Grip Weight Effects (Total Mass, SW, 1st moment, 2nd moment...)

[jammer13]

I know there have been many threads here about grip weight vs swingweight, but I thought it might be useful to look at it again from a slightly different perspective.  I've been building clubs as a hobby for myself and friends since the 80s, and as an Engineer,  I tend to analyze (some might say overanalyze) everything.  Recently, I tried some GP MCC Plus4 grips on my driver and fwy wood and noticed a feel and performance difference immediately which got my thinking about this again.

 

I have a very involved spreadsheet for club builds which calculates swingweight and I have generally used a 50g grip as a standard when specifying swingweight, even though that almost always wasn't the final swingweight of the build. So, I sort of discounted the grip weight effect on swing weight which I know is a common sentiment.  Ok, so back to the MCC Plus4 grips, in midsize, they are over 10g heavier than my usual midsize Tour Velvets, which to the SW scale, reduces the SW by ~ 2pts.  Is that what caused the change in feel and performance?

 

So, what club parameters were changed with the new grip-

Total Mass - Changed
Swingweight - Changed
Balance Point - Changed
MOI - No Change (Negligible)
Flex/Flex Profile - No Change

 

What I wanted to bring up was the balance point change.  This could be thought of as the first moment of mass of the club(mass * balance point distance), whereas the MOI is the second moment of mass of the club.  This first moment represents a torque on your hands when the club is not perpendicular to the ground and can operate either in-the-plane or out-of-the plane of the swing.  The MOI is pretty much an in-plane swing parameter only the way I think about it and is a measure of the resistance to rotation about an axis. Swingweight is somewhat of a proxy for the first moment although not a great one as it is based solely on the clubs mass and balance point, but uses a 14" fulcrum which doesn't correlate to where we hold the club.

 

My thoughts are that club feel is complicated and both the first moment and second moment contribute to the feel of the club and therefore how it is swung by the golfer either consciously or unconsciously.  I assume this why counterbalancing (affects first moment only) can work for some golfers.  I am somewhat ignoring the total mass effect, but that obviously plays a role as well.

 

TLDR - while changing grip weights to target a specific SW might not be very helpful (due to all the limitations of SW that have been discussed here before), it's also not helpful to ignore grip weight effects on club feel due to balance point changes.

 

Thoughts?

[Stuart_G]

17 hours ago, jammer13 said:

What I wanted to bring up was the balance point change.  This could be thought of as the first moment of mass of the club(mass * balance point distance), whereas the MOI is the second moment of mass of the club.  This first moment represents a torque on your hands when the club is not perpendicular to the ground and can operate either in-the-plane or out-of-the plane of the swing. 

 

 

If you want to look at first moment - that's fine.  But that's not the same as balance point or swing weight.  You  can't use either of those as a proxy for the first moment.

 

First of all (and most importantly) If you think about it, you'll see that adding butt weight will not increase the first moment any more than it increases the MOI - in fact less.  And it's for the same reason.  All the 'new' mass is being added under the hands - not any place that in will increase the torque on the hands.   Sure the balance point moves closer to the hands but the total mass  increases such that first moment stays the same.

 

Second, thinking of it just as a "torque on your hands" is fine for statics.  But in dynamics and what we feel during the swing, that is really almost all about how the club resists our attempts to move and accelerate it.  Total mass is the resistance to linear motion,  MOI is the resistance to rotational motion.  The first moment does not quantify resistance to any specific type motion. 

 

Of course the fact that the point of rotation isn't really a constant makes the MOI of the club about one single axis a very imperfect representation of that resistance to acceleration.   It's really the resistance to our attempts to rotate the club right at the transition point of the swing - not at all times during the swing.  At the very beginning of the take away when the velocity is still very low, first moment might certainly have some influence on feel.

 

However despite that, the first moment does have a small part in the dynamics as well.  In the down swing as we either try to "hold the lag" or let the club release, the first moment does result in a centrifugal force that helps release the club.  How important or significant that might be is questionable.

 

But since first moment doesn't change when counterbalance weight is added, basically what counterbalance effectively does is increase the resistance to linear motion with negligible influence on resistance to rotational motion about the hands in most of the swing.  

 

How does that help some people?   It's highly subjective so hard to say.  But my guess is maybe by helping smooth out the timing of transition without any potentially detrimental effect on the release timing - resulting in better full body sequencing relative to what they had before the weight was added.   Or maybe it just shifts our mental focus on which type of acceleration we might be concentrating on during the swing.   But the bottom line is that when it comes to the mind and perception, the possibilities are endless.

 

17 hours ago, jammer13 said:

it's also not helpful to ignore grip weight effects on club feel due to balance point changes.

 

Actually, experience shows us that it frequently is helpful.     Sure it's something one needs to be aware of - and it should be validated by actual testing.  But ignoring it - or more specifically NOT trying to compensate for it in any way - is usually the best way to go at first.   Then if testing shows some issues - only then should we try to do something about it.

Edited July 8 by Stuart_G

[RichieHunt]

I've put on and tied a lot of different grips.  When it comes to MOI (for the entire club, not the clubhead MOI), most of the time the MOI won't change if you go to a heavier grip *but* it's the same model.  But if you go to a new model that is heavier there could be some change in the MOI if the new, heavier grip has more of the weight toward the mouth of the grip than the butt end.  

And I would see a pretty decent sized change in MOI if I went to something like a JumboMax original grip that just weighs far more.  But again, there's likely some more weight toward the mouth of the grip to cause that change in MOI.

 

 

 

RH

[Stuart_G]

34 minutes ago, RichieHunt said:

I've put on and tied a lot of different grips.  When it comes to MOI (for the entire club, not the clubhead MOI), most of the time the MOI won't change if you go to a heavier grip *but* it's the same model.  But if you go to a new model that is heavier there could be some change in the MOI if the new, heavier grip has more of the weight toward the mouth of the grip than the butt end.  

And I would see a pretty decent sized change in MOI if I went to something like a JumboMax original grip that just weighs far more.  But again, there's likely some more weight toward the mouth of the grip to cause that change in MOI.

 

Don't know if you already thought of this - but my first thought would be more to how the grip cap might effect the "playing length" that the MOI machine "sees".   In essence it's possible (in theory) that a different grip cap size or geometry can shift the axis the MOI is being measured against in a way that doesn't reflect a change in where the player actually takes their grip relative to where the measurement is taken. 

 

A similar thing ("error"?) is a very common with swing weight machines.  At least on the pictures I've seen of the golf Auditor MOI machine it looks like the grip cap size would effect the results in that way.

 

But you can always do a basic check to your hypothesis by checking and comparing the c.g. location of the grip.   Not definitive of course but not a bad first check.

Edited July 8 by Stuart_G

[jammer13]

10 hours ago, Stuart_G said:

First of all (and most importantly) If you think about it, you'll see that adding butt weight will not increase the first moment any more than it increases the MOI - in fact less.  And it's for the same reason.  All the 'new' mass is being added under the hands - not any place that in will increase the torque on the hands.   Sure the balance point moves closer to the hands but the total mass  increases such that first moment stays the same.

Thanks for the response.  I should have done the calculations on the first moment, I had assumed some effect since I was using the butt end of the club as the axis.  Using that basis, I just calculated less than 0.5% difference in first moment, and less than 0.1% change in MOI for a 7-iron I just built with a 10 g grip weight increase - so pretty negligible.   If thinking about it as a force couple then the axis should maybe be somewhere in between the hands (4 inches from the butt?) and the first moment would be unchanged with a grip weight change.  All this, of course, with a drop of 2 points in swingweight.  Clearly then, first moment isn't such a factor on why some people "feel" the club differently when changing grips.

 

 

10 hours ago, Stuart_G said:

Of course the fact that the point of rotation isn't really a constant makes the MOI of the club about one single axis a very imperfect representation of that resistance to acceleration.   It's really the resistance to our attempts to rotate the club right at the transition point of the swing - not at all times during the swing.  At the very beginning of the take away when the velocity is still very low, first moment might certainly have some influence on feel.

I was thinking the first moment may more have a role in feel trying to keep the club on plane. Imagine a very tip heavy club (high first moment) causing the club to drop below plane especially at transition.  Not sure how much effect this really has. 

[jammer13]

4 hours ago, Stuart_G said:

But you can always do a basic check to your hypothesis by checking and comparing the c.g. location of the grip.   Not definitive of course but not a bad first check.

I have done this with several grip models, and they were all very close to 4" from the butt of the grip.  It's quite possible other model types could be different.

[Stuart_G]

1 hour ago, jammer13 said:

I was thinking the first moment may more have a role in feel trying to keep the club on plane. Imagine a very tip heavy club (high first moment) causing the club to drop below plane especially at transition.  Not sure how much effect this really has. 

 

It is known that for some people, head weight and shaft weight does have the potential to effect the path of the club for the down swing - which then results in a change to the club path relative to target line through impact.    Personally I think it has more to do with how a change in weight feel can effect the perception of how the club is moving (or needs to be moved) which causes an inadvertent effort by the player that results in the change in motion.  As opposed to any direct influence by the change in weight on the dynamics.   Other than maybe the first part of the take away, from what I've seen, most Biomechanicists tend to find that the effect of gravity as a whole on the swing dynamics is extremely small and usually ignored in transition and the down swing.    Or another way to put it is that the player has developed a certain expectation for what they should feel from the first moment at the top or in transition.  Then when that feel is changed due to weight added to the club, they subconsciously change the way they accelerate the club in order to get that expected feel instead of the 'new' feel.  But that's just my take on the matter.    The inconsistency of how people are effected and what percentage might be effected certainly points more toward an issue of proprioception than it does to dynamics.

[jammer13]

54 minutes ago, Stuart_G said:

 

It is known that for some people, head weight and shaft weight does have the potential to effect the path of the club for the down swing - which then results in a change to the club path relative to target line through impact.    Personally I think it has more to do with how a change in weight feel can effect the perception of how the club is moving (or needs to be moved) which causes an inadvertent effort by the player that results in the change in motion.  As opposed to any direct influence by the change in weight on the dynamics.   Other than maybe the first part of the take away, from what I've seen, most Biomechanicists tend to find that the effect of gravity as a whole on the swing dynamics is extremely small and usually ignored in transition and the down swing.    Or another way to put it is that the player has developed a certain expectation for what they should feel from the first moment at the top or in transition.  Then when that feel is changed due to weight added to the club, they subconsciously change the way they accelerate the club in order to get that expected feel instead of the 'new' feel.  But that's just my take on the matter.    The inconsistency of how people are effected and what percentage might be effected certainly points more toward an issue of proprioception than it does to dynamics.

I am onboard with the proprioception (feel) idea, I was just trying unsuccessfully to come up with a physical reason for a change in feel.  It would be ironic if my feel changes were simply because of the differences in grip itself (hardness, lower hand diameter, etc).

[RichieHunt]

7 hours ago, Stuart_G said:

 

Don't know if you already thought of this - but my first thought would be more to how the grip cap might effect the "playing length" that the MOI machine "sees".   In essence it's possible (in theory) that a different grip cap size or geometry can shift the axis the MOI is being measured against in a way that doesn't reflect a change in where the player actually takes their grip relative to where the measurement is taken. 

 

A similar thing ("error"?) is a very common with swing weight machines.  At least on the pictures I've seen of the golf Auditor MOI machine it looks like the grip cap size would effect the results in that way.

 

But you can always do a basic check to your hypothesis by checking and comparing the c.g. location of the grip.   Not definitive of course but not a bad first check.

 

 

I never really thought of that.  It's a smart idea.

Where I started to see this is when I went from the Golf Pride Velvet Wrap midsize to the SuperStroke Tour Wrap midsize.  IIRC, the weight is very similar and the caps were similar, but the MOI came out higher with the SuperStroke grips and I think the design had more weight towards the mouth of the grip.

 

 

 

 

RH