Thursday, December 15, 2011

Wishon On MOI vs. Swingweight

This comes from Tom Wishon ( in his latest eTech Report with regards to MOI matching vs. Swingweight matching.

TWGT was the first company in 2003 to introduce the equipment and procedures for matching golf clubs by their moment of inertia (MOI) as an alternative to the traditional method of building clubs to a matched swingweight. Since that time, more than 700 clubmakers worldwide have invested in the MOI measurement and matching equipment with which to build golf clubs to offer golfers a means of matching clubs in a set based on an actual amount of force generated by golfers during their swing.

Invented in the 1920s, swingweight has been the predominant method used by all golf companies for assembling golf clubs to a form of weight distribution balance. Swingweight has been agreed by technical experts in the golf industry to be an arbitrary form of weight feel matching, based simply on the use of a specific scale and not related to an actual physical effort generated by golfers during the swing. TWGT’s MOI matching is based on building each club in the set to require the same amount of effort from the golfer to swing the club to unhinge the wrist-cock angle and release the club to hit the ball.

One of the common questions we hear about MOI matching is the subject of this month’s technical article, “how does swingweight compare to the MOI of an assembled golf club, and vice versa?” From this come other questions such as, “Does swingweight offer the same weight feel if it is duplicated for different lengths and different total weights in golf clubs?” In other words, “is D2 at one length and total weight the same as D2 at a different length and different total weight?” Or, “If D2 is a golfer’s best swingweight, will all clubs built for this same golfer need to be built to the same D2 swingweight?”

To come up with a means to answer the question in a technical manner and illustrate the relationship of swingweight and MOI, TWGT conducted a series of simple exercises to compare the swingweight and the MOI in a series of different drivers. Drivers were built with 4 different weight shafts at 3 different lengths with 3 different swingweights for each length, with the MOI for each measured. Below is a table that reveals the MOI for each different example driver.


In this test, please understand we are operating on the basis that the MOI of the assembled clubs is a fair indicator of similar to identical swing feel among the clubs. We base this premise on not only our experience with golfers and clubs built to MOI, but from feedback we have received from many of the clubmakers who have built MOI matched clubs for many golfers. Therefore, the above chart information can be taken to show that when drivers of different length and different shaft weight are made to the same swingweight, because their MOI’s are different, the actual swing feel of the drivers will also be different. In other words, D2 at 46” with a 76 gram shaft will not swing and feel the same as D2 at 45” with a 68 gram shaft. The same is true for any other comparison of clubs of identical swingweight but different length and different shaft weight. As playing length and shaft weight both decrease, the MOI also decreases, which has the effect of changing the swing feel of the club as well as changing the force required by the golfer to release the club to impact with the ball.

Next in our test we tackled the question, “if we know that clubs of the same swingweight but different length and shaft weight do not have the same swing feel, what then could be done to the swingweight to allow these clubs of different length and shaft weight to feel closer to the same when they are swung?”

Again, for this answer we turn to the MOI of the test drivers for a possible answer. Note the data in the following chart


What the above chart says is that as playing length and shaft weight decrease, to achieve the same swing feel in the club, the swingweight should be increased. In other words, if you build clubs to swingweight and you are decreasing the length of an existing driver for a golfer or building a new driver for the golfer, as length and shaft weight decrease in the club, the swingweight needs to increase slightly to restore the same swing feel at the longer length and heavier shaft weight.

Finally, as a result of all this work to test assemble drivers to a wide assortment of different lengths and shaft weights, we felt it might also be beneficial to simply share the information gathered for what a;; these different combinations of headweight, shaft weight, grip weight and length came out to be with respect to the swingweight, MOI and total weight. Or as one Clubmaker told us not too long ago, “there is no such thing as too much technical information about golf clubs!”

Have fun, and of course we welcome any comments or questions you may have either through our clubmaker forum or by email at



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