If you’re into golf, you must have heard the term ‘MOI’. Pro golfers, instructors, club manufacturers always talk about it and how it can help you to lower your score. But what does it mean?
In this post, we’re going to get deep with the concept and explain what it does and why it’s a crucial factor for deciding on your club.
My name is Nick Foy, a golf coach at Foy Golf Academy, and I’m excited to help you learn more about the game of golf on my blog. Check out our golf training system that thousands of students have used to lower their golf scores.
Let’s dive into Moment of Inertia and its effect with golf clubs.
What is MOI in Golf?
As you already know, MOI stands for moment of inertia. Inertia is a concept of physics that indicates the resistance of changing state. For example, if an object is still, it will remain still unless you apply force to it.
Similarly, stopping a rolling or moving object would take force to stop. If there was no gravity or no air resistance, the rolling object will keep rolling infinitely according to Newtonian physics.
In golf, the moment of inertia means the resistance to twist at impact. When you think about your swigs with your longer clubs like the driver or the fairway wood, you can understand why the club face would want to turn. You’re putting tremendous pressure on the club through the shaft of the club.
Now, if you manage to align your swing exactly with the center of gravity and the target line, you don’t have to think about MOI. However, that’s not the case with players. Even if you manage to do it once in your life, you can consider it a miracle. Even the best of the bests misses hits from time to time.
It’s the miss hits that require MOI in golf clubs. If there was no MOI and you hit the ball with the toe of the club face, you’ll see shots that won’t even go near the target. The shots will create unnecessary curvature on the ball and change the shape dramatically.
Modern golf clubs often have an MOI rating that indicates how likely it is to resist the twist. Usually, the higher the MOI, the more forgiving the club becomes. While MOI in golf is a crucial factor, it doesn’t act alone. There is another very important concept of physics in action here.
And that’s torque.
The Relation Between MOI and Torque
If we break down the equation of torque, we get force, radius, and the angle between the two. In golf, force is the pressure you apply using your body and the radius is the length of your club shaft.
Now, we’re not going to get into the angle between the two. Because if we do, the entire calculation will become too complex to understand.
In simple words, you create the torque with your body. The more torque you can generate, the farther the ball will fly. As you twist your body away from the target and unwind during your downswing, there’s energy conversion happening.
MOI comes into play when you hit the ball. The ball has its own inertia. It means it will take external force to send the ball flying. You’re applying the force with the club head and the ball is returning some of it. As a result, there will be more torque at the club head. That’s the torque MOI is designed to resist.
How MOI is Measured?
So, how do the manufacturers know how much MOI to offer in a club?
The unit to measure MOI is grams per square centimeter. You can scale the equation to kilograms per square meter as well. But we’re going to stick to the former because the golf club heads can be measured in centimeters.
Does that mean the manufacturers should pack as much MOI into the club as possible? No. Because apart from the torque, there are other factors like club face angle, swing path, shaft length, angle of attack, etc. work actively.
If the MOI is not balanced with the rest of the parameters, the club will definitely feel weird and it can ruin your game if you continue playing with it.
How do manufacturers include MOI in their clubs?
Well, they do it by adding extra weight to the club head. You may have heard about perimeter weighting in clubs. Managing the MOI is one of the major tasks of the weight. Also, you’ll notice that the weight is pushed as far back as possible on larger club heads. It’s done to push the center of gravity back which helps to resist the twist.
How Different Clubs Have Different MOI
In this section, we’re going to look at the MOI in different clubs. We’re going to look at the drivers, the fairway woods, the wedges, the irons, and even the putters!
MOI in Drivers
MOI is most talked about when it comes to drivers. These have the longest shafts and the largest club heads of all. So, it’s relatively easy for manufacturers to manipulate the weight that controls the inertia.
If you own a driver, grab it and take a closer look at the bottom of the club head. You’ll notice the artificial weight that’s pushed back toward the edge of the head.
The MOI in drivers helps even novice players to hit consistent and straight shots from the tee. Many veterans will argue with you that using a high MOI driver will ruin your skills. But we beg to differ. If your goal is to have as much as possible when you’re at the course, you should use what you’re comfortable with.
What MOI does to the longer clubs is it helps get the club face squared up at impact. Even if your swing path is flawed and you approach the ball at an outward or inward angle, you’ll still see a straight shot because the MOI fixed the angle for you. That’s why high MOI clubs are known as high forgiveness clubs.
MOI in Fairway Woods
Fairways are very similar to drivers. But they have a smaller sweet spot so the MOI is lower as well. Some manufacturers even give names to their lineups to distinguish them from the other products. The ‘Twist Face’ technology by TaylorMade is one of them.
The bottom line is, the MOI might be a little low but it works very similar with fairway woods just as the drivers. The goal here is to give you an accurate and powerful shot.
MOI in Irons
There was a time back in the day when players were terrified of the irons. Most of the manufacturers only made blade designs that were tremendously hard to hit. If you miss a shot by any chance, you could expect to spend hours looking for the ball in the rough!
But those days are well behind us. Modern golf iron technology has made using these clubs easier than before. And a huge chunk of the thanks goes to MOI. Yes, golf irons also have MOI, even though they don’t look like it.
It’s for the MOI that more players can use the irons than ever before. Sure, they’re not as forgiving as drivers, fairway woods, and hybrids, but they’re very manageable. Instead of ending up in the deep rough for a bad shot, you can expect to at least close on the green.
MOI in Wedges
Wedge MOI follows the same concept as irons. It’s not massive. But it’s certainly there and novice players can feel it. The shots become straighter and more accurate.
Another reason why wedges are pretty low on MOI is the fact that players don’t use them for full swings. Pitching shots are already controlled by reducing the swing speed. So, players have better control over the face angle of the club.
MOI in Putters
So, does it even matter for putters whether they have MOI or not?
It might not look like it, but people miss hit the putters all the time. And where there is miss hit, there is MOI to save the day. Even though you’re simply rolling the ball on the green, you could benefit greatly from the inertia.
When you think deeply, you’ll notice that the majority of the golf shots take place on the green. Even if it’s a 3-par hole! The driver and the fairways are used only once. But putters may be used more than once.
That’s why it’s very important to have a putter in your bag that can forgive miss hits.
The concept of high MOI putters was not so common even a few years ago. There was a time when putters came in only two designs. The blade and the mallet. While blades were the primary choice of experts, mallets were chosen by novice players.
Fast forward to today, you’ll find various high MOI putters for sale on the internet. These are designed with the same goal in mind. To help you lower your score.
One of the main reasons you should invest in a high MOI putter is if you’re a high handicapper. As we said already, most of the shots at a golf course are played on a green. If you can master your gameplay on the green quickly, you can reduce your handicap quickly as well.
The Unspoken Side MOI
When we think about twists and torque on the club head, our mind instinctively goes to the horizontal twist. The twist is caused when you hit the ball with the toe or the heel of the club.
But what about the crown to sole twist? Believe it or not, the club head twists vertically as well! This is one of the main reasons why MOI is so important. You may not see many instructors or players talking about the crown to sole twist because the manufacturers have done a spectacular job of minimizing it!
Center of Gravity vs MOI
We’ve seen many players who confuse between the center of gravity and the MOI. They think both are the same when it comes to golf. While both of these physics terms are closely intertwined, they’re not the same.
Center of Gravity is directly responsible for the spin you generate on the ball. The lower the CG, the more backspin you’ll generate. It results in higher launching shots without compromising the distance or accuracy.
MOI, on the other hand, is the resistance to twisting when you miss the center of gravity on your club face. MOI’s job is to help you align the center of gravity and the target line.
MOI is something you may have seen in many club commercials, in the specs while you browse through different clubs on Amazon, or you may have heard fellow golfers talk about it after their sessions.
Now, you also know what it means and how it can affect your game.
The ideal approach for MOI is to always get custom-fitted. Because if all the other parameters like the club face angle, club shaft length, and your swing path are not coordinated, higher MOI won’t bring anything good for you on the table.