MOI in irons is a very small part of the equation. A move from an MOI that is 11.000 ou/in2 to 13.000 ou/in2, for instance, will move the number only about 5-7 points. The difference in the TS-1 and the Mizuno Hot Metal Pro is 2.0058, which would only account for approximately 7 points. The reason for the overall 51 point difference is more related to actual vertical cg location (.750 vs .815) on those two irons. 51 points is not much and most players would not be able to tell the difference in 50 points. Ralph has always sated that it is hard to notice even a 100 point difference. Personally I think you can see, over enough time and shots, differences in a 100 point differnce in the MPF. The fact that the TS-1 is in the Super Game Improvement category and the Mizuno Hot Metal Pro is in the Game Improvment category is just a result of where the numbers fell in relation to the threshold. both are very stable and the 51 point difference will most likely not be noticed when comparing. Other things could be noticed, like solidness of contact, trajectory, etc. because of the variance in the actual vertical cg location, but that is totally dependent on the player and their attack angle and path. It is important to understand that a high MOI combined with a bad actual vertical cg location is “Bad” MOI. Ralph describes this in his book and explains how the final MPF number is rewarded for high MOI with good cg locations and how the number is NOT rewarded for high MOI with a bad vertical cg location. An example is if you take an iron from the 1930’s that has an extremely long hosel, it’s MOI might be off the charts, like over 18.000 ou/in2, but it’s actual vertical cg is approaching 1″ and in towards the heel. That club can not be rewarded for it’s high MOI when due to it’s cg location it would be very difficult to play.
In all the irons we have tested, MOI has varied from a low of around 10.000 ou/in2 to as high as 20.000. In putters, MOI has varied from 2.000 ou/in2 to 93.000. that’s a big difference in putters and not so much in irons. MOI is a high percentage of the story on forgiveness in putters. Although it is a factor in irons, it is to a much smaller degree.