What
is MOI?
A Measure Of Forgiveness
MOI (Moment of Inertia)
It will be easier to understand MOI if you think
of it as an MOF (Measure of Forgiveness). Moment of Inertia is a
measure of a body’s resistance to angular acceleration (twisting).
In golf, MOI comes most into play
on imperfect contact, when the ball and the clubface meet someplace
other than the sweet spot. But the simplest way to illustrate the
concept is to put golf aside for a moment, and consider a weightlifter
like Stick Man, below.
In the sketch on the left below, Stick
Man has the weights on the bar close to his body. He will find it
relatively easy to twist the bar on his shoulders, because the MOI
of the bar is relatively low.
The Stick Man on the right will find
it more difficult to twist the bar back and forth. The bar weighs
the same, but because the weights are spread apart to the end of
the bar, the bar has a high MOI – in other words, it resists
twisting. That’s all we mean by MOI.

Similarly, in designing a driver, if we move weight
from the center of the club head to the toe and heel it will increase
the MOI and resist twisting at impact. Mishits will fly straighter,
and the club will be more forgiving when ball contact is made away
from the center toward the toe or heel. It will feel like it has
a BIGGER SWEET SPOT.
In hollow metal woods, the weight is all in the
shell and as far away from the center of gravity of the head as
possible. This gives it a high MOI and makes it very forgiving of
mishits, something most of us can relate to. The forgiveness in
these big heads enlarges the effective sweet spot in all directions
on the face – up and down as well as side to side. This is
why manufacturers have been making driver heads obscenely big and
as forgiving as possible.
Because it is so light, titanium has allowed the
club head to grow without adding so much weight that it becomes
uncontrollable. As an added benefit, its strength allows the face
to be made thin enough that it actually deforms and springs back
during impact, acting like a spring or trampoline.
The USGA, because of its concern about how far elite
golfers -- the best male amateurs and tour professionals -- are
hitting the ball, set a limit of 470 cc on the size of a driver’s
head. It had no real evidence to support its concern, only anecdotal
evidence. (While I was Technical Director, I often had to respond
to anecdotal claims of a magic club or ball that added 20 yards
to a golfer’s game. These claims – almost always “20
yards” – never held up to scientific scrutiny.) To avoid
criticism, the USGA hid behind the “traditional and customary”
clause: ‘It was just not traditional to have heads any bigger.’
(I sometimes think the real reason was that the USGA didn’t
want to offend or get sued by the manufacturers who couldn’t
make head covers any bigger than that size.)
When William Tell took aim at the apple on his son’s
head, he was preparing to fire a bow and arrow. Today, the vast
majority of golfers stand in the place of Tell’s son, and
the elite minority are the apple sitting atop our head. The USGA
is aiming at the apple, but unfortunately for us it has a double-barreled
shotgun in its hands. I don’t have to tell you what the results
are going to look like.
Ninety-nine percent of the golfing population doesn’t
hit the ball far enough. Research shows that the average male golfer
(a 90-to-95 shooter) drives the ball 192 yards, though we think
we hit our average drive 30 to 40 yards farther than that. A rule
that is trying to reduce distance will hurt the vast majority of
golfers more than it does the elite.
But even more than distance, we need all the forgiveness
we can get because, unlike the elite 0.001%, we don’t always
or usually hit the sweet spot. Bigger does not mean longer, though
it generally means more forgiving. Distance is not size dependent,
or dependent on MOI. COR (Coefficient of Restitution), or spring
like effect, is to some degree, but most clubs are already at the
COR limit, and this is most effective when impact occurs exactly
on the sweet spot.
Now, having passed a rule that it hoped would limit distance but
that addressed the wrong factor, the USGA is reloading its shotgun.
In an attempt to dissuade the long hitters from overswinging, the
USGA has now proposed a limit on the MOI of drivers. All indications
are that it will be adopted.
In explaining the reasoning for this proposal,
the USGA has admitted the truth about its head size limitation:
The distance that elite golfers are hitting the ball must be harnessed.
‘A high MOI will encourage the superstar to swing harder without
concern’.
So the rest of us are being penalized for what the
pros may be tempted to do. We, who don’t often hit the center
of the face and thus need maximum forgiveness, must accept restrictions
on the amount of help our club designers will be able to provide.
Make no mistake – this is what restricting
MOI means. The forgiveness built into a club means much less to
the pros than it does to us; if this were not true, pros would use
perimeter-weighted irons instead of blades. They don’t need
the measure of forgiveness the way we do. Yet this is what the MOI
issue is really about, or should be. Does it make much sense for
the USGA to limit this forgiveness property?
It seems reasonable to conclude from these recently
adopted rules and proposals (including consideration of a ball which
goes 25 yards shorter) that the USGA has lost touch with the majority
of the golfers who play the game. In regulating equipment whose
primary effect is to help the average golfer, the USGA is endangering
the future health of the game, which has been declining for the
past decade. (Click
here to see www.GrowingTheGame.org for my report of the analysis
of our survey, to which 18,400 concerned golfers responded.)

"Courses are too long so what
have I done to deserve this?"
What seems to be happening is that the USGA is adopting
a form of damage control to reassert its relevance in the equipment
arena. It is playing catch-up after the bad, litigation-inspired
decision in 1998 to permit the spring-like effect -- which the rules
explicitly prohibit -- that has allowed tour professionals to make
extraordinary gains in distance (over 25 yards) in the last 10 years.
Examples of this alarming behavior are the following
proposals and/or decisions to limit:
The length of a tee.
The size of the head.
The maximum dimensions of certain club heads.
The length of a club (except for a putter.)
A reduction in distance of the ball and NOW
The MOI of the driver.
This is not good for the game of golf or for the USGA. A governing
body needs the support of its constituents if it is going to lend
order, stability, and sound leadership to the game. It maintains
its leadership only though our following of its dictates and from
the respect of the governed – that is, you and me.
We are not being properly represented and we should let them know.
I’m not saying we should violate the rules, even when we think
they’re silly, but let’s persuade the USGA to stop making
these shortsighted rules to rein in the very elite who can as easily
be controlled by alternative course design and setup rather than
restrictive equipment regulation that has its greatest affect on
the rest of us.
______________________________
Frankly, What Do You Think?
Time to have your say. Click
below to
complete our survey re. the above article. We will report the results
in the next newsletter.
Click
here to tell us what you think!
Thank you for your input it will be helpful in changing direction
of our guardian’s thinking if necessary and thus build more
confidence and respect for this essential body, the USGA.
______________________________
Growing the Game
The analysis of 14,400 US responses of the 18,400 total concludes
Phase I of the study. The results are eye opening and show that
we need to pay more attention to real golfers if we want to improve
the health of, and participation in, the game.
Thank you for your support. We will initiate Phase II within the
next month, and at its conclusion ask for your support to help implement
the recommendations.
Click
here for the report “Growing the Game” Phase I
______________________________
Frankly
Frog News

The latest “Hot List” published in the most recent
edition of Golf Digest is a good read and informative, but don’t
look for the Frankly Frog there. The Frog was disqualified from
consideration by the editorial staff because the designer is the
Chief Technical Advisor to Golf Digest, and the magazine wanted
to make sure that there was not even a hint of a conflict of interest.
We suspect the real hidden reason is that the Frankly Frog is “Too
Hot” for the Hot List -- especially now that it is offered
in Pink and Black. The basic design is of course unchanged; the
designer, who has seen and passed judgments on more putters than
any golf club designer in the world, believes it is the best and
most effective putter anyone can create.
Please check it out and see what others are finding out about building
confidence on the greens.
Click here to find
out how to “Grip It And Ribbit”
______________________________
|