Funny how one thing morphs into another. Last week I mentioned MOI as a key metric when discussing club heads. This discussion is applicable to all clubs, but today we’re talking about drivers. Last week I started doing in person product trainings on the new products. When I do these, I like to spark a discussion that takes it deeper. Makes you think a little. One such question could be “Teaching or fitting – which comes first?” In this particular discussion, I asked “What’s the difference between MOI and gear effect? How does this apply to the new Paradym Smoke driver?” We had a great discussion. As I was driving down the thruway afterwards, I got to thinking what a great question this really was. I was pulling into my garage before I knew it. Let’s dive deeper, shall we?

Here is a brief description of MOI from last week and some of the other terms from this discussion.

First, we’ve all played golf. We all know what happens when we hit a tee shot on the toe. It starts to the right and hooks back towards the swing (and hopefully, target) line. This phenomenon is the result of several things – Gear Effect, bulge and roll in the club head design, AND by the amount of MOI designed into the head. The response will be different from every head with every manufacturer – physics and design dictate that. If you don’t believe me, grab 6 drivers. Get a mix of game improvement, players clubs, and several manufacturers. Head to your fitting bay. Hit shots with each in the center, on the toe and on the heel. Pay attention to the results. You may be very surprised. VERY surprised. They may tend to do similar things, but in differing amounts. THIS is a major step in helping you hand the right driver to a player – talk about a fun winter project!! If you see his miss is low and on the heel, you already know what club performs the best there because you tried it. Different clubs are designed for different folks.

I digress. Let’s answer the question.

MOI

MOI stands for Moment of Inertia. Essentially, it measures a body’s resistance to twisting. The higher the number, the more the body resists twisting. Why is this number important? If you hit a ball on the TOE of the club, what happens to the face? It wants to twist open, right?? If we (manufacturers) can increase the MOI of a clubhead, we can keep the club from twisting (as much) on off center hits.

Gear Effect

As you read about gear effect, you can see how the basis is very similar.

To answer the above question, we need to take a deep dive into Gear Effect, and understand the components of clubhead design that influence gear effect. To start, let’s dive into face shape. Ever wonder why a wood face isn’t flat like an iron face? This slight outward curvature on the club face is called bulge and roll. Bulge and roll has been a thing in club head design since the 1940’s. You can thank Spalding for this one. Through the years, we have found there is a correlation to the amount of bulge and roll a head needs and the depth of the CoG in the head. A deeper CoG head will twist MORE and will need MORE bulge and roll to compensate. This is why there is no bulge or roll on an iron. It’s also why older drivers tend to have a face that looks “flatter”.

The curves on the wood head club faces curve in two directions of every wood today. A HORIZONTAL curve is called BULGE and a VERTICAL curve is called ROLL. As a competitor has demonstrated, this curvature does not need to be uniform, but any club without some curve across the face would be rendered unplayable for almost any player. **In English, every wood club head made in the last 80+ years has had bulge and roll – this is not new technology. Bulge and roll are measured in inches relative to the radius of the curve (you won’t need to remember this). What does bulge and/or roll do? Simple – it accentuates the effect of hitting the ball in that place on the face. Say again?? If you look at the face of a driver, and we examine bulge (the horizontal curvature), the center portion of the face is square, the toe is open, and the heel is closed. So a shot struck on the toe will twist the head open as we discussed above, and the bulge of the face will make the face even more open. Wouldn’t logic tell you that you want a concave face (curving inward) rather than convex (curving outward)? Read on…

BULGE will start the shot to the right or left, so, as a manufacturer, we can alter the amount of bulge and roll to suit the intended player profile. For a player who does not make consistent contact in the center of the face, more bulge and roll will be better since more shots will end up closer to the target line. If the head didn’t have as much bulge and roll, it will be better suited to a very consistent ball striker (think tour player, club professional. top rank amateur player, etc.) as this player doesn’t tend to mishit the center of the club face as much or as often.

It is worth noting that roll has the same influence on the vertical plane. A shot hit high on the face will add loft the head, so roll will add loft the the top of the face to accentuate. There will also be less spin, so the resulting shot will not climb as high. The combination of gear effect and roll of the face will make this shot fly more like a normal shot. Remember, bulge and roll accentuates the DIRECTION the shot starts. Gear effect alters the spin to counter the initial shot direction. A shot on the toe opens the face of the head. Bulge opens it more. Gear effect spins it in the opposite direction to bring it back. A shot hit high on the face adds loft. Roll adds MORE loft. Gear effect reduces spin to give a more similar launch and trajectory. The reverse is true for a shot hit low on the face or on the heel. Starting to make sense??

Yes, but why would we want that?? Especially when the toe strike will cause the shaft to twist more causing the face to open more – (won’t it?)?? Why do I want the face to open even more when I hit it on the toe? Very good question!! you want that because this is where gear effect comes into play. Gear Effect occurs when the center of gravity of two bodies do not align perfectly with the direction of the collision. English, please… Sorry. The club head has a center of gravity (CoG). During the golf swing, it travels down a line prior to, during, and post impact (this is your swing line or swing direction). The golf ball also has a center of gravity. If the TWO CoG’s don’t align perfectly with the swing line at the moment of impact, Gear Effect will result. Gear Effect will put opposing SPIN on the two bodies – on our toe hit above, the driver head spins out to the right (clockwise), and gear effect results in a spin on the ball to the left (counter clockwise). Important to note is that this is relative to the CoG of the head, NOT the shaft axis. This is your TOE HOOK that we talked about above. We already knew it happened – hopefully now you understand WHY it happens.

If you’re still struggling with this one, think of it this way… You’re texting coming up to a red light and you rear end the car in front of you – the car you hit goes straight ahead, right? CoG1 and CoG2 are in line with each other in in line with the direction of travel. Hopefully you can visualize this and it makes sense. Now, in the same example, but you look up right before the collision, see the car ahead and swerve to the right. This time you hit that car on the LEFT rear corner, but with a car that is travelling LEFT. The car you hit will now go to the right and spin to the LEFT. CoG1 is now to the LEFT of CoG2, so the hit car will go right and spin left. Easier to visualize? Don’t text and drive. Moving on…

So, gear effect and Bulge and Roll work together. How much is too much (or too little)? It depends… Without bulge and roll, the toe shot would start closer to the swing line and potentially curve too much. As a good player, perhaps you WANT this. Perhaps you need to turn one over, so you hit it a little on the toe, and voila, a draw. Or, perhaps you can’t predict where you’ll hit it, so you need something that just ends up near the middle. Too much Bulge and Roll and the shot will start too far to the outside and won’t have enough spin to correct itself. This “magic” is left to the club manufacturer. We all have differing viewpoints on what is optimal and this is a big part of the reason why some companies clubs are more suited for some players.

Now we get to the basis of my question in that training session from earlier:

“What’s the difference between Gear Effect and MOI?”

Perhaps a bit more complicated than we thought at face value, eh? At face value, they both deal with correcting the result of off-center strikes. They do it in very different ways, and a club head designer will have to take BOTH variables into account when tweaking his design. Here’s the difference:

MOI makes the club head more resistant to twisting. Bulge and roll are built in and have nothing to do with how much the club twists – only what happens after it does – it’s a head shape specification. Gear Effect works with the resulting twist to produce a result that ends up closer to the swing (target) line. Gear effect will happen anyway. It’s effects can be minimized (or maximized) based on the relationship between MOI and Bulge and Roll. LOW MOI means the head must have LOWER bulge and roll (because the head will twist more on it’s own) OR the player must strike the center of the face (think Triple Diamond Face profile). HIGH MOI means the head won’t twist as much on an off center strike, which means we need MORE Bulge and Roll to produce a good result relative to the target line (think Max D face profile – we can make it look good AND be forgiving). As stated above, this interpretation is left up to each manufacturer. We all do what WE think is best.

What is the downside to high MOI and/or Gear Effect?

For most players, High MOI is a good thing. It will absolutely be more forgiving on off center hits. Head size, however, tends to be larger, which isn’t desirable for all players. Here’s the kicker… An off center strike will take energy away from the golf ball and transfer it back into the head at impact. MOI will try to counter some of this since it doesn’t allow the head to twist as much. Gear effect and bulge and roll do nothing to save ball speed – they simply try to save the direction to the resulting shot. Don’t believe me? Hit a shot in the center of the face and then one an inch towards the toe. Look at the club head speeds vs. ball speeds (smash factors if you’re a techie). Similar club head speeds with much less ball speed, right? Next, look at the face angle on the two shots. Notice how the toe shot is more open, yet the distance from the target line isn’t that far off? This is gear effect and bulge and roll working for you. Does it have to be this way??

Insert Paradym Ai Smoke. Does it have to be this way? Most manufacturers say yes, and they try to optimize the bulge and roll or MOI to produce a straight shot. This doesn’t address the energy lost/ distance lost on that strike. Callaway used Ai technology to look at precisely what happens at the moment of impact on an off center hit, then we doubled down on the Ai technology to figure out if there is a way to maintain ball speeds on off center hits – or, quite simply, lose less. The result is a design that goes farther all across the face – not just in the center. MOI has to be there or the head would twist (we don’t talk about MOI because it’s further down the list of impressive things to talk about – Marketing talks about the most impressive features first). Ai was able to design “micro sweet spots” all over the club face so it is indeed “sweeter from every spot”. Not only does this utilize high MOI, but it de-couples gear effect from MOI. Ai can counter gear effect with these micro sweet spots – they don’t start off line OR curve (as much). Off center shots with Paradym Ai Smoke fly longer and straighter due to higher ball speeds all across the face. Each model is player dependent, and these micro sweet spots are in a different location on each head. You want to fix the problem? FIX THE PROBLEM.

As you read the passage above, THIS is the fundamental difference between our driver and the competitors clubs that are out there. We have found a problem and fixed it. We used technology in R & D to address and correct problem spots. Many of these others also found a problem and have worked hard to make their solution more livable. We have the largest R & D team with the largest budget in the industry. This is the reason that Callaway is the #1 driver in Golf.

As you look at our advertising for this new driver, you’ll notice what looks like face tape on the face of a driver that shows smaller circles with “+X yards” all across the face. This is a comparison to a traditional (Last years Paradym) driver face, NOT vs. the center of the face. Don’t get too excited, the ball isn’t going longer on a low heel shot that it is off a center strike. Put another way, this is what a player is losing when they hit the ball there with any other driver.

Consider the example above of a player who hit a shot on the center vs. a shot on the toe. I was fortunate enough to have a staff player comply during his Paradym Ai Smoke fitting. He hit a shot on the center of the face followed by one 3/4″ to 1″ on the toe. The second shot was 2 yards shorter and on the same line as the one on the center. His ball speed was 1 mph slower 1″ on the toe. Also consider, as you watch the video reviews above that they are comparing Ai Smoke vs. Paradym. Paradym was the most technologically advanced driver, best performing driver ever made. Talk about a high bar…

As you begin to fit this driver, may I suggest you compare bad one to bad one. Not good one to good one. Not averages to averages. Use face tape and compare a toe shot to a toe shot on new vs. new or new vs. his current. Most players don’t play golf in the center of the face all day long. Compare it to how they actually play golf.

Happy fitting.