Moment of Inertia

An article from Tom Wishon Golf Technology

Now that TWGT has made it possible for clubmakers to offer real MOI matching of clubs within sets, we have received a lot of questions about what MOI matching is and how it can offer clubmakers a better way to build clubs that truly are identical in swing feel. The purpose of this section is to acquaint clubmakers with MOI matching so that they can determine if they wish to offer this very exciting and scientifically proven method of matching clubs to improve the consistency of impact.

What is MOI Matching?
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.

Is MOI Matching a new high-tech clubmaking concept?
Not at all. Actually, we believe from our research that back in the 1920s when swingweight was developed, its originators were aware of the principles of MOI matching and tried to make swingweight matching of clubs the same as MOI Matching. They failed because the principle of the swingweight scale they developed could not truly accomplish the task of measuring the MOI of a golf club. Over the decades since the development of swingweight, engineers familiar with the principles of MOI have always been in agreement that MOI matching would truly make all clubs within a set swing with exactly the same feel, while swingweight matching could not.

Has MOI Matching ever been done previously in golf clubs?
Yes, there were two previous times in golf equipment history in which companies engaged in the sales of assembled golf clubs attempted to offer MOI matched golf clubs for sale. First, in the 1970s, a company named Sounder Golf offered sets of woods and irons which were purported to be matched by weighting the clubs at specific points within the shaft. The company promoted its clubs through the use of a device which would allow the shop to set two clubs in a pendulum swing motion to show how the Sounder clubs swung back and forth precisely the same in synchronous motion. When two swingweight matched clubs were placed in the same device, the identical swing weighted clubs swung back and forth in different pendulum motion. The Sounder clubs never caught on for two reasons: 1) Sounder was under-capitalized and unable to generate enough demand through their marketing programs. 2) Every set of Sounder clubs was built to only one specific MOI. Because golfers are different in strength, tempo and swing mechanics, one MOI measurement could never fit the MOI requirements of each golfer.

In the late 1990s, Tommy Armour Golf Company introduced their EQL model clubs to the market. By making all of the woods the same length and same total weight as the 5-wood, and all of the irons the same length/total weight as the 6-iron, the company did achieve a true MOI match for all the clubs within each segment of the set. This concept failed for two reasons; first, because the one MOI measurement to which all the EQL woods and irons were built did not fit all golfers, and second, because the concept of all woods and all irons being the same length was much too radical for golfers to accept.

“About 10 days ago, I received my new 550 irons with Series 5, R-flex shafts. 550M for the AW through 8 Iron and 550C in the 7 through 3 iron. I am a part-time clubmaking hobbyist and have previously made my own irons and always swing weighted them and continued to struggle with accuracy and consistency, playing like the Marines, left, right, left, right…..until 10 days ago. I am a 3 handicapper, and was at my wits end because almost all of my strokes over par were due to bad iron shots.

“My clubmaker, Frank Grasso of Golf Tec, in New Jersey, made up three demo 5-irons and I selected the one with the R-flex shaft. He made up the set MOI matching the irons. I am happy to report that I am hitting my irons more accurate and consistent than I ever have. I am still experimenting with ball position and yardages, but the 550’s are a great improvement.

“So far 90% of my misses are 2-3 yards short, where I can get up and down and save pars, as opposed to my old misses which were in bunkers or across cartpaths and almost never getting up and down. These irons are also sneaky long… sometimes it feels like I missed the shot and it ends up perfect. As for the MOI matching, every club in the set plays and feels the same and are effortless to swing. 4 weeks ago, I was ready to take a break from golf, and now, thanks to my new 550 irons, I can’t wait to get to the course toplay or practice.”
– Thanks and keep up the good work, Mike Hayes

How is the right MOI determined for each golfer?
Virtually all golfers who play frequently may have noticed they have a “favorite club” or clubs within their current set, or within a previous set of clubs. A “favorite club” may be defined as a club with which the golfer is most consistent over all others, and which the golfer has the utmost confidence in their ability to hit the ball solid and on-center more often than the other clubs in the set. After research and testing, TWGT believes that a one reason golfers have “favorite clubs” is that the MOI of those clubs happens to match the strength, tempo and swing mechanics of the golfer noticeably better than the MOI of other clubs.

There are two ways clubmakers can find the right MOI for any golfer. One is to ask the golfer to bring forth a “favorite club” from any set they may own or have used. The “favorite club” is measured for its MOI using the TWGT MOI Matching System, after which the other clubs are then built to match the MOI of that “favorite club(s)”.

The second is to build a test club based on the fitting recommendations you make for the golfer after going through the entire fitting process you follow. By manipulating the headweight of the test club with lead tape, it can be possible to find a headweight to “rest of the club” ratio that will result in a high percentage of on center hits. Once done, the test club is measured for its MOI, and the TWGT MOI Matching System is used to guide the clubmaker in building all the other clubs in the set to have the same MOI.

Does MOI Matching change the fitting process for the golfer?
No. MOI Matching is simply a replacement for swingweight matching in the fitting process. Clubmakers will fit golfers for the best clubhead, shaft, grip and length based on the same fitting procedures that they have developed and with which they are confident. Once the heads, shafts, grips and the lengths are determined by the clubmaker, then MOI Matching is brought in to guide the clubmaker in how the clubs will be assembled with regard to final headweight, and in some cases, final length adjustments.

Is there any aspect of the fitting or performance of the shafts that is changed by MOI Matching?
Very rarely, if ever. As we said, the selection of the shaft is made on the basis of the same fitting procedures the clubmaker is comfortable with using to identify the best shaft for the golfer’s strength, swing speed and swing characteristics of downswing transition, downswing tempo/acceleration and wrist-cock release.

However, it is very likely that because of the final head weighting requirements of the MOI Match for each club, the frequency progression of the shafts will be different than if the clubs were swingweight matched. Normally, if the progression in butt frequency was 4cpm between clubs in a swingweight matched set, the progression will change because of the different headweight changes in the MOI set, and NOT because of any change in trimming of the shafts. In all of our testing, and in the reports of actual MOI fittings that clubmakers have done, we have yet to hear of one case in which the golfer required an adjustment in the tip trimming to offset the different progression of frequency from shaft to shaft within the set that came from the MOI matching headweight requirements. In short, 99% of the time we believe the MOI matching will not affect the golfer’s perception of the shaft fitting.

What will a golfer notice when switching from swingweighted to MOI matched clubs?
No BS, we have yet to hear from a clubmaker using the MOI system who reported that a golfer for whom MOI matching was performed did not notice a difference in the swing feel of all of the clubs in the set, and a minor to significant increase in the percentage of solid, on-center hits with their clubs. If the golfer “waggles” each MOI matched club, if they are sensitive to the feel of each club, they will detect a progressively increasing headweight feel as the clubs get shorter in the set. But as soon as the clubs are swung full, the golfers all report that they can close their eyes, switch clubs in the set, and not really detect any difference in the total swing feel of the clubs from each other.

If I take a set of MOI matched clubs and then measure each club on a swingweight scale, what will I see?
Depending on the MOI each club is made to possess, the swingweight of the clubs in am MOI matched set will normally increase from the longest club in the set to the shortest. However, what the longest club’s swingweight is compared to the shortest, and what the progression in between can be quite different, again, depending on the MOI to which the clubs in the set are built, the lengths each club is fit to the golfer, and the weight and balance point of the shafts chosen for the golfer.

Will the woods and irons all be built to have the same single MOI?
No. TWGT testing and feedback from many of the clubmakers using MOI matching in their work has showed that because woods and irons are so different in their length ranges, better results were obtained by matching all the woods to one MOI, and then matching all of the irons to another MOI, with both chosen specifically for each golfer either on the basis of the “favorite club” or the “test club” approach.

What about the wedges – should they be built to have the same MOI as all of the rest of the irons?
Again, this was another aspect of MOI fitting and matching that TWGT has spent some time investigating. What we found was that any of the wedges that are chiefly used by the golfer for less than a full swing, it should not be matched to the same MOI as the rest of the irons, each which are predominantly used with a full swing. In general, because many golfers do use the PW and AW (gap wedge) for full swings more than they do the SW and LW, it is ok to make the MOI of the PW and AW the same as the rest of the numbered irons. But for the SW and LW, they are better off being built individually to an MOI or swingweight based on the principles taught in the book, Common Sense Clubfitting: The Wishon Method.

How about the putter – should it be MOI matched?
Most definitely finding the right MOI of the putter for each golfer’s feel and stroke mechanics would improve putting consistency on the greens. However, this is far easier said than done at this point in our MOI research. In the woods and irons, because there are multiples of each type of club, it is not difficult to ask a golfer to provide a present or past wood and iron that has been a “favorite club”, to which all of the other woods, and then all of the other irons would be MOI matched. But with the putter, it is not that practical to ask a golfer who is not putting all that well to bring in a “favorite putter” to act as the MOI guide – logic says if the golfer had/has a favorite putter, he/she would be using it at present and thus not need to change the MOI!

However, if the golfer DOES presently like the stroke feel of their putter but was interested in trying a different head model in a new putter, then the favorite putter should be MOI tested to provide the MOI benchmark for building or altering the new putter so that it had the same stroke feel the golfer likes.

How does the TWGT MOI Matching System work?
TWGT offers two different options for club makers to learn and perform real MOI matching. The difference between the two is in the speed and procedures of measuring the MOI of any club and the procedures for actually building the MOI matched clubs.