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Clubhead Geometry In Pictures | Hireko Golf Blog

Clubhead Geometry In Pictures

Part 3 In Response To The Customer Driver Design Campaign

In Hireko’s “We want YOU to be a part of the design process for our new 2010 driver” campaign, we showed you one rendition based upon your comments. We need your driver to first start with a solid foundation therefore we would like to take this opportunity to tell you the pros and cons on each shape or geometry so you will have a more informed understanding on why manufactures select the different shapes.

If you haven’t paid attention lately, you might have noticed drivers, fairways and utility clubs are now available in a plethora of geometric shapes. This wasn’t always the case. For a very long time, wood head shaped changed very little.  One of the reasons was the wording in the Rules of Golf, the official set of rules and regulations that the golf club designs must abide by.  There was and still is a small passage called the “Plain in Shape” rule:

“The club must not be substantially different from the traditionally and customary form and make.”

In fear of having a head deemed “non-traditional”, manufacturers made relatively little change.  But as heads transformed from wood to steel and then to titanium and other exotic materials, manufacturers started to push the envelope to help differentiate their products. But is there is a rhyme and reason behind these geometric shapes?  And if so, which one may be best for you?

Moment of Inertia
One of the hot topics in golf is the term Moment of Inertia or MOI for short.  Moment of inertia is a measurement of the clubheads ability to resist twisting about a known axis.  A higher MOI is supposed to be a strong indicator as to the forgiveness of a clubhead. At impact, the golf ball is not always struck in line with the center of gravity, resulting in the head twisting and consequently consuming energy that could be imparted to the ball.  A club with a higher MOI will resist the twisting more so than a lower MOI value.

XMOI Hybrids

Drivers went from being solid and made out of persimmon or laminated maple to metal in the early 1980’s.  Even though the size of the heads is approximately the same, the metal woods increased their MOI over their wooden predecessor by about 25%.  This is because the metal heads were not solid, but a hollow shell with a very lightweight density foam injected to dampen sound.  All the weight that would have been in the center of the head was distributed to the perimeter, thus the term “perimeter weighting”. Since the advent of the petite size metal drivers of the early 1980’s, the MOI has increased nearly three-fold in modern drivers.

Golf clubs (drivers in particular) have limits on size (or volume) as well (460cc). If we want to have the largest possible club, then the maximum the dimensions would be a 5” (12.7cm) from heel to toe and 5” (12.7cm) from front to back.  However, if you looked at the first 460cc driver heads, they were no where close to filling the 5” x 5” box.

Because the volume or size of the club is tied directly to the MOI, it will have limits as well.  But there are a couple of other things that can be done to increase the MOI.  One is to better utilize the shape, like in the direction of the new “geometric-shaped” clubheads.

Pear or TraditionalDriver Geometry 2
Before we get to those shapes, let’s first take a look at the benefits of the pear or traditional shaped clubheads. These are the narrowest from front to back, have a more forward and perhaps higher center of gravity than any of the other categories.  When you look at the crown, it will most likely have a nice rounded top. However, their beauty is often compromised as these will possess the lowest MOI value for more workability, which is preferred by better players. Make no mistake. The modern 460cc “pear” shaped driver is still considerably more forgiving than their smaller predecessors. Examples of the traditional shape in our current product line would be the Acer XP905 and iBella Obsession.

SquareDriver Geometry 3
One of the first unique shapes to become commercially available was square – after all, square justifies plain in shape, but perhaps not the interpretation of traditional that the founding fathers of golf had envisioned.  The square shaped help to push more weight to the rear two corners represented by the black shaded areas.  This pushes the MOI about 12% higher given the same volume and front to back dimensions as pear shaped driver.

The obvious benefit is to increase the MOI of the head for maximum forgiveness, which is recommended for golfer with more mid or higher handicaps to hit the ball straighter.  To some, the downside of the square shape is its unconventional and sometimes bulky appearance. Examples of the square profile are the Acer Mantara and Power Play System Q2 series.

TriangularDriver Geometry 4
The triangular shape pushes weight further rearward in producing a more “pointy” shape.  This shape promotes a higher MOI than the traditional shape, but not quite as high as the square. The triangular shape produces a unique appearance at address.  Traditionalists who have played for many, many years might be taken aback by the shape, but golfers new to the game have had no problems with the appearance at all. Although the face height are not much, if at all different than the “pear” shaped heads, often times they may have the appearance of being shallower. This is partially due to the fact they are broader from front to back and slope down quickly in rear part of the head as they are nearly absent of any skirt. Examples of the triangular shape are the Acer XK and Power Play Caiman (use you imagination a little).

Driver Geometry 5
The bullet shape is more full-bodied than the triangular. These are not only broader from face-to-back than the traditional shape to move the center of gravity rearward for added stability, but also more material is pushed to the corners.  The purpose of the bullet is to produce a higher moment of inertia closer to that of a square shape, but with a more traditional appearance to appeal to a wider range of players.  Examples of the bullet shape are the Dynacraft Avatar XMOI and the iBella Bellisima.

The down side to some of the geometric designs is in order to achieve the 460cc volume some of the dimensions need to be modified.  By making the clubhead broader from front to back, the club is generally made shallower. Therefore some golfers may have to tee the ball down slightly lower compared to a deeper faced Driver Geometry 6club they might have owned.  The shallower face does lower the center of gravity as well and lends itself to creating a more rearward CG to help launch the ball higher (and sometimes with less spin as well).

We hope that helps explain the differences aside from the obvious appearance at address and allows you to make a more informed decision on what you would like to see in YOUR new design.


  1. Duncan Fraser says:

    So far I’m with you. The one thing I would like to see on a new driver would be a hotter face. It seems that most just have standard titanium face. What about bata ti or some other harder material to increase ball speed. The shapes of the head is important but so is ball speed.

  2. John Huheey says:

    It is always good to go over what has been taught us. You no it is rare that the “GOLFER” ever asks us “why” the shapes are what they are”.
    They real question will be ,”what is next that will give them 20 yards!” Were are you going from here on design?

  3. Bill Berninghausen says:

    A crown that’s concave, or scooped, toward the rear edge gives my eye a sense of where the club’s sole is. Makes it easier to ‘clip the tee’ or sweep the grass. Examples are Maltby’s Glider Driver or Cleveland’s HiBore. And it puts incrementally more mass nearer the sole.

  4. Bruce Gerhold says:

    This design problem hearkens back to my Mechanical Engineering design courses. One of the main issues it to design the part to fit the purpose. To me, you appear to be heading down the path of just another driver that looks like “brand X”. Why not design a club head within the rules and intended for one purpose – hit the ball straight and far.
    The traditional shape was simply the shape that could be manufactured in mass quantity from wood. Why in the world did this shape carry over into metal?? The material properties are completely different; thus, the shape should differ to take advantage of the properties.
    The real question here is do the “Rules of Golf” require the driver head to have a “traditional” shape? If not, then let’s consider the real driver function and geometries that may accomplish this.
    A second question is why do essentially all drivers weigh 200g? I suspect this too is a carryover from wood club heads and not really a requirement. What makes no sense at all is a ladies club weighs the same as one for a seniou, a junior, a mans, or a pro’s despite the obvious differences in strength and swing speed.
    Take off the blinders and design a club: be bold and creative.
    If added discussion is of interest, contact me and we can proceed.


  5. Frank Mazane says:

    I find that most of the OEM driver heads are kicking the ball way up in the air even when I put in shafts that are supose to keep the ball down. I’m guessing that i should be playing a pear shape. Where the C.G. is not as low. ?

  6. Jeff Summitt says:


    The OEM drivers may be kicking the ball up in the air for another reason other than the lower more rearward CG. They may very well have vanity lofts or where it may say 10.5 on the sole, but the actual loft of the driver is a degree or two higher than that.

  7. Jeff Summitt says:


    The problem with using beta titanium is two fold. One it is more expensive. We can easily pass the cost onto the customer as it is not that much more when you look at the whole scheme of things. The bigger issue is the rebound effect. The USGA put stipulations on springlike effect (a pendulum test). We can easily meet the limit with standard 6-4 Titanium. So the advantage of a thinner beta titanium would be nullified to make sure that the club conforms to the Rules of Golf. The only other reason to use beta titanium is for weight savings that may allow us to squeeze a few more grams elsewhere.

    The biggest concentration should be properly fitting the golfer to obtain that magical 20 more yards with no additional effort by the golfer.

  8. Jeff Summitt says:


    The reason why the original metal woods took on the more traditional shape was the “The club must not be substantially different from the traditionally and customary form and make.” clause in the Rules of Golf. The shape we were alluding to that is different can be found at the following link: http://blog.hirekogolf.com/?p=731.

    I really haven’t gotten into the nuts and bolts on why the shape may hit the ball straighter as of yet. But remember there are limits on how far the ball can go – at least center shots.

    The weight on heads have remained relatively the same (except for juniors which are typically lighter) because of inventory reduction and building to a spec length and swingweight. The overall weight and heft of the club (not head weight) is often controlled by shaft weight and length. Yes, there are preference for varying the weight a little lighter or heavier, but this would require that the head be made adjustable for weight. We have customers who want this adjustability and the other half want nothing to do it.

  9. My comments have to do with how great existing heads are. I made my 88 year old brother a Mantarra XL 12 degree driver with a Grafalloy Attack Lite A flex shaft 46 inches long and back weighted it to a c-4 1/2 swing weight. My brother has been playing golf for 50 years and has a handicap of 8. Beats golfers much younger.
    Jim said this is the best driver he has ever owned. I made the same club for myself, same shaft 44 1/2 with a weight of c-4 1/2. My golfing budies cannot keep up with me. Great club. Don’t see that any changes are needed except make the head a little lighter if possible.

  10. Pastor Chris says:

    Thank goodness we have a very precise and quantifiable guideline in, “…the traditionally and customary form and make.” My dream driver would have the traditional outline from the top and side, but would have these shapes created by 2 two-dimensional pieces that intersect behind the face, (Like X and Y axis planes with a face instead of the Z axis) which is attached to the top, and an abbreviated sole on the bottom. The face would be a bit smaller than the outlines, so that the driver head “shapes” could act as aerodynamic fins to help guide the swing and reduce drag. Total volume would be small since it is not a hollow form, and the weight could be located wherever it was needed dimensionally to put the desired MOI exactly where desired. Think a cross between very anorexic versions of the new aerodynamic drivers, and Cleveland’s new niblick. Might need some cut out behind the face to allow spring effect, because the fully supported face may be too hard. It should be easy to make, as little to no welding is required, and the whole thing could be investment cast with very little CNC machining done to touch things up. I have no idea how you could get this past the rules committee, though, except to trot out every other fringe club that has been approved and hope for the best in comparison.

  11. Bruce Gerhold says:

    Thanks for the reply. I am aware of the USGA desire for the club head shape, but their idea of “substantially” appears to be rather broad. The progression from “wood” driver shapes to square, then high MOI shapes suggests the USGA is open to shape changes. I favor a driver with a round club face – easy to manufacture, easy to design a constant COR for off center hits, and lower frontal area for lower drag = higher club head speed. Attach a bullet shaped piece on the back of the face to increase MOI and you could have a shape made to hit the ball.
    I really fail to see any relationship between shape and hitting straight except for the obvious MOI relation that helps maintain a square club face by resisting rotation. I think the shape of the old “woods” was simply a manufacturing issue; not related to performance.
    The rules of golf limit the coefficient of restitution, COR, (as measured by the characteristic time) of the face, not distance. Anything we can do to attain higher club head speed will increase distance. Lower aerodynamic drag due to reduced frontal area my just be that path.

  12. Ron DePriest says:

    I like the design of the Acer XK. The cup face is a must for distance on off center hits. If you could design the head with a thinner crown, possibly even use a carbon crown, and a beta-ti face, an adjustable weight system could be used to change the COG and the flight bias of the driver. This also helps with swing weighting. Also, if you could design the sole to where the club sets up the same at address every time, this would help the golfer that has problems squaring the clubface.

  13. Timothy D Watson says:

    Thanks for the nice and informative article, Hireko. My commits on the various options listed here are these:

    A square profile is a nice indicator of what the face angle should be. It is easy to properly align a closed or open face when you have a square profile to aim with. On the other side, in my opinion, non-square faces look awful on square clubheads. Still, performance wise, I think at least one side of the clubhead being square is very useful.

    The triangular profile is exciting to me. It looks fast and gives me a psychological boost. The triangle is fun, but may make me swing to hard. Thinking fast and thus swinging too fast is a big disadvantage. Additionally, the face of the club looks smaller on triangles, resulting in less confidence on my part. The triangle is the club I wish I could use, but can’t.

    “Skirtless” clubheads just plain look better to me. The skirtless heads I have used in the past have almost all been top performers. From what I have heard, they are less aerodynamic, though. I believe the positive psychological influence of a skirtless club is greater than any possible aerodynamic (or otherwise) performance advantage. My impression is that the skirtless driver probably performs better, regardless of what I have heard, anyway.

    I think scooped crowns are interesting, but wouldn’t the crown just going straight back to the skirt or sole be more efficient and save some mass that can be redistributed for the same affect or greater than a scoop. A straight line is shorter than a curve to the same point. An extreme scoop might help me with visualizing the sole position like Bill Berninghausen mentioned. I really like that idea.

    All of my thoughts considered and combined, I would say that a geometry with the heal a slightly rounded square and the toe side a very pointed triangle would be good. The face would not extend far towards the toe, but would be normal on the heel side. There would be no offset.

    The main difference with “Hereko’s 1st Response” in my profile would be the back of the driver’s clubhead. I would want it square with the target, not pointing like an extremely open clubface. Additionally, an extreme scoop combined with the no-skirt configuration would be preferred by me. I would not want any ridges inside the scoop to strengthen the crown or encourage closing the face. Those things are not as big a factor to me as the “Berninghausen Scoop” idea.

    I do not need a sole that aids in alignment on a driver. I hold the head above the ground (no contact) at address like I would want to swing though the ball and not take any divot. I would appreciate a sole designed to eliminate turf drag when contact with the ground does occur, though. Not anything overly elaborate, just a “T-Sole” with a relatively great deal of depth to the recessions on each side of the area behind the face. The “T-Sole” has no recession behind the face along the middle.

    Anyway, just a thought, but I find limiting design emphasis to the geometry of the head not good. Geometry is not THAT big an issue to me. Geometry is exciting and needs to be perfected for modern standards, but simply, the durability of the head is my main concern. Gigantic, 460ish, mostly constructed of 6-4 titanium drivers have very thin side walls and sometimes weak welds or brazing. They don’t hold up to frequent, repeated, and prolonged use. Make a high quality 320cc driver with my preferred geometry, and I’m sold! I don’t consider buying drivers larger than that, and have been that way for a long time after much testing of that conviction.

  14. Timothy D Watson says:

    I should explain the specifics of why driver head durability is so important to me. I have had a wonderful, unlimited driving range pass for two years. I love the driving range and use the pass as much as I can manage to make the time for. Since I first got the pass (for $100, excellent deal), I have increased my driver swingspeed by 30mph. I had to change all of my old shafts because they eventually broke from not being suitable for my new swing!

    Anyway, each bag of balls at the range contains approximately 35. During an “inactive period,” I hit three bags (105 balls) once in a month. I usually use just my driver for all of the balls. During a “driving range fever” period, I can hit nine bags (315 balls) twice a week, for two weeks (1260 balls total), all with my driver. I use my driver a lot.

    The most balls I have ever hit with a 320cc+ driver before it broke are around 630 (105/month for six months). If I have “the fever,” I can hit 630 balls in just one week! I can not afford (and it would be too aggravating) to break a driver every week to six months. I play all year. The smaller titanium drivers that I use now last an exponentially longer time. I have not managed to wear one out yet. The paint job goes crazy and the face flattens slightly, but that is it.

    Even if I used my driver only 18 times every week on average like a normal (but still active) golfer might, it would only take around eight months to need another one. That is still a short time. I know other golfers that break their drivers this often, so my numbers should be meaningful. Modern drivers do not last long enough.

  15. gemma says:

    Just wondering if you could tell me whether the Ping Rapture V2 driver is the traditonal/pear or the triangular? I am comparing it with the Mizuno MX 500 and would like to know if there is anything substantial that stands out in the difference of these two drivers?
    Thank you

  16. Jeff Summitt says:


    The Rapture is a traditional shape. The Mizuno is a carbon crown head designed to lower the CG and launch the ball higher. Ping concentrated on crown and face structures to help optimize performance and sound.

  17. James H says:

    If I were making a line of clubs this is what I would do. And I will just use the Caiman Line as an example

    1. My first club would be called the Caiman Black Label – The black label is the same shape as the normal Caiman with same “eyes” but really made for low handicappers (Called black label because players that hit from the “tips” or black tees would play this driver). It would have neutral bias for workability and with same black PVD finish. and a semi-pear/triangular shape. It would come in 9, 10 and 10.5 degree lofts (also, if I were to make a ladies model, it would be pink or deep purple with black or red “eyes). The fairway and hybrids would match the look of the driver. However, the irons would be gun-metal black, cnc milled blades.

    2. The Caiman Blue Label – This one is for mid-handicappers – The blue label has a deep blue PVD finish and has a bullet shape. This driver would come in draw and neutral models. For mid-handicappers, this club would come in 10, 10.5 and 12 degree lofts. Fairways and hybrids would match look of driver. The irons would be similar to the xmoi transitional hybrid set but the 5-pw would be traditional irons.

    3. Finally, The Caiman White label – This one is for high-handicappers – or players hitting from the white tees. This model would have a chrome pvd finish with a white crown. It would be square shaped with lofts of 10.5 and 12. Fairways and Hybrids would match look of driver. Irons would be exactly like the xmoi hybrids but with a chrome finish with white cavity back insert.

    Yes, I realize you were just asking for driver ideas, but I need to tie it all together

  18. Jack Sullivan says:

    Can you also talk about cup-face technology. Thx

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