Stupid question for MOI experts

[Nick West]

This is probably a dumb question, but what the hey.....

 

 

This question was spawned by someone here telling me that weight in the butt area of the shaft has little to no affect on the club, based on MOI measurment info. I'll admit I'm still a little hazy on the concept, but anyway....

 

Here's the question: MOI measuring, measures the resistance of a club put under load from the head to the grip...now, I'm guessing that I'm probably probing deeper than is probably necessary but, shouldn't the measurement extend up through the players arms, and not stop at the end of the grip (the midway point)?

 

I think we can all agree that some amount of weight in the grip WILL make a difference in a swing (eg: 5lbs), but that whatever weight that would be added with any grip available will not register into a discernable range...and that's cool...I understand that, although I would like to know just what that amount is, but that's another question...I digress.

 

The force generated in a golf swing really starts in the body and is tranfered through the arms, and through the shaft, ultimately ending up in the club head. That being the case, any weight that is added midway (at the butt end of the club) actually MIGHT affect the transfer of energy, BUT....this wouldn't be detected in MOI measurement, because MOI measurement stops at the butt of the club.

 

Whereas, swingweighting, although somewhat of an arbitrary form of measurment, has had the benefit of being adapted to capture the best "feel" of a club to a player...and as vague as that is, it might have more merit? Does this make sense?

 

 

Also, on a completely different note...why can't I click and drag to highlight text on this forum? Makes it a little difficult when editing having to backspace through paragraphs to get where you want.

[Nick West]

Oh man.......nobody?

[TomWishon]

[quote name='Nick West' timestamp='1330568818' post='4407453']

This question was spawned by someone here telling me that weight in the butt area of the shaft has little to no affect on the club, based on MOI measurment info. I'll admit I'm still a little hazy on the concept, but anyway....

Here's the question: MOI measuring, measures the resistance of a club put under load from the head to the grip...now, I'm guessing that I'm probably probing deeper than is probably necessary but, shouldn't the measurement extend up through the players arms, and not stop at the end of the grip (the midway point)?

Whereas, swingweighting, although somewhat of an arbitrary form of measurment, has had the benefit of being adapted to capture the best "feel" of a club to a player...and as vague as that is, it might have more merit? Does this make sense?

[/quote]

NICK:

We have a lot of experience with the MOI of the whole club during the swing since our company developed the first process and equipment for measuring the MOI of an assembled club.

First of all, any MOI for any object has to be defined by a radius of rotation. For the MOI of the whole club it is possible to define two different radii of rotation. One is the golfer's spine because during the backswing and downswing we rotate the club around the axis of our spine. The second one is the wrist-c o c k angle - as we unhinge and release the club to hit the ball, this too is a radius of rotation for the whole club.

When we developed the process for matching the MOI of clubs to each other as a way to duplicate the swing feel of all the clubs, we had to decide which one of these two axes of rotation we felt was better for creating this practice of MOI matching. We chose the wrist-hinge release for a couple of reasons, but we certainly could have done it using the spine as the MOI's axis of rotation.

So when we measure the MOI of a club with our equipment, we are using the very end of the grip as the hub for the MOI's axis of rotation since the very end of the grip is very close to where the wrists unhinge to release the club to hit the ball.

With the end of the grip as the origin of the axis of rotation of the club, now you can start to understand why adding weight to the very end of the grip won't change the club's MOI nearly as much as will adding weight to the clubhead. Broken down into the most simplistic terms for explaining all of this, the basic math forumula that defines MOI is MOI equals the mass of the club times its length squared. Now it's a little more complicated than that because you actually have to figure out the mass at every point of length and sum all these up. But basically what happens is that because the length is a squared property in the MOI equation, that means two things - one, the longer the club the more dramatically the MOI increases, and two, the farther from the axis of rotation you place any mass (weight), the more effect it has on the MOI.

Hence when you add weight to the grip end, you are adding weight at a point that is very close to the axis of rotation so it has the least effect on changing the MOI. But when you add weight to the clubhead, you are adding mass at the point farthest away from the axis of rotation so the MOI increases dramatically.

When you add weight to the grip end, you do change the MOI for sure, just not nearly as much as you change the MOI when you add weight to the head.

As to the comparison of MOI matching of clubs to swingweight matching, MOI is a real quantitative measurement of the club's resistance to being swung in motion about its defined axis of rotation. The higher the MOI of the club, the more effort it takes the golfer to swing the club. And the higher the MOI of the club, the more load the club puts on the golfer so the more effort the golfer has to exert to swing the club. When you make the MOI of all the clubs to be the same, you are scientifically and quantitatively making each club require the same exact amount of effort to swing.

Swingweight comes close but it is an arbitrary, "made up" factor. Swingweight matched clubs each require the golfer to exert a little different amount of effort to swing each club. Therefore, it can be said that if you play with a swingweight matched set, you have to come up with a different amount of swing effort to swing each club - and logic says that could increase the chance of the golfer being more inconsistent with his tempo, rhythm, timing, point of release, keeping the club on plane and on path.

Since we and several hundred clubmakers have worked with MOI matching for several years now, we do now have a much better PRACTICAL understanding of MOI matching vs swingweight matching. As such, we are not talking night and day here for all golfers. But overall, we do see that when you nail down the right MOI for each golfer's strength, transition force, downswing tempo, swing aggressiveness and sense of timing, you do tend to see a little better shotmaking consistency.

Sorry for the length of this, but it was necessary to clearly explain the answers to your question. If there is anything not clear from this, by all means ask away and I'll try to do a better job of explaining things.

TOM


PS - by the way, MOI can also explain why the golf industry's move to greatly increase driver length over the past 30 yrs has been SO BAD for a high percentage of golfers.

Remember I said that length is a squared property in the MOI equation? When you increase the length of a club, you dramatically increase the MOI of the club. And when you increase the MOI of the club, you increase the load that the club puts on the golfer. In turn with longer length, the golfer has to exert more effort to swing the club. For less athletically inclined golfers, for golfers who do not have stellar swing characteristics, having to exert more effort to swing the club causes swing elements to break down.

Most notably, for most average golfers who struggle with trying to keep their swing path from going too much outside in and for golfers who do not have a late release, a longer length driver puts so much more load on the golfer that it causes them to really have a hard time trying to prevent swinging over the top/outside in AND it causes them to have a hard time trying to hold on to the wrist c o c k angle during the downswing.

This is all scientific fact that pretty much proves that when the golf companies increased driver length from 43 to the 46 1/2 it is today, they actually were hurting the changes of a very large segment of golfers to ever hope to hit the driver to the best of their given ability.

[Nick West]

Thank you very much, Mr. Wishon, for your response. I've been having a hard time understanding this, but I think I'm starting to get it.

1. I still have a few question though, if you don't mind. So, if the MOI is the measurement of resistance around an axis, is that the same thing as centrifugal force? Same ball park?

2. Why did you opt to not include the MOI around the spine (I'm guessing the force transfered from the shoulder, through the arm of the player, through the shaft, and ultimately into the clubhead)? Why is the measurement of balance only relegated to the club itself? Should the balance be calculated from the source of the energy all the way into the clubhead?

[GooseHook]

Like Tom said, MOI can be measured about any point. The total MOI of a golf club factors in the MOI of the head, the mass of the head, and it's length. Us geeks call it the Parallel Axis Theorem. Centripetal force is an inward force exerted by rotation, and acts through the shaft towards you. I'm not sure how much effect it has on the swing.

Just as a high MOI club or head is resistance to twisting on off center hits, a high total MOI club requires more force to generate rotational momentum. For objects in a straight line, you have F=ma, but for rotating objects your angular momentum= MOI x angular velocity. Thus, more effort needed from your swing to generate the same speed.

[TomWishon]

[quote name='Nick West' timestamp='1330654900' post='4415697']
Thank you very much, Mr. Wishon, for your response. I've been having a hard time understanding this, but I think I'm starting to get it.

1. I still have a few question though, if you don't mind. So, if the MOI is the measurement of resistance around an axis, is that the same thing as centrifugal force? Same ball park?
[/quote]

Nick:
There are both centripetal and centrifugal force at work during the golf swing. Centripetal is the force of the club back on the point of rotation of the club or rather you holding on to the club during the swing. Centrifugal is the force trying to pull the club out of your hands during the swing.

I've seen studies that indicate centrifugal force during the swing with a driver is in the order of 40-50 lbs for an average golfer all the way up to as much as 90 lbs for a very strong and fast swinger of the club such as Tiger. None of our work in modeling this or analyzing it seems to indicate that there is anything close to substantial about centrifugal force on the performance of a golf club as long as the weight and length of clubs remains within even a very wide range of specs.

[quote name='Nick West' timestamp='1330654900' post='4415697']

2. Why did you opt to not include the MOI around the spine (I'm guessing the force transfered from the shoulder, through the arm of the player, through the shaft, and ultimately into the clubhead)? Why is the measurement of balance only relegated to the club itself? Should the balance be calculated from the source of the energy all the way into the clubhead?
[/quote]

Because we really felt that WHAT THE MOI would be for each golfer had to be a custom fitting decision that could match to each golfer's own way they swing. When you look at rotation around the spine vs the rotation of the wrist c o c k release, the release differs much, much more among golfers than will the rotation about the spine.

Yes, for sure the AMOUNT of rotation about the spine, meaning the backswing length, will differ but that's not as important in our book for determining unique custom fitting parameters that could help golfers be more consistent as is the release. Also, in all our studies about the golf swing as it relates to clubfitting decisions, the wrist c o c k release stands as without question one of the most important swing motions that separates good players from less skilled players.

In looking at MOI about the spine, do keep one other thing in mind. In terms of the swing versus the performance of the golf club, it is the downswing that is FAR, FAR, FAR more important than the backswing. Once we have completed the backswing and are ready to go on the downswing, we have set our wrist-hinge angle. From that point on, as long as we hold that angle, the presence of the arms in the swing acts pretty much like a constant with respect to the load of the club on the body. Only when we start to unhinge that angle does all that change.

Unhinging that angle is the release, and does form that other axis of rotation for the MOI of the club. So if one of the biggest points of swing difference among golfers is their release, and if we fit the MOI of the clubs to each golfer's release, then we are in our opinion doing more to customize the swing feel of the clubs to the golfer than if we had set the MOI with respect to the spine angle.

That was our thinking on this decision in our MOI matching project development. I will also say it could have been done to the spine as the axis of rotation, but we felt it would potentially be a little better if the release were chosen as the axis of rotation for the clubs' MOI for matching purposes.

TOM

[pingfool]

understanding MOI is a bit tricky...

appreciate TW sharing infinite wisdom on the subject

if i may steer questions in this direction ---

1. why does driverA have higher MOI than driverB?

2. How does COG affect MOI? e.g. different head shapes 910D2 vs. D3

3.how does weight of shaft affect MOI? e.g. 39gram shaft vs. 65gram shaft

4. how MOI affect forgiveness on off-center impact

thank you in advance!

[TomWishon]

[quote name='tmfool ' timestamp='1330705423' post='4419139']
understanding MOI is a bit tricky...

appreciate TW sharing infinite wisdom on the subject

if i may steer questions in this direction ---

1. why does driverA have higher MOI than driverB?

2. How does COG affect MOI? e.g. different head shapes 910D2 vs. D3

3.how does weight of shaft affect MOI? e.g. 39gram shaft vs. 65gram shaft

4. how MOI affect forgiveness on off-center impact

thank you in advance!
[/quote]

First of all, everyone needs to be clear on the fact that the MOI we're talking about so far in this thread is the MOI of the fully assembled golf club and not the MOI of the clubhead itself. MOI of the head has to do with how forgiving is the head for shots hit off center. MOI of the club is all about getting each club in the set to swing with the same feel and effort. So I will assume your questions are all about the MOI of the full club and not the head on its own.

1. Two drivers can have quite different MOI's if their lengths are different, if their shaft weights are different, if their headweights are different and if their shafts have different balance points (weight distribution). Length is the BIG ONE in terms of a difference in length having a very large difference on the final MOI of the assembled club.

2. I'll assume when you talk about the center of gravity (COG) that you are talking about the COG of the head on its own, not the COG of the fully assembled club. There is some effect on the finished club's MOI from where the COG is in the head, but it is VERY minimal. Meaning once a golfer finds the MOI that best matches to his strength, his swing force, and his sense of swing tempo/timing, if the golfer then switched to a different head with all his right specs but with a different COG position and still retained the same exact MOI on the assembled club, he really wouldn't notice any difference in swing feel or tempo consistency.

3. The heavier the weight of the shaft, the higher the MOI of the club will be. Also remember that almost every time a golfer changes shaft weight, he also changes the headweight along with it. For example, the amount of headweight needed to make a D2 with a 65g shaft is different than the headweight needed to make a D2 with a 39g shaft. So that too affects the MOI and automatically comes along with the shaft weight change. How much a shaft weight difference will affect the MOI of the finished club also has to do with WHERE on the shaft most of that weight change in the shaft is placed in the design of the shaft. A tip heavy shaft is going to affect the MOI of the club more than will a butt heavy shaft design. But in any shaft weight change it is eminently possible to adjust the length or the headweight to end up with the same MOI as before, if that is desired by the golfer.

4. The MOI of the finished club has no bearing on the off center hit performance of a club. Off center hit performance is affected by the MOI of the head on its own and also by the face design (i.e. variable thickness face vs uniform thickness face). However, the MOI of the finished club most definitely will affect HOW OFTEN YOU HIT THE BALL OFF CENTER vs ON CENTER. that right there is one of the biggest potential benefits of MOI matching of clubs in a set and getting the MOI matched well to each golfer's individual strength and swing tempo/swing force characteristics.

Hope this helps,
TOM

[pingfool]

Great stuff!

need to digest some of this more to fully appreciate how much knowledge you're sharing.


at the risk of getting ahead of myself...


my first reaction/conclusion is that ultra lightweight drivers w/ soft tip shafts -- that are currently labeled "game improvement" -- may NOT have the most MOI


and, if this is true, many of these drivers marketed as "game improvement" may not be good "fits" for the casual golfer looking for the most help.

my apologies if i have misinterpted or if above is misleading

thanx again TW

what a great resource for WRX community --

BRAVO!