Effects of Clubhead Features

Center of Gravity ( CG )

The center of gravity can vary in three different dimensions:

Heel-to-toe:	There 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 works. 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.
Face-to-back:	This is the cause of "gear effect".
Height:	Aha! This matters...

A low CG tends to give a high trajectory (flight line) to the ball, and vice versa. So:

• 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.

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.

Most 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.

Face Angle

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 symptom.

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.

Gear Effect

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.

Grooves

Clubs used to have two kinds of grooves:

• V-grooves, also known as "normal" or "traditional" grooves.
• 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, compared grooved 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 nothing more.

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:

		SPIN RATE
		V-Groove	Square Groove
Dry Fairway	Balata	11441	11794	( +3%)
Dry Fairway	Surlyn	7845	8770	(+11%)
Wet Rough	Balata	5646	7987	(+41%)
Wet Rough	Surlyn	3307	4174	(+26%)

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 clubface treatment. ("Soft cover" refers to the balata from the 1980s. But I would expect the same from a modern urethane cover.

Lie Angle

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.

Loft Angle

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 determinant of 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 again soon?

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 from 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.

Offset

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 to a square position.
• 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.

Sole 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.

The "camber" 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 camber. A 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 camber:
• 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.

A head with a zero or negative bounce will tend to dig into the ground when it strikes it. A positive bounce will skim along the ground.

• If your swing uses a downward strike hitting ball then turf, a negative bounce means you'll take a "beaver pelt" divot with relatively little effort.
• If your swing is a sweep that contacts the ball at the bottom of the arc, a positive bounce may save a slightly 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 some following 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":

"The 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 effort."

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 experimented with 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 distance.

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 I've seen.
• 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.

Weighting

Different designs of clubhead advertise their advantages differently:

• "Bigger sweet spot is more forgiving." (Perimeter-weighted clubs, frequently referred to as cavity-back.)
• "Puts the weight directly behind the ball." (Blade or "muscle-back" clubs.)

Believe it or not, they're both telling the truth (as we hinted earlier 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 weight of all that peripheral weight is also right behind the ball, the ball will 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 clubhead.

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 (Ping 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.