EQUIPMENT LESSONS FROM MY TRIP TO OHIO At the RSG-Ohio Open in September, I learned a bunch of things about golf clubs. I'll try to fold them into the next issue of the Club Design Notes, but let me put them down and post them while they're still fresh. I might add that most of these come from a wonderful talk with Jeff Summitt, the co-author of "Modern Guide to Shaft Fitting", one of my favorite golf club theory books. Thor managed to get us an "interview" during our Dynacraft tour, and Jeff sat and handled the group's questions (mostly Rick Nelson's and mine) for almost an hour before he had to leave for the PCS convention. Many thanks, Jeff, if you're reading this.... DESIGN NOTES: - Does flat-frequency matching (as opposed to, say, a "Brunswick slope" frequency match) have any validity? Jeff Summitt thinks that most golfers will not find flat frequency easy to hit, though a few might. Those that might are probably new golfers with no "feel concept" to unlearn, but even they will probably find a sloped frequency better. If, OTOH, we talk about a REDUCED-slope match, Jeff is more optimistic. It's not clear that most golfers need as steep a slope (over 4 cpm per club) as you get from Brunswick shafts, or from trimming most steel shafts to the manufacturers' recommendations. A smaller slope, though not the zero slope of a flat-frequency match, might be good for a lot of golfers. According to Jeff, the reason that flat-frequency is probably erroneous is that frequency is measured with no tension on the shaft; it's hanging immobile, except for the vibration being measured. OTOH, during the swing, there's considerable tension coming from centrifugal force, which tends to stiffen the shaft. The additional length and clubhead speed of the longer clubs magnifies this stiffening effect, so their raw frequency measure should be lower (more flexible) to allow for this added dynamic stiffening. (I haven't done the math, so I don't know yet whether I buy this completely. The longer clubs also have heavier heads, which should contribute to the centrifugal stiffening. So if centrifugal stiffening is a valid effect, I'm not sure which way it should slope.) - I finally got a chance to ask Jeff about the role of torque in the DSFI. Torsional stiffness contributes to the DSFI "stiffness", but not as much as lateral stiffness. (Lateral contributes more by an order of 2.5. That is, DSFI is a function of the square root of lateral stiffness and of the fifth root of torque.) Jeff said its contribution to the DSFI is in "feel", but not in accuracy or distance. If you make a shaft laterally stiffer and relax its torque to give the same DSFI, it may feel the same at impact. But that says nothing about the way torsional "release" affects the clubface angle -- the way lateral "release" is well-known to affect it. So I still recommend that, if you can afford it, choose a torsionally stiff shaft and get the right "feel" from the lateral flex. That means you should choose the shaft by frequency, not DSFI. The way I do it is to find a steel shaft with my DSFI target, and try to select a shaft with the same frequency. (Of course, I try to derate this by the length and weight I expect of my finished club.) - With a clubhead mounted, most shafts vibrate torsionally in the vicinity of 800 cpm. (This corresponds to the lateral vibration frequency we all know and love at around 250-300 cpm.) This gives a "time constant" of about 10 milliseconds. While considerably shorter than the lateral time constant of about 30 milliseconds, it's still more than an order of magnitude more than the time the ball spends on the clubface. Therefore, most of the conclusions about "the shaft is a string at impact" apply to axial rotation as well. - I had an opportunity quite a few times over the course of the weekend to swing drivers with way-oversize heads (titanium, aluminum, duralumin, and stainless). With most of them, I tended to slice the ball, which is not my normal tendency with a driver. (My bad drives are normally pushes or duck hooks.) Somewhere along the way, someone -- don't remember who -- offered the following plausible explanation... The main benefit of oversized heads is extreme peripheral weighting. This increases the moment of inertia, and therefore makes the club more forgiving of off-center hits. BUT... it also increases the club's resistance to the wrists squaring up the face, causing a slice. If you think about the complete role of MOI, this makes sense. - There has been some debate (including debate in RSG) about where to place the fulcrum about which you measure the moment of inertia of a club when MOI-matching a set of clubs. I have always used the butt of the club, but I put this question to Jeff. He said it should be the hinge between the arms and the club during the swing -- naturally! The surprising part was that he says photographic studies show this varies from golfer to golfer. For some, it's the wrists (my conjecture, which justifies using the butt). For many, it's the point at which the grip overlaps or interlocks, which puts it 3"-4" down from the butt. PRODUCT AVAILABILITY: - GolfWorks is going to be adding square-grooved irons to its 1997 line. Now I'll have an alternative to Golfsmith, which until now is the only clubhead vendor where square grooves are the default. Unfortunately, Dynacraft is not intending to do the same. - Neumann leather grips are back! GolfWorks has them in stock. (They've been unavailable for about a year now. I'm not crazy about them, but I know some others are. Terry Horn take note!) - "The Modern Guide to Shaft Fitting" is now out of print. They will begin printing only after Jeff Summitt has had a chance to update the information in it for a new edition. He estimates this as taking at least a year.