MOI – A Cautionary Tale

[MountainGoat]

I spent the winter building the worst set of MOI-matched clubs I’ve ever made. I’ve made a kajillion MOI-matched sets before, so before Howard or Stuart tell me I don’t know what I’m doing, I actually do know what I’m doing.  I also have the equipment to do it, thank you very much.

This particular set involved Maltby TE Forged heads, AMT White S300 shafts and MCC+4 grips. I slaved over the MOI matching to the point that the ungripped variance is no more than plus or minus 2 units across the whole set. The resulting gripped values are less than plus or minus 5 units across the whole set. From that standpoint, they are a numerical success.

The problem is that they play like s**t.  Furthermore, the resulting swing weights make no sense at all.  They run from D0.6 to D4.8 in completely arbitrary increments. There is no discernible pattern whatsoever. 

Hence, if you’re building an MOI-matched set with AMT shafts but without MOI measurement equipment and are only using progressive swing weight as a guide, you might be in for a surprise.

Me? I don’t know how to fix these things. I’ll probably pull the shafts and start over with something more conventional than AMT White.

[Howard_Jones]

Sorry for that, but if you actually have been reading what ive been writing about AMT and MOi matching....you would not have done it, thats the short version.

[MountainGoat]

There should be no reason you can't MOI match a set with AMT White. If anything, you ought to get a tighter SW dispersion.

 

 

[Howard_Jones]

What play length increments did you use?

[Golfrnut]

I’ve measured out three sets now with AMTs, and the MOI variance on those would put the spread at about 2 SW across the board in order to MOI match. With your set being around 4 points, something doesn’t seem right unless the AMTs are way out of spec.

[Howard_Jones]

Why dont you both post ALL club specs....

[MountainGoat]

Play length -- I shoot tor a 37 1/2" 7-iron.

Just a little more background... When I first assembled this set, I SW matched it. The resulting MOI spread was about half of what it would have been with a 'standard' set of shafts. I remade the set and MOI matched it thinking that the SW spread would be half of what it would normally be. I was wrong, and that's what I'm sharing here. It's was considerably more, and it followed no discernible pattern.

I temporarily conclude from this exercise that AMTs are intended to be SW matched with the benefit being a lower MOI spread than conventional shafts. This would be a good thing from a playability standpoint. I also suspect that the progressive weighting of these shafts results in balance point issues that confound real MOI matching.

I don't recommend attempting to MOI-match AMT shafts by using a progressive SW formula. If you want to MOI-match them, use an Auditor Speed Match and be prepared for some odd SW increments. I probably wouldn't recommend that either.

Bottom line -- If you build with AMT shafts, I recommend you SW match them.

 

[Howard_Jones]

You have more or less found the same i have, what i can see from the numbers ive been doing is that AMT is "MOI matched shafts", and that we might be able to make it good by MOI matching them if we keep 4/8" between clubs, but NOT if we go 3/8". If we use flat SW value and 4/8", they will not be far off on MOI, but since AMT has a progressive BP to equalize the drop in shaft weight, we mess that up if we try 3/8" starting in the short end, and get a head weight progression that simply look "strange". AMT has a total weight progression as SW matched that dont fit us all, so its also a question of how the player swing his clubs, just like the difference is between SW and MOI. (same swing for all = MOI, or progressive more power the longer we wants to move the ball = SW) AMT tries to combine the two, but with a slight actual resistance progression as we go longer, but the large drop in total weight as we go longer might not be easy to adapt to for players who comes from constant weight, and even harder if they are used to Descending weight.

Did you use 4/8" or 3/8" on this MOI project? and what head weight progression did you end up with?

[MountainGoat]

I try to keep head weights running at 7g intervals, but that's always a challenge. After that, I adjust length to get the desired MOI. I got a bunch of weird length intervals with this set.

I believe you and I are saying essentially the same thing. My recommendation is that people using AMT shafts utilize SW matching and accept the useful probability that the resulting MOI spread will be a little tighter than with standard shafts. I don't recommend MOI matching with these shafts.

 

[BREWMASTER95060]

hi mountaingoat

I am interested and curious if it wouldn’t be too much trouble could you please post total finished club weight and Balance point.

trim shaft weights if you have them.

thank you

[MountainGoat]

I'm sure I'll regret providing this data, but here it is. I don't have the shaft trim weights, because I trim to length after installation.

FYI -- Gripped MOI was 2730 plus or minus 5. Ungripped MOI was 2670 plus or minus 2.

[Howard_Jones]

Just a quick input, let BP be a measurement from the tip side and up, thats how shaft BP for shaft specs is delivered.

BP from the butt side and down is used for SW calks, so it dont hurt to have it from both directions.

[MountainGoat]

It’s not something I ever measure, so I don’t know the convention.

[Howard_Jones]

You should, since shaft BP matters for actual MOI or SW...

Counter weighted shafts = light tip side and heavy butt, so BP end above the center of the shaft.

AMT is opposite, to compensate for progressive lower shaft weight, BP is moved progressive against the tip side as we go longer....and when you started to change butt length individual for all, you messed that up, and moved BP "off" from where the designer placed it.

Here is how AMT White looks like (their spes is opposite of the norm and from butt against the tip), but here you see that the long and light irons has shaft BP closer to the head side vs the short

BP is moved average 0.325 inch from shaft to shaft as average (8.25 mm), while shaft length goes up 0.5" or 12.7 mm, so BP is pushed against the tip for each shaft longer.

 

[MountainGoat]

Interesting information, Howard. Thank you.

When I began this project, I did so with the knowledge that the shaft weights were progressive. I did not know that the balance points had been manipulated, as well. That characteristic explains my odd results (as I speculated in a post above). Hence, my method of MOI-matching would not have lead to a satisfactory outcome. I'm left with a set of clubs that are MOI-matched, but otherwise feel a little odd.

In any case, I'll leave this thread with my recommendation that clubs made with AMT shafts be SW-matched, with the result being a tighter MOI spread than might be achieved with a standard set of shafts. For myself, although I'm not looking forward to doing these clubs all over again, I'm going back to my old pals -- TTDG. They ALWAYS perform as expected.

 

[Howard_Jones]

I think its this variable BP who makes them odd, and the numbers ive done for #2 MOI or Area MOI shows that as 4/8" the shafts themselves is MOI matched with a tolerance of only plus minus 2.5 grams cm2 while iw we go 3/8" using the #9 as starting point, we have modified the shafts to become Ascending MOI, and with a head weight progression of only 5.1 grams between clubs. MOI contribution from the shafts alone is 238 to 243 in a 4/8" set but change to 224 to 244 (243) if we go 3/8" so i think its 3/8" thats the problem with them, NOT MOI matching who should be strait forward, but ONLY as 4/8" between clubs when we use AMT.

Standard 4/8 set up (BLUE FIELDS) Contribution to MOI from the shafts alone

A Classic DG Constant weight is like the values you find in the row for the #9 iron where our #3 would be 275 Grams cm2

PS! all numbers here is #2 MOI or area MOI, thats why the values is a few hundred points lower than Auditor returns.its the SHAFTS contribution to MOI as change i want you to look at, since shaft MOI drops into the long, we have to compensate with more head weight in that end, and thats why head weight progression drops down to only 5.1 grams average

[Noodler]

 

You've never stated whether or not you're actually using an MOI Auditor machine in your build. How did you create an MOI matched set? What was your method with these AMT shafts?

[MountainGoat]

Yes, I used the Auditor. Once head weights are adjusted to spec, I arrive at the desired ungripped MOI by adjusting club length.

[Noodler]

 

I have built a set of MP-15 irons with the original AMT S400 Tour Issue shafts. I didn't run into what you did because I don't vary shaft length to achieve an MOI match. That's not a common practice among builders of MOI matched sets. My resulting set was MOI matched and the measured swingweight values were in a tighter range than when using constant weight shafts. Their MBI was almost spot on which also is not typical except when using ascending weight shafts.

So why not use tip weights to adjust the MOI to match?

[Golfrnut]

Yep, not a product of the AMT shafts at all...it’s a product of the technique used to build them.

[MountainGoat]

Peer review is over. Sharing experience here is always a mistake.

 

[Noodler]

I'm glad you shared. And it is a cautionary tale. There have been many GolfWRX'ers that have reached out to me looking for a "poor man's" method to do MOI builds using AMT shafts. As far as I know, there still isn't one precisely for the reason that your build ended up "challenging". It's because of the way True Temper plays with the balance point of the AMT shafts so that they can be ascending weight, but still work out easily for a standard swingweight-matched build using normal components.

[Golfrnut]

 

I mean...c’mon man. Look at this from the outside looking in. You created a thread...went pretty brash in your first paragraph naming names and basically trash talking and directly naming two members here...unprovoked at that...told everyone that AMT builds screw everything up...only to find out that you hodgepodged the build with a few different build techniques? It wasn’t the shafts in this case, it was applying the wrong techniques to try to complete the job. Shafts...not the issue in the end with why the build is all over the place.

[Golfrnut]

FWIW, I have had three sets across my machine. SW matched, 1/2” gaps, not the greatest of shaft tolerances on weight, I’ve seen only about a 30-35 point spread. To even them up to the mid iron MOI spec at 2700, it would be less than a 2 gram head weight change on either side of the set. It would be a much smaller variance going about it that way than trying to mess with butt cutting lengths.

[BREWMASTER95060]

golfnut,

 

If I’m reading your post right i agree. shafts trimmed 1/2 Increments looks like you get the swing weight and pretty close to MOI match.

head shaft MOI-grip

255 110 2690.76

261.85 113 2690.59

269 116 2690.26

276.5 119 2690.05

284.75 121 2690.59

These formulas are approximations but they’re really close.

shaft=(1/3*(shaft wt)/1000)*(2.54*(shaft length))^2

head=(head wt/1000)*(2.54*club length)^2

club length will be close but the correct value would be butt to sweet spot on club face.

5 iron BP = 27.7

9 iron BP = 26.5

diff= 1.2 or .3 between clubs

that is about right

BP= ((grip wt)*(grip BP))/(total club wt) + ((shaft wt)*(shaft BP))/(total club wt) + ((head wt)*(club length))/(total club wt)

club length should be

butt to head sweet spot measurment.

 

 

 

[Golfrnut]

 

The spread ran from the mid 2680s to the 2710s for all three sets. That would be less than 20 pts each way from the target iron...not bad in my opinion. Depending on who you want to read info from, even varying head weight by only a gram on either end of that set would close the gap for the set to within about 20 pts, which some have said is not going to be discernible to most golfers anyway. 20 points is only worth a gram or two of head weight, that's feeling the difference of one SW point when comparing a 3 iron to a PW. Would I try to build to that wide of tolerance? No. I would certainly probably be okay with it though if I was assembling without a MOI scale or picked up a set off the shelf and it was that close.

I have tried MOI matching before using the poor man's procedure. I didn't care for it much. Too much of a SW spread to get comfortable with. The AMTs on the other hand have made me a much better supporter of it. Probably something to be said to not only the MOI portion of it, but also the MBI side of it too which is much better accounted for with the ascending shaft weights.

[Noodler]

 

Yes, I would have to completely agree with you on that last part. MBI is the attempt to quantify the actual weight DISTRIBUTION across the club components in the context of the overall MOI. It surprises golfers to learn that you can have the same MOI on different sets of clubs, but not have them necessarily "feel" the same when swung. So not only does swingweight matching never actually match the "dynamic feel" when clubs are swung, but MOI also falls short in many cases if the weight distribution is wildly different. MBI can be "simplified" by looking at the percentage of the overall club weight present in the head versus the rest of the components. I have found that looking at this weight distribution is actually the final piece of the puzzle when it comes to being able to truly match the feel of two different sets of clubs. Of course the shaft bend profile plays into this quite a bit, but if the MBI isn't close, then you don't stand a chance of truly duplicating the feel of your favorite club(s).

BTW - My definition of an MOI match means that the MOI values for the set are within 10 std. deviation points. Most of my matched sets are less than 5 (so they're pretty well matched from an MOI standpoint. :) ). On the MBI side of things, I'm not nearly doing as well, but the AMT type shafts get you so much closer. That's why ascending weight shafts are a welcome addition to the MOI builder's toolkit.

 

[BREWMASTER95060]

“MBI side of it too which is much better accounted for with the ascending shaft weights.”

yes!!

[RichieHunt]

I agree. The only time I would fit to MOI by length is with the driver or 3-wood. But, if it's not fairly close to the length I'm comfortable with with the driver and 3-wood, then I look for a different shaft.

 

But, I've never built irons to MOI by length. The length and lie angles are just too important to performance.

 

 

 

 

 

 

RH

[MountainGoat]

I re-built my irons with TTDG-S300s using my supposedly suspect method and they came out exactly as predicted. The ungripped MOIs are plus/minus 3 units, and the SW progression is as smooth as a baby's bottom. So is the flex slope. Length Intervals closely approximate 3/8".

Adjusting MOI by adjusting length is very common. When you build clubs to 3/8" or 10mm or 10.7mm intervals, that's what you're doing. I've been doing this for at least 15 years.