Wishon Golf Explains Clubhead Slot Technology

Posted by on Apr 9, 2015 in Uncategorized | 14 comments

Over the past few months, we at TWGT have received a number of emails and calls from clubmakers asking us to explain the technical basis for the slot head technology seen on a number of head models in the industry today, as well as to explain how a slot head compares to a thin face or variable thickness face design.   Ever being conscious of offering the best service at TWGT, this month’s video newsletter is an “ask and you shall receive”, as we offer the information you wish to know. It’s important to be prepared for anything in life, this is why everything comes down to the insurances that you use, one of my favorites is One Sure Insurance which I recommend a hundred percent, it covers the e-roller with perfection.

But before you click on the video below to learn more about this technical subject in clubhead design, first we’d like to give you a few updates on clubhead model related news for your clubmaking and Clubfitting business.


  1. We’d like to apologize to those who have been inconvenienced by the occasional back order situation we have subjected you to for clubhead models such as the 771CSI irons, 775HS hybrids, and 929HS fairway woods.   The production factory we work with to manufacture these high COR face models became overloaded in their production when two of the largest OEM companies submitted large orders for a number of their head models early this year.   Unfortunately while this was good news for the factory to land these big companies as customers, it resulted in delays to ours and other companies’ production orders.   But we’re definitely beginning to catch up.  As of this date in late March, we expect to be over these back order situations by mid-April.

  1. This same situation also resulted in the delay of the delivery of our new models, the HM Series wedges, 950HC woods and 590DIH driving irons.   Shortly after you get this email we will be filling all present orders for the HM wedges.   However, the factory’s delays have forced the delivery of the 950HC woods and 590DIH driving irons to mid-May.  We’re very sorry about this because we know you have been waiting patiently for the new clubhead models.

  1. A number of new promotional aids to help in your work to sell custom fit clubs to your golfers will be finished and ready to help you in your work by mid-April.   Watch for an email around that time in which we will introduce these additional ways to help you increase your business.

And now on to the technical explanation of slot head vs thin face clubhead design technology.   As always, if you have questions about any areas related to the information in this technical discussion, please ask and we are always happy to answer.


Tom Wishon Golf Technology
The Leader in Custom Clubfitting Design and Technology


  1. Is it possible to design a wood head that has both slot technology as well as a variable thickness face? In theory wouldn’t that give you the benefit of both worlds?

    • TALEN:

      IT’s interesting you had the same thought after viewing the explanation of current slot head technology. I did too when I was in the middle of the shooting of this video. So within a week after I finished the video, I sent one of my production factories a model and a design for a driver prototype that not only had a variable thickness face, but had slots all 360* around the face AND a cup face construction with a special and very new type of bevel around the edges of the face. All these elements on the same prototype to help all work in combination with each other to try to see if the off center hit performance would be more consistent all around the whole face. None of these elements can make the on center hit performance any better than what any companies can do today. Since there is a limit to the COR of the face in the rules, and since pretty much all companies have been making drivers as close to that limit as what is possible in mass production, there is nothing more that can ever be done for on center hit performance improvement. But off center hit performance can be eeked a little bit better and better I think, so that was what came into my head as well after doing that slot explanation video.

      Testing on this prototype will begin in early August and we’ll see how it goes from there. My gut feel is that it will be a nice driver, but that it won’t be stunningly or remarkably better than what we can do with a non slot head with a cup face and variable thickness face such as in our 919THI.

      Thanks for your thought !!! I’ll laugh if you don’t mind and say that your message proves that “great minds run in the same direction” HA!!! Take care and best wishes in this great game,

    • Thinking of the head flexing, if a club just has a top slot if you hit high in the face and just the top of the club flexes then will a very small degree of lift angle be added from static to dynamic as the ball is struck? So if you have slot on the sides will this not add dynamic face open and closed angle on off center hits? So I would conclude your face flex to be better than rear of face perimeter flex for directional control of off center hits.

    • KEITH

      Using slots in the body of a hybrid or wood head to try to enhance the flexing of the face has some very limiting factors involved. First of all, it is highly doubtful that very many of the slot type heads even allow the face to flex inward more. LOTS of variables are involved there – how thick is the head from the edge of the face to the slot, how thick is the metal in the slot, what is the metal the head is made from and what is its final yield strength, and then a big one – if the point of impact is closer to the edge of the head nearer to the slot, the face can flex a little more than if the impact is down closer to the center of the face. And with impact up high or low, closer to the slot, now you lose ball speed from the impact being off center.

      Then you have what you are saying which is the fact that no slot head has its slots all the way around the outer perimeter surrounding the face because for one, it would be extremely difficult to impossible to make the head with a continuous slot running 360* around the outer edges of the face. So when you have areas of a slot that are separated by non slot portions on the top/sides/sole of the head, this stops the face from getting any sort of consistent help from the slots to make the face area flex inward anymore.

      For your question about impact occurring higher on the face and thus closer to the top slot on a head, no this flexing if it happens does not cause an increase in loft at impact in any way. Any shot hit high on the face of a wood will launch at a slightly higher angle but not because of the action of the slot. All wood faces are made with a specific radius from top to bottom on the face (and toe to heel as well ). Vertical face radius on a wood is called ROLL. Horizontal face radius is called BULGE. When the face is radiused from top to bottom, this automatically makes it so there is a little more loft at the top third of the face and a little less loft at the bottom third of the face. If you are talking about a typical 460cc size driver with a normal 53-55mm tall face, the top of the face can have +2 to even +3* more loft than it has in the center of the face where the loft of the head is measured. Likewise, the bottom of the face can have 2-3* less loft than the center of the face. How much more loft there is at the top of the face (and less at the bottom) depends on 1) how tall the face is, and 2) what radius of roll the designer used on the face. More roll radius = more loft change at the top and bottom of the face.

      So when you hit a driver high on the face, this is the biggest reason you see a higher launch – up there due to the vertical roll radius there is more loft. It has nothing to do with any supposed flexing of the face from any sort of slots. In truth, these slot head drivers and woods are mainly marketing BS. The few slot head irons do contribute to face flexing though because those slots on irons are fully through the sole or face which is different than the way the slot head drivers and woods are made. What makes the face flex the most is its thin-ness compared to the yield strength of the alloy from which the face was made. The ball is only on the face of a driver for 4 ten-thousandths of a second before it takes off. And the maximum a legal conforming driver face flexes is around 1/16″. All this means that by the time the impact causes any vibration or movement of the front top area of the head, the ball is already gone from the face. So even if the top or bottom of the head could flex a little more from a properly designed slot, it really could not have much of any effect because of the lightning fast moment of impact of the ball with the face.

      Hope this helps, TOM

    • I think the slot probably makes that part of the club stiffer as it will be thicker and like adding ribs to a flat sheet of metal. I picked up one of your 525 FD’s, I believe this has no roll and helps stop a low face hit being de-lofted. Its working well so far! (my sterling irons should also be built by january) Thanks for your time and effort on all your designs

    • KEITH

      How a slot works or if it even does depends completely on the yield strength and thin-ness of the metal in the curved area of the slot itself. The slot itself is really constructed just like a spring in that it is a 180* curve of metal. But if the wall thickness of the curved area of the slot is thicker and or made from a higher yield strength metal, then the slot acts like a stiffening brace to in essence do nothing to add or change the face’s flexing. If however the wall thickness of the slot is very thin and the metal is less strong but highly elastic in its modulus, then it could slightly act like a spring to flex. On the other hand, since none of the slots travel continuously 360* around the perimeter of the head, it becomes highly unlikely that any slot design could be doing anything to enhance the action of impact with the ball on the face. Thanks for your kind words of encouragement and the very best to you in this great game,

  2. Tom, why not just determine the load displacement on a clubface when placed in some kind of compression test bed apparatus that will simply apply a constant and concentrated load over various points on the clubface and allowing the face to flex freely?

    Perhaps a concentrated load of say 100# will adequately depress the clubface, and then move the load around the clubface to determine the differences. The amount of yield can be easily measured without resorting to dynamic testing and the resultant “smash factor” over the club face.

    In this way you can verify the differences between the slot and variable face thickness clubs. Controlled constant loading can be just as, if not better than dynamic loading results fraught with variables. Irons can be easily set up for such testing, but the drivers would have to be cut to isolate the driver face.

    • Steve:

      You do not have to do anything even close to what you are suggestion to determine for sure if the slot heads do anything to change the ball speed or the smash factor. Smash factor with a good launch monitor tells you everything you ever want to know about whether a slot head OR ANY HEAD TECHNOLOGY has the ability to increase distance for any golfer, for any impact location.

      Smash factor is directly correlatible to COR of the face. COR is directly related to the amount of face flexing and energy transfer to the ball. You cannot fool it. So if the ball speed divided by the head speed is 1.50, then whatever the face or head design is, is totally and fully optimized as good as it can ever be for distance. Period. if the smash factor is less than 1.50, then it is not. So whether you are talking slot head, thin face, cup face, this alloy or that alloy, smash factor tells everything you ever could want to know about the efficiency of the face for energy transfer, and from it, for distance potential.


    • Chris…. I understand the indirectly calculated correlation between Smash Factor and COR, but what I was suggesting is a direct way to measure clubface deflections over the entire clubface with an applied static point load. In this manner you can directly measure the deflections at any point on the clubface without resorting to hitting a golf ball subject to Hertzian deformation.

      Just press down with a concentrated load on any point on the clubface and see how much it yields, thus uniformly comparing the slot face and variable thickness face deformation under controlled loading.

    • Steve:

      We do pretty detailed and sophisticated FEA on face designs from lots of work in this area over the years so we are quite confident we know the amount of face flexing for our head designs. This is one of the ways we have been able to correlate the modeling to the results when we see the actual hitting tests with robot and Trackman. so here again, there is no real reason to change the way we look at these things because it would just come out with the same results.

      Thank you,

  3. Tom,

    Nice video about the slot technology. I was a bit surprised that you didn’t mention the PGA COR mandated limits in your video. It seems to me that, with the COR limits, design isn’t nearly as important as the limit itself. Now, if your argument is that slot technology won’t achieve the same COR as the variable thickness design, then I would understand that, but I didn’t hear that in the video.
    Definitely appreciate the website and all of the great information you provide.

    Kelly L.

    • Kelly

      Thanks much for your interest in viewing the video. The reason I did not clearly or unequivocably say that the slot heads do or do not have their COR up at the limit of the rules, or say specifically what their COR is, is because at the time of shooting the video I had not gotten any of the OEM slot heads to actually test to say exactly what these parameters are. But since then I have had the chance to test two of the OEM slot heads and on these two particular ones, the COR for robot hitting was calculated to be 0.79 based on a smash factor of 1.40. But I have to be very careful not to make this a sweeping generalization of ALL slot heads because I cannot say that unless I have the actual chance to test ALL slot head models. POint is, from my 29 yrs in head design and over 18 yrs now in high COR face design work, there just is no way that a slot on its own can allow the face to flex inward enough to achieve a COR up close to the limit in the rules of golf. Nor can it as I said, offer the same amount of face flexing over its entire face area because the slot that is supposed to be responsible for allowing the face to flex inward to achieve a higher COR does not extend all the way around the body of the front areas of the head near the face.


  4. Hi Tom,
    Very interesting article…but what is your opinión about the technology employed by Ryoma Maxima with both crown and sole flexing at impact.Last Christmas , the day after the night before I parted company with nearly US$2,000 and bought one of these, replaced the Crazy Boron shaft for a 55g Wishon S2S White and I am hitting it longer than any of my wide arsenal of drivers.Not only me but also my teacher and a scratch golfer who happens to be my nephew.
    In my opinión Ryoma with their system are fooling the 0.83 COR rule because it is conforming.Add to that that I made a mistake and clicked on the V type model which is the Tour versión.
    Best regards,
    Note : The technology is fully explained at http://www.tourspecgolf.com

    • JUAN:

      No matter what method of head and face design is used to try to increase the ball speed of a shot, the measurement of the smash factor by a good launch monitor tells you precisely how much energy and distance a head design can generate. Smash factor is the ball speed divided by the clubhead speed. For a clubhead with a precise 0.830 COR, the smash factor cannot be more than 1.495 when the ball speed and clubhead speed are both measured perfectly accurate.

      I have yet to see, and I have been told by many clubmakers who have also conducted smash factor hitting tests with the slot heads, that none of the slot head models can achieve a smash factor of 1.495. Yet the clubmakers also have seen that when they have a head with a thin face design that is actually a 0.830 COR measurement, the smash factor is ALWAYS at the limit of 1.495. So a slot head design will not generate more ball speed for any given clubhead speed as a well designed and perfectly manufactured thin face design with an actual COR of 0.830.

      The reason is because the slot head models only have the slot located near one area of the face. If the slot really does allow the face near the slot to flex inward more to increase the COR and increase the energy transfer of the clubhead to the ball, then why don’t the slot head models have the slot made to be all 360* around the face so the whole face could flex more? Where there is no slot on these heads, the face cannot possibly flex inward as much as it could in the area of the face close to the slot. But with a good thin face design, the WHOLE FACE can flex inward.

      I recommend you watch this video to learn more about slot head design compared to thin face, variable thickness face design – https://www.youtube.com/watch?v=lj-m6sIQuGc

      Thank you,

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