'Moment of Inertia' ... what's it

all about? Is it just a big twist?

By GRAHAM DALLAS

(If you missed Graham's first article last week about club lofts being 'tweaked' to produce longer hits, scroll down to find it)
The latest buzz letters in golf are M O I - short for Moment of Inertia. The advertisements are telling you that with a high M O I driver you’re going to hit it farther and straighter. Well, we’ve heard this before, haven’t we?
M O I is basically the clubhead's resistance to twisting with off-centred strikes. The higher the M O I, the less inclined it is to twisting.

Tim Wishon describes this beautifully as the spinning as an ice skater throwing out their arms to stop spinning. So, by moving the weights further from the centre of the clubhead, it will become more resistant to twisting.
And so, as clubheads have increased in volume over the years, so has their M O I. You never heard about this, until recently, as the advertising men were focusing on "bigger is better." Then the governing bodies stepped in and capped the size of the driver at 460o; closing that marketing opportunity.

So you can’t increase M O I by getting bigger, let’s do it by cHanging the shape. Square and triangles are becoming the favoured shapes of the marketing departments. You know how it goes, “Give us something that looks different, a massive budget, and we’ll sell shed loads”.
What they don’t tell you is how much changing the shape increases M O I or that it is minimal when compared to simply fitting the shaft correctly. Let me explain this, as it is never advertised.
Steel shafts have one spine, graphite shafts have two. The spine is the shaft's most resistant point to flexing. When the shaft flexes, the natural forces in the shaft (which are considerable) will want to get the spine to where it flexes least.

The only thing stopping this occurring is your grip. If you hit the ball off-centre, the force of the clubhead wanting to twist will be added to the shaft's desire to twist. We’ve all felt the result of extreme cases - the club twisting in our hands.
So what we have to do in identify the spine (there are simple ways for club makers to do this), mark it and then fit the club so the spine is pointing towards the target, or directly away from the target.

For the purists among you we make a little adjustment to shaft alignment to compensate for head mass. Then, with off-centred hits, the shaft will be working to correct the fault rather than to amplify it.
Fitting the shaft this way will increase your club's M O I infinitely more than the latest shape. So you ask me, surely the major manufacturers do this when making clubs?

Well I can tell you, having worked in this industry for around 25 years, that I have only come across two who do so and they only started doing this in 2008. You will be surprised to know that they are Golfsmith and Benross.

Of course, all good clubmakers will do this for you are a matter of course.
So if you really want to increase your M O I, don’t buy the latest shape, just get your shafts aligned.

Editor's note: If you are really interested in the technical side of club manufacturing, you should log on to Ralph Malby's website: http://www.ralphmaltby.com/

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Karyn & Graham Dallas, the wife-and-husband team at Kirriemuir Golf Club pro's shop, are advertising Tg54.com on our sister website, www.kirkwoodgolf.co.uk

Switch over now and find out what it's all about. Scroll down and look in the first column when you get there.