Force and Golf - Part III

In part III, I will discuss the role that force plays in equipment and clubfitting.

Again, let's go back to our golfers I have used as examples of a 'full sweep' release (Shane Bertsch).



And here's our 'snap' release in John Senden.




SHAFT FLEX

I feel Tom Wishon has a pretty good tool to help figure out what type of shaft a golfer needs. You can check this out at:

http://forums.wishongolf.com/shaftfit/ShaftFit.asp

The components that they ask for are:

- Clubhead Speed
- Downswing Transition
- Wrist-cock release position

The only thing about this is that it recommends Wishon's own type of shafts, but he does have a variety of them in different characteristics.

The other thing we have to remember is that when we 'tip trim', it makes the shaft stiffer and will make the ball launch higher with more spin.

But, what we'll see is that the faster the clubhead speed or the harder the transition or the later the wrist cock, the stiffer the shaft tends to become. The only thing that has a bit of variance to it is the tip trimming.

I tell people this:

I can hit some tremendous shots with a shaft that is too weak of a flex for my golf swing. But, the issue is the consistency of being able to to hit those shots. That's because it becomes more difficult for me to time when that shaft is going to kick. IIRC, Dr. Sasho Mackenzie (http://people.stfx.ca/smackenz/publications.html) states for every 1 cm of that shaft kicking, it will close the face by 0.7* and add to the dynamic loft. That's in part why we tend to hit it higher and hook shafts that are too weak for us. The shaft kicks too much, too soon for us to handle.

Thus, somebody like Senden with the snap release, that club is accelerating much quicker than Bertsch'es full sweep release. Even if they were swinging the same clubhead speed, the difference in acceleration has to be accounted for. Thus, somebody like Senden needs a stiffer flex shaft to help the club not kick too much, too soon. And Bertsch needs a weaker flex so he can get the proper amount of kick.


WEIGHT


In the past, we've generally seen Tour golfers with more of a snap release have heavier swingweights. And that's typically what clubfitters do for golfers.

While the principle was somewhat logical, what we now know about MOI matching, I think we have a far superior alternative.

Swingweight of course...is a measurement of the dynamic weight of the club when we are swinging it.

MOI (for these purposes) measures the amount of force required to swing the club.

So swingweight is measuring the gravitational pull of the club as we swing it. But, MOI (for these purposes) is measuring the force required which is Mass x Acceleration.

Since I purchased my MOI machine, I am simply amazed at the accuracy of readings it gives. For instance, I hit my Wishon 555C 4-iron extremely well, but stuggled with the 3-iron. Finding out, the MOI for the 4-iron was 2,702. The 3-iron was 2,625 (they should be +/- 5 from the base MOI). I put some lead tape on the 3-iron and started hitting the 3-iron instantaneously better.

I also have a set of Mizuno TN-87 irons. I always struggled with the 8 thru PW, but hit the 3 thru 7-irons quite well. When I measured them on the machine, the 3 thru 7-iron were all in the range between 2,727 - 2,740. When I measured the 8 thru PW, they were in the range fo 2,655 - 2,670.

The concept of using swingweight was a good attempt as well as making the swingweight heavier for 'snap' release swings. If the club is too light for a snap release swing, the club could be accelerating too quickly for that light of a weight and then the golfer may wind up making a drastic adjustment to their swing.

But, since we have ways to measure the MOI, we can get a more accurate and important measurement.

We also have to remember this...I can have 2 different Mizuno MP-68 6-irons. I can make them the the same length and the same exact swingweight. But, they can have very different MOI readings.

I could simply put a heavier shaft in one of the 6-irons and backweight it enough until the swingweight matches the other 6-iron with the lighter shaft in it. But, the mass in both clubs is different and it could possibly affect the acceleration quite a bit as well.

MOI matching does make you hit the ball great. But, what it does is it helps get rid of those clubs you always seem to not hit as well as the rest of the clubs in the bag. Why? Because you don't have to alter your swing to get the right amount of force required to swing the club.











3JACK
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