Understanding Putters: Head Styles and MOI

October 2, 2012

You may have asked yourself at some point in the last decade, “why am I seeing so many putters that look like space ships? I guess people are really into mallet putters.”

If you’ve said this to yourself, your observation is certainly accurate. In recent years, mallet putters have started to take greater and greater market share from more traditionally-styled putters like the PING Anser and Wilson 8802 styles. The reason? Well, that’s a bit more complex.

As pointed out in the last chapter (see https://thepowerfade.com/2012/09/17/understanding-putters-offset-face-progression-and-various-neck-styles/), traditional Calamity Jane style putters were heel-shafted blades, just like every other iron. This putter was used by virtually everyone–Bobby Jones, Bobby Locke, Walter Hagen, etc. Aside from the advances already mentioned in this series (toe hang, offset), the Calamity Jane style putter was, well, tough to hit. Anyone who’s tried to roll a heel-shafted blade (i.e., Wilson 8802) knows the feeling. You think you’ve hit a good putt, but the feel is like you missed the face, and the club twists so much in your hands it almost falls out. In all honesty, I personally have great admiration for anyone that can play well with the true blade style putter. It is an extremely difficult piece of equipment to use effectively.

In the late 50s, Karsten Solheim joined the game of golf. Perhaps his greatest contribution was in crafting the PING Anser. Karsten learned golf later in life, but was not good at putting. He did what golf equipment lovers everywhere have been searching to do since–fix the equipment rather than the stroke. Now, a good stroke works with a lot of putters, and every person who reads these posts is encouraged to take a putting lesson with a PGA pro just to make sure you’ve got everything right.. However, this entire series is about maximizing the stroke you have by choosing equipment to match it, so we agree with Karsten’s approach (at least to some degree).

With an engineering mind, Karsten reasoned that he could make putting easier if he changed the balance of weight on the putter. He reasoned that if he moved the weight from the center of the putter to the outside, the putter would not twist as much if it were not hit perfectly. His “Anser” was to make a putter with a cavity between two weight pads. It’s now the standard of design for putters:

What Karsten reasoned was actually a concept known in engineering as “Moment of Inertia”–“MOI” for short. Without getting too technical, MOI is an object’s ability to resist twisting based on its geometrical shape. Typically, this is achieved by rearranging weight. If you think of it this way, think of a bar with two 5 pound weights. Put the weights at the center and then try to turn it with your hand; it’s not too difficult. Now put the weights on the end of the bar and try to turn it. The task becomes more difficult. Even though nothing has gotten heavier or lighter (the weight is the same), you have made it harder to turn. Or, think of it this way: grab a club by the grip and try to swing it; then, grab a club by the head and try to swing it (with the butt end facing the ball). Which can you swing faster? The weight hasn’t changed. The arrangement of the weight has.

In engineering, MOI is the counterpart of mass in an angular analysis. When you’re pushing an object, the more mass, the harder it is to push. When you’re turning an object, the higher its MOI, the more difficult it is to turn. Mass plays a part in MOI, but the arrangement of the mass can greatly change the result.

So, you’re saying “OK, once again JK, what does this have to do with putters?”

If a club head is designed with higher MOI, it automatically becomes harder to turn than a club head with lower MOI. If it’s harder to turn, that means that a less-than-pure strike of the club will not cause as bad of a result. Here’s an example: let’s say two putters are identical except for the fact that putter A has a lower MOI than putter B. A player using either putter can strike either one purely and the result will be similar. But no one (not even the pros) hit every ball perfectly. So, let’s assume the player hits a putt one-half inch from the center of the putter face. This is where the difference shows up. Putter A will twist more, go further offline, and lose more energy than putter B in the same situation. Because putter B has a higher MOI, a miss is less costly than with putter A.

But what does this all have to do with odd-shaped putter heads?

Typically, putters with more weight balanced away from the center of gravity result in higher MOI. Since a typical putter is about 330 grams, a blade putter (like a Wilson 8802) is made of steel, with all the mass right beside the ball. Since there’s less volume, a relatively high density material (like steel) is needed to get enough weight to make the putter usable. See photo below:

With a typical mallet, the material might be aluminum, have plastic parts, or be some other lighter material with heavier weights positioned at extreme points on the putter head. For example, the TaylorMade Ghost Spider, LG’s putter:

Do you see how, looking from the bottom, the putter is hollow with some plastic (i.e., lightweight) material filled in? Do you see how the putter has air gaps in the middle of it? Do you see the two weights in the back? Those two weights are tungsten weights–they have very high density and represent a large part of the mass of the putter. The body of the putter is made of aluminum, which is very low density . All of this helps the putter resist twisting by increasing its MOI.

The reason why these putters are getting so big, therefore, is the attempt to move the weight to the perimeter of the club, as far away from the center as possible, to prevent twisting on off-center hits.

Many people mistakenly believe that a mallet putter has higher weight than a blade putter. Many people will buy them because they think they want something heavier than they’re used to. However, most mallet putters are about the same weight as blade putters–right in the 330-gram range. The reason for this is that the typical putter manufacturer wants most putters to feel about the same in the player’s hands regardless of head shape. The distribution of the mass, however, changes.

Now, none of this is meant to say that you’ll be a better player with a higher MOI putter. I personally use an Anser-style putter and prefer its look and feel to almost any mallet. However, for someone who may be having a bit of trouble making a consistent strike on the center of the putter, the following options may be helpful…