Moment of Inertia (MOI)

Equipment
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The machine has a software program you can use to help determine it.

It has 3 methods one can use:

1. Assembled Club Method - This is for when you already have your set assembled. Here you input the data: Current Club’s MOI, the ‘target’ MOI, total weight and the length of the club. It will then tell you how much weight is needed. Obviously, you can add weight simply with lead tape. I’ve found that 1-gram = 10-12 points. This software is more for those using a hosel weight. I’ve found that the software works pretty well for the hosel weights. My 3, 4, 6 and 7 irons came out right on the money. My 5, 8 and 9-irons were about 1 gram too light. Still…I just added 1 gram of lead tape and I was now matched. I know the Wishon guys recommend 3/8" club length increments instead of the standard 1/2" increments in order to make MOI matching easier. However, that’s not mandatory. That’s probably why the 5, 8 and 9-irons were off by 1 gram…my clubs are at 1/2" increments.

2. Single Length Method - This is if you make your clubs all one length. As Wishon pointed out, Tommy Armour’s EQL irons were single length irons. The MOI matched. But, just because the MOI matches, doesn’t mean that it’s the best MOI for the golfer. Either way, I’ve never used this method.

  1. Component Method- This is if you have the components of the club and measure the MOI thru the ‘dry assembly’ method and you now want to determine how much weight to add. This requires you to input: Current Club’s MOI, the ‘target’ MOI, total weight and the length of the club. The only difference is you need to also input the balance point of the club as well. I plan on sending some irons heads to the Iron Factory soon to be re-chromed and I just want the re-chroming and the lie and lofts done (along with the ehad weights at a certain weights). When I get them back, I will install the shafts, but I will use the Component method to MOI Match the clubs. I will also use the 3/8" increment method to make the MOI matching easier.

3JACK

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I haven’t gotten around to seeing what the MOI difference would be if I put lead tape on the toe or the heel of a club versus on the hosel or right behind the sweetspot.

Technically, I don’t think it really matters. Meaning, if you want to add lead tape to make your clubs at, say…2750 kg/cm^2……you can add the lead tape wherever you want to until you get the MOI to 2,750 kg/cm^2. However, it would be interesting to see what something like 4 grams of lead tape would change the MOI to depending upon where I place it.

Anyway, there are a few things I’ve discovered.

  1. When I started this, I was told by one of Wishon’s employees that they prefer to use 3/8” club length increments because it makes the MOI matching easier. I was not sure exactly what he meant by easier, but now I do. If you are to use hosel weights instead of lead tape, the 3/8” increments are easier because hosel weights pretty much only come in 2, 4, 6, 8 and 10 grams. So if you need to add 7 grams, your MOI won’t be quite on the money. Since my shafts are at ½” increments, I’ve had to add about 1 gram or less of lead tape to about half of my irons. Not a big deal, but if you’re looking for cosmetics, 3/8” increments is probably the way to go.

  2. Do not buy the hosel weights for steel shafts from GolfSmith. I bought some and they do not fit my .355 tip shafts. They might fit the .370 shafts, but I think that is even a long shot because they are pretty big in diameter.

  3. I have Cleveland RC85 Driver, 3-wood and 4-wood with Dynamic Gold X100 shafts in them. They came out at 2,860, 2,860 and 2,805 kg/cm^2 respectively. So those with those similar clubs will probably come out to a similar MOI.

  4. I measured the MOI of all of my spare sets, which are mostly vintage clubs. The MOI’s can be wayyyyy off. Generally though, you’ll find that the MOI for longer irons is much heavier than the shorter irons. That’s why swingweight matching sucks, it creates short irons that are way too light and often times, long irons that are too heavy.

  5. If you are going to MOI match vintage clubs, I think you might have to consider a lighter shaft. I own and game a set of Wishon irons (driver & 3-wood, too). What I’ve noticed is that Wishon made the heads lighter than even modern day equipment and in particular, vintage clubheads. I think Wishon’s idea is that if you fit the golfer for MOI…all you have to do is add weight to the clubhead in order to match up the MOI. If your clubheads are too heavy of an MOI, then you have to find a way to subtract weight, which can get a bit dicey with the head.

I plan on having the Iron Factory re-chrome a set of Hogans and I believe the heads will be significantly heavier than my Wishon heads. The problem is that I add a ½” length to my shafts (1* flat) and that would create a very heavy club. For example, I had a 67 Hogan Percussion 5-iron re-shafted with a KBS Tour shaft (130g) and it came out to a 2,790 MOI which is wayyy too heavy for me (I play at 2,725 which produces a D-6 swingweight for my 7-iron).

So what I will probably wind up doing is getting the KBS Tour 90 gram shafts to install into these Hogans and just add weight to the clubhead to get the MOI where I want it.

3JACK

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Last night I fooled around with the MOI machine and some lead tape.

I had 4 grams of lead tape.

First, I took two 2-gram strips and put them on the back of the club head, behind the sweetspot. The difference was +40 kg/cm^2. This was expected. I then tried to move the lead tape towards the toe and the heel. I saw virtually no difference in MOI. I even cut the strips in four 1-gram strips and still saw no difference.

Where I started to see a difference is once I removed it from the back of the head to the hosel. I was using a MacGregor 985 Tourney Custom and it has a 3-inch hosel. So the further up the hosel I put the lead tape, the more of a difference I saw. However, it still was not a major difference. I then ‘backweighted’ the club and that’s where the difference was noticeable. The MOI changed, but only about +8 kg/cm^2. Big difference between +8 and +40.

I’ve been asked about MOI and backweighting. I don’t backweight my clubs, but I do know that Wishon (where I learned about MOI fitting/matching) sells backweights as well as hosel weights. My guess is like swingweight, backweighting almost has the opposite effect on MOI. I think the difference is that you will increase the MOI with backweighting (where often times you can make the swingweight lighter with backweighting). But, it will be a much smaller increase in the MOI. The backweights that Wishon sells are much much heavier than the hosel weights. We’re talking about 60 gram backweights versus 4 gram hosel weights. So that’s where I derive the conclusion that backweighting does increase MOI, but by a much much smaller amount.

3JACK

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Does that mean that we should swing heavier dead weighted clubs at higher altitudes?? just kidding…

but seriously… in simple terms (for my feeble mind), how does having the MOI matched in your set help? … my understanding is that your feel is improved…

I have my set deadweighted the way Lag reccomends. (but the swing weights aren’t all the same)… the weight is in the hosels and on the back with lead tape… should all of the weight be behind the ball? or does it matter?

If someone could help me understand how this would improve my game I would appreciate it… I still don’t quite get it.

Zack

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I’ve said this before, but fine tuning the swing weights and club balancing is much more critical for swingers, because for them the club is passively free wheeling into impact, so with the club doing all the work, it’s balancing and physics need to be paid great attention too.

For hitters, who are gripping it firmly, taking control of the club themselves, and actively firing into impact, creating their own pressures by holding shaft flex, this kind of stuff is not nearly as critical. A heavier club helps the hitter’s spacial awareness, and the ball likes the added mass in the head at impact for compression and energy transfer.

The stiffer your shafts, the less shaft deviations affect things also. Spining shafts and frequency matching is also more critical for swingers.

What 3Jack is putting forth here is very good information for players taking a more passive hand release approach toward hitting a golf ball.

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When we measure the swingweight of the club, we are measuring what the weight feels like when we swing the club. When we measure the MOI on this machine, it’s measuring the amount of force required to swing the club. Weight is the amount of gravitational pull an object has. Force = mass x acceleration.

The problem with swingweight is I can take, say…2 Hogan Apex 6-irons. I can even make them the same length and get the swing weights to be identical. However, one Apex 6-iron may have an entirely heavier shaft and I may add backweight in order to get it the same swingweight as the other Apex 6-iron.

I can do a myriad of different things like that and still get them to produce the same swingweight. However, those differences change the mass of the club and they change the acceleration required to swing the club as well. Throw in different length clubs, then you have much different forces required to swing the club.

I have measured about 25 different sets of clubs so far and I tend to see the same thing in almost every single set….the MOI for the 3 thru 7 irons is much higher than MOI for the 8-PW. Meaning, the 3 thru 7-irons require more force to swing the club than the MOI of the 8-PW.

And what happens is the golfer can now be more easily thrown off by clubs that require more force or less force to swing them. And I don’t think it really matters that much if you are doing ‘ABS Hitting’ or ‘ABS Swinging’ because even if you apply the same amount of force every single time you swing, if one club has an MOI of 2,750 kg/cm^2 and another iron has an MOI of 2,700 kg/cm^2, that imbalance makes it easy to be thrown off.

I was told that all you really need to MOI match is to check your impact on impact tape and the ball flight. I was told you will see a before and after kinda like this:

theclubdoctors.co.uk/images/p021_1_02.jpg

theclubdoctors.co.uk/images/p021_1_00.jpg

I was actually surprised how accurate this was with the irons. I used my 7-iron and while I wasn’t as wild in the ‘before’ photo, the dispersion tightened up just like the ‘after’ photo once I got the MOI right that it fit my swing.

With the hybrid, 3-wood and driver, the impact dispersion was bigger…but it still reduced once I found my MOI for those clubs. What also surprised me is how much better the ball flight was once I fit myself for MOI.

My feeling with MOI fitting/matching is that since the force required to swing the club is the same…and since the force required to swing the club closely matches your swing….the amount that you will be ‘thrown off’ is reduced tremendously and that’s why the impact dispersion tightens up so nicely.

What I’ve found now that my set matches up is that my impact dispersion is still tight, but the mis-hits are usually a little thin or fat. If I miss towards the heel or the toe…I usually just barely miss. And those small misses are always the same. So if I barely miss off the toe with a certain club…I have yet to miss off the heel with that club. Same with if I miss slightly off towards the heel. And I believe that’s probably me just needing to bend the lie angle 0.5 to 1 degrees.

From what I’ve seen, it really doesn’t matter where you stick the lead tape on the club from an MOI perspective. Although I think sticking it behind the sweetspot probably produces a better feel when you hit the shot.

I think it greatly improves face contact and ball flight. It can also get it so one can properly fit themselves for lie angles as well. And right now, I’m starting to believe that it can be beneficial to a golfer’s swing because they don’t have to worry about being thrown off by clubs having drastically different MOI’s. When that happens, you can start struggling with a particular club and that can convince you that you need to change your mechanics when in reality, the club’s MOI poorly fits you.

3JACK

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A student recently sent me a set of Dynas that Lag had made for him, just to get the lofts & lies checked and to remove the lead tape that Lag had put on and replace it with some tungsten powder in the tips as the leadtape had seen better days. I was chuffed to see that my loft & Lie machine was set exactly the same as Lags, just a couple of the irons needed tweaking. But I was quite suprised at just how close the irons were to being MOI matched by Lag.

Lag_spec_moi.png

I would have expected the line to be more of a flat U shape with the long irons high and the short iron high, with the mid irons a bit lower.

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Vow thats amazing.
On a side note, do you think lead tape an loose weight over time from clubs rubbingagaisnt each other.

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I used to find that lead tape lasts about a season before it starts to fall off, so now I try to only use tungsten powder in the tips, but you need clubs which are already pretty heavy to be able to do that. I agree, Lags line is pretty amazing there, I would almost be happy with that using a MOI machine, anything within 10 points either side of what you are aiming for is a match as far as i’m concerned.

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What craft steps might account for how John achieved mostly MOI matched results?

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On a standard swing weight matched set of clubs, you would see the moi very much as the set in the graph above (Red line). But Lag really steps up the weight on his short irons, so you would expect the line not to fall so much in an ABS set, maybe even step up some with the short irons.

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I was not talking about the lead tape falling (which will be abvious) but loosing weight from the tape bu rubbing??? :unamused:

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That’s not exactly MOI matching, but given the circumstances of trying to feel the heft of the clubs, it’s amazingly close. It doesn’t surprise me that the clubs without the lead tape looked like they did. Almost on cue, the 9-iron and PW of ANY set I work with is usually way too light. Even the Wishon irons I own, that’s the case. In face, I own a Gap Wedge from Wishon where I had to add 17 grams of weight to the head. That mean a 9-gram hosel weight and 7-grams of lead tape.

But it goes to show that good players can really feel the difference between thye MOI of clubs more keenly. I don’t think I could take a set and come that close to matching them myself without my MOI machine. But, when I match the MOI and there is one club only 10-20 kg/cm^2 out of whack, I can feel that.

What I have found is that for the best fitting from a heft perspective, a golfer should not only understand MOI, but also look at the weight of the individual components (clubhead, shaft, grip) along with the total static weight. I’ve found that my optimal MOI with the irons and wedges is 2,725. But I have also found that I’m much better with 2,725 with a moderate grip weight (50 grams), moderate shaft weight (110-120 grams) and heavy head weight. I have some wedges that were built to 2,725, but originally the grip (58 grams) and shafts (125 grams) were much heavier and I couldn’t hit them consistently. I then switched to a 50 gram grip and a 108 gram shaft and hit them great now.

For drivers, what I found was that the driver MOI will be about 100 kg/cm^2 more than the irons for optimal MOI. Obviously, my optimal driver MOI is at 2,825 kg/cm^2. Originally, using a modern ‘frying pan’, I had the driver at 45-1/8" long. It had a total weight of 321 grams. Eventually on the advice of Tom Wishon, I made the club 44-3/8" long. When I did, the MOI of the club dropped dramatically. So, I had to find a heavier version of the shaft I’ve been using. I did and in the end, the 44-3/8" driver at 2,825 kg/cm^2 now weights 334 grams.

When I started to hit it, I found that directionally I was much more accurate. I was also much more consistent. And in the end, I was losing about 1 mph of clubhead speed on Trackman from the longer 45-1/8" driver. However, my launch angle was better on Trackman, so in the end the ball lauched a little higher, spun a little less and I was actually hitting it further even though I lost 1 mph of clubhead speed.

3JACK

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Ritchie,

The mass of the club obviously has an effect on the ball flight and speed of the ball at separation. Are any of the machines out there taking this into consideration… for instance you might plug in a number for head weight before you start striking balls?

Also pre and post impact clubhead velocity should be accounted for. The less the clubhead slows down post impact the deeper the compression into the golf ball or the more efficient the transfer of energy is going to be. This is basic chapter 2 TGM stuff I think Homer got right.

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This is an interesting thread. I like the straightforward concept of MOI much better than the somewhat arbitrary concept of swing-weight.

I do have a question and some comments.

My question:

What is used as the rotational axis of the club in this context? I assume it is a line that is perpendicular to the shaft that touches the butt-end of the grip? I.e. if the gripped shaft is ‘I’ adding the rotational axis creates ‘T’.

My comments:

(In my comments I will assume that my above assumption is correct)

A unit for MOI is kgcmcm or kgcm^2 (not kg/cm^2). For example: A small 4 g (0.004 kg) piece of lead added 20 inches (50 cm) from the butt, contributes (0.004 kg * 50 cm * 50 cm) = 10 kgcm^2 to the MOI.

Adding any mass to the club adds to the MOI, unless the mass sits right at the butt-end. For example:

Adding 10 g (0.01 kg) at the butt end adds (0.01 kg * 0 cm * 0 cm) = 0 kgcm^2 to the MOI.
Adding 10 g (0.01 kg) 4 inches (10 cm) from the butt end adds (0.01 kg * 10 cm * 10 cm) = 1 kgcm^2 to the MOI.
Adding 10 g (0.01 kg) 40 inches (100 cm) from the butt end adds (0.01 kg * 100 cm * 100 cm) = 100 kg*cm^2 to the MOI.

I have a theory for the observed changes of the effect of changing grips. Assuming a 10 inch (25 cm) long grip, with the mass uniformly distributed across the grip, a 60 g (0.06 kg) and a 120 g (0.12 kg) grip add the following contribution to the MOI respectively:

((1/3) * 0.06 kg * 25 cm * 25 cm) = 12.5 kgcm^2
((1/3) * 0.12 kg * 25 cm * 25 cm) = 25 kgcm^2

A small effect, that is much smaller in reality, because most of the grip weight is near the butt-end, where it doesn’t effectively contribute to MOI.

Now assume that different grips have different end-cap thicknesses, or assume other reasons why the differences in butt-shape might sit in the MOI machine differently, pushing the club 0.5 cm out when changing from grip 1 to grip 2. Consider a 200 g (0.2 kg) club-head that sits or measures at 100 cm from the supposed axis of rotation with grip 1, and the same clubhead at 100.5 cm with grip 2. In these cases the clubhead adds the following contributions to the MOI respectively:

(0.2 kg * 100 cm * 100 cm) = 2000 kgcm^2
(0.2 kg * 100.5 cm * 100.5 cm) = 2020 kgcm^2

As you can see there is quite a bit of ‘sensitivity’ to a minor length change. I think that some sort of real or ‘measured’ length-difference goes a long way in explaining the differences observed when changing grips.

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The further the weight is placed away from the butt end of the club, the more the effect is on the MOI.

For instance adding 10 gms to the head of a

Driver will add about 120 point
3 iron will add about 100 points
Wedge will add about 80 points

Place that weight in the tips and it will reduce by about 10% cause it’s closer to the butt end.

Placing the weight at the butt end will hardly make any difference at all.

I think MOI matching is a much better way of doing things than simply measuring swing weight which can be cheated with light grips, long shafts etc or simply measuring dead weight which again can be cheated with heavy grips or backweighting. A combination of correct shaft length, progressive dead weights and MOI matching is the way to go IMO. And knowing your component weights too, like Ritchie says

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The MOI machine only measures the club’s total MOI. It’s primary objective, IMO, is that when you fit the golfer for their MOI properly, their face contact dispersion will be much tighter. Essentially, you have a club that requires a certain amount of force to swing it. You are trying to match up that force with the amount of force the golfer applies in their swing. So if you have a mis-match, it’s more difficult for the golfer to make precise contact.

Trackman measures clubhead speed at impact.

I’m just saying that I think MOI is great. But, to take it a step further in trying to fit clubs for your swing, I think people should know the weight of each of the components. I use a small digital kitchen scale and measure the heads. shaft and grip. You would be surprised how head weights vary and vary badly. The quality control isn’t exactly great. That’s why I use Wishon equipment. He understands this, has stringent toleranaces for head weights and then measures the head weights and labels then when you get them shipped. And I have measured every head I’ve ever gotten from him and there has never been a discrepancy between his head weight measurements and what I’ve measured.

Swingweight is just faulty for the simple fact I could go to 5 different people and measure the swingweights and get 5 different measurements. The idea in itself was good, but the execution was poor. Now we have something better and actually scientific.

3JACK

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So is it safe to say that such a ball striking/ swing analyzing machine as I described above it not available to golfers yet?

I agree that swing weighting is very overrated as a concept. Dead weighting can be also. Most of the gear we set up we use a matching set of shafts, and grips… so the variance would mostly be in the head weights… so as we progressively dead weight the clubs in a way that puts more mass in the short irons than typically is offered, that is the last step of the process… the dead weighting. My feeling is that because we are significantly heavier in our sets than most standard releases, the effect upon shaft weight and grip weights tends to be minimized.
Irons are for accuracy.

The whole idea of golfers worrying about how far then hit their irons seems very illogical to me. I don’t see any advantage of hitting a wedge 150 over a 7 iron the same distance. One should be able to hold most greens with a 7 iron, and the 7 iron will fly the ball at a lower trajectory which with cut through the wind better and actually doesn’t have to travel as far in the air on the shallower arc. It actually is the short cut to the green compared to skyballing a wedge into the stratosphere.

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The problem with swingweight is that if you put on a modern 46g lightweight grip which is say 9gms lighter than an older grip (which is what some are like now), the swing weight of the club will go up by about 3 points. So D2 becomes D5 even though the overall weight of the club goes down.

If you just focus on deadweight, then the grips might be heavy (lots of old grips are really heavy) but there is no more mass behind the ball.

A MOI machine will pick up on these things cause it measures where the weight has been added to the club. It’s not perfect cause if you fit a lighweight shaft and put some more weight on the head, you will have a high MOI but it could still be a fairly lighweight club.

I think you would like the way a MOI machine works Lag, its not perfect, but much more in line with your thinking of how a club should be weighted than the other methods of measuring a club.

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Most often we use heavier vintage grips, classic cords etc. The Mints are a bit lighter, so those sets might just have a bit more mass in the heads to get the dead weights up… which doesn’t hurt. Better than going the other way around.

I mostly use my eye and just feel the club, and if it feels light, I check the weight and then add more if it needs it.

I am sure the MOI is a good method.