Britt and Jim, when asked about the MPF of a particular iron head, you usually give the preliminary numbers, saying that the final numbers will be very close to that. Two questions: what process do you use to get those preliminary numbers, and how can we do something similar without drilling into the sole? (I assume you will reference Ralph’s MPF book.) Thank you, and thank you for all the great work you do for us and for golf! Michael
Ralph was very transparent in the method and the process. Anyone can see and do the measurements. You do not have to drill the hole in the sole. I am actually simply punching the sole now and measuring. I can get an extremely accurate rearward number without drilling and can measure MOI without the hole in the sole. It has become more difficult over the last several years to drill holes in some of the iron models. Different materials in the soles, hollow constructions and the fact that we can measure just as accurately without drilling has lead to the change. Also saves a lot of time. The preliminary numbers were always done without drilling and as I have said, the variance after drilling was, most of the time, statistically insignificant.
In it’s simplest form, if you get the horizontal cg and subtract the basic vertical cg from that number, you will get a general MPF number. Of course this does not account for the rearward cg and the MOI. You can do the rearward and use the book to help you calculate what the actual vertical cg would be to get you a little closer. MOI requires a MOI device of some kind and that is usually cost prohibitive for most to do. MOI in irons only effects the number by a few points, so it has the least effect on the final number. High MOI combined with a low actual vertical cg has the most positive playability effect. A high MOI with a high actual vertical cg will not, and a low MOI is not a positive no matter the cg location. Ralph explains it all in the book and probably better if I just refer you there if you want to get into the detail on the MOI / cg formula.
Britt Lindsey