Measuring Closure Rate and Grip Roll or Twist on GEARS

[Warlock]

How does GEARS measure 'Closure Rate'?  I've looked at their website but it doesn't seem to go into detail on the method they used. 

For example , when I looked at this AMG video (who use GEARS)  , I couldn't understand how the 'clubface closure rate' could be decreasing for the 2 Golf Pros as the club approached impact . Also the magnitudes seem very small compared to the article I read from Dr Sasho MacKenzie (unless I've misinterpreted something).

 

 

What is 'rate of closure' and can it help your golf swing?

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Rate of Closure is an emerging term you might have heard in golf instruction. We asked Dr. Sasho Mackenzie to explain what it is.

 

Edited February 15, 2022 by Warlock

[iacas]

2 minutes ago, Warlock said:

How does GEARS measure 'Closure Rate'?  I've looked at their website but it doesn't seem to go into detail on the method they used.

The video says it.

• Grip roll is around the axis of the shaft or grip.
• Clubface closure is relative to the plane at that point in the swing.

2 minutes ago, Warlock said:

For example , when I looked at this AMG video (who use GEARS)  , I couldn't understand how the 'clubface closure rate' could be decreasing for the 2 Golf Pros as the club approached impact.

Why couldn't it be "decreasing"?

It closes faster at some parts of the swing than it does at other parts. It's still closing even during the relatively "slower" parts.

[saevel25]

1 hour ago, Warlock said:

I couldn't understand how the 'clubface closure rate' could be decreasing for the 2 Golf Pros as the club approached impact .

It's like saying a car slows down to a stop sign, but is still moving. It's decelerating, but it still has a velocity. 

How fast the club face is turning over is slowing down, but not stopping. 

[Warlock]

8 hours ago, saevel25 said:

It's like saying a car slows down to a stop sign, but is still moving. It's decelerating, but it still has a velocity. 

How fast the club face is turning over is slowing down, but not stopping. 

Please see Dr Phil Cheetham dissertation link below slide 22 and check out the graph of  Handle Twist Velocity (I'm assuming this is the same as Grip Roll) vs Clubhead Closing Velocity where they are highly correlated  (they are both measured in degrees/sec as in GEARS).

If the Grip Roll is increasing so should the Clubhead Closing Velocity but that isn't happening in that AMG video.

Dissertation (philcheetham.com)

You will also note that the minimum Clubhead Closing Velocity is about 1000 deg/sec  while Dr Sasho MacKenzie says in his article the following:

"RoC peaks near impact and a typical range for any group of golfers, regardless of level, would be between 1800 °/second and 3600 °/s. "

The AMG video is showing Closure Rate for those 2 golfers at impact as being -258.87 deg/sec and -359.62 deg/sec.

See GEARS link below and look for Closure Rate

Gears Golf: Club and Ball Metrics - Gears Sports

Closure Rate is a measure of the rotation of the club face as it approaches the impact point. This measurement is calculated relative to the club’s path.

Also, Michael Neff in his video below defined Grip Roll as "how much the grip is turning in plane' .  That sounds like an angular measurement , not a rate as shown in the AMG video (degrees/sec) and in the video below.

Yet the Gears metric weblink I posted above defined Grip Roll as :

Grip rotation is an angular measurement that measures the rotation of the shaft between the top of the backswing and impact.

So the above definition seems to clarify what Michael Neff said in his video but why is it showing as a rate in GEARS? I'm assuming there is some error in the definition of Grip Roll as I am guessing it is the same as Dr Phil Cheetham's definition of 'Handle Twist Velocity'  (which is a metric term also used in GEARS but defined differently).

Edited February 15, 2022 by Warlock

[Warlock]

So I'm still confused about how they measure 'Closure Rate '. Do they take some instantaneous vector normal to the clubface and compare how quickly it changes with respect to the instantaneous vector clubhead path direction?  That sounds more like a rate of change of D-Plane angle.

Edited February 15, 2022 by Warlock

[Warlock]

Looks like I've found a video that explains 'Closure Rate' and its not measured the same way as Dr Sasho MacKenzie or Dr Phil Cheetham.

It does seem to be related to the rate of change of D-Plane .

 

 

[iacas]

@Warlock, two things before I get into this…

• This isn't something I've had to use with students in GEARS, and honestly isn't something I expect to use within GEARS with students, so I haven't looked into it much. If the numbers in GEARS are completely useless because it turns out that they're measuring the rotation of the shaft relative to Alpha Centauri's orbit around Ursa Major, it wouldn't really matter much to me. 😄
• I'll ask a few people who should know, and put it out for discussion amongst GEARS owners, and will report back. My answers below represent my best "knowledge" at this point.

Let's try to be picky about the words we use, etc. "Closure rate" alone can mean a lot of different things. Closure relative to what? If we're talking about the clubhead, are we talking relative to the target line or the instantaneous path of the swing?

12 hours ago, Warlock said:

How does GEARS measure 'Closure Rate'?  I've looked at their website but it doesn't seem to go into detail on the method they used.

The answer I've gotten, as I've said, is this:

• Grip roll is measured as the twisting around the shaft. So if you look at the butt end of the club, it's twisting 3:00 to 12:00 or vice versa.
• Clubface closure is relative to the path.

I think this video segment shows this relatively well (should start at 7:30):

I believe GEARS measures the "face" as perpendicular to the yellow line, which is basically an extension of the bottom groove for the "closure rate." In other words, if the face is going to hit the ball with a 0.0° path and the perpendicular to the leading edge is 0° as well, but some "x" time before when the path was 5° right but the face was 10° right, then that would be 5°/x rotation (where, again, x is some unit of time).

In the video above, the one golfer is 43° open at 6, which let's assume is 40 milliseconds before impact, and we'll assume he hits the ball square to the path (he almost surely doesn't, but he's probably close): 43/0.04 = 1075°/second.

12 hours ago, Warlock said:

For example , when I looked at this AMG video (who use GEARS)  , I couldn't understand how the 'clubface closure rate' could be decreasing for the 2 Golf Pros as the club approached impact.

Well… Taking this in parts, and addressing the "could be decreasing" part first: I have to believe you understand that a clubface can still be "closing" but doing so at a slower speed. If something is "closing" at one point at (to make up a number) a billion degrees per second, but then slows down to closing only 10 million degrees per second, it's still closing. Just not as quickly.

Sasho's article also says:

The club is swung down and around the body on the forward swing, which presents the Inclined Plane knob. Turning this knob to zero would result in moving the clubhead in a vertical plane like a Ferris wheel (0° from vertical). At a driver speed of 90 mph, an Incline Plane knob turned up to 30° from vertical (a steep move through impact) contributes about 800 °/s to RoC. Cranking the knob up to a relatively flat 45° from vertical, increases the contribution to 1200°/s. There may be reasons to change the pitch of your swing, but reducing RoC shouldn’t be one of them. Tour players tend to have relatively similar vertical swing planes with driver (40° to 45° from vertical) and most amateurs are too vertical already.

Which… doesn't really seem to jive with the numbers I'm seeing from, for example, this multiple-time major winner:

GEARS tells me that at A6 and A7, the numbers are (rounded to integers):

• A6: 775°/sec grip roll, 512°/sec closure rate, 27.4 rpm closure rate^
• A7: 1745°/sec grip roll, 514°/sec closure rate, 431 rpm closure rate^

^ Why are these numbers different?

BTW, the path here was 1.86° out with a face 2.73° open. The frame here is just before impact.

The fact that 512° and 514° are similar, but 27.4 rpm and 431 rpm are wildly different, but both are listed as "closure rate" makes me wonder about a lot of things here. 😛

The thought just occurred to me that maybe the "rpm" one is the shaft rotational rate and the "°/s" is the clubface's rotational rate?

2 hours ago, Warlock said:

Please see Dr Phil Cheetham dissertation link below slide 22 and check out the graph of  Handle Twist Velocity (I'm assuming this is the same as Grip Roll) vs Clubhead Closing Velocity where they are highly correlated  (they are both measured in degrees/sec as in GEARS).

That's because: CCV = HTV sin (θ) + SPV cos (θ) where θ is the Lie Angle. Again, it's the frame of reference and how you're measuring it.

2 hours ago, Warlock said:

If the Grip Roll is increasing so should the Clubhead Closing Velocity but that isn't happening in that AMG video.

This assumes they're using the same frame of reference for "clubface closure."

2 hours ago, Warlock said:

"RoC peaks near impact and a typical range for any group of golfers, regardless of level, would be between 1800 °/second and 3600 °/s. "

So… handle twist velocity (HTV) plus

Since sin(58°) is ~0.84, you're adding two big numbers together. 1075°/second HTV adds about 911 RPM closure rate if measured that way, plus the angular rate of speed of the clubhead which is going to be quite high itself.

2 hours ago, Warlock said:

 

Gears Golf: Club and Ball Metrics - Gears Sports

 

Yes, it says:

Closure Rate is a measure of the rotation of the club face as it approaches the impact point. This measurement is calculated relative to the club’s path.

Specifically, an angle is measured between the face of the club and the path of the club as shown. Closure Rate is the rate of change of this angle measurement (in degrees/second) of the club’s face relative to the club’s path.

That says to me what I said above: it's the face angle relative to the path. What I'm not 100% certain of is whether it's, say, the spin axis/D-plane or just the leading edge normal relative to the path.

There's also this, in the new "Graphs" section (the graphs were re-done in the latest release). This shows a peak "Taylormade Closure Rate" of nearly 2780°/s.

2 hours ago, Warlock said:

Also, Michael Neff in his video below defined Grip Roll as "how much the grip is turning in plane' .  That sounds like an angular measurement , not a rate as shown in the AMG video (degrees/sec) and in the video below.

I'm not sure what you mean about an "angular measurement" versus a "rate." If you have an angular measurement that's changing over time, that's an angular rate of change.

2 hours ago, Warlock said:

Grip rotation is an angular measurement that measures the rotation of the shaft between the top of the backswing and impact.

That's just defining when it's measured. It only measures it for the downswing. See the graph above. The dotted line is the change of direction of the club head.

2 hours ago, Warlock said:

So I'm still confused about how they measure 'Closure Rate '. Do they take some instantaneous vector normal to the clubface and compare how quickly it changes with respect to the instantaneous vector clubhead path direction?  That sounds more like a rate of change of D-Plane angle.

I believe that's about it.

51 minutes ago, Warlock said:

Looks like I've found a video that explains 'Closure Rate' and its not measured the same way as Dr Sasho MacKenzie or Dr Phil Cheetham.

It does seem to be related to the rate of change of D-Plane.

I don't think you should call it the "D-Plane" because it's more like the actual path, and the leading edge/shaft normal (perpendicular to the leading edge and the shaft). The D-Plane is normal to the FACE, not the leading edge/shaft. You could add or take off loft relative to the path and the "closure rate" would be affected a bunch, so maybe stop saying "D-Plane."

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So, it seems like you've arrived at the same conclusion as what I said up above:

12 hours ago, iacas said:

• Grip roll is around the axis of the shaft or grip.
• Clubface closure is relative to the plane at that point in the swing.

I said "plane" but the plane is the tangent to the path at that point, so that's what I was saying.

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From the video up above:

To the last image, I will add this: GEARS doesn't continue to measure grip roll past impact, so I'm not sure if they're measuring the rotation from shaft parallel to shaft parallel, or if they're extrapolating it somehow.

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All that said, my questions are:

• Why are the RPM and the "closure rate" marked the same? Hmmm, maybe it's the Cheetham/Sasho measurement for clubhead closure rate: 431 rev/min * 360°/rev * 1 min/60 sec = 2,586°/sec. That's pretty close.
• Actually that might be my only question. Maybe in GEARS the "°/sec" is showing relative to the path or instantaneous plane, and the rpm is showing relative to the target line.

I think that's all the questions I have now.

[Warlock]

Many thanks for this reply.

[Warlock]

Still trying to get this clear in my head:

Gears 'Closure Rate' is the rate of change of the angle between these 2 vector directions in deg/sec

1. An instantaneous vector direction  perpendicular the leading edge of the club or the bottom groove.

2. A vector showing the instantaneous clubhead path direction (which I assume is the path of the sweet spot or the 'Geometric Centre'  of the golf clubhead).

The AMG video I first posted shows 'Grip Roll' increasing its rate deg/sec  all the way into impact . Which I suppose means an increasing rate of closing clubface rotation of 'point 1 vector' above. 

But if Gears 'Closure Rate' is decreasing from say P6.5-P7  doesn't this infer that 'point 2 vector' above is changing in such a way that it is counteracting the closing rate of 'point 1 vector' above?  That there is a change in clubhead path from P6.5-P7  that is more 'out -in' approaching impact ?

Does that make sense? 

[Pretzel]

Closure Rate is an angular velocity. It is the speed at which an angle is changing, nothing more than that.

In this case the angle is the measured difference between the direction your clubface is pointed and the direction of your swingpath. If your path is neutral (0 degrees open or closed) and the clubface is 2 degrees open, then the measured angle is +2 degrees. If your path is 2 degrees open (in to out) and your clubface is 2 degrees closed then the measured angle is -4 degrees.

A low Closure Rate means your clubface angle is relatively constant over time when compared to the swing path. A high Closure Rate means the clubface is rapidly opening or closing relative to the swingpath. Low closure rates are beneficial for controlling the trajectory of the golf ball, because the difference between clubface angle and path angle is the largest factor in what direction the ball will curve and how tilted the spin axis is (how much the ball will curve).

As you approach impact, the club continues to wrap around your body and the path of the club changes. Unless you come heavily over the top, your downswing starts on a substantially out to in path because you're swinging along a circular arc. As you approach the bottom point of your arc (where impact is located, approximately), this path will point more directly towards the target. In the follow through the path again changes as the clubs wraps back around your body, making the path change to be more out to in than it was at impact. That's the counteracting item that you're missing, because the swing is on a diagonal plane (look up 5 Simple Keys' Diagonal Sweetspot Path for a good explanation) instead of a vertical plane.

 

Edited February 16, 2022 by Pretzel

[Warlock]

4 minutes ago, Pretzel said:

Closure Rate is an angular velocity. It is the speed at which an angle is changing, nothing more than that.

In this case the angle is the measured difference between the direction your clubface is pointed and the direction of your swingpath. If your path is neutral (0 degrees open or closed) and the clubface is 2 degrees open, then the measured angle is +2 degrees. If your path is 2 degrees open (in to out) and your clubface is 2 degrees closed then the measured angle is -4 degrees.

A low Closure Rate means your clubface angle is relatively constant over time when compared to the swing path. A high Closure Rate means the clubface is rapidly opening or closing relative to the swingpath. Low closure rates are beneficial for controlling the trajectory of the golf ball, because the difference between clubface angle and path angle is the largest factor in what direction the ball will curve and how tilted the spin axis is (how much the ball will curve)

 

Yes , that makes sense , but if the 'Grip Roll' or 'Handle Twist Velocity' is increasing as the club approaches impact but the 'Closure Rate' decreasing , then I must assume that it's due to a change in clubhead path.

Edited February 16, 2022 by Warlock

[Pretzel]

2 minutes ago, Warlock said:

Yes , that makes sense , but if the 'Grip Roll' or 'Handle Twist Velocity' is increasing as the club approaches impact but the 'Closure Rate' decreasing , then I must assume that it's due to a change in clubhead path.

I went ahead and edited my earlier post after reading further to see the specifics of your question. Sorry for the confusion, but the explanation you're looking for is now included in my previous post at the bottom.

The path is changing throughout the downswing because it travels along the diagonal sweetspot path that wraps around your body, not a vertical path straight away/towards the target. Think of it like holding a hula hoop vertically up/down versus laying it at an angle, with the hoop being the path your clubface traces as you swing back and through. You can see how the path angle, relative to a target you might be aiming at, changes throughout the downswing.

Edited February 16, 2022 by Pretzel

[Warlock]

42 minutes ago, Pretzel said:

I went ahead and edited my earlier post after reading further to see the specifics of your question. Sorry for the confusion, but the explanation you're looking for is now included in my previous post at the bottom.

The path is changing throughout the downswing because it travels along the diagonal sweetspot path that wraps around your body, not a vertical path straight away/towards the target. Think of it like holding a hula hoop vertically up/down versus laying it at an angle, with the hoop being the path your clubface traces as you swing back and through. You can see how the path angle, relative to a target you might be aiming at, changes throughout the downswing.

I am aware that the club path changes but the confusion I have is regarding the AMG GEARS video I first posted . This is a tour pro golfer whose GRIP ROLL is increasing ~944 deg/sec at P6 (shaft horizontal) to 1734 deg/sec at P7 (impact). 

Yet the 'Closure Rate ' increases from -525.44 deg/sec (P6)   to -613.10  deg/sec (P6.5)  but then suddenly decreases to -359.62 deg/sec (P7).

As per the GEARS method of measuring 'Closure Rate' , if the 'Grip Roll' is increasing (ie. increasing the rate of closing clubface rotation), then the club path must be moving from outside the target line at P6.5 then back into impact by P7. That's the only way I can perceive how the 'Closure Rate' can decrease from P6.5-P7 while the 'Grip Roll' is increasing.

Edited February 16, 2022 by Warlock

[iacas]

7 minutes ago, Warlock said:

As per the GEARS method of measuring 'Closure Rate' , if the 'Grip Roll' is increasing (ie. increasing the rate of closing clubface rotation), then the club path must be moving from outside the target line at P6.5 then back into impact by P7. That's the only way I can perceive how the 'Closure Rate' can decrease from P6.5-P7 while the 'Grip Roll' is increasing.

Have you considered the possibility that the clubface hitting the ball could affect the "clubface" in that moment? As you know a toe hit will open the face even though the grip end could still be twisting the other direction in that moment.

[Warlock]

7 hours ago, iacas said:

Have you considered the possibility that the clubface hitting the ball could affect the "clubface" in that moment? As you know a toe hit will open the face even though the grip end could still be twisting the other direction in that moment.

 

For those AMG golfers in the 1st video I posted the 'Closure Rate' is slowing down between P6.5-P7 and not just at impact , so it is possible that the clubhead path is less in-out from P6.5-P7 than it was from P6-P6.5. 

You mentioned a possible reason why Dr Sasho Mackenzie/Phil Cheetham ROC measurements at impact could be so different to Gears 'Closure Rate' measurement, that they could be using different frames of reference . 

Dr Phil Cheetham used AMM3D for his research and a  'Global Frame Of Reference' (ie. the origin or zero point)  positioned behind the golfer. 

 

Wouldn't the room which holds the Gears cameras be the 'Frame Of Reference' ?  

 

Edited February 17, 2022 by Warlock

[iacas]

36 minutes ago, Warlock said:

Wouldn't the room which holds the Gears cameras be the 'Frame Of Reference' ?  

You're not understanding what I mean there.

45 minutes ago, Warlock said:

so it is possible that the clubhead path is less in-out from P6.5-P7 than it was from P6-P6.5. 

Of course it is, but I think you're still missing out on the fact that the closure rate is relative to that instantaneous path. It doesn't matter where the path is pointing — the "closure rate" is relative to that direction, not the target line.

[Warlock]

11 hours ago, iacas said:

You're not understanding what I mean there.

Of course it is, but I think you're still missing out on the fact that the closure rate is relative to that instantaneous path. It doesn't matter where the path is pointing — the "closure rate" is relative to that direction, not the target line.

I sent an email to Dr Sasho MacKenzie about the 'Closure Rates' at impact for those 2 Pro golfers on the AMG video.

His reply:

"Those numbers seem low even if they are measuring the rate at which the face closes to the path.  My numbers line-up with Phil's data, Rob Neal’s data, and Ping data.  "

[iacas]

6 hours ago, Warlock said:

I sent an email to Dr Sasho MacKenzie about the 'Closure Rates' at impact for those 2 Pro golfers on the AMG video.

And I've talked to him, too. Again, understanding the frame of reference — "degrees" relative to what — is important.

You're reading a lot into ONE frame of ONE video from four years ago. Especially in light of stuff like this:

On 2/15/2022 at 11:07 AM, iacas said:

Again, that measurement gets to 2780°/s or so.

The part at the very end highlights just the little bit at the end. Though the measurements are older, the GEARS software is the latest version as of today.