Jun
07
2007

Moment Of Inertia?

Posted by Double Eagle in Equipment

Stack and Tilt Golf Swing Videos by Medicus Golf

As I tuned into the final round of the Memorial tournament on Sunday, I noticed something as I watched the commercials in between play: the scientific engineer buzzwords and acronyms are becoming more and more mainstream. In one commercial, they actually explicitly called out the club’s M.O.I. How many people even know what that is?

I thought I’d lay out a couple of the technical buzzwords so when you tune in, it’ll be familiar territory.

MOI, or Moment of Inertia is a fancy way of describing how a club torques or twists both in the downswing and at the moment of impact. The club head is affixed to the shaft at a single point. The MOI is really a measure of how the club resists torquing. If you hold your driver by the grip in one hand and grab the head in the other hand and give it a twist, you’ll notice that the head turns a little. At the moment of impact, the force on the club is tremendous.

The center of gravity of the club helps to define the sweet spot, or the spot where there is little or no twisting force applied to the club at impact. Off-center hits cause that twisting action that robs distance and affects direction. Companies expend a lot of research and development effort reducing the twisting effect that results from off center hits.

COR, also known as Coefficient of Restitution was in the news several years back as the manufacturers were on a mission to make drivers hotter and hotter. It’s nothing more than the measure of the energy preserved when two objects collide. Perfect energy transfer would be a COR of 1.0. It’s easy to see why this is an issue. As club makers were finding ways to get this closer to 1.0, distance off the tee was increasing. If you consider two drivers, identical in all ways except COR, the driver with the higher COR will drive the ball further when both are swung exactly the same. To stop this trend, the USGA stepped in and mandated a maximum COR of .83.

Those are a couple to get you started. If you want more info about MOI or COR, or information about other technical club specifications and concepts, check out this golf club FAQ over at About.com.

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There are currently 2 responses to “Moment Of Inertia?”

  1. 1

    The Square Golf Driver Revolution said:

    [...] And they can’t make the faces any more springy because they’re already at the maximum coefficient of restitution (COR). So the only place left to go is shape and because of the requirement on proportion of heel to toe [...]

    Posted on August 18th, 2007 at 2:59 am

  2. 2

    Golf Terms - Club Anatomy Edition said:

    [...] mass around the edges of the club (called “perimeter weighting”), which increases the moment of inertia. That means that if you hit the ball off center (on the heel or toe), the club head is less likely [...]

    Posted on October 9th, 2007 at 11:16 pm

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