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MOI

  • 4:20PM - May 19, 2008RE: MOI

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    keyser, you need to ask a Physicist. Sorry

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  • 3:37PM - May 19, 2008RE: MOI

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    Ralph, thanks for the reply, lots of great info:) But I am still confused to what it actually means. A kilo calorie for example is the energy that it take to heat one liter of water by one degree celcius. I know the MOI is a measurment of much force it takes to move or twist an object. But what does the actual number mean… does 5900g-cm2 mean it takes that weight to move the object at a certain speed around it´s CG(maybe it´s too complicated for me to understand… numbers aren´t my thing)??

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  • 11:56AM - May 19, 2008RE: MOI

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    Keyser, here’s the short answer; 5900 grams per centimeter squared is an absolute measurement expressed as a number that describes the moment of inertia of an object (golf clubhead) about a given axis (the horizontal center of gravity of the clubhead). It further describes how difficult it is to change its angular motion (rotation on off center hits) about that axis (the horizontal center of gravity of the clubhead). So, the only thing that I can say about the number itself is that it basically stands on its own as simply a measurement of MOI.

    Here is the long answer for those of you who need to know more about Moment of Inertia; The U.S.G.A limit for the maximum allowable driver head moment of inertia (MOI) is 5900 g-cm² plus a tolerance of 100 g-cm² making the absolute maximum driver head MOI 6000 g-cm². The term g-cm² stands for grams per centimeter squared. Regarding MOI some confusion can exist because the numbers used to express it in our industry can be in different units. In other words, the Maltby Playability Factor for irons (MPF) uses oz-in² (ounce/inches squared) in its calculations. One popular putter manufacturer (and some others) use kg-m² (kilograms per meter squared). A number of golf club manufacturers use g-cm² (grams per centimeter squared) as already discussed. The MOI machine that is used in my Golf Club Design Studio can provide MOI readings in 13 different unit formats. The point here is that a simple conversion factor can be applied to each MOI format to convert directly and accurately to any other MOI format, so all the various format designations basically mean the same thing. Below, I have provided a chart using an example of a 5900 g-cm² driver to show other equal readings and I have also provided the conversion factors for those interested.

    Understanding and Converting Different Moment of Inertia Format Readings Example of All Readings Being Equal 5900 g-cm² = 32.26 oz-in²= 5.9 kg-m² (or 5.9K is also used)

    How to Convert Readings 5900 g-cm² divided by 182.9 = 32.26 oz-in² 32.26 oz-in² multiplied by 182.9 = 5900 g-cm² 5900 g-cm² divided by 1000 = 5.9 kg-m² 5.9 kg-m²mutiplied by 1000 = 5900 g-cm²

    Definitions of Terms Kg-m² = kilograms per meter squared g-cm² = grams per centimeter squared oz-in² = ounces per inch squared

    The MOI measurement for modern day drivers is a function of five basic mass and dimensional properties; the heads size, material, shape, weight and center of gravity location. Since the head size is limited by the U.S.G.A. and the head weight is dictated by the swingweight we desire, this leaves shape, materials, and center of gravity location as the easiest variables to significantly modify to achieve higher driver MOI.

    The high M.O.I. on today’s high technology drivers doesn’t mean much if you have the ability to hit the ball every time on the heads exact horizontal center of gravity location (hopefully located in the center of the face). However, any mis-hits off of the faces horizontal center of gravity (so-called sweet spot) will feel much more solid, lose less distance and go straighter. The reason for this is that the higher M.O.I on large headed drivers better resists clubhead rotation on off center hits vs. lower M.O.I. driver heads. This clubhead rotation occurs around the horizontal center of gravity whenever the ball is not struck perfectly and results in less force (distance) applied to the golf ball. Modern large headed drivers with higher M.O.I.’s simply have less rotation on off center hits resulting in less distance loss and better directional control. It can be said in golfer’s terms, that they also have much larger sweet spots than lower M.O.I. smaller sized driver heads. Couple all this with much higher C.O.R.’s, increased vertical gear effect, more rearward centers of gravity, lighter golf shafts, the improved flight characteristics of modern golf ball designs and you have the reason why modern large headed drivers hit the ball so much longer and straighter than smaller headed drivers.

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  • 8:22AM - May 18, 2008MOI

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    Ralph, what does the actuall MOI measurement mean, if it´s 5900g-cm2, what is that telling me, it takes 5900g per square centimeter to do what?

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