If you watch enough TV commercials, Instagram memes and YouTube influencers, you probably have heard a few things about “moment of inertia” and how the latest drivers are breaking new barriers in stability on off-centre hits (that’s what moment of inertia, or MOI, means, by the way).
Our historical Hot List data suggests, however, that when it comes to MOI, while the landscape has changed, the difference in that scientific measurement might not explain why drivers today are better. Let’s look at what it all means, and how a higher MOI could potentially help you.
First, a refresher. MOI refers to the degree to which a clubhead remains stable (doesn’t severely recoil) on an off-centre hit. The less recoil, the more an off-centre hit retains energy, and the higher the MOI. It’s not important what the units of measurement are (grams-centimetres squared, if you’re counting), but the twisting is measured around any axis through the club’s centre of gravity. The Rules of Golf limit how much a clubhead can resist twisting around a vertical axis. That limit is 6,000.
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The impression is that drivers today are much more stable in terms of twisting from heel to toe. Historically, that is true. Overwhelmingly so. The first steel-headed drivers from the early 1980s had an MOI number about 1,500. Today, many drivers boast MOIs 3,500 to 4,500 points higher.
While we don’t have the MOI for all the drivers on this year’s Hot List, data from a representative sample suggests the average is about 500 points higher than what we saw about 15 years ago. The measurements were conducted by Tom Mase, a long-time member of the Golf Digest Hot List Technical Panel and emeritus professor of mechanical engineering at California Polytechnic State University. Mase measured the drivers’ mass properties for Cool Clubs, the clubfitting chain whose outlets have been a fixture on the Golf Digest list of America’s Best Clubfitters.
The increase in MOI of drivers today is noteworthy as a number, but what’s telling about MOI is that when the R&A and USGA set the legal limits on forgiveness, they upped the original stricture from 4,800 to 6,000 because the benefits beyond 4,800 were thought to be marginal at best, at least for elite players. There’s a complicated physics reason for this, but just rest assured that MOI increases beyond a certain point can have diminishing returns because you have to miss shots more extremely to get the smallest of benefits.
Nevertheless, one benefit that seems clear is that a more forgiving driver can free up a better player’s swing. As Ping’s Erik Henrikson, director of golf science, told me, “Research shows that if you can induce the feeling of performance, players will perform even better, and that only encourages you to push your own level of performance even further.” The drivers being played on tour have become more forgiving. In short, more players are using the same drivers that were designed for us choppers, as opposed to relatively low-stability, more “workable” heads like they might have years ago.
What should the average golfer be thinking about here? MOI is about making bad shots less bad. As Titleist’s director of club R&D Chuck Golden told me, “The first thing that people kind of forget but need to realise is that MOI is really not about distance gain, it’s about mitigating distance loss on off-centre hits. MOI does not make shots straighter, and it does not improve the spin and launch consistency across the face. Spin and launch consistency are a function of the face material that you’re using, where your centre of gravity is, how you’ve engineered the curvature of the face, and MOI. It’s all those things working in concert with one another.”
Here’s a tip for seeing if higher MOI is right for you: check your impact pattern after five driver swings. If it makes a tight circle near the face’s centre, seeking the highest MOI should be less important to you. If after five swings, your driver face looks like the after-effects of target practice from a chimpanzee let loose in a shooting gallery, explore drivers with more MOI.
Three things to watch for:
1. Opt for a driver with as much MOI as you can within the shape you prefer, but never so much that it negatively affects your ability to square the face at impact. Higher MOI drivers often are super-oversized, which can require more effort to close the face.
2. Opt for a driver with as much MOI as you can provided it doesn’t lead to shots launching with too much spin. A higher MOI driver might often have the centre of gravity further away from the face and higher, two aspects that can produce more spin. Note: too much spin is a bigger problem for faster swingers. Most golfers can combat it with loft or ball adjustments.
3. Opt for a driver with as much MOI as you can provided it does not reduce your clubhead speed. While it is true that if you want distance, ball speed is king, the foundation for ball speed is swing speed. Every mile per hour of swing speed raises your baseline ball speed, and remember… MOI only preserves ball speed, it doesn’t create it.
In the end, bring your driver with you when you start driver shopping. Don’t just measure how your very best hits compare, though. Look at those slight mis-hits, maybe even some of your worse misses. If those are better, further, straighter, you’ve found a reason to consider an upgrade. Is MOI part of that reasoning? There is no doubt.
