Single-Length Irons:

Products

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 principles.

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.

Summary

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.
  • 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 negligible.)
  • 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.
    • Since 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.
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.

Model Brand Set
Makeup
Range
(yd)
[1]
Gap
Shape
[2]
Head
Weight
(grams)
Lie
Angle
Offset
(mm)
Comments
One-Iron One-Iron 3i - LW 103

(196 - 93)
273 63.5 3.2 Only assembled clubs
iMatch MyOstrich 4i - PW 88

(190 - 102)
272 - - No longer in business
Pinhawk Value Golf* 4i - LW 100

(193 - 93)
272 62.5 3
Sterling Wishon* 5i - GW 95

(191 - 96)
274 63 4 - 2.5 "Long" irons are hi-COR
5-hybrid available
In1Zone Diamond Tour 4hy - SW 91

(190 - 99)
273 63 3.2 5 hybrid or 5 iron choice
King F7 One Cobra 3i - GW 101

(197 - 96)
272 62.5 5.5 - 1 "Long" irons are hi-COR
Only assembled clubs
King Forged One Cobra 4i - GW 89

(185 - 96)
275 62.5 2 - 1.3 Only assembled clubs
i-Win Integra 5i - LW 87

(183 - 96)
272 62.3 6.6 - 2.3
  1. 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.
  2. My original plan for the table was to boil down the gap shapes to flat, proportional, and dysfunctional (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 here 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.

Descriptions

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

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:
  • 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.
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.
 

iMatch

MyOstrich 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

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 architecture.

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.



Sterling

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 effective.

Jaacob 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 works superbly.

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.

In1Zone

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 disappointed.

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".

(Added 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.

Cobra 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 roost.

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.
 

Cobra 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 offering.

It's 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 bad thing.

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 whole set.

i-Win

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.

Unfortunately, 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.

The 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.

Mathematical and computer model

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.

Then 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

In 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:
  1. 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.
  2. Use 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.

Then 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)
Length (inches) 265 270 275 280
36 80 79.5 79 78.7
36.5 80.3 79.8 79.3 78.9
37 80.7 80.2 79.7 79.2
37.5 81 80.5 80 79.5
38 81.2 80.7 80.2 79.8

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)

Here is the table filled out with the SwingPerfect speeds (assumed to be correct), the algebraic approximation, and the error between them.

From SwingPerfect Approximate formula Error
Length
(inches)
265 270 275 280 265 270 275 280 265 270 275 280
36 80 79.5 79 78.7 80.00 79.50 79.00 78.50 0.00 0.00 0.00 -0.20
36.5 80.3 79.8 79.3 78.9 80.33 79.83 79.33 78.83 0.03 0.03 0.03 -0.07
37 80.7 80.2 79.7 79.2 80.67 80.17 79.67 79.17 -0.03 -0.03 -0.03 -0.03
37.5 81 80.5 80 79.5 81.00 80.50 80.00 79.50 0.00 0.00 0.00 0.00
38 81.2 80.7 80.2 79.8 81.33 80.83 80.33 79.83 0.13 0.13 0.13 0.03

As 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