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Bowling Ball Specs: What the Numbers Mean

When starting out in the game of ten pin bowling, the numbers game that is involved is not all that important, aside from how many more strikes you can get than your buddies.  Bragging rights still matter, after all.  Most beginners are simply comfortable using the house bowling balls provided by the bowling alley and although some of the grips are a bit iffy, as long as you’re not walking away with blisters after a night of fun, the science of bowling ball specs is not much of an attribute.

Once you move on from a recreational bowler to taking on a league slot, the bar slides up a bit higher and even if you’re not competitive, the plastic house ball is not always going to suffice.  When it comes time to go shopping for your own bowling ball, prepare to be slapped with the world of geometry and understanding the numbers involved is critical when making your final choice when building your pin-destruction arsenal.

If you’ve had an opportunity to see some of my bowling ball reviews, you may have noticed some of the technical specs that I include in them.  Granted, some of the numbers are basic, but let’s pull back the covers and go over the details of some of the meanings of these values.  I’ll use the specs of my current strike ball, the Storm Reign Bowling Ball.

Example Technical Spec Sheet


As you can see, there are a lot of numbers on the spec card.  There are some obvious values here such as “LBS.” for the weight of the bowling ball and the factory finish values telling us how fine the polishing finish was used after sanding down.  But there are many other factors included such as, “RG” and “DIFF” and “Flare”.  So what do these mean and why should you pay attention to them?

Drilling Into the Numbers

Every bowling ball that is to be used on the lanes is to be approved by the USBC (United States Bowling Congress) and with each ball, there are limits to how the bowling ball is constructed as well as how the bowling ball will respond to specific bowling styles.  Again, using the Storm Reign bowling ball, here are the different specification and their meanings (some values covered are not visible on the spec sheet above, but are still important to understand):

Coverstock: Reactive Pearl
RG: 2.55
Differential (DIFF): .052
Flare: 4″ – 5″
Length: 15.5
Backend: 16.5
Box Finish: 1500 Grit Polish

Now that we’ve gone over the actual specifications of the bowling ball, let’s go over the definition of each attribute:

The coverstock is responsible for the actual contact with the lane, but also is important is the type of coverstock as it must allow for the dynamic of the inner workings – or core – of the bowling ball to react correctly.  There are several different types of coverstock including: Polyester, Standard Urethane, Reactive and Particle Resin.  Each coverstock plays a different role in how the ball reacts with the oil on the lanes, for example, a Polyester coverstock have  a smoother surface and are ideal for rolling straight balls.

RG (Radius of Gyration)
The RG, or radius of gyration is a measurement of the effective weight distribution in a ball as it relates to the moment of inertia. It essentially is an indication of the resistance to rotation motion. It is equal to the square root of the moment of inertia divided by the weight.  If you are this much into the math, bless you.

Differential (DIFF)
This property determines the track flare potential. The maximum allowable differential RG is 0.080 inches. The more the differential RG, the more potential for track flare. Track flare increases the friction between the ball and the lane and determines how much flare or arc the ball will produce while traveling the lane.

Track flare is the migration of the ball track from the bowler’s axis upon release to the axis at the moment of impact with the pins.  Increased track flare gains greater rotational energy and hitting power.  Decreased track flare creates greater ball skid. No track flare will have a ball rolling on an oily surface each revolution.

Length is an indicator of how far a ball will travel down the lane before the bowling ball begins to hook.  The higher the number, the further down the lane it goes before the ball will hook into the pocket.  Length does not include skid produced by lane conditioner, additional fine sanding, or the use of “liquid sandpaper” polishes.

Backend is an area of the lane closest to the pins (identified as the last 15 feet of the lane).  This area of the lane is not typically oiled, but oil does moves to the backend due to bowling activity.  The value here provides a value on which the ball is expected to generate the most power after the hook.  The higher the value, the more powerful the backend motion is.

Box Finish
The box finish the the factory polish grit used upon completion of construction of the bowling ball.  Using a different finish can affect the way the bowling ball interacts with the lane so be careful if you decide to have the bowling ball refinished while at the pro shop.

What Say You?

Playing the numbers game can be somewhat confusing but once you have them down, your bowling ball reaction and roll can almost provide you with as much entertainment as a master illusionist.  What specs do you pay the most attention to when picking out a new bowling ball and how do these values measure up to your standards?