cleochiro, after I read your question my immediate thought was to tell you to get the MPF book for irons and read through it. I still think you should get the book, but I also feel a real succinct answer will help a number of people understand MPF better. So, thanks for asking the question.
MPF uses the center of gravity location in the horizontal and vertical axis’s and also the moment of inertia (MOI) to calculate a number.
The main playability factors from these 3 attributes are the horizontal and vertical centers of gravity. The farther out the horizontal center of gravity (“C” Dimension) from the hosel the more stable the clubhead is through impact. Also, the more solid the hit more of the time and in general better directional control consistency.
Regarding the vertical center of gravity, the lower it is will result in more solid hits more of the time and more consistent trajectories. The golfer’s intent should always be to hit the ball with the clubhead’s center of gravity below the golf balls center of gravity and a lower cg accomplishes this.
The basic MPF number is derived by subtracting the actual vertical center of gravity from the “C” Dimension. After that MOI and a few correction factors are added or subtracted to get the final number.
Maltby General Rules of Thumb Concerning MPF: 1. If you hit the ball low on the club face and not solid you should first find an iron with a very low center of gravity and with a “C” Dimension of at least 1.350” and preferably higher (Super or Ultra Game Improvement categories). 2. If you have any directional control problems and you are not a low handicap, look for irons with a “C” Dimension over 1.450” and a higher MOI number (again Super or Ultra categories). 3. If you are a sweeper of the ball look for very low vertical centers of gravity. 4. If you are a low handicap player who hits down and through the ball and must play blade type irons, at least go for blades that fall into the “Game Improvement” category as a minimum. This will assure you of getting good built-in playability and not being stuck with an iron that requires a perfect hit every time to hit it solidly. I think you get the idea here.
Everyone also needs to understand this; There are a number of other playability factors that MPF does not take into consideration. One of these is “effective sole bounce” which is comprised of the bounce angle, the sole width, the front to back sole radius and the leading edge grind. Another is the club length, the shaft and it’s bending qualities. Another is the head weight (swingweight and total weight factors). How about grip size? These are all fitting variables that need to be addressed individually.
The intent of MPF is to be a tool for anyone to look at their golf game and determine what MPF category they fit into. This will make playing the game easier and avoid the frustration of trying to play some low MPF iron that only a tour pro can play. No one should ever go below the “Game Improvement category” in my opinion because the clubheads simply become too hard to play. They are less solid hitting and much harder to hit with any consistency. I personally will not play irons that are below “Super Game Improvement” because at my age this simply works out better for my game and consistency. Notice that through out this answer I have used two words the most; solidness and consistency. This is what you are after if you want to improve your game. The absolute most stupid remark that I have ever heard is from the player who wants to play with low playability irons because his mis-hits provide him feedback regarding his swing. So, in a match this player would rather be in the bunker on a mis-hit iron shot that may have landed on the green with the same mis-hit on a higher MPF iron. This simply does not make sense.
