ShaftLab - 1
Let's start by repeating the brief
history of ShaftLab given earlier.
the early 1990s, the R&D lab for TrueTemper shafts came up with
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.
after this article was first released (2007), TrueTemper stopped making
ShaftLab available. They discontinued it, both as a product and for
in-house fitting use. (I don't know if they still use it for research.)
is an instrument that allows measuring and recording the shaft bend
during the swing. In order to do that, TrueTemper engineers rigged a
golf club to measure its own bend and send the reading to a computer.
The computer records and displays the shaft bend in a variety of ways.
Once TrueTemper "product-ized" the ShaftLab, it added software to
interpret the recorded bend and prescribe a shaft of a particular flex
for the golfer.
That was very brief. Let's go into
some more detail.
How it works
let's look at the instrumented golf club.|
TT engineers attached four strain gauges to the shaft at 90º
intervals. A strain gauge is a device whose electrical properties
change when it is stretched or compressed. When a shaft bends, the
outside of the bend gets longer and the inside gets shorter. So a
strain gauge on the outside of the bend will experience stretching, and
one on the inside of the bend will experience compression.
strain gauges on a ShaftLab club are arranged so that two measure
lead-lag bend (the red ones in the picture) and the other two measure
toe-heel bend (the green ones; only one is visible, the other being
hidden behind the shaft). For instance, if the shaft experiences "lead"
bend, the red strain gauge on the left is compressed and the one on the
right is stretched. This produces an electrical differential that is
sent to the computer.
How is the signal sent to the
far (as of 2007), the club is tethered to the computer by a flexible
cable. There have been many user requests to use some sort of wireless
technology, but so far TT has not seen fit to do the modification.
the computer gets two sets of signals from the golf club:
the amount of lead-lag bend, and the amount of toe-heel bend.
"sees" the bend as a point on two-dimensional graph. For instance, the
red triangle in the X-Y graph at the left represents a bend that is
considerably toe-up and somewhat lagging.
computer's job is
to save these points often enough to give a smooth curve of the bend
during the swing. I think they sample every millisecond, but it may be
every 2 milliseconds. The result is that the computer can plot the
shaft bend variation with time for as much of the swing as you'd like.
As the software comes from TT, the plot is designed to cover the downswing and looks
blue trace is the heel-toe bend, and the red trace the lead-lag bend.
The swing is that of tour pro Peter Jacobsen. TrueTemper includes with
the package the ShaftLab plots for a variety or tour pro swings. When I
had an opportunity to play with ShaftLab, it was the 1999 edition -- so
I have the pro swings from that product. I'm sure it is a different set
of pros today.|
We can see from the graph that
Jacobsen has a
fairly long downswing: about 570 milliseconds from start to impact. (Later we will learn this isn't exactly true.) If
we didn't read this from the graph, we could see it at the top of the
page, where the software tabulates a few important parameters of the
this form of plot is certainly interesting, there is another plot that
is at least as informative, that doesn't come with the ShaftLab
software. (I used the Excel spreadsheet's plotting capability to
generate it from the ShaftLab graph for Jacobsen.)
the right is a time-lapse picture of the X-Y plot we saw earlier on
this page. The blue numbers next to the X-Y points are the milliseconds
before impact. So we are tracing the two bends -- toe-heel and lead-lag
-- for the 570 milliseconds of Jacobsen's downswing. A few points worth
noting, which are typical characteristics of a pro swing:
first 400msec of the swing (more than 2/3 of the downswing), all the
bend is toe-up, with very little lead-lag bend at all.
swing then turns into the [Toe-up, Lag] quadrant of the graph.
- With a little less than 100msec left to impact, the total bend peaks, a combination of toe-up and lag bend.
only the last 50msec do we see the bend get to toe-down, then show some
lead. The actual direction of bend here is very chaotic. We will go
into the reasons below, but you can also see this from the canonical
ShaftLab output graph above.
in the ShaftLab product?There are two interesting
things to say about the product that TrueTemper ships:
1. The clubs:
The instrument comes with four clubs: a driver and a 5-iron each in
right-handed and left-handed versions. All the swings for fitting are
made with these clubs. The shafts are all TrueTemper S-flex steel
shafts, so they are very predictable from sample to sample. Therefore
every ShaftLab trace you will see should be comparable, even if taken
on different ShaftLabs.
2. Fitting software:
ShaftLab is sold as a high-tech fitting tool. It would be nice if it
lived up to that billing. Unfortunately it falls short in several ways:
consulting for a ShaftLab owner. His approach is to use the same
parameters the ShaftLab software uses for fitting, but he converts it
into a frequency rather than a TrueTemper shaft model. That way, he can
select from any shaft he wants. It would be nice if ShaftLab did this.
But an obvious conflict of interest prevents TT from adding this
capability. So you are basically paying a high price
$6000, down from several tens of thousands a few years ago) for a
device that tells you to spend more money with TrueTemper.
important, ShaftLab is less a fitting tool than a sales tool for
TrueTemper shafts. If it were a fitting tool, you would expect the
fitting recommendation to be by specification. Instead, it consists of
a list of shafts, all
made by TrueTemper, that would be acceptable for the
golfer whose swing is being measured.
everything about the swing is taken into consideration in making the
recommendation. The only aspect of the shaft that TrueTemper fits is
the bulk stiffness. Think "butt frequency".
ShaftLab can and can't tell usLet's
start this by discussing the assumptions
Do I agree with these
assumptions? Some yes, some no.
- The shape and size of
the shaft bend trace is sufficient to tell you what you need to fit the
swing to a shaft.
shape and size of the shaft bend trace does not vary with club length.
(The instruction manual does have graphs to scale the recommended
frequency with club length. But this just covers the standard
frequency-length slope, not the possibility that the golfer would
actually swing the club differently if it is longer or shorter.)
shape of the shaft bend trace will not materially change if a different
shaft is used. The only thing that will change is the size. In other
words, the trace magnitude scales
with shaft stiffness.
One final limitation. It's
not a flaw but, given all the things that ShaftLab can do, it's worth
mentioning it can't
do this. And, while it is not important for fitting, it is important
for ShaftLab's role as a research tool. ShaftLab separates the bending
into toe-heel and lead-lag, but it can't relate that to in-plane vs
out-of-plane. A few pictures
(from Jack Nicklaus' book "Golf
to show what I mean...
assumption says that shaft profile does not matter. But it does! These
days, driver fitting is done with profile and weight as much as overall
flex. So ShaftLab at best is really only doing part of a fitting: the
overall stiffness of the shaft.
- This assumption is
contrary to my observations. I have seen golfers who have a definite
ideal club length, and their swing mechanics change for longer clubs.
At the other end of the spectrum, I know some very tall golfers whose
swing mechanics break down if the club is too short; it hurts their
posture. I have never tested this assumption on a ShaftLab directly,
but I suspect the swing changes due to seriously wrong length will
affect the parameters ShaftLab uses to recommend a shaft.
believe this assumption. We'll discuss
it in a lot more detail as we get into the lessons ShaftLab
the start of the downswing, the club's heel-toe plane (green line) is
aligned in the same direction as the swing plane (blue line).||At the
moment of impact, the clubface has squared and the lead-lag direction
is aligned with the swing plane.|
At the start of the ShaftLab trace, heel-toe bend is the same as
in-plane bend. This continues for a while into the downswing. But as
soon as interesting stuff starts happening to the shaft bend, this
relationship ends. Then, at impact, lead-lag bend is the same as
in-plane bend. But this is not true even a few milliseconds either side
of impact. In order to relate shaft bend to any analytical model, it is
important to know the in-plane and out-of-plane bends, rather than
heel-toe and lead-lag bends. ShaftLab cannot tell us this.
line: I think ShaftLab is one of the best fitting technologies out
there. But it is still far from perfect.