Lessons from
ShaftLab
Dave
Tutelman -- October 20, 2007
In
the early 1990s, the R&D lab for TrueTemper shafts came up with
a
measurement tool they called ShaftLab.
Its purpose was to find out more
about how golfers bend the shaft during the downswing. It did that job
admirably. In fact, it created such a stir that TrueTemper decided to
market it to clubfitters as a high-end shaft-fitting tool. They have
indeed sold some, though it is hardly common to find one in a custom
club establishment. It is still too expensive. Also, it is
limited
in function for the price; it is closer to cost-effective as a research
tool, which is how it started its life. At the 2017 update of this article, ShaftLab has long been discarded by TrueTemper.
This article
covers what
we have learned from ShaftLab. I am an engineer, and I wrote the
article from an engineer's point of view. There aren't any equations.
But if graphs throw you for a
loop, you may have trouble with it. For you, the conclusions
are stated concisely in the Executive
Summary on this page. But understanding how we come to these
conclusions will require wading
through the graphs and the physical reasoning.
Contents
- Executive summary. Just
the facts, ma'am.
- What
ShaftLab is. How it works, what it can do, and what it can't
tell us.
- What
TrueTemper learned. In 1994, Ed Weathers of TT wrote an
article for Golf
Digest explaining what he believed ShaftLab taught us about shaft bend.
- Lessons from the data. We
can deduce things from looking at the traces, including lessons that
Weathers' article did not cover.
- More lessons from the data.
The ShaftLab literature purports that a trace constitutes a downswing.
That turns out not to be true. We look at the implications of this new
information.
- Raw data. Tables of results, and the traces themselves.
Executive Summary
This
section simply states the lessons that ShaftLab has taught us. To learn
how ShaftLab works and how we gleaned these lessons, you will have to
read the rest of the article:
- Just about
all swings of real golfers fall into one of three profiles:
- Double
peak
- Single peak
- Ramp
- A closer look at what ShaftLab is really measuring reduces this to two profiles useful for fitting:
- Clubhead
speed is not a reliable indicator of how much you bend the shaft.
- The
biggest factor in shaft fitting is maximum bend of the
shaft. This
seems to be TrueTemper's conclusion; I'm not sure I agree with it.
- Changing
shaft flex does not increase your clubhead speed.
- "Kick
velocity" does exist, but it isn't a very large component of clubhead
speed. For good swings (like the pros'), kick velocity is at less than
5% of their clubhead speed. More surprising, it doesn't affect clubhead
speed; things that boost kick velocity retard angular velocity from the
hands by about the same amount.
- At impact, just about every
golfer has the shaft bent with clubhead lead (shaft bent forward) and
toe droop.
- Bend at impact is influenced by a lot
more than just "centrifugal pull" on the center of gravity of the
clubhead.
- Frequency
is useful as a measure of shaft stiffness, but don't read too much into
it. For instance, it is not an indicator of the "free response" of the
shaft during the downswing.
- At impact, the net bend
of the shaft is nowhere near the target line.
- The
biggest bend during
the swing is between toe-up and lagging. For most swing patterns it
occurs about 100msec before impact, but earlier for a single-peak swing.
Last modified
11/07/2017