Bowling Ball Specs Cheat Sheet to Layouts & Ball Motion

This is my personal cheat sheet to bowling ball specifications.

Every ball made these days is pretty complicated so understanding these specs (even at a very basic level) will go a long way to improving your understanding of ball motion and the potential a ball has to improve your arsenal.

For starters their are two different types of balls: symmetric and asymmetric.

Symmetric vs Asymmetric Bowling Balls

Symmetric balls tend to have low differential whereas asymmetric balls tend to have high differential – the difference between the maximum RG and minimum RG of a bowling ball.

When a bowling ball’s differential is higher the ball has the potential for more flare.

Although any ball with a high differential has the potential for maximum flare on a bowling lane any random asymmetrical ball in your bag will usually flare more than the random symmetrical ball because they naturally have higher differential values as a rule of thumb.

Simply put – Asymmetric bowling balls will flare more resulting in a stronger skid/flip ball reaction – frequently this means a stronger back-end with a comparatively weaker mid-lane read.

Read more technical info here:

What the Heck is RG and Why Should I Care?

Every bowling ball has at least two axes.
The “X-axis” is commonly known as the the low RG axis of a bowling ball. This axis travels through the core from the top of to the bottom with the pin being the top of the ball.

The “Y-axis” on the other hand is commonly known as the high RG axis of a bowling ball which is exactly 90-degrees offset the X-axis.

In a symmetrical ball the y-axis is exactly the same all the way around the ball just as the equator of earth is the same all the way around the planet.

In an asymmetrical ball there is actually a single point on this equator line that is called the preferred spin access (PSA) and is marked as a specific point 90-degrees off the pin (or top of the ball).

This PSA access is sometimes referred to as the z-axis because it’s the only access point that is offset the x-axis that remains the same on both sides.

The X-axis follows the most stable and preferred rolling axis of the ball. It travels through the pin to the opposite side of the ball.

The Y-axis would be perpendicular to the X-axis and although it would be relatively stable it wouldn’t be the preferred spinning axis of the ball. With friction the ball would want to migrate to a more stable rolling axis, ultimately the X-axis which rolls perfectly around the pin.

In an asymmetrical ball the main pin is also paired with a second marking min called either the PSA Indicator Pin or the Mass Bias (both names are interchangeable and mean the same thing).

In an asymmetrical ball this is the Preferred Spin axis (not the X-axis as it is in symmetrical balls).

Asymmetrical balls will migrate or flare towards the PSA axis as it is preferred.


In a symmetrical ball the thumb hole will be the preferred spin axis (PSA) although it will be a weak PSA compared to the PSAs in asymmetrical balls.

In symmetrical balls the Pin-to-PAP distance is the largest determinate for ball reaction aside from coverstock.

A 3.375″ Pin-to-PAP distance will yield the strongest ball reaction because this will force the ball off the hand into the most unstable ball roll possible for the symmetric core. This high level of instability results in maximum track flare which is why the ball will have the strongest reaction (change of direction).

Pin-to-PAP distances that are greater than this will read the lane progressively later (and less aggressively) as you approach the maximum 6.75″ distance.

Distances that are shorter than 3.375″ will read the lane earlier but to a lesser degree as the distance gets closer to zero.

No matter whether you go high or low with your Pin/PAP distance your ball reaction will be muted because track flare will be lower on both sides of the scale.

Pin/PAP distances that are on the high side will operate in conjunction with the ball’s larger radius of gyration (RG) measurement while distances on the lower side of the scale will operate in conjunction with the ball’s lower RG measurement.

In general high RG balls read the lane late and low RG balls read the lane early.

Each ball has an RG spread which compares the lowest possible radius of gyration (or spin) to it’s highest possible radius. The difference is neatly called the differential and the bigger the differential the more potential the ball has for track flare.

If the Pin-to-PAP distance is exactly at 3.375″ then you can take advantage of the maximum track flare possible on a bowling ball.

If you want the ball to err on the side of reading late then the Pin/PAP distance should be just over 3.75 inches and it should be just under if you want your ball to err on the side of a early read.

If you want a ball to read late but strong then you should choose a ball with a high maximum RG and a wide differential and set your Pin-to-PAP distance to 3.375″.

If you want this same ball to read late but weaker then the 3.375 inch distance should be expanded in the direction of 6.75″.

Conversely a ball the reads early and strong should have a low minimum RG with a large differential and set your Pin-to-PAP distance to 3.375″.

If you want this same ball to read early but weak then the 3.375 inch distance should be shortened in the direction of zero inches.

Usage notes:

In general a longer Pin/PAP distance will conserve energy through the heads and mid-lane reserving it for the back end.

This can be helpful for situations where there is burn in the heads or mid-lane. The longer Pin/PAP distance will help the ball skid over the burn area reserving as much energy as possible for the backends.

On the flip side shorter Pin/PAP distances will read earlier leaving less energy available for the backends.

On fresh patterns, heavy oil, long conditions, or even super short patterns a shorter Pin/PAP distance can be a great tool for controllable and predictable movement that flattens out a lot on the backend of the lane.

In the middle of the spectrum the strongest layout distance of 3.375 inches is usually conducive to transition games, heavy oil conditions, and generally longer patterns.

How About The Shape of the Curve?

Beyond the RG being small or large, the differential being big or small, and the Pin-to-PAP distance being short or long the shape of the ball’s change in motion can be altered a bit by altering the VAL intersection with the Pin-to-PAP plane.

If the angle that the planes intersects is around 25 degrees then the the direction change of the ball at the break-point will be more abrupt.

If that angle is 35-40 degrees then the direction change of the ball will be smoother and more continuous (less abrupt or angular).