Scott, the answer is “sometimes”. When you add weight to the rear of the club, you do two things; first you move the center of gravity slightly farther rearward and secondly, you increase the swingweight, total weight and the head weight of the club. All of these changes increase the amount of bending in the shaft as it comes into impact. So, you can be changing some of characteristics of ball flight. It would take a launch monitor or simulator to get the exact results (range testing is also very good) of the actual changes that would occur.
Moment of Inertia Made Easy
The best way to understand and explain moment of inertia (MOI) is to demonstrate it. I have taken a series of photos which explain how to do this. First, keep in mind that MOI is a measurement that determines the resistance of clubhead rotation on off center (off horizontal center of gravity) hits. MOI has very little effect on exact horizontal center of gravity hits.
Demonstrating MOI is easy. Give it a try!
Photo 1
This is a very sophisticated MOI machine made by Inertia Dynamics which is a division of Rockwell International. This is the same unit that Nike and the USGA use plus a number of other major golf club manufacturers. It is interesting to note that The GolfWorks was one of the very first companies to buy and use this machine. We have had it since 1995.
It works by mounting any object on the spindle making sure that the centerline of the spindle projects through the objects center of gravity. In this photo we are measuring moment of inertia through the horizontal center of gravity plane, thus the clubhead is mounted on the horizontal center of gravity. If we wanted to know the vertical center of gravity we would mount the clubhead on its toe with the mounting point projecting through the vertical center of gravity. Actually we can make MOI measurements on any clubhead axis we desire as long as the mounting point on the MOI machine projects through the center of gravity plane.
The horizontal MOI is the only axis that the USGA has a limitation on (that’s a USGA rule) and is by far the most important in explaining playability differences from one club to another. The manufacturers use other MOI axes (mostly vertical) in their advertising when making claims but these are more minor and difficult to put into actual playability differences that a golfer would detect.
Photo 2
This photo shows two objects that look like dumbbells. Each one is the same exact total weight and also the individual components are the exact same weight. The only difference is that one has the weights positioned toward the middle of the rod and the other has the weights positioned out onto the ends of the rod.
Photo 3
The dumbbell with the weights toward the inside is a low MOI weight distribution and measures 15.025 oz–in² (ounce inches squared).
Photo 4
The dumbbell with the weights toward the outside is a high MOI weight distribution and measures 95.696 oz-in². Note that this dumbbell’s weight distribution produces an MOI that is over 6 times greater than the dumbbell in photo 3.
Let’s assume that these two dumbbells are actually putters. You could basically impact the ball almost anywhere on the face and hardly feel any twisting of the clubhead. The putt would also feel solid and would roll almost the same distance as a center face hit. A high MOI clubhead (any club in the bag) will produce much more energy to the ball on any off center of gravity hit vs. a low MOI clubhead. If you struck a putt off center of gravity with the low MOI putter in our example, the putt would feel unsolid, the putter head would rotate at impact and the ball would come up far short of the hole.
You can easily demonstrate high and low MOI by using any two wedges or putters. Actually, any other golf club will work, but their lengths are quite long and make the demonstration more cumbersome.
Using one hand, grasp the two clubs with the heads toward the middle. This is a low MOI demonstration. Simply rotate the two clubs like an airplane propeller, but only rotate them approximately 1/3 revolution clockwise and then 1/3 revolution counterclockwise and keep repeating a few times. Notice that the clubs rotate rather effortlessly and you can rotate them quite fast.
Photo 5
Next, reverse the clubs and grasp them with the heads toward the outside. You now have the grips overlapped in your hand. Next, rotate the clubs as before. Note that this is now very difficult to do as the MOI is very high because the clubhead weight is on the very outside vs. the inside. This configuration greatly resists rotation in the opposite direction. Every time you go from clockwise rotation to counterclockwise rotation it feels as if you will never get both clubs stopped. Also remember to point out that you have not changed the total weight of the two clubs, only the weight distribution of the two clubs, which also changed the MOI.
Photo 6
Click here to get Ralph’s Insider Emails
Article Discussion
-
5:37PM - Jul 27, 2007RE: Moment of Inertia Made Easy
#14
Report ThisRalph Maltby
-
-
- 588 Comments
-
7:16PM - Jul 24, 2007RE: Moment of Inertia Made Easy
#13
Report ThisScott
-
- Guest
Can I make my metal woods fly slightly higher by adding lead tape to the rear of the club? What can I realisticly expect from doing so?
-
10:02AM - Jul 18, 2007RE: Moment of Inertia Made Easy
#12
Report ThisRalph Maltby
-
-
- 588 Comments
Mike, no plans immediately for a more rounded sole on any of our hybrids. You might be pleasantly surprised at the playability of the Trouble Out fairway metals. The bounce sole design would work very closely to a more rounded sole design meaning they both eliminate or minimize any tendency for the clubhead to dig. With the very low center of gravity and a more rearward center of gravity the Trouble Out plays equally well as an easy to hit fairway metal or as easy as a hybrid. The KE4 hybrids have also received many favorable comments from our customers and I have never heard even one negative comment of their playability.
-
9:04AM - Jul 18, 2007RE: Moment of Inertia Made Easy
#11
Report ThisMike Blanch
-
- Guest
Ralph, great site you have. I appreciate your quick responce to my question. I’m looking forward to building a complete set of KE4 woods, hybrids & irons. I’m sure I’ll have many more questions I need answered, like this one. Will any of your future model hybrids be built with a sole contour like the old Taylor Made “K” sole Burner fairway woods? I would love to see a hybrid with a rounded sole. I have installed a hybrid shaft in my TM K sole 3wood head, it plays ok, but I know it’s old technology mated to a new shaft. (41 1/2”). Swingweight adjustability is one of the reasons I gravitated towards the KE4 line. Thanks again for your time.
-
3:10PM - Jul 17, 2007RE: Moment of Inertia Made Easy
#10
Report ThisRalph Maltby
-
-
- 588 Comments
Mike, the KE4 Beta driver is a 4 piece forged head and the KE4 driver is a cast head. The KE4 Beta is 460cc’s and the KE4 is 450cc’s. Everything else is basically the same. The difference in price is solely based on the fact that cast heads cost more to make. There has always been the debate on which is best, cast or forged titanium in drivers. The truth is it makes no difference in playability. If there are differences in the head only, it would be design variables or manufacturing quality variables. There are casting houses that are better than others and there are forging houses that are better than others. So, picking the top grade head manufacturers is as important as the driver head design itself. Both the KE4 Beta and the KE4 driver are made at the highest quality factories which also produce some of the major OEM’s heads right along side our production. I personally qualify the original samples of all Maltby clubs and I am also involved in all the testing. None of our testers (including myself) and the data collected showed no or very minor differences in these two heads when each was set up with the exact same specifications. There is a slightly different sound from each driver which everyone picked up on, but it is not tinny and still pleasant. So, you are fine with the KE4 Beta model and I would not worry about the 1/2 degree difference in loft angle as this is quite minor.
-
9:05AM - Jul 17, 2007RE: Moment of Inertia Made Easy
#9
Report ThisMike Blanch
-
- Guest
Ralph, my swing speed with driver is in the low 90’s. I want to build a KE4 driver. I purchased the newer KE4 Beta 10 deg. headand KE4 60F shaft. my local golfworks store had the older KE4 ***embled, and I could outdrive most top name brands with it. What will be the major differences between the beta and regular KE4 drivers, using the same shaft, swing weight and length. The driver I hit was 10.5 deg.
-
10:40AM - Jul 9, 2007RE: Moment of Inertia Made Easy
#8
Report ThisRalph Maltby
-
-
- 588 Comments
Brian, the main advantage of the 460cc head size is its ability to be more forgiving on off center and slightly off center hits. Since it is the longest club in the bag, most golfers tend to have a harder time hitting a driver in the best spot every time. If impact decals show that you are very consistent with center face hits then you will only get marginal improvement. This may not apply to you personally, but one of the things I really like about the bigger heads is the fact that they make the clubs overall length appear shorter. This is particularly good for seniors who have lost driving distance because they can make the driver length longer to get back some if not all of the lost distance and not get the feeling that the club is unwieldly long. Of course, if you seriously lose directional control, the added length is too much. Brian, I cannot put any statistics to accuracy, but I do think you will hit the larger driver head longer and straighter. Again, how much, I do not know because we are all different.
-
5:04AM - Jul 8, 2007RE: Moment of Inertia Made Easy
#7
Report ThisBrian Zins
-
- Guest
Ralph, I’m still not comfortable with a driver head bigger than 400cc. Is there a substantial difference between that and a 460cc head’s MOI? How much harder am I making the game by not switching? Is there some way you could put that into accuracy statistics? Thanks!
-
12:15PM - Jun 24, 2007RE: Moment of Inertia Made Easy
#6
Report ThisRalph Maltby
-
-
- 588 Comments
Jeff, it is far more of a swing thing in squaring up the face than it is MOI. The advertising and myths that circulate would have you believe that the high MOI’s and the farther out horizontal center of gravity location from the hosel can cause this problem completely on their own. It is true that these factors can make the clubhead more stable and reduce clubhead rotation, but it is so minor compared to everything that the golfer does and how the club itself is made. If a golfer has problems squaring the face (particularly on a driver), I immediately go to the shaft to see if it is the correct one. I then look at the face angle of the driver to see if it is open, square or closed. I next check the length of the club. Next is the grip size correct? The greatest benefit to high MOI drivers is their ability to hit the ball greater distances and with better directional control on off center hits. You cannot have to much MOI.
-
3:54PM - Jun 23, 2007RE: Moment of Inertia Made Easy
#5
Report ThisJeff Cole
-
- Guest
Hello Ralph is there a point with MOI where it gets so high that it is hard to square up the clubface? Me personally I have tried other more forgiving clubs and they just look so big that I have a time trying to square them up. What do you think?
- 1
- 2