What Does MOI Mean In Golf?

What Does MOI Mean In Golf?

There has been an awful lot of discussion from equipment manufacturers of late around MOI with the release of drivers such as the TaylorMade Qi10 Max and the Ping G430 Max 10K, and it seems that they have assumed that everyone knows what MOI means and what it actually signifies.

But that simply isn't the case so let us explain.

The acronym MOI means 'Moment of Inertia' and in a golfing context this is a measurement of a clubs stability and resistance to twisting.

When you strike the ball towards the toe of the club, the impact pushes against the toe of the face and that forces it slightly open. The result is probably a start line out to the right. Likewise in terms of the heel, the impact causes the face to close slightly.

Why is that important?

Well, golf clubs with a high MOI mean the face twists less on off-centre strikes which in theory should mean that more ball speed is retained on off-center strikes translating to more distance, and with less opening and closing of the face, dispersion is likely to tighten up.

Higher MOI drivers tend to feel a lot nicer at impact when mis-struck also. This is once again due to less face deflection twisting the club harshly in the the players hands. 

The most forgiving drivers in golf will generally have the highest MOI properties and can reduce curvature due to minimised gear effect. 

Gear effect occurs when the ball makes contact away from the center of the face. This off-center impact will cause the club face to change the direction it was pointing (deflection) and will alter the spin axis as the ball will run back towards the Centre of Gravity. Essentially, during the impact the ball and face are interlocked like two gears, this is why it's called 'Gear Effect'. This gear effect adds curvature to your shots, so the more stable a clubhead is, the less gear effect will interfere and the straighter a ball will fly.

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How do club manufacturers boost MOI?

The main way equipment manufacturers boost MOI is by moving weight around in the head. Essentially the further back, away from the face you can place weight, the higher the MOI reading and the more stable the clubhead will become.

You can think about this in human terms too. If you were stood with your feet close together and I gave you a little push, the likelihood is that it wouldn't take too much effort to knock you off balance. However, if you had one foot placed further behind you, it would become more difficult as you would have more stability.

It is not just moving weight back that helps boost MOI, moving weight wide will also have an effect. Ping, TaylorMade and Mizuno have all done the same thing with their G430 Max 10k, Qi10 Max and ST-Max 230 drivers respectively. They have squashed the head down vertically to spread the dimensions wider and further back. This has in turn created more extreme locations to be able to place internal weight, thus increasing MOI.

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All of this explains why manufacturers, when they are talking about MOI, use the word in relation to forgiveness in the clubhead. But it should be acknowledged that there are several MOI's in golf clubs, for example there is the MOI of the club-head around the shaft and the entire club in relation to the golfer.