A Fitting Question
TECH NOTE 23: A times I think fitting is a bit of a "black art". There are number of fitting approaches out there. Dynacraft has their DSFI approach while Golfsmith calls theirs the RSSR system. These systems use the golfer's clubhead speed as the main determinant of how stiff the shaft should be. A number of shaft manufacturers have likewise put out charts that relate clubhead speed to stiffness. The Dynacraft approach goes a step further and includes the shaft's torque in their computations of best fit. Just what is trying to be accomplished with these various approaches? I assume were trying come up with a shaft that the golfer can hit the best. Does that mean the shaft will be perfectly unloaded at impact? Does clubhead velocity have anything to do with this? The shaft does not bend because of its velocity. It bends because of its acceleration. The shaft bends because of a force and remember that force equals mass times acceleration not mass times velocity but the two are certainly related. A guy swinging 120mph most likely has more acceleration than a woman swinging at 70mph. Take a swing like Doug Sanders or Allen Doyle and compare it with an Al Gieberger. They may both have similar swing speeds but it would seem Al has less peak acceleration.
There are various approaches in the fitting systems to account for this acceleration. True Temper has its Determinator which records peak acceleration during the swing. There's the Tempo Trainer, which measures the club head speed as well the time from takeaway to impact. These give hints at acceleration and can be used to tweak the fitting process. There is one device out there that actually records a continuous acceleration during the swing. This strikes me as the ideal way to determine the proper shaft stiffness. It has a built in algorithm that determines the proper frequency for the golfer based on his acceleration profile. This sounds great but it seems to occasionally come up with some really weird results. I was fitted at 295cpm at 44". This club is almost unbuildable, being in the triple X category. I did succeed in building the club by finding the stiffest steel shaft I could, over tipping it and adding a 2" butt extension. The club was indeed unhitable. I've also seen fits down in the 180-cpm regions for guys with pretty hefty swings. However, what I hear from the majority is that it does a pretty good job. The approach makes a lot of sense to me.
Having gotten the stiffness of the shaft just right there is still some weird things that can happen. This is where my confusion comes in. For instance I've built a number of fairway woods using the Large Marge head from Tour Golf. This head looks something like the old Big Bertha, as you might expect, but it has a very nice additional feature. It has a weight port in the sole of the club head. All of the fairway woods I built were very well liked. I got a number of "best club I ever hit" responses. On the other hand I've built a few Large Marge drivers trying my best to match the fairway wood I had previously built. Every damn one was just awful. I have no explanation. A friend built a driver for customer. His carefully picked the frequency and aligned the spine. He used a driver head from Golfsmith. I forgot which one. The club was absolutely unhitable by everyone who tried it. He went back to the shop, pulled the head and replaced it with a different style Golfsmith head. Everything else remained the same. Same swing weight, same frequency, same length, and same shaft alignment. All agreed the new club was the best thing since sliced bread. How do you explain something like that? I'm convinced there's a whole lot about the fitting process we just don't understand. At least I don't understand it.
Some years ago Fenwick demonstrated a technique they called "modal analysis". With an actuator attached to the middle of the shaft they forced it to vibrate at its first, second and third harmonics. By monitoring the vibration patterns of the head they claimed they could tell if the shaft and head combination were compatible. They claimed from their analysis some combinations would be absolutely unhitable while others would be great. It sure sounded to me like they were onto something. They actually published a few lists of typical driver heads and which Fenwick shaft was best suited to the head. It sounded like a great idea but it seems to have vanished.
Well if any of you out there have a few answers I love to hear them. Most fitting systems seem to work fairly well but why do we sometimes get these weird results. I would think the ideal approach would be to have a whole bunch of test clubs for the customer to try out. I'm sure many of you have similar stories.