MOI Special Report

If swing weight measurement is to determine the weight of a golf club from its mass in respect to its balance point, then MOI measurement is to determine the centrifugal force in respect to its swing weight. Both of these when applying on a golf swing, it is simply reflected as a feeling of how much force does a club requires to be swung in respect to time within the swing motion.

How does this apply to golf swing?
In simple understanding, if I could match irons set according to MOI instead of SW, I could switch from iron to iron maintaining the same rhythm with the same swing force, where as in SW I have to adjust my rhythm accordingly.

MOI approach:
To accurate measure MOI in golf club, it requires expensive equipment like MOI machine
Yet, Dave Tutelman had done extensive research and provide the poor-man fitting method (reference 4) which I currently adopt. Below is where I begin the long struggle of clubs fitting process.

MOI Equation:

MOI = Lc2 * (H + S/3) + 10 * G			S is weight of the shaft	Lc is length of the club
			H weight of the head	G is grip weight

First attempt:
Used an ½ SW point per ½ inch method. Picked my favorite 7 iron, starting from C9.5 and progressively reduce ½ SW point to 3I and increase ½ SW point to PW.

Match 2: MP 32 + 1150GH + Golf Pride DD2
IRONS	T W	WH + WS	WH + WS + TW	W S (+Grip)	WS	L S	W H	W H + T W	MOI	MOI / 1000'S	Jeff's MOI	SW
3	6	400	406	162	112	38.75	238	244	422,940	423	141	C7.5
4	6	407	413	163	113	38.25	244	250	421,374	421	140	C8.0
5	5	413	418	163	113	37.75	250	255	417,568	418	139	C8.5
6	6	420	426	162	112	37.25	258	264	418,619	419	139	C9.0
7	4	428	432	163	113	36.75	265	269	414,673	415	138	C9.5
8	6	435	441	161	111	36.25	274	280	417,058	417	139	D0.0
9	6	444	450	163	113	35.75	281	287	415,444	415	138	D0.5
P	6	453	459	162	112	35.50	291	297	421,844	422	140	D1.0

Result: MOI is random

Second attempt:
Used more precise measurement: +/- ½ SW point and 1.35 SW point per inch (0.675 SW per ½ inch), progressively increasing SW from 3I to PW.

Match 4A: MP32 + 1150GH + Golf Pride DD2
IRONS	Actual TW	WH + WS	WH + WS + TW	W S (+Grip)	WS	L S	W H	W H + T W	MOI	MOI / 1000'S	Measured SW
3	4	400	404	162	112	38.75	238	242	419,936	420	7.5
4	5	407	412	163	113	38.25	244	249	419,911	420	8.0
5	7	413	420	163	113	37.75	250	257	420,418	420	9.0
6	7	420	427	162	112	37.25	258	265	420,006	420	9.5
7	6	428	434	162	112	36.75	266	272	418,274	418	10.5
8	8	435	443	161	111	36.25	274	282	419,686	420	10.5
9	9	443	452	162	112	35.75	281	290	418,852	419	11.0
P	8	453	461	162	112	35.50	291	299	424,364	424	11.5

Result: MOI is more uniformly distributed yet it is still unsatisfactory

Third attempt:
Manually adjust tip weight and computationally match MOI at 420 range

Match 4B: MP32 + 1150GH + Golf Pride DD2
IRONS	Round TW	WH + WS	WH + WS + TW	W S (+Grip)	WS	L S	W H	W H + T W	MOI	MOI / 1000'S	Ref Target SW	Actual SW	Adjusted SW
3	6	400	406	162	112	38.75	238	244	422,940	423	7.475	9.0	8.0
4	7	407	414	163	113	38.25	244	251	422,837	423	8.15	8.5	8.5
5	9	413	422	163	113	37.75	250	259	423,269	423	8.825	10.5	10.0
6	9	420	429	162	112	37.25	258	267	422,782	423	9.5	10.0	10.5
7	8	429	437	162	112	36.75	266	275	422,326	422	10.175	11.5	11.5
8	10	435	445	161	111	36.25	274	284	422,314	422	10.85	11.5	12.0
9	12	443	455	162	112	35.75	281	293	422,687	423	11.525	11.5	12.5
P	10	453	463	162	112	35.50	291	301	426,885	427	12.2	2.5	12.5

Result: MOI range is tighter while PW is specifically left with high MOI. I figure SW is more important for wedges due to partial and finesse swing for short game. Overall SW is bumped another 1 ~ 2 point from assembly.

Final assembled attempt:

Mizuno MP32 + Nippon Shaft 1150 GH + DD2
IRONS	Round TW	WH + WS + Grip	WH + WS + TW	W S (+Grip)	WS	L S	W H	W H + T W	MOI	MOI / 1000s	Ref Target SW	Actual SW	Adjusted SW	Raw SW
3	6	400	406	162	112	38.75	238	244	422,940	423	7.475	9.0	8.0	5.0
4	7	407	414	163	113	38.25	244	251	422,837	423	8.150	8.5	8.5	5.0
5	9	413	422	163	113	37.75	250	259	423,269	423	8.825	10.5	10.0	5.5
6	9	420	429	162	112	37.25	258	267	422,782	423	9.500	10.0	10.5	6.0
7	8	429	437	162	112	36.75	266	275	422,326	422	10.175	11.5	11.5	7.5
8	10	435	445	161	111	36.25	274	284	422,314	422	10.850	11.5	12.0	7.0
9	11	443	455	162	112	35.75	281	292	421,409	423	11.525	11.5	12.0	6.5
P	10	453	463	162	112	35.50	291	301	426,885	427	12.200	12.5	12.5	7.5

First Test Impression:

number of balls tested: 180 balls location: Lake Success Driving Range
Overall the “new” irons sets are lighter than my previous set by average of 8 grams in static weight. How much is 8g in static weight differs? Not much since my swing weight is kept at the same range. However, it is a lot easier for me to switch from club to another club, especially noticeable with 3I. I have tried on randomly chosen iron from one club to the other and I could not feel any difference in swinging force. Using the same rhythm to swing each club, the feel is tremendously rewarding, even though PW is felt much heavier than 3I in static weight, they are comparable similar in motion. There is virtually not much change in trajectory, height and distance, but I feel it is much easier to produce desired shot with each club under MOI matching. This set of iron is suddenly more forgiving than ever.

Equipment used:
Mizuno MP32 3I ~ PW + Nippon shaft 1150GH Tour stiff + Golf Pride DD2
Digital scale (Accuracy +/- 1g)
Golfsmith shaft puller + swing weight scale (Precision 0.5 SW point) + golf clubs making essentials
total cost: $126 for 9 Nippon Shafts + $4.56 DD2 grip each

References:

1. Tom Wishon on MOI:
http://www.wishongolf.com/moi.php

2. Definition of Moment of Inertia:
http://en.wikipedia.org/wiki/Moment_of_inertia

3. Why your golf club is obsolete:
http://www.calgolftech.com/whats_new/driver57.html

4. Dave T’s club design notes:
http://www.tutelman.com/golf/design/swingwt4.php?ref=#measure_moi