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Video Transcription: Driver Center of Gravity
The center of gravity is something that's tossed around a lot in golf lexicon. It's not something that really is given enough credit, and most people don't understand it enough.
We're going to talk about the center of gravity in detail, looking at several different driver heads here and discussing the massive impacts that determine what the center of gravity has on ball flight.
You can balance a driver head on a point to find the center of gravity
You can see here I've got a simple little device set up. It's just a little clamp with a pen in it, and I've got a driver head here, balancing on that point. This is how you determine the center of gravity.
There are two ways to measure center of gravity; both on the face - by balancing on the face as I have here - and you can also measure how far back the center of gravity is away from the face by balancing it on the sole. Both ways you can measure where the true center of gravity is on the head.
Why is this important?
When you look at a head, everybody looks at the center of the face and they say, "That's where I want to hit the ball. You want to hit the center of the face; that's going to give us the highest ball speed, the best spin, etc."
Unfortunately, 9 times out of 10, that's actually not true. There are a lot of reasons for that, and I'm going to talk about them.
First of all, as you can see here on this head that I have balanced, you would assume that the actual center of gravity would be right in the center of the face, but unfortunately that's not the case. As I pull this head off of here, you can actually see that there is a small dot here that I've drawn on with a marker. This dot actually represents the true center of gravity.
Measuring to find the center
What does the center of gravity do in terms of performance for a club?
Long story short, it gives you the highest energy transfer with the minimal twisting of the club face at impact. There are other things that it's going to influence as well and we're going to talk about those, but those are the main keys.
Now as I look at this face, the actual center of the face - this is about 2 1/4", in terms of height from the top to the bottom, so at 1 1/8" we would say that that would be the actual center of the face.
This black dot - here's 1 1/8" here - the black dot is actually 3/8" above the actual center of the face. What that means is if I hit this ball in the center of the face, which is below this mark, I will actually get a little bit of twisting, in terms of how much the face moves at impact, and I will lose a little bit of ball speed More importantly, the biggest key is it will alter the spin rate drastically.
Let's talk about each one of those in a little bit more detail.
If I hit the ball low on the face where I will benefit is, this is the max COR on the face, or the coefficient of restitution. In other words, this is the point on the face where the face can actually deflect the most, to absorb the most energy without over-compressing the ball.
Obviously, the farther you are away from the outer edges, that's where the face can bend the most, just like on a trampoline. If you imagine a trampoline you played on as a kid, if you jump right in the center that's where it gives you the most kick, and as you move farther and farther away from center you lose a little bit of kick until you get far out on the edge, and then you lose a lot.
Granted, there's not actually a trampoline effect in measuring coefficient of restitution. The truth is what it's actually beneficial for is keeping the ball from over-compressing. By having the face give a little bit, it keeps the force of impact from absorbing too much energy of the ball.
It helps the ball fly off the face faster, so it's not actually that it springs the ball off the face. The difference is more...imagine hitting a marshmallow with a golf club. That marshmallow is going to completely compress and smash into the face. There's not going to be any energy to send it off the face.
Now, if you hit a marshmallow with something very, very soft, it would have a chance of reflecting off the face. That's what the coefficient of restitution is really valuable for.
The next time somebody tells you that there's some trampoline effect on the ball, launching it off the face, it doesn't happen. Anyway, that's one thing.
The Cobra head is broad (above) while the Ping has a dip (below)
Now we know that actually moving up to the true center of gravity, where this dot is, that we're going to lose a little bit of COR there. How much, it's hard to say. It's going to vary from head to head.
This is a Cobra head, a long drive head that's actually 6° and it's got a pretty broad face, and it doesn't do anything crazy in terms of dipping in.
What I mean by that is, if you look at this Ping head - this is a Ping G5 head - there's a big dip right here where the actual face gets a lot smaller from top to bottom than it is out here on the toe. We'll talk about this head in a minute, but this is actually a problem because, just like all the other heads, the true center of gravity is above the center of the face.
As we move closer and closer to the edge of the face, there's more and more ball speed that we're going to potentially lose because our COR goes down, the closer we get to the edge.
Now, as this is moving closer to the edge, this is actually not that far away from this big dip here. This head actually loses more ball speed than a similar head - say this one here, which is a Nakashima head - than some of the other ones. The reason for that is because it's just getting closer and closer to the edge.
Now, as I go back to this Cobra head, having a nice, big, flat face here with no crazy design ideas in here, I can still get a pretty good COR even though I'm 3/8" away from the true center of the face. I'm still going to get a good COR rating.
Again, as I move closer and closer, just like we were on the trampoline, the farther and farther we get away from center, we lose more and more ball speed. This isn't that drastic, but it definitely does have an impact.
Then we know, if we don't want to hit it in the exact dead center because the center of gravity isn't there, what are we going to do to make up for losing a little bit of ball speed there?
The simple thing is that the higher your swing speed is, the more and more important spin becomes. That's where the center of gravity becomes very important, to understand where it is on your driver head.
Gear effect increases, the farther you get from the center of the face
You're talking, the higher your swing speed is the more you're throwing away distance by actually hitting it in the center of the face.
There are a few things. Now as we get into looking at where this actual dot is, where it was balanced on the face, the true center of gravity, being above the center of the face we know that we've lost a little bit of COR here, but the farther you strike the ball below - say I was to hit the ball here, versus higher up on the face - the farther I get below that center of gravity the more the gear effect takes place.
In other words, when I hit it low on the face, or relatively low - even if I hit it in the dead center of the face but below the center of gravity - it's actually going to spin more. It can become drastically significant, thousands of RPM potentially, depending on your swing speed, depending on your angle of attack and other things. Just by missing by 1/4" you can increase it by as much as 1000 RPM.
That's why understanding that the center of gravity is actually more important than the center of the face.
You can lose a mile or two an hour of ball speed by missing the center of the face a little bit, by hitting it actually on the center of gravity because the COR is a bit lower, as I mentioned, but even there you'll make up for the distance in loss of ball speed by lowering your spin rate.
The closer you get to being on the center of gravity - or even above the center of gravity, which I'm going to talk about in a minute - the more you're going to lower your spin rate. This is why it's OK, it's actually preferable, not to actually hit it in the center of most faces of most drivers these days.
I have several here that we can take a look at. Here's a Titleist head, where the actual center of gravity is about 1/4" above the center of the face. Here's a Nakashima head where again it's about 1/4" or so above the center of the face.
All of these heads that we've tested, we get the biggest bang for the buck hitting it on the center of gravity or above it, primarily because of spin. As we get closer and closer to hitting it on that center of gravity, spin rate goes down and we still get a tremendous amount of energy transfer with minimal twisting.
The farther we get side to side, now we're starting to talk about side spin and those types of things. We're just assuming that we hit it relatively close to the center here, and around that center of gravity.
We know, A, hitting it in the center of the face is not the best thing to do. You'll get great energy transfer. It'll feel really solid, you'll get a great kick, you'll have high COR, but you're going to get high spin as well and spin is more detrimental than throwing away a mile or two of ball speed in hitting it just slightly higher on the face.
Here's the other catch. At some point there's a point of diminishing returns, depending on how high you hit it on the face versus your club head speed.
With this driver head, this is a 6° long drive Cobra head. I've taken my loft/lie gauge and measured where the actual center of the face is, or where the center of gravity is. In doing so, we've found that the true loft at that point on the face is actually 7°.
Now the 6° head, if I hit it perfectly where the club head is designed to transfer energy, avoid twisting, optimum spin rate, etc., I'm actually going to have a 7° driver at impact, assuming the shaft doesn't kick. We're just assuming everything is constant here.
Using the loft/lie gauge to measure loft at the actual center of the face
That's not too bad. Going from one degree to another is not so bad, but here in an example with the Titleist head - this is a 983 head - it's a 9.5°. Where the center of gravity is, the loft is actually 11.5°, so now you've gone from a 9.5° driver to an 11.5° driver.
Obviously, the higher your swing speed is, the more that becomes an issue. You may not want 11.5° of loft. You may actually want 9° or 8°. Without getting properly fitted there's no way to know without using a launch monitor.
This is where it becomes very, very important because each head that you're possibly buying of the shelf as a random deal, which is the worst thing in the world you can do if you're serious about your golf game.
Here's a 7.5° Ping G5 head. The actual center of gravity spot is at 9°. I've written it on here with pencil so I can see that. A Nakashima head that's at 8.5° is actually at 9° in the center of gravity. Now, the center of the face is actually 8.5°. I know this because Nakashima hand measures all their heads before they put the loft on there.
Most manufacturers, they simply have a degree of tolerance of a degree or so in either direction. Your 9.5° Titleist could be 8.5° or it could be 9.5°, you don't know. It could be 10.5°.
With Nakashima, they actually CNC machine the loft after they measure it. It's not just stamped on there at the time of production, so it's a little bit more costly for that but you know when you order an 8.5° head, the center of the face is actually 8.5°. That's a very good benefit of getting hand-picked heads.
Now we've got ball speed, we've talked about the COR, we've talked a little bit about spin rates, in terms of what that's going to do. The next thing that we want to talk about in looking at a head like this is the true loft.
Now we're looking at this 8.5° head is actually 9°. Where does the tradeoff happen between having too much loft on the head, versus hitting it too high on the face and having not enough spin?
In doing a ton of research with our FlightScope launch monitor, we have found that somebody who gets the optimum launch numbers - let's say they've gone through a fitting process, they know that their launch angle is 12° or 13°, or whatever it is that we've found that's optimum for their swing speed, their angle of attack and so on - that they can err on the side of being above that center of gravity up to, on most heads, 1/4".
In other words, you can still actually hit this 8.5° head 1/4" higher, which would take you from about 9° of loft to about 9.5°, almost 10° of loft, and still get away with it. That one extra degree of loft is counterbalanced by the vertical gear effect.
I know there's a lot of discussion out there about vertical gear effect and how much it actually impacts spin rates and so on and so forth. All the research that we've done shows empirically that it has a dramatic impact, the higher your swing speed.
If you're measuring somebody who's swinging at 80 miles an hour on a daily basis, or those are the types of golfers that you've come across, or that's your swing speed, it's not going to make that much of a difference.
When you get to somebody at 110, 120, 130 miles an hour, vertical gear effect becomes huge. The more positive your angle of attack, the more you're coming into the ball on a positive angle, the more it becomes even more important.
Do note that the vertical gear effect does have a significant impact, the higher your swing speed and the higher your positive angle of attack is, in determining optimum launch conditions for you.
For instance, in using this head - an 8.5° head - it's OK to actually hit it higher on the face because the vertical gear effect will take over for a higher swing speed player and even though he's getting 10° of loft and we may actually want him to be at 9°, his launch angle has gone up a degree but his spin rate's gone down.
The actual apex of the flight might actually end up being the same because the spin rate might be 200, 300, 400 RPMs less, which may not sound like a lot but when you're talking about optimizing everything, 400 or 500 RPMs is a big difference. Again, the higher the swing speed player, the more that becomes important.
There are three things, now, that we've discussed. We've got the max COR, which we know is in the center of the face, the farthest point away from all the edges. That's going to give us the highest potential ball speed.
The problem is, the spin rate is going to typically be higher there because the center of gravity is above the equator of the ball when we're striking it. We know that we need to measure the center of gravity. The only way that can be done is taking the head off.
Again, if you're a serious player you need to pull that head off, get it measured and put a dot on it. I just take a permanent marker, put a little dot on there, done. It's on there and now you know exactly where you need to hit it on the face every time for optimum distance.
Mark the true center of gravity
We've got the actual center of gravity marked. Now we know the true loft because we can use a simple loft/lie gauge to measure the actual loft. Once we have the actual loft, we know what we're dealing with in terms of launch conditions so when we do a fitting or we want to know what we're looking for in terms of conditions, we can get the right head with the right loft for your launch conditions.
Then we know, in terms of hitting it slightly above that, we can get the highest launch conditions with the lowest spin rates.
Let's take a look at one other piece here. Dealing with the actual construction of the head, one of the big things that we look at is the actual mass of the head. In other words, how much does the head weigh? I've got a scale here. It's just a simple little gram scale. I'm going to weigh a few of these different heads, just to give you an idea.
This one here, the Cobra head, 194 grams. Compare that with the Ping, 198, so a little bit heavier with the Ping head.
The Nakashima has a weight system, so this one's going to come in really light because there's no weights actually in it. This is all the way down at 186, and then the Titleist head all the way up to 203 grams. There's a tremendous difference from one head to the next.
What difference does the mass of the head make?
If we look at a simple little application here that allows us to mimic driving conditions and launch conditions and spin rates and ball speeds and club head speeds, we can also input the mass here.
On the low end, the lightest head that we can actually play with - the Nakashima head requires that we put some weights in there - was the Cobra, which was at 194.
Simulation software shows us what happens when we change different variables
I'll punch that in here. We're just going to assume someone is swinging at 100 miles an hour, hitting a great, solid shot, 3° positive angle of attack, getting 11.5° launch angle which is a little bit low. This person is going to carry the ball about 235 yards with 194 gram head.
Now we look at that Titleist. We're at 235 there. Now I'm going to put the Titleist numbers in, which was 202. It picked up 2-2.5 yards of carry, so it's not that dramatic at 100 miles an hour.
Now when we go up to 120 mile an hour player, let's say, he's at 296 carry with these conditions, which again aren't optimum, but just to give you ballpark figures. At 296 with the Titleist head and 293; again it's about 3 yards of difference.
It's not that dramatic of a difference in going from those lighter heads to heavier heads, but there are some heads on the market that are under the 190 gram mark, and there are some heads that are 205-206.
For instance, Cobra made an L4V head in 2008 that was very, very heavy. Some of them we measured came in all the way up to 206-208 grams. Then we've measured some heads from Stolz golf, who specialize in trying to make a very long driver, a 46" driver. In order to keep the swing weights within spec, they made a super-light head, 180-185 grams.
Now you're talking massive differences in terms of head weight. If we just punch in two extremes, 180 grams he's going to get 289 yards of carry, and the heaviest L4V was about 208 grams, so between those two he's carrying it 298 and the other one's carrying it 289 so it's about 9 yards of difference for a high swing speed player with relatively decent launch conditions.
Changing the variables shows us how the swing will be affected
The best case scenario there in terms of the mass of the head you might pick up, from one extreme to the other, 9 yards or so; just call it 10 yards in round numbers.
You will notice that a lot of Tour players, they do what's called hot melting their heads. They put this rattle glue - rat glue - on there. It's basically just designed to help stop rattles in the head when epoxy or other things break loose in there.
It also helps deaden the sound and gives them a little bit more of a solid feel, based on what they hear because feel and what you hear have a lot to do with each other in terms of driver performance.
A lot of Tour players are used to that. The older heads, the smaller heads, didn't have such a high rattling, tinging sound so that's why a lot of those guys do it. There's a little bit of performance benefit in getting a little bit higher mass head, but you can see even in the best case scenarios, with a very high swing speed player, we're talking a total of 10 yards.
If you are trying to eke out every single last bit of yardage, 10 yards can be a significant difference, from one extreme to the next. In general, there might be a tradeoff of going to a very heavy head because you won't be able to swing it as fast. It's just simply physically heavier, and 20-30 grams does make a big difference.
That's what you might find in terms of getting the heaviest head that you could play. It's not going to make a tremendous difference. On realistic expectations, you could change maybe three yards with putting the heavier weights in some of these adjustable heads and those types of things, but I wouldn't expect much more than about three yards.
