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Iron face impact: Origins of "fourth-groove axiom" (not law)?


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I have been interested in golf club design and ideal impact characteristics for years.image.png.40e4eaad96848e69acdc0041fbe88f61.png

 

One item that keeps popping up is what I will call the Fourth Groove Law. In a dozen or so articles from fitters and instructors, the expert says that iron shots tend to fly truest if you have center impact on the horizontal fourth groove. And, articles on face impact decals for irons generally have diagrams with center circle in vicinity of fourth groove.

 

Nobody ever talks about the fifth or third groove being ideal. Does anybody know the origin of or research behind the 4G.L?

 

Edited by ChipNRun
Original Header = "fourth groove law" // Better term is "axiom"

What's In The Bag (Summary as of October 2020)

 

Driver:  Tour Edge EXS 10.5°, weights neutral   ||  FWs:  Calla Rogue 4W + 7W

Hybrid:  Calla Big Bertha OS 4H at 22°  ||  Irons:  Tour Edge CB Pro Tungsten 4i-9i

Wedges:  Calla MD3: 48°, 54°... MD4: 58° ||  Putter: Ping Sigma G Tyne (face-balanced)

Ball: Calla SuperHot (Orange preferred)  ||  Bag: Sun Mountain Three 5 stand bag

For details see:  Pending (need protocol to embed file list).

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I believe maximum club to ball velocity efficiency should be achieved by driving the clubhead CG through the ball CG (0.84").  Since iron clubhead CG varies throughout an iron set and between differen

I've never seen any reference to it either - but then my research tends to be mostly scientific papers, not fitting articles or other publications that have fitters as the primary target audience.

I guess it could be a generalization but I've got a set of Apex MBs with the smaller groove so 4 grooves up is lower on them than the set of X Forged CBs I'm using.  This doesn't sound scientific enou

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I believe maximum club to ball velocity efficiency should be achieved by driving the clubhead CG through the ball CG (0.84").  Since iron clubhead CG varies throughout an iron set and between different iron designs by tenths of inches then the 4th groove law would be a gross approximation at best.  I have never seen iron clubhead to ball impact discussed at this level of detail.  Should be interesting to see what crops up in this discussion.

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I've never seen any reference to it either - but then my research tends to be mostly scientific papers, not fitting articles or other publications that have fitters as the primary target audience.

 

If there is any basis for it beyond just a layman's simplification of the c.g. location (which I suspect is the source of the 'rule'), we'd likely only find out about it from an actual club designer.

 

Edited by Stuart_G
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I was hoping someone would/could do some more research into this utilizing the modern day launch monitors. I know GC Quad measures clubhead dynamics, surprised a guy like Bryson hasn’t talked about this topic. Maybe he has and I just didn’t see it.

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Callaway Epic Flash SZ 15* w/GD Tour AD TP 7x

Callaway Apex hybrid 18* w/GD Tour AD IZ 85x

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Callaway X Forged 5-PW w/PX6.0

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I get more than my fair share of good results with my irons, but I am swinging at or over 80 mph with irons ,  whether I am on the 4th groove of my iron shots is not a concern and I just don't pay that close attention. I have a decent repeatable swing,

But, the 4th groove impact position on every iron shot seems rather unattainable.

Unless, you re doing it already, consistantly



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  • ChipNRun changed the title to Iron face impact: Origins of "fourth-groove axiom" (not law)?
21 hours ago, Stuart_G said:

If there is any basis for it beyond just a layman's simplification of the c.g. location (which I suspect is the source of the 'rule'), we'd likely only find out about it from an actual club designer.

14 hours ago, PhlashPhace said:

I guess it could be a generalization but I've got a set of Apex MBs with the smaller groove so 4 grooves up is lower on them than the set of X Forged CBs I'm using.  This doesn't sound scientific enough to be called a law and it's hard to even call it a generalization.

 

1 hour ago, puttingmatt said:

But, the 4th groove impact position on every iron shot seems rather unattainable.

 

WRXers, If you revisit the original thread panel, you will see that I have changed the title wording from "Fourth Groove Law" to axiom.

 

As Phlash noted, 4G is not scientific enough to be a law.

 

I did some surface searching into scientific method realm, and axiom comes close to what we're talking about. An axiom is "a statement or proposition which is regarded as being established, accepted or self evidently true." In our case, accepted would be the closest fit.

 

image.png.40e4eaad96848e69acdc0041fbe88f61.pngLots of people in golfdom talk "fourth groove" as ideal impact point. This would capture Stuart's idea of a "layman's simplification of CG location."

 

Some of you may recall from HS math that seven axioms (or assumptions) are the basis of Euclidian geometry. (The Euclidian bit is also a good thing to remember in case you end up on the Jeopardy TV show.)

 

Another tidbit: The online Thesaurus identifies 52 synonyms for axiom

What's In The Bag (Summary as of October 2020)

 

Driver:  Tour Edge EXS 10.5°, weights neutral   ||  FWs:  Calla Rogue 4W + 7W

Hybrid:  Calla Big Bertha OS 4H at 22°  ||  Irons:  Tour Edge CB Pro Tungsten 4i-9i

Wedges:  Calla MD3: 48°, 54°... MD4: 58° ||  Putter: Ping Sigma G Tyne (face-balanced)

Ball: Calla SuperHot (Orange preferred)  ||  Bag: Sun Mountain Three 5 stand bag

For details see:  Pending (need protocol to embed file list).

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It's just a generalization to give us a visual of what is required to achieve solid contact in the vertical aspect.  Remember the "Tour Striker" training aid?  The one that has the bottom of the face rolled off, so that the bottom grooves are unplayable.  This was intended to force the player to learn to drive the COG (sweet-spot) under the center of the ball, with a down and through AOA and forward shaft lean.

 

Solid contact in the vertical aspect of impact is achieved by getting the Actual Vertical COG of the head design -at or below the center of the ball.  If the COG comes in a hair above the center of the ball, then contact is somewhat "thin"

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