What is MOI ? "Moment of inertia," or MOI, is a property of physics that indicates the relative difference in how easy or difficult it will be to set any object in motion about a defined axis of rotation. The higher the MOI of an object, the more force will have to be applied to set that object in a rotational motion. Conversely, the lower the MOI, the less force needed to make the object rotate about an axis. What is MOI Matching ? The MOI of any object is a measurement of its resistance to being placed in motion. Related to golf clubs, if each club in a set requires a different amount of force to swing the club (set it in motion), it stands to reason that the golfer cannot be as consistent swinging each different club in the set, as if each club were built to require the same force to swing. In its most simple form, this is what sets MOI matching apart from matching clubs to the same swingweight. Swingweight matching does not make each club within a set the same in terms of the amount of force required by the golfer to make the swing 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, back in the 1920s when swingweight was developed, its originators were well 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 with which we are familiar 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 MOI 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 swingweight matched clubs were placed in the same device, two identical swingweighted clubs swung back and forth erratically. The 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. Much later, in the late 1990s, the Tommy Armour Golf Company introduced their EQL 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 an MOI match between the clubs. This concept failed again because the one MOI measurement to which all the EQL woods and irons were build did not fit all golfers, but also because the concept of all woods and all irons being the same length was much too radical for golfers to accept. How is the right MOI determined for each golfer ? Virtually all golfers who play regularly have noticed they have a "favorite club" or clubs within their current or a previous set of clubs. A "favorite club" may be defined as a club with which the golfer is most consistent over all others in the set, 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 very good reason for the fact that golfers do 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 other clubs. Therefore, the concept of TWGT MOI Matching is based initially on asking 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)". From testing with many golfers, and now from hearing from clubmakers who presently use the TWGT MOI Matching System in their work, we are very satisfied that the "favorite club" procedure is successful for identifying a suitable MOI for the golfer. Does MOI Matching change the fitting process for the golfer ? No. MOI Matching is 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, and then MOI Matching is brought in to guide the clubmaker in how the clubs will be assembled with regard to final head weight, 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 golfer is comfortable with using. However, it is very likely that because of the final head weighting requirements of the MOI Match, the frequency progression of the shafts will be different than it would be if the clubs were only swingweight matched. Normally, if the progression in butt frequency was 4cpm between clubs in a swingweight matched set, the progression will change in some cases, but only because of the head weight 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 are performing, we have yet to hear of one case in which the golfer required an adjustment in the tip trimming to offset the progression of frequency from shaft to shaft within the set. In short, 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 ? 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 an increase in the percentage of solid, on-center hits with the clubs. If the golfer "waggles" each MOI matched club, they may think that they detect a little different head feel. 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 of the "favorite club", the swingweight of the clubs in a 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 in the set as well. Will the woods and irons all be built to have the same single MOI ? No. TWGT testing along those lines showed that because woods and irons are so different in their length ranges, better results were obtained by matching all the woods to a "favorite wood" MOI, and then matching all of the irons to a "favorite iron" MOI. 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 spent time investigating. What we found was that any of the wedges that are used by the golfer for less than a full swing most of the time the wedge is used, it should not be matched to the same MOI as the rest of the irons which are almost always used for a full swing. In general, because many golfers do use the PW and AW (gap wedge) more for full swings 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 to a lower MOI than the rest of the irons. How about the putter – should it be MOI matched ? Most definitely, finding the right MOI of the putter for each golfer would improve performance on the greens. However, that 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 would be using it at present and thus not need to change the MOI. However, if the golfer DOES presently like the 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