Moment of Inertia Matching
Conventional Swing Weight Matching
Most golf club sets have been "matched" by swing weight since the early
1920's. Swing weight is the measurement of a golf club's weight
about a fulcrum point which is established at a specified distance from
the grip end of the golf club.
In essence swing weight is an attempt to ensure all clubs within a set "feel" the same when they are swung. Most everyone is familiar, or least has seen, a swing weight scale. Weight is distributed in the club head in order to achieve the desired swing weight number as desired by the individual player based on what swing weight number feels most comfortable to him or her. The object is to build all the clubs in the set to the exact same swing weight number as measured on the swing weight scale.
Although swing weight matching makes sense and has been the accepted standard for matching golf clubs for many years, I believe, as do many other clubmakers, there is now a better method of matching clubs. This method is known as Moment of Inertia (MOI) matching).
Moment of Inertia (MOI) Matching
MOI
matching is accomplished much differently that swing weight matching.
The object of matching sets of golf clubs is to provide a method to make
them feel the same during the swing. Swing Weight Matching does
not make each club identical with respect to the physical effort
required to actually swing the golf club. MOI Matching yields golf clubs
which require the same precise physical effort to swing.
Determining the correct MOI for an individual golfer makes it possible
to build an entire set of golf clubs that require the most natural
physical effort to swing from club to club. I'll provide a brief
description of the concept of MOI and MOI matching as defined by Tom
Wishon of Tom Wishon Golf Technology:
"The MOI of any object is a measurement of its resistance to being placed in motion around a defined axis of rotation. Related to golf clubs, if each club in a set requires a different amount of force to swing the club (set the club in motion to rotate around our body), it stands to reason that the golfer cannot be as consistent swinging each different club in the set. In most simple form, this is what sets MOI matching apart from matching clubs to the same swingweight. Swingweight matching does not make each club the same in terms of the amount of force required by the golfer to swing each club and hit the shot. MOI matching does. However, because golfers can be quite different in their strength, tempo and swing mechanics, the right MOI must be identified and fit for each golfer to allow the concept to properly work."
MOI values are determined by a mathematical formula which input these values, with other constant values to determine a proper MOI value. Is MOI matching a new concept? The answer is no, it's been attempted by at least two different companies, Sounder and Tommy Amour, over the years but failed for one basic reason. These companies both built MOI matched clubs; however, the problem was that every set of clubs were built to one specific MOI value.
This concept assumed every player would benefit from the same MOI value, which is not the case. An MOI value must be determined for each individual player. An MOI value which is perfect for one player would not necessarily benefit another player because everyone has different physical characteristics such as height, strength, tempo, swing speed, etc.
Are the mathematics involved in determining MOI values complicated? For the average person, the answer is yes. Although I have a strong mathematical background based on my electronics training while in the Navy, manually figuring MOI values would be a lengthy and tedious process. Fortunately an MOI analyzer which runs with associated software has been developed to measure and compute individual MOI values. This equipment makes MOI matching much less time consuming and very accurate.
Swing Weight versus MOI
What is the relationship between swing weight matching and MOI matching?
To make a golf club swing weight heavier you can increase the head weight and/or extend its shaft length. Either of these variables will provide more resistance to swinging the golf club and lead to heavier swing weight and a higher MOI value.
The opposite is also true. Reducing the club head weight and/or shortening its length will result in a club where swing weight and MOI are reduced.
All of the specifications used in targeting a swing weight are the same influential factors that will increase or decrease a golf club’s MOI. Arriving at the swing weight value and the MOI value utilize completely separate procedures.
The objective of swing weighting is to build a set of clubs with a similar swing feel. Although the clubs feel similar, they will require a slightly different amount of swing effort from one club to the next. If the MOI of each club were to be measured, they would not match.
The objective of MOI matching is to create a set of clubs that require the same amount of strength and momentum to swing. An MOI matched set will guarantee the same dynamic consistency utilizing the same swing for all clubs within the matched set. I am convinced that MOI matching is the state of the art method of matching golf clubs. Since MOI matching cannot be accomplished for the "masses", manufactured clubs purchased "off the rack" can only be swing weight matched. MOI matching can only be accomplished through a 'one-on-one' custom fitting with an MOI qualified clubmaking technician.
Not all clubmakers are "MOI Qualified". A clubmaker must either have a background in physics and mathematics OR be qualified in the operation of the equipment and software developed specifically for MOI matching in order to properly match golf clubs using the MOI method.
Creating an MOI matched set of clubs can be accomplished in one of two primary ways. The first technique is for the golfer to supply a "favorite" club; ie, a club the golfer has no difficulty in hitting. The goal would be to document the MOI of that club and then build a set to match.
The other method would be to swing a club and make adjustments to the weight of that club using lead tape. These adjustments would be made until the player finds a feel they like while also demonstrating the ability to hit consistently good shots and then build a set to the MOI specifications of this club.
I hope I was able to explain the basic concept of MOI matching and how it differs from swing weighting.
