So last week was a long read. A golf physics class, if you will. If you’re reading again, I admire your commitment to learning your craft. Ironically, after I wrote last weeks piece, I went into Callaway University to polish off the new modules. I thought I’ll start with the easy stuff, so I went to the fitting section first (yes, that should be done AFTER you do all the other modules). Lo and behold, the first module in the fitting section was a well done piece by Corey Newman – he’s the head of our fitting team in Carlsbad. He discussed MOI, Gear effect and bulge and roll. You can watch this 17 minute video en route to getting your Callaway University credits up to speed. As I watched, of course, my brain started to wander. What happens inside a game improvement driver head?

A little history… 40 years ago, nothing was forgiving. You had to learn how to hit the golf ball or suffer the consequences. 30 years ago, it dawned on us that we could make the game easier. Heads got bigger. Pronounced offset was added to driver heads (giving offset a bad name for life, haha). People could actually hit the driver now. So, drivers got longer. And bigger. And longer again. And so on, until both were maxed out. 15 years ago, engineering took over. How can you keep the same size and make ball go far AND straight. Ahhh. The ultimate quest.

In this section, when I write about club heads, I usually write about distance. Today, let’s talk about direction. It builds nicely off what I wrote last week.

A very brief recap. MOI makes the head stable. It resists twisting on off center hits – a very good thing for a shot struck NOT on the center of the face. The face is shaped with bulge and roll to start the ball on the correct line to optimize the laws of physics imparted on the ball with non-centered contact. Gear Effect puts opposing spin on the ball as a result of off center contact – also a very good thing for a shot not struck on the center of the face. Got it? Good. Let’s go!!

Game Improvement drivers (read: Anti-slice drivers) have been a thing for 30+ years. The problem with the early ones? They were U-G-L-Y!! The Killer Whale. The Pod. Remember the Whistler? HAHA. Cobra had a half inch of offset. Wilson, Square Two. Yuck. To all of them. But, they served a purpose. They enabled frustrated people who struggled to play the game an option that helped them enjoy the game.

As manufacturers, we’ve tried to get better. We’ve tried to make a driver head forgiving without it looking like it’s a science project born from an erector set. We’ve gotten a LOT better. These drivers look good now. Really good. In fact, in many instances, you can’t tell which one is the Standard model, and which one is the “Anti-slice” model. Faces are square. No more offset. You can’t see the magic. How is this done??

With a 460cc head size, there is a lot of real estate on the sole, rear and inside the head to reposition weight to accomplish all we need to. So much so that it can become difficult to explain your way out of what is actually done without it sounding like you’re selling invisible beans with the promise of a beanstalk. So, here’s you’re blueprint to the magic:

We know this player is not a consistent ball striker. As the club gets longer, the contact will get less consistent. We need to start with a wide face and a deep head. This moves the Center of Gravity DEEPER in the head, which results in a larger sweet spot. This means distance control will be more consistent on a wider range across the club face.

Often the face is slightly shallower. This is often a result of the 460cc head size limit. If we HAVE to go deeper, and we WANT to go wider, we have to cut somewhere. Face height is often the victim of this cut. Several drivers over the years have tried cut away crowns (a hole in the top of the head), or a concave crown (Cleveland did this 20 years ago or so) to maintain face height. Aerodynamics of the head suffer when this is done (meaning the club swings slower and distance is lost). Crown strength also suffers, which also results in a loss of ball speed/ distance. Having a shallower head means that the Center of Gravity is also LOWER. This creates less spin and a higher launch – very suitable for a player who fits in this profile.

I mentioned offset is gone now. We don’t need it. We simply move the weight (internally or externally via a weight port). Personally, I like the external weight port – you can change out the value for swing weighting purposes. Here’s the part where you have to think…

What does moving the weight towards the heel do? If you say “it makes it easier to close the face.”, you would be partially right. However, how much weight will an 8 or 12 gram weight have on a 330 gram golf club? And, do we want that player fixing his miss to the right by slinging the face closed? I’d say we don’t. So, what does moving the weight towards the heel do?? It shifts the Center of Gravity of the club head AWAY from the center of the clubhead and moves it TOWARDS the heel. Duh, you answered your question with the question.

Remember last week’s discussion. What makes the ball go straight? When the center of gravity of the club head, the center of gravity of the golf ball, and the swing line are all in line with each other, the ball goes on that line. Remember?? So what happens when the center of gravity of the club head is INSIDE the center of gravity of the golf ball relative to the swing line?? You got it – it puts counter clockwise (hook) spin on the ball. Are you smiling and shaking your head yes?? 😉

All in, if the swing line is straight and the face is square with center contact, this will result in a shot that goes straight (remember your ball flight laws?). If the weight is more towards the heel, the shot will curve left – it will start straight, but curve left because of Gear Effect. It doesn’t start right because there is no bulge in the center of the face. Still with me?

Now, let’s add the slice swing piece by piece. First, we’ll use a square path, center strike but an open face (relative to the target line). That shot will be one that starts right and curves right. Having a clubhead that has weight biased towards the heel will produce spin that counteracts the slice spin. It may still go right, depending how open the face is, but hopefully it’s in the right rough instead of the right trees. That is success. If the extra weight in the heel is just enough to help the player close the clubface (to square or less open), this could be a really good shot.

Now let’s add in an out to in path and an open face. We may actually get lucky here. This swing should produce a shot that starts to the left and curves to the right, correct? Perhaps this swing could leave the clubhead in a position where the CoG of the head is closer to the swing line at impact, which would result in less gear effect, and less curve to the right. The weighting of the clubhead could move to match the players swing. The result could be very good. The head is using gear effect by design to make the head more forgiving. With the High MOI in todays heads, there isn’t much energy lost, so the resulting shot will be pretty good. Using gear effect by design… Now I think that’s cool!!

We have one more trick up our sleeve… What about the lie angle of the head? Moving the lie angle more upright will start the ball further to the LEFT. For your open faced player, this can be a nice assist. A more upright head will offset the bulge of the face a little bit (bulge wants to start the shot to the right, Upright lie starts the shot to the left). Together, they could be straight.

Last one… What about a good player and the sliding weight?? Essentially, this “tweaks” where the CoG is located so the player can optimize it based on where he hits the ball on the face. It essentially fiddles with gear effect to allow the player to guard against a certain miss. Often we can use this to prevent the dreaded two way miss for the better player.

As you look at shots, keep in mind what the player is doing to create the shot. If you see a path going left and a face pointing right, look at the impact on the face. If the shot is straight, and everything is telling you it shouldn’t be – you know the head is doing it’s job. Don’t be content with just the result. ALWAYS try to understand WHY the ball did what it did.

There you have it. Gear effect. A physics liability is now integrated into the design of clubs to optimize the ball flight for almost every level of player.