Dave Tutelman --
August 19, 2007
Updated November 21, 2015
Updated November 12, 2016
Having established the principles
I intend to use in evaluating single-length iron sets, this page is a
compendium of iron sets on the market, measured against those
Bear in mind that this study is done using computer modeling, based on
the published specifications of the clubs. I do not
have the resources to do a lot of testing with real clubs.
On this page, I have a brief description of each of the products on the
market that I have had a chance to analyze. Let me stress that I am
analyzing them based on their published specs and computer modeling. I
have not actually tested the clubs in the flesh. In evaluating range
and gaps, I am using the same golfer model that I used on the first
page of the article.
Let's start with a table that summarizes the descriptions. There is more detail, including a gap graph, in the descriptions
themselves. They are listed in roughly chronological order of their
appearance on the market.
- The golfer has a clubhead
speed of 80.1 to 80.3 mph, based on the clubhead weight. (Since all the
models in late 2016 were in the low 270s of grams, the speed spread is
- The angle of attack is zero, and the
dynamic loft is exactly the same as the nominal loft of
the clubhead. The assumption is that
the novice golfer
is the most likely target for a single-length set. Note:
- If you have forward shaft lean, you will tend to incur
more long-iron droop.
- If you have a higher clubhead speed than 80mph with a
7-iron, you will tend to incur less long-iron droop.
most (not all, but most) better players have both shaft lean and higher
clubhead speed, the effects tend to oppose and to some extent
cancel each other out.
(196 - 93)
(190 - 102)
longer in business
(193 - 93)
(191 - 96)
irons are hi-COR
(190 - 99)
hybrid or 5 iron choice
|King F7 One
(197 - 96)
irons are hi-COR
Only assembled clubs
|King Forged One
(185 - 96)
(183 - 96)
- Range is from
the lowest-loft club through the gap wedge. Sand and lob wedges are not
usually used as full-swing clubs (though they may be). Moreover, it is
common for SW and LW to be purchased separately, not part of the set of
irons. So I have removed the SW and LW from the comparison of range and gaps.
- My original
plan for the table was to boil down the gap shapes to flat, proportional, and
(i.e. - anti-proportional). In trying to classify the gap graphs, I realized that gap shapes are
a little a bit like clouds; different people may conclude
differently what they look like. So I'm putting a thumbnail
of the graph itself. I'll interpret the shape in the detailed section
on each iron.
But it is instructive to look at how the early entries
did a good job of flat gap (One-Iron) or proportional gap
(iMatch and Pinhawk). Some of the later entries seem to have just
rushed in with a loft lineup they were familiar with, and wound up with
somewhat dysfunctional gaps.
The descriptions contain more detail than you can put in a table like
the one above. The most important part of each description (at least
for me, your mileage may vary) is the distance and especially gapping
information. It is the most significant difference from model to model,
in terms of what it can do for (or to) your game.
Each of the gap graphs shows the gap (the bold, red line) using the
assumptions discussed above (about 80mph clubhead speed and zero AoA). It
also has a plot of a perfectly flat gap lineup and a proportional gap,
each to give the same range the set of irons has.
One Iron Golf has been in the
business of single-length sets for years, long before it was
fashionable. They date back to the 1990s, and are mentioned in each of
my articles on the subject.
Look at how well their set tracks the constant-gap ideal. Only two of
the eight gaps are more than one yard from the constant-gap line.
The heads are modest cavity-back designs, game improvement clubs but
not extreme. The shape and cosmetics are not current, more like 15-20
years ago. They have a constant 3.2mm offset for all clubs.
The company only sells assembled sets of clubs, not components. They
custom build the clubs, where the parameters of customization are:
The bottom line for me: if these heads were on the market as
components, I would be interested in them. I'm not crazy about
their fitting method; it only scratches the surface of what a real
clubfitter does. But it is still a lot better than buying off the rack.
- Length, based on your wrist-to-floor measurement.
- Shaft flex, but only selected from TrueTemper steel
shafts. They don't say how they infer your proper shaft flex, nor which
TT steel shaft[s] they use. The words on their web site suggest they
align the spine, but I have never seen a TT steel shaft with a spine
big enough to bother aligning.
- Grip size: standard or 1/8" oversize.
golf is no longer in business, and the iMatch model is not
available. I couldn't even find one used on eBay.
So this is included only for historical interest. That, and the very
nice approximation to a proportional gap lineup. Except for one gap of
droop at the low-loft end (which we understand and sort of expect),
this does very well at proportional gapping. It tracks the dotted green
curve (the ideal proportional gap) rather well.
At the time the iMatch was being designed (2008-2010 IIRC), I was
working with Tim Hewitt, the architect of iMatch, on another project. I
had occasion to discuss iMatch with him, and he took a real systems
approach to the set. He did not feel constrained by what "the market"
was doing, and went for larger loft gaps at lower lofts -- which is
exactly why this gap graph is so attractive.
Pinhawk was introduced by Value Golf, and is now sold by Hireko as well. Its loft lineup is
very similar to the iMatch (5° loft gaps at the low-loft end and 4°
loft gaps at the high-loft end). As a result, the gap graph is very
similar to the iMatch. It does a good job of tracking proportional
gapping, except for one drooping gap at the low-loft end and one gap a
couple of yards high between PW and GW. All in all, a well-executed
The heads have a modern game-improvement cavity. The offset is a
constant 3mm. If I were building a set for myself or a friend, my
search would certainly begin here -- and likely end here as well.
The Sterling single-length irons were
a joint project of Jaacob Bowden and Tom Wishon. Bowden heads up the
Sterling brand, which sells assembled clubs custom-fitted. There is no
indication on the site how the fitting is done, so I have no comment on
the quality of fit. Wishon retired from the component business soon
after the Sterlings were complete. He sold his brand and products to
English component supplier Diamond Golf International. So it will be up
to them whether and how to offer the Sterling heads.
As with many Wishon designs, there is some innovative technology
involved to make it work. He also chose a 4°/5° loft split, like iMatch
and Pinhawk. But unlike those predecessors, he put the 4° at the
low-loft end. At first look, I thought the gap pattern would be a dysfunctional
distaster. But Tom did something pretty clever; he put high-COR ("hot")
faces on the 5- through 7-irons, giving them about five more yards of
distance. This "pre-accelerates" them, so they are already somewhat
compensated for low-iron droop. The resulting gap graph looks a little
humped, but it never wanders very far from a flat gap. Very clever, and
Bowden sent me some corrections too late to make it into the
calculations. I hope to include them in the next iteration of this
article. In the meantime, here are some of the things I'll have to
address next time:
- The hot faces are .83 COR, rather than
the .82 I used in my modeling. That will probably increase the 8-gap by
less than a yard, and the same for the range.
- They have introduced a 4-iron (but not a 4-hybrid).
|I went ahead and plotted what the gap shape would
look like if all the Sterling irons were a simple cast face, not a thin
flexible face. The resulting graph shows a 5-yard discontinuity between
the 7-8 gap and the 8-9 gap. Those two gaps are identical for the real
Sterling irons, which contributes to the flatness of the overall shape.
And it is explained completely by the fact that the 7-iron is the
"longest" club in the set with a hot face. So that bit of technology
The head itself looks closer to a blade than a game improvement club;
the cavity is pretty shallow. But there is a lot of weight down low, so
it should be easy to get the ball airborne. The offset is progressive,
but a very mild progression from 4mm to 2.5mm.
A few attractive and unusual features of the product:
- You can replace the 5-iron with a 5-hybrid matched to
the rest of the set.
- The bodies of the irons are soft carbon steel, so
customization by bending is easy, and over a greater range than other
single-length irons (which are cast 431 stainless steel -- still
bendable, but not as easily, or over as great a range). Of course, the high-COR faces are
not carbon steel, but they don't have to be.
Diamond Tour Golf, a supplier I often do business
with, introduced a single-length set. They call it In1Zone, consistent with the
InAZone brand they use for other recent clubheads. Since I like many of
their products, I looked forward to this. Sorry to say, I was
The loft lineup they chose is the same "modern" loft lineup they use
for their conventional-length irons. And that lineup is the result of
the Loft Wars,
with the smallest loft gaps for the lowest-loft clubs. As you would expect,
the result is a dysfunctional gap shape, with the "long" irons having
less than half the gap of the "short"irons.
The heads themselves are attractive, and I'm sure they are competent;
Diamond Tour would do no less. They look like modern game improvement
clubs, and have a constant offset just over 3mm. The #4 is a hybrid,
and you have a choice of hybrid or iron for #5. If the gaps were
reasonable rather than dysfunctional, I would consider them
a contender for "best in show".
Mar 1, 2017) I just received an email from Roger White, who tells me
that the In1Zone clubs are very easy to bend, especially considering
they are cast stainless steel. While he agrees that the gap lineup is
dysfunctional off the shelf, it is not hard to fix. He now has a set
consisting of 5-iron through sand wedge, which he has bent to 5° loft
increments from 20° to 55°. That required a bend of 4°, a bend of 3°,
and all the other bends 2° or less. His report of distances suggests a
very workable gapping between 10 and 15 yards. There is still a slight
tendency towards droop; the 5-6 iron gap is 10 and both wedge gaps are
15. But that is still a substantial improvement on the way the clubs
come from the manufacturer.
King F7 One
In the Fall of 2016, Cobra announced that they would
be making the new single-length irons for Bryson DeChambeau, and that
they would be a regular product offering as well.
Unfortunately, there were no specs on the Cobra site, just hype. It
took the MyGolfSpy.com site to post
information useful for analysis. But there was enough information there
to start, and here are my conclusions.
I didn't expect much from the set once I saw the loft lineup. The loft
gaps, starting at the 3-iron and working toward the gap wedge, are
3-3-4-5-5-5-5. That sounds like a prescription for a dysfunctional gap
shape. When I did the work of computing the distances, the shape was
peaked, with a very sharp maximum gap between the 7- and 8-irons. To
the right of that (all those 5° loft gaps), it follows a very nice
proportional shape. But as soon as you get into the less lofted irons
also having smaller loft gaps, the distance gaps drop like a rock. We
have four clubs worth of droop, not just one.
BTW, this happens even though the 4-iron through 7-iron have flex
faces, increasing the ball speed. The long-iron droop would be even
worse without it. The problem arises
from the consequences of the loft wars coming home to
Will they sell? If the single-length irons have a significant market,
they should sell very well. We have only one big-name OEM in the
market, and an interesting pro using and endorsing them. They look
good, and the range is a creditable 101 yards. And let's not forget
that the OEMs have been selling conventional-length irons with
dysfunctional gaps for over a decade; people don't seem to know nor
care. So yes, they probably will sell.
King Forged One
On the same page at MyGolfSpy.com
is the club that
DeChambeau is more likely to be using -- if he is using a generally
available product at
all (and not something completely custom). Cobra seems not to be making
as much noise about the Forged One club, but it is also a single-length
shape is closer to flat than peaked. That might be guessed by the loft
lineup. The loft gaps are 3-3-4-4-4-4-5; that would suggest a serious
long-iron droop (and there is), but flatter across the rest of the set
(and it is). Of course, that gives a more modest range of 89 yards. Of
course, given that it is a forged "players' club", we might expect the
golfer to have more clubhead speed -- so neither the droop nor the
reduced range would be as much of a problem. A strong player with lots
of clubhead speed might experience a relatively flat gap, not at all a
If you need any
further evidence that the Forged One and the F7 One are for different
markets (player's vs game improvement) you need only look at the
offsets. The F7 One has the largest offset progression of any
single-length set I evaluated in 2016, going from 5.5mm for the 3-iron
to 1mm for the gap wedge. Compare this with the Forged One, where the
offset is much smaller, and only progresses from 2mm to 1.3mm over the
Integra is now in the game. They are a respected component company; I
know from experience that their products are of good quality. They
are available through Value Golf, the company that brought you the Pinhawk single-length irons as well.
the i-Win suffers from the loft wars -- not as much as some other set
perhaps, but the long-iron gaps are still 2° less than the short-iron
gaps. (Their pattern is 3-3.5-4.5-5-5-5.) The result is a peaked gap
curve, with a proportional gap below the 8i and dysfunctional gaps from
5-iron to 8-iron.
offsets are very progressive (6.6mm to
2.3mm), indicating a game-improvement target market. That is even moe
than intuition might say, because the set begins at the 5-iron. Given
that the set has
only seven clubs, the range of 87 yards is not bad.
As usual, the technical details are only interesting if you are
interested. If you're not, you shouldn't lose any understanding of the
results by not reading this.
Obtaining distance from impact parameters
This part is relatively easy. I used Max Dupilka's Traj30 program
to compute the trajectory. It takes impact parameters and gives a lot
of output about the ball flight. The only output I used was the carry
distance. The inputs were:
- Clubhead speed:
see below for how this was determined. But it doesn't much matter. The
clubhead speed model gave only a 0.3mph range -- from 80.0 to 80.3 --
over all the clubs considered. So the effect was negligible.
- Clubhead mass was taken directly from the specs for the club.
- Loft was taken directly from the specs for the club. (Remember our assumptions of zero AoA and shaft lean.)
- COR was taken to be .77 for most of the clubs. Where a "hot" face was involved, I took a guess based on how insistent was
the advertising about ball speed. There were only two such models, and
even then only for the less lofted clubs. I used .82 for the Sterling
and .80 for the Cobra F7 One.
Perhaps total distance would
have been better than carry distance, but I don't have a program that
can give total distance. Actually, it is hard to compute -- starting
with the fact that it is strongly dependent on the characteristics of
the ground where the ball lands. The runout can be very different for a
hard fairway and a soft green.
again, there is an argument that carry distance is the proper measure.
Most iron shots carry a strategy based on where the ball lands.
Usually, when an iron is used, the goal is to land the ball at a
particular spot on the green. So one could argue that carry distance is
exactly the right measure.
A word about the choice of program
Traj30 gives pretty accurate results for irons. I'd have preferred to
use TrajectoWare Drive, but we are still in the experimental stage when
it comes to spins higher than 4000rpm. It is fine for driver
(and maybe some long irons), but we don't trust the distance numbers
yet for short irons. Late word in!
I am having trouble with Traj30 on my computer. I have finished all the
calculations, but if I have to go back and re-do any -- or evaluate a
new market offering -- I may need to find a different program and
re-run everything with it. I hope that does not come to pass.
Finding the clubhead speed
order to have comparable results, I wanted to apply the same swing to
each club in the study. This could have been done by making all the
clubs exactly the same length and using the SwingPerfect
computer program to simulate the swing. But I didn't want to manually
enter the data for every swing. (With 20:20 hindsight, that might have
worked for the single-length sets; it would only need to be computed
once for each set, since the head weight is the same across the set.)
So I did things in two stages:
- Given a head weight, find the
length that will give the same heft measure for the club. This was
done, and the length was sufficiently insensitive to small weight
variations that it came out 37.5" for all the clubs within one
decimal point. So I won't go into any more detail about how I did it.
SwingPerfect to find how clubhead speed varies over the relevant weight
and length, then come up with a simple formula that approximates it
well. We are talking about a very small range of weight and length.
Let's look at this -- even though the total clubhead speed range was
only 0.3mph for the range of interest. (I want this "on record" in case
I need to do something like this again.)
My approach was to
find a set of swing parameters for SwingPerfect (things like torque
profiles and initial angles) that gave the results we were seeing on
the first page of the study. Those turned out to be: 40 foot-pounds of
arm torque, zero wrist torque, 170° shoulder angle, and 90° wrist cock.
I set up a table of head weights and lengths. The weights were 265g to
280g in 5g increments. The lengths were 36" to 38" in half-inch
increments. I used SwingPerfect to populate the table with clubhead
speeds. Here is the table, imported directly from Excel.
|Speeds from SwingPerfect|
||Head Weight (grams)
Just by eyeball, we can see that clubhead speed changes by::
- Almost exactly a half mph per 5 grams of head weight, which is 1/10mph per gram.
- Almost exactly a third of a mph per half inch of length, which is 2/3mph per inch.
Writing this algebraically, starting from the top-left cell in the table:
Speed = 80 - 1/10(weight - 265) + 2/3(length - 36)
is the table filled out with the SwingPerfect speeds (assumed to be
correct), the algebraic approximation, and the error between them.
you can see any error is less than a tenth of a mph for most of the
range in question. Certainly a useful formula for our purposes.
Last modified -- 12/17/2016