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Bowling Ball Mass Bias, Originally Posted: 12/1/2013; Updated: 2/2/2023

There are several factors related to the surface of your bowling ball which assist a pro shop professional when it comes time to map a drilling layout.
One of the factors the pro shop must identify is the “Mass Bias” location.
The part of a bowling ball in which the internal mass of a bowling ball is closest to the outside edge of the coverstock is commonly referred to as Mass Bias. This does not include the Pin.
The “Pin” locator is best defined as a polyester or urethane stem which is positioned in the weight block to hold the core in place as the coverstock is poured into the ball mold during the manufacturing process.
This “Pin” represents the top part of the weight block and is usually represented by a colored dot on the surface of the ball.
Bowling ball mass bias helps control the shape of a given ball reaction on the back end of the lane. When the mass bias marker on the ball surface is moved to different locations, it will affect your ball reaction.
There are four basic locations you can put the mass bias on a bowling ball:
On your track
On your Vertical Axis Line (VAL)
Halfway between the track and the VAL
Past your VAL
Asymmetric bowling ball core designs will have mass bias markers on the ball surface but symmetric balls will not.
Symmetric balls do have slight mass bias influence, but not sufficiently to require a marking indicator.

Depending on a given layout for an asymmetric bowling ball, the pro shop professional will choose relative positioning of the “Pin”, the Mass Bias, and the Positive Axis Point (PAP) locations to influence ball motion.
Normally, a weak layout, a moderate layout, or a strong layout are selected so the ball motion for a given player will best match the lane conditions.
The mass bias marker is one such location on the ball surface to assist the pro shop professional when planning a drilling layout.
If you have questions about mass bias or any other factor used to map out given drilling layouts, consult your pro shop operator for additional information.
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