Effects of Clubhead Features
of Gravity ( CG )
center of gravity can vary in three different dimensions:
are some that feel that increased
toe weight helps pull the clubhead through the ball and prevents
slices. I'm not convinced yet. However, the Ping Zing seems to indicate
that Karsten is convinced. Same for Golfsmith's Square Toe models,
Acer's "flow-weighted design", and several heads from ProSwing. So
either it works, or people are buying based on the perception that it
That may or may not be true for irons. For
woods, the gear effect
will make it work just the opposite. By moving the weight towards the
heel, you are promoting a hook. That is because more of the clubface
will be on the toe side of the CG, and gear effect causes a toe hit to
hook. But it takes a lot of weight to move the CG appreciably to the
heel or toe. Weight screws in the 10g range are not going to have
much effect on CG placement -- and therefore not much effect on
trajectory. The newer drivers have weight screws closer to 16g, and
that has a measurable, if not totally dramatic, effect.
cause of "gear effect".
A low CG tends to give a high trajectory (flight line) to
the ball, and
vice versa. So:
Many peripheral-weighted (cavity-back) clubheads have a big sole
flange, that keeps the CG low and gets the ball airborne. In fact, many
heads in the past decade (since perhaps 2007) have the CG far enough
behind the face to get some benefit from gear effect.
- If you tend to have
trouble getting the ball airborne, go for a low CG.
- If you want to keep your shot lower out of the wind, go
for a high CG. But a low dynamic loft, due to either a low clubhead
loft or a head that is hooded at impact, is even more effective. If you
try to counter a high loft with high CG, you may sabotage your intent
badly. The reason is that a high CG increases backspin due to gear
effect; if that happens, the ball will balloon, which is just the
opposite of what you want.
- If you want your drive to carry a long way in the air,
go for a low CG.
- If you want your drive to roll a long way, don't assume
a high CG is the way to go. A high CG may lower the trajectory, but it
will increase backspin. It isn't clear what effect that has on roll
after landing; that will depend heavily on the loft, and also somewhat
on the ball.
short-hosel or no-hosel clubheads are designed for a low CG. For
instance, in the early-to-mid 1990s, Acer made two nearly identical
clubheads, the M160J and the M360J. Same loft angle (10
degrees), but the short-hosel 160 gives a high flight, while the
high-CG 360 gives a flat trajectory and lots of roll.
- It is possible to get woods with
an open face angle or a closed one. For instance, some closed-face
woods are advertised as "curing" a slice. I don't think it's a good
idea to deal with a slice by getting a hook-tendency club. Much better
to find out what's causing the slice (it's probably doing other bad
things to your game as well) and cure the disease rather than the
More important than whether the face angle is open or
closed is whether the golfer sees
it as open or closed. The golfer's individual perception
can result in addressing the ball with the face left or right -- and by
more than the ½° to 1° of face angle variation in the club. Of course,
this varies from golfer to golfer, as well as from clubhead to
clubhead. There are a lot of compentent clubheads out there; you should
be able to find one that "fits the eye" of the golfer you are fitting.
- One of the more misunderstood
terms in golf club design is "gear effect". It is tossed around to the
extent that the naive think it's magic and the skeptical think it's
pure hype. Actually, it is real and explainable. For the explanation,
see the section on
Impact. For a lot more detail on how it works and what it can
do, I have an article
on the subject.
When I first wrote this article, people referring to gear effect were
talking about horizontal gear effect only. Today, we know that vertical
gear effect plays a huge part in ball flight. If the force exerted on
the ball by the clubhead is not exactly through the CG of the clubhead,
then spin is imparted to the ball. The farther the line of force from
the CG, the more spin is imparted. Summarizing:
- If impact is toward the toe of the club, gear effect
will impose hook spin on the ball.
- If impact is toward the heel of the club, gear effect
will impose slice spin on the ball.
- If impact is above the CG of the clubhead, the backspin
(mostly due to loft) will be reduced, sometimes markedly.
- If impact is below the CG of the clubhead, the backspin
will be increased, perhaps contributing to ballooning and a steeper
angle of descent.
- Clubs used to have two kinds of grooves:
- V-grooves, also known as "normal" or
- Square grooves,
also known as "U-grooves".
- Today there is far less variation in groove shape. In 2010,
the USGA and the R&A instituted a new rule for measuring
grooves that does not allow nearly as much effect as the old square
grooves. There is some difference between clubheads in their grooves,
but not enough for me to endorse one approach over another. Whatever
turns you on.
- Before I leave the subject of the clubface
treatment, I'd like to point
out a few studies that should be the last word on the subject.
The first of these, reported in Cochran and Stobbs,
clubs against clubs with perfectly smooth clubfaces. Their surprising
conclusion was that short irons give the same amount of spin to the
ball whether or not they have grooves, and whether or not their faces
are roughened. (Qualifiers: for five-irons and longer, grooves did
impart maybe 10% more spin; also, the experiment only applies to shots
from the fairway.) So the advertising hype about "milled faces" or
"soft copper faces with hard tungsten carbide particles" are hype and
The second study compared the
performance of square grooves with V-grooves. It was reported in Golf
Digest, December 1986. Their major conclusion supports the notion that
square grooves give an advantage from wet rough, but very little if any
advantage where the clubface itself strikes the ball dry and clean.
(The latter result supports the earlier study by Cochran and Stobbs.)
Here are some spin rates from the Golf Digest study:
By the way, this
table also points up rather dramatically the
spin advantage of a 3-piece ball with a soft cover, regardless of the
treatment. ("Soft cover" refers to the balata from the 1980s. But I
would expect the same from a modern urethane cover.
- If your swing plane is more
upright or flat than normal, you'll probably want a lie angle to match.
That's a simplistic view. In order to design and build a club with a
non-standard lie angle:
- Check the strong interaction of club length with lie angle.
- If you intend to achieve the angle by bending the head,
check the item
on clubhead materials in this section.
- The larger the loft angle, the
higher the flight of the ball. Also, generally, the shorter the shot.
(We will see an exception with drivers later.)
While the trajectory is affected by the CG of the head and flex profile
of the shaft, the loft angle is by far the biggest
how high the ball will fly.
When I first wrote this in the mid-'90s, there was a
standard set of lofts for irons. The 5-iron was 28°, and the lofts
varied by exactly 4° from each club to the next. In the late '90s, the
manufacturers of irons indulged in "loft wars",
breaking the standard
and leaving chaos that continues to this day. The table on the loft
wars shows the change over the decade from 1994 to 2004, but the trend
has not stopped at all. I have reviewed the major
considerations for loft in my article on
single-length clubs -- where loft is the only way to
differentiate distance. But almost everything there also speaks to a
conventional set, so let's talk a little about custom-fitting the loft.
Beginners may want a little more loft,
to get the ball airborne. But remember that this problem may go away
soon after you begin the game, especially if you're reasonably
well-coordinated and athletic; do you really want to go club shopping
Heavy hitters with strong hand action
may want a "strong" loft (a lower loft angle), to get more distance and
keep the ball lower and out of the wind.
The best clubfitters will have a final fine-tuning session before
turning over new irons to the golfer. We have already talked about the
function of the session to dynamically fit the lie angle. If there is a
way to measure the distance of each shot, this is a perfect opportunity
to set up the lofts at the same time as the lies. Ideally, you should
set the lofts so that:
- The longest and shortest clubs can be reliably hit by
the golfer being fitted, and...
- There is a good, functional set of distance gaps
each club to the next.
One caveat about bending: if
you intend to change the loft angle by bending the head, check the item
on clubhead materials in this section.
- The "offset" of the clubhead is the amount by
which the leading edge (bottom) of the clubface is set behind the plane
of the front of the hosel. The more the offset, the more the clubhead
trails the shaft as it swings through the ball. Offsets range from zero
(typically in clubs for low-handicap golfers) to as much as 7mm in
"game improvement" clubs.
What the offset does is add a little
assurance that the hands are ahead of the ball at impact, a common
shortcoming of beginners. Since it delays the clubhead's striking the
ball, it has the beneficial (for beginners) effects of:
- Increasing the likelihood that the clubface has closed
- Changing the effective loft at
impact, probably to increase the loft. (However, some experts seem to
disagree and believe the loft is decreased.)
- The term "progressive offset" refers to a set where the
long irons are
offset more than the short irons. The theory is that most golfers who
need offset in order to square the clubhead need it more for the
longer, unlofted clubs.
If you gave an expert golfer whose
swing was grooved for zero-offset blades a seriously offset club, the
result might be snap-hooks and sky balls, because the club would then
be over-lofted and face-closed at impact. He/she doesn't need the help
of offset to get the hands "through the ball". But this is not just
physics and geometry. In both cases, squaring up the face and
increasing dynamic loft, the
effect due to physics and geometry is not large. For a typical golfer,
a 7mm offset might add just under half a degree of loft and allow about
half a degree of face closure.
Still dramatic differences do happen. I have my own
anecdotal data. In 1998, I got a newfangled TaylorMade Rescue, the
first hybrid on the market and a seriously offset club. It quickly came
to be my go-to club for a long shot when I could not afford a miss to
the left. In 1999, I took a series of lessons that put an end to my
slice. By the time I was hitting my other clubs straight, the Rescue
was likely to leave me two fairways to the left. To this day, my
hybrids have to be "onset" (the opposite of offset; the entire face is
in front of the hosel). So I have no doubt that perception more than
physics causes the effects attributed to offset.
Bounce and Camber
- The "bounce" of the
sole is the angle the sole makes with the ground when the club is held
at a normal address. More specifically, it is the angle from the
leading edge to the lowest point on the sole (or middle of the sole, if
"lowest point" isn't applicable). The term comes mostly from sand
wedges, which have
a substantial positive angle on their flange that keeps them from
digging into the sand and burying.
of the sole is
the curvature. There are two different kinds: heel-toe camber
(illustrated in the section on Club
Length, and sometimes referred to as "rocker") and face-back
clubhead that has a lot of both kinds is frequently advertised as
having "four-way camber".
In the hope of reducing
confusion, I'm adopting some terminology I've seen used by Golfsmith.
The heel-toe curvature will henceforth be referred to as "rocker"
in these notes and my r.s.g. posts. The term "camber"
will be reserved for the face-back curvature.
The diagram is a cross-section of an iron head, probably a
wedge. In the diagram:
- The bounce is the wedge angle of the red triangle.
- There is some ambiguity in the numerical measurement of
- Sometimes (usually for wedges) it is the length of
the yellow line.
- Other times (usually for irons) it is the length of
the green line.
with a zero or negative bounce will tend to dig into the ground when it
it. A positive bounce will skim along the ground.
- If your swing uses a downward strike hitting ball then
bounce means you'll take a "beaver pelt" divot with relatively little
- If your swing is a sweep that contacts
the ball at the bottom of the arc, a positive bounce may save a
fat hit from becoming "play the divot, it went further than the ball".
A little face-back camber added to such a clubhead will reduce the
slowing of the clubhead from friction with the ground.
- Note that both swing styles are valid, and are taught by
of pros. The touring pros used to take big divots with their irons and
sweep their fairway woods. Jack Nicklaus' tape and book "Golf My Way"
tends to encourage a sweeping swing with most clubs (even though that
point isn't made explicit). Today's pros are more like Jack and Tiger,
taking fairly shallow divots with their irons -- though very few try to
pick them clean, with a zero angle of attack. The most-preferred method
these days is a shallow but negative angle of attack, hitting the ball
first and then the ground.
Now let's talk about rocker
(heel-toe camber, but I won't remind you again). I believe it's very
important, and I prefer more of it. Quoting from Golfsmith's
"Golf Clubs - Design and Repair":
soles of all clubs, both woods and irons, should have some contour from
heel to toe, so that when the sole touches the ground the contact point
will be directly under the sweet spot. This contour is particularly
important in the irons where divots are normally taken. With a flat
soled club, the slightest error in the lie angle would cause either the
toe or the heel to dig in at impact while the contoured sole has a
built in margin of error. Also, the contoured sole takes a narrower
divot, which permits the club to cut through the ground with less
I agree with what they say about the irons.
However, I also find it makes a surprisingly large difference in woods,
even the driver. My most common mis-hit with a driver is scuffing the
ground before I hit the ball. Most drivers have a fairly flat sole
plate, so a corner (usually the heel for me) catches the ground and
turns the club; when I scuff a drive with a conventional-sole driver, I
usually hit a duck hook.
I convinced myself of this in the early 1990s, when I
two new drivers:
- Golfsmith's Big Gun
has accentuated rocker. Most of the times that I scuffed it, I got a
high draw instead of a duck hook; I lost a little distance, but usually
got away with a respectable drive.
- Acer's M160J
has a keel sole, the reductio ad absurdum of rocker. When I scuffed the
ground with that keel, it always dragged in the center of the clubhead,
without turning the club. You couldn't tell from the direction or
trajectory of the ball that I had scuffed; it just lost a little
- I practice what I
preach with irons, too.
- In the
past, I have used a sweeping swing that hits the ball without much
divot. My irons were Golfsmith Tour Model IV, with relatively little
bounce, and even that mostly due to as accentuated a 4-way camber as
- This year, I have learned to hit down
on the ball. I have built myself a new set, with a sole better designed
to take a divot (less camber and no bounce).
- Sole Width
- A narrower sole has less friction with the ground. However,
if you hit
it fat, a narrower sole won't provide as much saving "skim" on the
surface; it'll tend to dig. In other words, if you are quite repeatable
with your swing and almost never hit it fat, you'll probably want a
narrow sole. A wider sole is a feature of game-improvement clubheads
for the less-precise golfer.
- Different designs of clubhead advertise their
- "Bigger sweet spot is
more forgiving." (Perimeter-weighted clubs, frequently referred to as
- "Puts the weight directly behind
the ball." (Blade or "muscle-back" clubs.)
- Believe it or not, they're both telling the truth (as we
in the section on Physics). But let's dispel a myth right now. "Weight
behind the ball" does not lead to more distance. If the net
of all that peripheral weight is also right behind the ball, the ball
go every bit as far. Perhaps counterintuitive, and definitely different
from what traditionalists would have you believe, but true nonetheless.
If you almost always hit it on the
sweet spot, you'll appreciate the increased "feel" from a muscle-back
blade. If you're less precise, then your concern is minimizing the
damage from your off-center hits, and a cavity-back is called for. But
remember, that feel from the blade is really due to the increased
feedback to your hands
when you miss the sweet spot. They should feel exactly the same if your
impact for both is on the sweet spot.
Before you discount this due to a wording
difficulty, let me say what I mean by "sweet spot". I have seen too
often a refusal to discuss substance because, "The sweet spot is a spot,
dammit! It doesn't have size, so it can't be bigger nor smaller." That
shows an obsession with high-school geometry and an ignorance of real
engineering considerations. Engineers always work with tolerances, not
pure absolute numbers. And the sweet spot of a golf club has to be
considered in terms of tolerances. So let's define the sweet spot -- as
an engineer would.
The sweet spot is the area on the face of a golf club
where, if the ball is struck there, the ball will go the maximum
distance, to within a specified tolerance (say, 1% or 2 yards).
Without stating the tolerance, the sweet spot is a
dimensionless point. As soon as we mention tolerance, the sweet spot
becomes an area that allows you to engineer forgivingness into the
There are a variety of patterns for distributing the
weight in a
peripheral weighted club, but they probably don't have much to do with
which popular model the club looks like. The important variations to
look for are:
- A big bottom flange: low
CG helps get the ball airborne and makes the sweet spot taller. It is
more forgiving on "thin" hits.
- A reduced bottom
flange (concave like the Ping Eye 2, or even cutaway like the Ping
Zing): maximum heel-toe weighting to widen the sweet spot. It is more
forgiving on heel or toe shots.
- High square toe
(a late '90s Golfsmith designs) or extra metal at the top of the toe
Zing): supposed to help the clubhead "swing through" the ball and avoid
a slice. I don't have any intuition for why this should work, and in
fact it seems at odds with gear effect. But I've
seen it in enough disparate places to give it some measure of credence.
However, I think there is something more easily explainable at work.
This moves the CG of the clubhead toward the toe, making it more
forgiving to toe hits. I believe that toe hits are a more common error
than heel hits, for non-expert golfers.
- Concave or undercut bottom flange. This allows more
material to be
not only low but back away from the clubhead. This moves the CG of the
clubhead back. The major reason to want this is increasing gear effect
(so it is significant for irons as it is for woods).
- Relatively small cavity: this might be due to one of
two things, one good and the other bad:
- Some companies make a forged cavity back club. (See
the section on clubhead materials
for more on this.) Such a head has the softness and alleged feel of a
players' blade, but somewhat more forgiving. Not as forgiving as a cast
cavity-back clubhead perhaps, but a good match for some better golfers.
I keep a set of these for practice-only rounds. They demand more
accurate ball striking than my normal game improvement irons, but
mishits are not as harsh nor off-course.
- Sometimes an indication of a cheap club (both price
and quality). Have
they had so much trouble with the strength of their heads that they
kept the basic structure and performance of a blade but put in enough
cavity to look "fashionable"? I wouldn't get one unless I knew enough
about it to know this wasn't the case.
modified May 6,2020