The white coats are coming!! The white coats are coming!! OK. It was the Red Coats and that was almost 250 years ago. The white coats are the engineers and with new products coming you will be inundated by and overwhelmed with specs and stats. It’s going to make your head spin. So, over the next few weeks I’ll bore you to death by explaining what this all means. I’ll try to do it in a relatable way and I’ll group several together so they make sense.

First up. What the heck is MOI? MOI stands for Moment of Inertia. In English, it refers to a body’s ability to oppose rotational forces. It’s resistance to twisting. Why is this important? Grab your putter. Hold the shaft lightly about 12” from the head and let the head hang down. Gently tap on the center of the face. See how the head doesn’t rotate? Now tap further and further towards the heel or toe. See how the head moves? Try it with a 7 iron or a driver. It does the same thing. The more forgiving the club head, you will get less rotation the further out you tap. This is MOI. Every golf club has MOI. The more forgiving, the higher the spec. Take a driver. MOI specs are over double what they were 10 years ago. This means today’s heads don’t twist as much on off center hits as one from 10 years ago. A shot hit 1” off the center of the face on your 2010 driver will curve more and lose significantly more energy (ball speed) than the same impact location on a driver from 2023. Today the ball flies straighter and the distance is much more consistent. Good one vs. good one, today’s driver is a little better, but bad one vs. bad one, the difference is shocking. After all, minimizing the damage caused by the bad ones is how we score better in golf.

In general, the higher the MOI, the better. The USGA does restrict how high it can be, so we will not be able to continue to improve this spec. In the early days, MOI was increased by simply making the heads bigger. Today, different materials and manufacturing techniques are what drives these gains.

Next up, Am I a Gear Head if I understand Gear Effect? Haha. So you’ve heard the term, but what is it? Ever hit a “Toe Hook”? That’s caused by gear effect. MOI plays a part too. What is it though? Can you picture two gears with interlocking cogs? When one spins one way, the other spins the opposite way. That’s gear effect. Yeah, but what is it?? What causes it and how does it relate to a golf club? Gear Effect happens when two bodies collide and their center of gravity’s don’t align with the desired travel direction. English please….

Imagine you could look straight down on a club head at the moment of impact. Head is square and travels down the line, with a center strike the center gravity of both bodies is in line with the direction of travel. Essentially no side spin is created by this collision. Now, imagine the path and face are still square, but impact is 1” on the toe. The center of gravity’s of the ball and the club head no longer line up. The force of impact will open the face starting the shot to the right. This means the club head is rotating clockwise. The golf ball will rotate in the opposite direction – counter clockwise. Time to cheat. Look at your watch. Move your finger from 3 past 12. That spin is going…. Left. The shot will have hook spin on it. A shot hit an inch on the toe side of center will start to the right and hook back towards the center. As MOI is higher, the head won’t twist as much (as a lower MOI club), so the face won’t open as much and it won’t get as much hook spin imparted on the ball at impact. Gear Effect is not just limited to the heel/toe (horizontal) plane. Vertical gear effect is a factor also, however it wasn’t as much of a thing years ago as it is today. Ever heard the phrase “tee it

high, let it fly”? Essentially, the spin is lower for shots hit high on the face vs. low on the face. 4 years ago, we had drivers that had a 1300 rpm variance in spin traveling up and down the club face. Today it’s about 400 rpm. So, what happens? Imagine the toe hook example from above. Face opens, opposite side spin imparted. Now move impact to the top of the face. Same thing happens, but in a different direction. Face will add loft, and spin will go the opposite of backspin (reducing backspin, not changing to topspin). Ever hit a “flyer”? Today, we try to control head movement in this direction too…. We do this in part by increasing the MOI of the head.