BBGM (BBTG) - Correct meaurement?

[joostin]

I've posted this before in threads showing different club measuring methods, but got around to some better pictures off a 3D model.  Those different methods also affect bottom of bore to ground measurements, BBGM aka BBTG.  I'm sure there's no right or wrong, but how would you prefer?  Does anyone even care if someone calls out 1-1/2" BBGM, but then you measure the same thing as 1-1/4"?

 

I'm showing 3 methods: 1) USGA style "backside" of the hosel (let's just assume 60° ruler).  2) Down the center of shaft like GolfWorks says to (though they have rulers that measure backside 🤷‍♂️)... same as the Mitchell ruler, I believe down centerline.  3) The old ruler on the floor on the backside of the club.

 

BBGM measured with these methods are shown below in the top right boxes.  Possible difference of almost 1/4", and it would be worse if the hosel is thicker or a heel is sticking out the back.  To calculate the differences, the trigonometry works out as shown in the other text boxes:

 

 

 

 

 

I measure clubs like USGA, but to me down the centerline of the shaft makes the most sense because you'd already measure a shaft itself like that.  Then the hosel thickness or heel of the clubhead doesn't affect the where it sits on a ruler.  Btw, this is all applies regardless of how you measure the grip end (without grip, to side edge or end of grip cap).

 

Do you care?  Should people not report BBGM numbers at all on wrx without a warning or disclaimer? *⚠️ 😢

[Stuart_G]

 

32 minutes ago, joostin said:

I'm showing 3 methods: 1) USGA style "backside" of the hosel (let's just assume 60° ruler).  2) Down the center of shaft like GolfWorks says to (though they have rulers that measure backside 🤷‍♂️)... same as the Mitchell ruler, I believe down centerline.  3) The old ruler on the floor on the backside of the club.

 

#3 should only ever be a quick check.  It should never be used when any accuracy is required.

 

 

32 minutes ago, joostin said:

I measure clubs like USGA, but to me down the centerline of the shaft makes the most sense because you'd already measure a shaft itself like that. 

 

Measuring the shaft length by itself is going to give you pretty much the same results whether you measure off the side or down the center.   So there really is no disparity for either method when comparing how the shaft vs the club is measured.

 

 

 

 

[joostin]

3 hours ago, Stuart_G said:

 

 

#3 should only ever be a quick check.  It should never be used when any accuracy is required.

 

 

 

Measuring the shaft length by itself is going to give you pretty much the same results whether you measure off the side or down the center.   So there really is no disparity for either method when comparing how the shaft vs the club is measured.

 

 

 

 

Right, method #3 is definitely the least accurate method, and measuring the shaft by itself off the side isn't really any different than down center.

 

Here's maybe a better representation using a driver in my DIY ruler/fixture... The heel sticks out farther than the hosel, giving a clear 1/4" BBGM difference between method 1 and 2 (the iron above was only 0.15" difference):

 

 

Which BBGM is right?  Rulers out there measure both ways.

Someone measuring on his/her own just has to be consistent with the method chosen.  But if a guy buys a cut shaft and asks for BBGM info from someone else who measures differently.... 🤷‍♂️

 

Related:  For the driver above, if USGA guy measures the club length at 45.00", the shaft-centerline guy will measure 45.25".

[Stuart_G]

12 hours ago, joostin said:

Which BBGM is right? 

 

Silly question. The way I do it, of course 🙂

 

Quote

Rulers out there measure both ways.

Someone measuring on his/her own just has to be consistent with the method chosen.  But if a guy buys a cut shaft and asks for BBGM info from someone else who measures differently.... 🤷‍♂️

 

And to add to the confusion, I've seen some people post BBGM numbers that are measured from the tip of the adapter instead of the tip of the shaft.

 

The simple answer is don't depend on anyone else for the BBGM.   And there really isn't a big need to get it from someone else.   If you're buying a shaft, the only thing they should be asking is the cut shaft length  (with or without the adapter).    If the listing for the shaft shows anything else, the seller probably doesn't have a clue as to the subtleties of these measurements so no other numbers should be trusted anyways.  So just get them to measure the shaft length, that's a lot harder to mess up - or maybe I should say easier to get the details of how it's measured.

 

The other case where BBGM comes into play is when someone wants to know what will happen going from head A to head B.  In that case the difference will be the same irrespective of the method.    So it's only potentially an issue when you get the BBGM of head A from one person and the BBGM of head  B from a different person.

 

For any other case, you shouldn't really need to get the BBGM from someone else outside of casual discussions.

Edited March 14, 2021 by Stuart_G

[joostin]

2 hours ago, Stuart_G said:

 

Silly question. The way I do it, of course 🙂

 

 

And to add to the confusion, I've seen some people post BBGM numbers that are measured from the tip of the adapter instead of the tip of the shaft.

 

The simple answer is don't depend on anyone else for the BBGM.   And there really isn't a big need to get it from someone else.   If you're buying a shaft, the only thing they should be asking is the cut shaft length  (with or without the adapter).    If the listing for the shaft shows anything else, the seller probably doesn't have a clue as to the subtleties of these measurements so no other numbers should be trusted anyways.  So just get them to measure the shaft length, that's a lot harder to mess up - or maybe I should say easier to get the details of how it's measured.

 

The other case where BBGM comes into play is when someone wants to know what will happen going from head A to head B.  In that case the difference will be the same irrespective of the method.    So it's only potentially an issue when you get the BBGM of head A from one person and the BBGM of head  B from a different person.

 

For any other case, you shouldn't really need to get the BBGM from someone else outside of casual discussions.

Can't lie, I was hoping for someone to just pick one or the other, you know, like "Professors @Stuart_G and @Howard_Jones say down the center is the real deal" 🤣.  Someone bite and give me some vindication lol.

 

I know no one questions BBGM or club length especially if they have some kind of ruler.  The only place I've seen it spelled out was in that GolfWorks diagram in my OP.  It was only a few years ago when I started getting into club specs, and considered getting this Dynacraft ruler plate, below, when I thought "wait, this is not the same as other rulers I've seen" (DIY incl. Tutelman's, or even the Hireko Ruler Buddy).  Some DIY posts and youtube vids had theirs down center too, but not all.

 

It's really a simple trig problem, as shown in the OP pics, but somehow couldn't find anyone else on google questioning that method vs this:

Heck, soling against a pin is not the same as soling against a flat surface (flat surface finds the true bottom).  I ended up taking USGA for my own method because they're "official" (yet wrong IMO 🤣).

 

The Titleist iron in my OP must have been reverse engineered off an actual one, and clearly the bore was 1.50" from the backside (USGA).  I would guess, at best, that's how Titleist designs their irons. 

 

I hope this thread can at least be a Public Service Announcement for the few that have read this far.  If giving out a BBGM (BBTG if you will) to someone else I'd recommend "BBGM-center" or "BBGM-USGA", or "BBGM-C" or "BBGM-U".  Something like that.  It can catch on 🤞

[Stuart_G]

33 minutes ago, joostin said:

Can't lie, I was hoping for someone to just pick one or the other, you know, like "Professors @Stuart_G and @Howard_Jones say down the center is the real deal" 🤣.  Someone bite and give me some vindication lol.

 

Personally I prefer the USGA method - it's much less prone to operator error e.g.  making sure the center of the shaft is aligned with the axis or the lie angle matches the club.  It's also much easier to make your own ruler for that method instead of having to buy one.  I've also never much liked club rulers that used a pin instead of a plane/block due to the complex and variable nature of the sole geometry one can find.

 

For those reasons I would guess that along the backside is a much more widely used method particularly among hobbyists and probably even factory set-ups.  I also suspect it's been much more widely used through the history of club making.

 

My guess is that someone came along, took a look at some of the same errors you did and thought "it should be through the center instead - that's the 'real' playing length"  without actually taking the time to figure out if there was really a problem that needed to be solved.   Then created some fancy jig/club ruler and marketed it as being "better" to try to convince others.   That's typically how multiple methodologies and standards get created.

 

 

 

 

Edited March 14, 2021 by Stuart_G

[lefthack]

Which is correct?

[joostin]

53 minutes ago, lefthack said:

Which is correct?

Haha, bottom. The clip-hooks are always slotted so it's supposed to be accurate when pulled or when pushed to accommodate the thickness of the clip... at least before they oval-out. Though that top one looks like it's missing a few hash marks 😉.

[lefthack]

10 minutes ago, joostin said:

Haha, bottom. The clip-hooks are always slotted so it's supposed to be accurate when pulled or when pushed to accommodate the thickness of the clip... at least before they oval-out. Though that top one looks like it's missing a few hash marks 😉.

Measure twice, cut until it fits.

[joostin]

8 hours ago, Stuart_G said:

USGA method - it's much less prone to operator error

I do like that easiness and dummy-proofness of USGA.

 

I just see posts sometimes of people dead-set over 1/2" from a manufacturer build, when that 1/2" could easily be 50% off from expectation, not even counting the other things that can vary from OEM to OEM.  I guess the more people can build their own clubs the better.

[Howard_Jones]

3 hours ago, lefthack said:

Measure twice, cut until it fits.

Thats 100% true
We SAY : "Measure at least twice, cut once",
- but the truth is we shall always cut "on the long side" of the cut mark and grind down to target to avoid cutting it to short, so we are not done after first cut, only 2 steps closer.

[Howard_Jones]

11 hours ago, joostin said:

Can't lie, I was hoping for someone to just pick one or the other, you know, like "Professors @Stuart_G and @Howard_Jones say down the center is the real deal" 🤣.  Someone bite and give me some vindication lol.

 

I know no one questions BBGM or club length especially if they have some kind of ruler.  The only place I've seen it spelled out was in that GolfWorks diagram in my OP.  It was only a few years ago when I started getting into club specs, and considered getting this Dynacraft ruler plate, below, when I thought "wait, this is not the same as other rulers I've seen" (DIY incl. Tutelman's, or even the Hireko Ruler Buddy).  Some DIY posts and youtube vids had theirs down center too, but not all.

 

It's really a simple trig problem, as shown in the OP pics, but somehow couldn't find anyone else on google questioning that method vs this:

Heck, soling against a pin is not the same as soling against a flat surface (flat surface finds the true bottom).  I ended up taking USGA for my own method because they're "official" (yet wrong IMO 🤣).

 

The Titleist iron in my OP must have been reverse engineered off an actual one, and clearly the bore was 1.50" from the backside (USGA).  I would guess, at best, that's how Titleist designs their irons. 

 

I hope this thread can at least be a Public Service Announcement for the few that have read this far.  If giving out a BBGM (BBTG if you will) to someone else I'd recommend "BBGM-center" or "BBGM-USGA", or "BBGM-C" or "BBGM-U".  Something like that.  It can catch on 🤞

Like ive said before, it does not matter what ruler or system we use, as long as we use that system from the start to the end. The issue if any is when we shall share and exchange measurements, then we are in a desperate need to know what measure standards this measurements comes from to make them useful at all.

All measurements we do will always be "relative" just like the gauge on a loft and lie machine. Dont think for a second that your #6 iron is 31* TRUE LOFT because the gauge on a Mitchell bending machine said so, but you can be 100% sure that if you bend it in the same machine to 32*, the CHANGE is 1*.

Thats why TRUE specs dont really matter, the tools we have is really only useful for RELATIVE measurements and we are just fine with that as long as we dont mix values from 2 different systems.

Since i used a Mitchell ruler, MY standard method for measurement of BBGM was:
Play length measured down the center of the shaft, minus net shaft length, minus grip cap.
OR if the club was un-gripped its even better. Play length ex grip. minus net cut shaft = BBGM.

Edited March 15, 2021 by Howard_Jones

[joostin]

10 hours ago, Howard_Jones said:

Thats why TRUE specs dont really matter, the tools we have is really only useful for RELATIVE measurements and we are just fine with that as long as we dont mix values from 2 different systems.

Since i used a Mitchell ruler, MY standard method for measurement of BBGM was:
Play length measured down the center of the shaft

Thanks for the insight Howard.  It's safe to say anyone reading this thread will agree on using measurements relative to their own.

 

Again - and not to criticize right or wrong - we already have two of the most knowledgeable golf equipment people on earth, and one prefers USGA style, one uses down center.  Relative to themselves I'll never question a build length or BBGM number, but any sharing of BBGM will be problematic.

 

I saw this vid from @RyanBarathWRX of wrx.  His diagram is definitely USGA style.  The ruler in the shop looks USGA style, but instead of a flat backside like the red ruler above or my DIY one, it has a dowel pin on the front side of the shaft to butt up against, taking out any heel variance sticking out the backside.  This would still give a 0.11" difference BBGM than measuring down center (1/2*0.370 / tan(60°), assuming the ruler goes off the backside of the shaft:

 

So everyone please just think twice... after measuring twice... before giving or taking any BBGM numbers to or from anyone else.  (Or go with BBGM-C, BBGM-U 😉)

[Nessism]

Just curious but does anyone build clubs based on BBGM?  The only time I pay attention to that is when buying pulls.

 

For measuring club length, the truly important thing, I use a Mitchell club length ruler.  It's a fabulous tool that's foolproof to use.  I measure without a grip because it's easier and leads to more consistency between clubs.  Simply dry fit the head on the shaft, lay it on your length measuring tool, mark the desired length and then cut the shaft to length.  That's what I do anyway.  I can't even tell you what the BBGM is on any of my clubs because I never determine that.

 

 

Edited March 15, 2021 by Nessism

[Stuart_G]

43 minutes ago, Nessism said:

Just curious but does anyone build clubs based on BBGM?  The only time I pay attention to that is when buying pulls.

 

For the more sensitive players, it can play a part in how the shaft plays and what tipping might be required (along with the head weight).  

 

But other than that, no.   I certainly don't.

 

Now I do measure more as a side note than using the value as part of the build.  I do tend to carry shafts over from one head to the next in the drivers and woods and it's nice to know how the playing length will change for a shaft/adapter that's already been "built". 

 

Edited March 15, 2021 by Stuart_G