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How Iron Heads Were Tested
Our tests prove that all models of iron heads, once they are assembled with the exact same shaft, perform equally in spite of their metal alloy makeup, formed by casting or forged, shaped as cavity back of muscle back or their measured COR (coefficient of restitution or trampoline effect).
We have been bombarded with ads from the major club manufacturers promising improvements from last year’s models in their latest iron head designs. They move the weight distribution up one year and down the next. They hollow out, add plastic inserts and increase the complexity of the back of the face that never contacts the ball. The design of the face that the ball sees, is constrained by the USGA rules on spacing, shape and depth of the grooves, even the radius of the groove edge where it merges with the face, the surface finish, and an 0.83 limit on the COR. With all these constraints, the club manufacturers hands are tied. So don’t look for a lot of improvement in spite of their claims. Be suspicious of any claim that uses the word “promotes” when referring to a “benefit”. These words reflect luke-warm enthusiasm and a defense against being proven wrong.
But let’s not get ahead of ourselves. Here are the tests that I administered to prove that iron heads have not improved much, at least in the last 20 years. To compare iron head designs, I randomly selected a mix of muscle backs and cavity backs to form a 6 iron head-test set. Some designs were 10 years old, some more recent. Some were cast and some were forged. One of the heads, the Wishon 770 cfe, was reported to have a COR of 0.815, near the USGA limit of 0.83 and the rest varied down to a low of 0.77 COR. Only the head models varied between test clubs, all the other factors were held constant: shaft length, shaft model, shaft flex, swing weight and grip. So any difference in playability could be attributed solely to the head design.
The chart on the left shows the result of one older player tested with the 5 different 6-irons from the head-test set of clubs.
He was able to generate a difference in average carry distance between iron head models of less than one yard !
Even more shocking is the observation that the spread of distance from the longest to shortest shots was larger for the cavity backed, called game improvement, head models than for the traditional muscle backed models.
Two more players were added for a total of three players tested hitting the same six iron head models shown above. Data from Player A who has a 14 handicap and player C with a 2 handicap is plotted along with Player B with a 12 handicap whose test was shown above.
The chart on the left shows that after only 5 or 6 shots, no matter the skill level of these three players, all the iron heads they tested achieved almost identical average distances, as shown in the chart below. That chart depicts the distribution of distances achieved by many players hitting shots with different iron head models.
Finally, data from more than 50 players was added to the original three shown above. The average difference in distance hit between iron head models, after 7 shots with each, ranged from 0 to 2 yards. No one could achieve more than a 2 yard difference between any of the iron head models we tested.
All Iron Heads are the Same
The average yardage difference between iron head models achieved by over 50 players tested was less than 1 yard!
Industry ads claiming iron head design improvements from year to year are just marketing hype.
The lesson learned by this test:
- Keep your old irons
- But fix your driver by cloning the dynamic characteristics of your favorite club into the shaft of the driver.
You will love your driver. It may become your favorite club !!