affecting Core Performance

The performance of a core (how it works) depends on its mass properties (how heavy it is and how big it is).

There are specific things that matter when bowling with a drilled ball. This includes the low RG, total differential, intermediate differential, and the orientation of the low and high RG axes relative to the bowler’s positive axis point. In addition, the ball’s static imbalances also play a role.

The shape of the ball’s core affects how it performs. The core’s shape affects how the ball behaves when it is thrown. But only to a certain extent. The core’s shape also affects how heavy the ball is.

For example, if two bowling balls have cores with different shapes, but they have the same mass when they are drilled, then they will have the same on-lane performance.

Another major factor that many people don’t think about is coverstock maintenance. Make sure you keep your bowling balls clean for the best performance.

Urethane Balls

Urethane bowling balls are not as popular as they once were. They do not hook as much as other types of bowling balls. They are best suited for straight bowlers who need a ball that will not hook too much.

Plastic Bowling Balls

Plastic (or polyester) balls are the most common type of bowling ball. They are less expensive than urethane or reactive resin balls and are good for beginners. Plastic balls are not as durable as urethane or reactive resin balls and will not last as long.

Reactive Resin Balls

Reactive resin bowling balls are more expensive than urethane or plastic balls. They have a shell of reactive resin surrounding the core. The reactive resin makes the ball hook more.

Will a Bowling Ball Core Affect My Performance as a Bowler?

According to Ronald Hickland, the effect of certain layouts and the mass properties through drilling and core shape will affect performance.

He used three different types of core shapes for their performance test: a simple pancake core, a symmetrical core shape, and a High Mass Bias asymmetrical core shape.

The first layout for the balls has the pins 5.5 inches away from the bowler’s positive axis point, with the Mass Bias at 45 degrees. The second layout has the pins 3.5 inches away from the bowler’s positive axis point, with the Mass Bias at 45 degrees.

None of the bowling balls were drilled with weight holes. This allowed for all core mass property changes to be purely a function of drilling. All of the balls have a 4 ¾ total span. The finger holes are drilled with a 31/32 inch bit 1.5 inches deep. The thumb hole is drilled with a 1-inch bit 2.5 inches deep.

The test involved actual physical measurements and computer design software to give us a detailed look at the mass properties of the ball. They also collected performance data during the testing and evaluation.

If you are looking for a full list of bowling terms click here.

Testing the Pancake Core Shape

The 5.5-inch ball is a little bit heavier than the 3.5-inch one. This means that it will move differently when you roll it or throw it.

They collected performance information from both of these bowling balls.

The 3.5-inch layout gave the ball more hook and backend. The 5.5-inch pin went further down the lane and to the left before hooking back to the pocket. In general, the 3.5 inch pin was a stronger performing ball for the pancake core shape than the 5.5-inch pin layout.

Testing the Symmetric Core Shape

The 5.5-inch pin drilled ball has more mass than the 3.5-inch pin drilled ball. This means that it will move slower and have more force when it hits something.

However, the Mass Bias is higher in the 5.5-inch pin drilled than the 3.5-inch pin for both cases. More gross weight is removed from the 3.5-inch pin from the 5.5-inch pin in both cases.

The 3.5-inch pin layout gave less hook than the 5.5-inch pin layout. The 5.5-inch pin layout had more backend recovery this time as well. Overall, the 5.5-inch pin was a stronger performing ball for the symmetric core shape.

Test 3 – The High Mass Bias Asymmetric Core Shape

The 5.5-inch pin drilled ball has more of a mass bias value than the 3.5-inch pin drilled ball. This means that there is more difference between the masses of the two balls, and the 5.5 inch ball has a higher mass.

By comparison, it can be noted the 3.5-inch pin layout in this case went longer than the 5.5-inch pin layout and had significantly less backend recovery. The 5.5-inch pin layout hooked earlier still and had more overall hook than the 3.5-inch pin. Overall, the 5.5-inch pin was a stronger performing ball for the High Mass Bias asymmetric core shape.


The different tests show that the mass property values, in terms of Mass Bias and differential, tend to increase as the pancake shape goes to a symmetrical shape to a High Mass Bias asymmetrical core shape.

The results show that if a property has high mass values, the performance of a drilled well will be better than if the property has low mass values.

The drilling can change the mass properties differently as they move from pancake to symmetrical to High Mass Bias asymmetrical core shape. This is because of how the weight blocks are impacted by the drilling.

So, which one hooks more?

Different bowlers have different statistics. This means that the performance effect of the core and drilling can change the results. The more asymmetrical the core is, the stronger the overall performance will be.

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