USGA on U grooves: Impact on GCA?

[Garland Bayley]

...
I meant the Pinnacle comment as a joke. I don't necessarily think it would carry like a ProV1 and it certainly wouldn't have been playble from 100 yards in for a good player.

     
Of course it would carry like a Pro V1!

[TEPaul]

Garland:

To a seemingly fairly large extent the Tech Center appears to agree with you.

I'm sure you can see what I'm trying to do here. I'm trying to coalesce this discussion down to try to figure out how much importance to attach to the subject of spin rate.

I realize it's not the only thing---eg the only factor, I just want to figure out how significant it is given the various other factors involved in ball performance.

[Brent Hutto]

Garland, which of these do you not believe?

1) The ball's initial launch trajectory is always lower than the effective loft of the clubface at impact.

2) The fact that it comes off the face at an angle lower (more horizontal) than the clubface effective loft is because it rolls slightly up the clubface.

3) The roll up the clubface produces backspin.

4) The more it rolls up the clubface, the more backspin and therefore the greater the difference between clubface effective loft and initial launch angle.

Because if those four things are true, then indeed there is an inverse relationship between backspin and launch angle for various golf balls for any given impact parameters (meaning effective clubface loft and clubhead speed at impact).

A quick Google search turns up this short, easy to read paper available online that gives algebraic expressions for the relationships between backspin, launch angle and the conditions of impact:

tinyurl.com/2npsec

However, its formulas do not have parameters for golf ball characteristics. I don't have a reference available for real differences between high and low spin golf balls. But as you will see from equations (10) and (11) on pg. 564 there is of necessity an inverse relationship between amount of backspin and launch angle with effective loft and clubhead speed held constant.

I suspect you'll find somewhat more detailed ball characteristic discussion in Jorgenson and there are neat high speed photos in Cochran and Stobbs. Both of those are referenced in the linked article, among other references.

P.S. Let me point out that the simple formulas in the Penner article assume a constant radius and MoI for the golf ball, which is course is very much not the case. It is from relative differences in the radius, MoI and COR of the ball as it deforms (compresses) that differences in the spin and launch angle of various real-world golf balls arise. You're unlikely to find an easy-to-read, public treatment of this non-linear behavior.

[Garland Bayley]

Brent,

The url given requires login by a member.

[Garland Bayley]

Brent,

Drivers have bulge and roll. The higher the ball rolls up a driver face, the higher the loft of the driver is.

Does your reference take that into account?

[Brent Hutto]

Ooops, I'm reading it from behind my University's firewall which probably grants us subscriber rights. Nothing I can do to get around that for you AFAIK. Sorry, but life's too short to try and duplicate formulas and diagrams. It's not particularly important anyway, just the first thing that popped up when I Googled.

P.S. If I could find the non-linear formulas that actually include ball deformation, that would be worth the effort of finding a way to post.

[Brent Hutto]

Drivers have bulge and roll. The higher the ball rolls up a driver face, the higher the loft of the driver is.

Does your reference take that into account?

Nope, but the rolling motion only moves up a fraction of an inch of the clubface because the ball dwells on the clubface for less than a millisecond.

[Bryan Izatt]

Do you have any idea if it's a significant or insignificant effect?  If the rpms were 500 less does that make the launch angle 1* higher?

It's not a huge effect with a driver. Something like a a couple of degrees launch angle difference between a high-spin ball and a low-spin one. Then again, some people doing club fitting will spend a lot of time trying to get one more degree more or less launch angle.

Here's how it shows up. If you were to measure the three important impact angles (clubface loft, added dynamic loft due to the shaft kicking forward, upward travel of the clubhead due to playing the ball forward and teeing it high) then you might expect the sum of those to give you the inital launch angle of the ball. In the real world the ball always comes off anywhere from a couple degrees to several degrees lower than that effective total clubface angle. That's because it rolls up the clubface, producing spin in the process.

Keep in mind that this works in the direction that the typical high swing speed player is trying to get. They want high launch and low spin off the driver. Well, getting the ball to spin a couple thousand rpm less also makes it launch a degree higher so if anything it just makes spin/launch fitting work a bit easier than if it worked the other way around.

With wedges and short irons it's a big deal. I think a high-spin ball comes off a pitching wedge as much as four degrees lower than a low-spin ball.

Brent,

You start by saying it's not a huge effect with the driver, but then say later it wiuld be several degrees, meaning 3 or more.  That's huge in the fitting process.  

Later you say that reducing spin by a couple of thousand (2,000) rpms would result in a 1* change in launch angle.  A couple of thousand rpms is huge.  A thousand rpm difference would be large.

I did look at your url and of course I couldn't get through to it. Without too much work could you do a CTRL PrintScreen and save it to a jpeg file and post it or e-mail it to me.  You've got me really intrigued by the paper and the formulas.

[Brent Hutto]

Let me try to say it more clearly...

a) The launch angle is always lower than the effective loft.

b) With a low spin ball launch is just a little bit lower than effective loft, with a high spin ball it's somewhat "more lower".

c) In any case, it is a very small effect in the same direction as most fitting sessions are trying to achieve so it's no big deal.

If you're choosing a golf ball to give you low-spin and high-launch then a tiny little bit of the high-launch comes for free with the low-spin, that's all I'm saying. Not worth getting worked up about, purely a trivia tidbit I thought I'd share since you guys were interested.

I can't say how much difference in angle corresponds to such-and-such amount of spin because I've never seen that data published (although it gets measured every time someone compares golf balls using a state-of-the-art launch analyser).
What I can say based on numbers I've seen is that with wedges a high-spin ball can launch four degrees lower than a low-spin one but that corresponds to a difference of several thousand rpm. Plus it's at a high loft which exaggerates the difference. So it has little to do with driver fitting but I happen to have seen the numbers.

[Bryan Izatt]

"The late upshoot is a function of the initial ball speed and the lift created by the spin.  The faster the initial horizontal speed the longer it would take for the lift to overcome the horizontal speed."

Bryan:

Does a modern age ball like a ProV have less initial horizontal speed than the old high spin softer balata ball?  No, I expect that the ProV1 would have a higher initial horizontal speed than the old high spin softer balata ball for the same driver speed

And if it doesn't then why doesn't it stay down initially like the old high spin ball did?  Because it has a higher initial launch angle for the reasons listed in previous posts - higher loft,  lower kick points in the shafts, higher teeing, more of an upswing.  Brent and I are still debating the effect of spin on initial launch angle.

And what about the difference in spin rate between the two balls regarding that initial low trajectory (or not)?  Brent and I are still debating the effect of spin on initial launch angle.  IMHO the spin would not account for the difference between your perception of the old low initial launch angle and the current high ones.  What initial launch angle do you think there was in the old days (8*?).  Current optimal launch angles are in the 12-13* degree range.

It may've been just a ballpark remark but i recall the tech center mentioning the old balata ball probably had a spin rate of around 3,000rpm while these modern age balls are closer to 2,000rpm.  From my experience, my spin rate is around 3,000 to 3,200 rpms with modern equipment and balls.  My swing speed at 103 mph is marginal as far as gaining an advantage from high launch low spin.  Low spin for higher speed swingers is in the low 2,000's.  The old balata ball probably spun in the 3,000's range for pros.  The upshooters were probably getting higher than that, but I have no data.

[Bryan Izatt]

Tom,

You seem to be continuing to be puzzled by the old upshooting trajectory and spin rates and launch angles.

One more time, initial launch angle has little to do with spin rate (subject to resolution of the discussion with Brent).  The trajectory after launch depends on launch angle, ball speed, lift (caused by spin), drag and gravity.  In that context trajectories are fairly well understood and have been mathematically modelled.  

For your old upshooting shot, initially the high initial high horizontal velocity overcomes gravity and lift.  As the drag slows the ball down the ball will upshoot if the lift (caused by high spin) outweighs gravity.  Eventually the spin decays and the horizontal velocity decays due to drag and the ball drops due to gravity.

The modern trajectory starts with the ball launched at a higher angle.  Again the initial high velocity overwhelms gravity and lift forces so the ball rises at a relatively straight angle.  As the velocity decays the trajectory flattens.  If the lift (caused by the lower spin rate) and gravity are about equal the ball will travel a flat trajectory until the spin decays enough that the gravity overcomes the lift. The ball will descend on a flatter trajectory than the upshooter does.

Hope that helps.

[Garland Bayley]

...

Does a modern age ball like a ProV have less initial horizontal speed than the old high spin softer balata ball?  No, I expect that the ProV1 would have a higher initial horizontal speed than the old high spin softer balata ball for the same driver speed
...

     
So are you saying Titleist reduced the COR of the balata ball for some reason?

That would be quite a reach IMHO.

[Bryan Izatt]

Brent,

I wasn't too worked up about it.  I was just trying to understand.

I'd be inclined to agree with your comments about the launch angles with wedges.  But, as always if you could point me to the data I'd certainly be interested in seeing it.  

As for the driver my feeling was that the spin impact on launch angle would be relatively minimal (I'm guessing a fraction of a degree for the spin differences we're talking about), as you seem to be saying now.  Even if there was someone who had studied this and mathematically modelled it in all of its intricacies, I doubt I would be able to do the math involved anymore.  (Although I wouldn't mind trying).

In any event, I guess I was also trying to make a point with Tom that spin rate doesn't have a significant enough impact on launch angle to account for his perception that balata balls all launched lower in the old days.  They used to launch low for the reasons stated in other posts here, not because of their spin rate.  You onside with that?

[Bryan Izatt]

...

Does a modern age ball like a ProV have less initial horizontal speed than the old high spin softer balata ball?  No, I expect that the ProV1 would have a higher initial horizontal speed than the old high spin softer balata ball for the same driver speed
...

     
So are you saying Titleist reduced the COR of the balata ball for some reason?

That would be quite a reach IMHO.

No, I think they've increased the COR of the Pro V1 compared to the old balata balls.  

[Garland Bayley]

...

Does a modern age ball like a ProV have less initial horizontal speed than the old high spin softer balata ball?  No, I expect that the ProV1 would have a higher initial horizontal speed than the old high spin softer balata ball for the same driver speed
...

     
So are you saying Titleist reduced the COR of the balata ball for some reason?

That would be quite a reach IMHO.

No, I think they've increased the COR of the Pro V1 compared to the old balata balls.  

Tom Paul has said that the data he has seen from the USGA would put the COR of the Pro V1 and the Pinnacle at the same level. I think the data from the balata ball should say the same. Remember, the Pro V1 has to pass the initial velocity test just like the balata balls had to.

[Bryan Izatt]

...

Does a modern age ball like a ProV have less initial horizontal speed than the old high spin softer balata ball?  No, I expect that the ProV1 would have a higher initial horizontal speed than the old high spin softer balata ball for the same driver speed
...

     
So are you saying Titleist reduced the COR of the balata ball for some reason?

That would be quite a reach IMHO.

No, I think they've increased the COR of the Pro V1 compared to the old balata balls.  

Tom Paul has said that the data he has seen from the USGA would put the COR of the Pro V1 and the Pinnacle at the same level. I think the data from the balata ball should say the same. Remember, the Pro V1 has to pass the initial velocity test just like the balata balls had to.

I don't think Tom said he saw any data.  He said they speculated that you'd get similar distances.  Why do you think the balata ball would be the same?  Clearly the Pinnacles were longer than the balata balls back when.

Indeed all balls have to pass the initial velocity test.  Does that mean they are all exactly maxed out to the limit?  And what about distance performance below or above the test speed? Are you suggesting that all the manufacturers' work in the last 5 to 10 years on materials, cores, mantles, covers, etc hasn't in some way created balls like the Pro V1 with COR's that are higher than the Titleist balata balls?  Aren't Pro V1's just a Pinnacle at the core with a marshmallow cover for short game spin?  Weren't Pinnacles longer than balatas?

[Bryan Izatt]

Brent,

Some further info that sort of supports your contention.  It's from the USGA's Dr Quintavala's much maligned report on the EFFECTS OF CLUBHEAD SPEED ON DRIVER LAUNCH CONDITIONS.  It's empirical data from their testing of launch conditions at various driver speeds.

The preamble to the results table states:

"Some basic trends can be observed from this data. First, a clubhead speed increase of 39% results in a ball speed increase of about 37% in all cases. This is due to the declining coefficient of restitution with impact speed, as discussed in the next section. Second, the launch angle decreases with increasing impact speed, about 0.7 degrees +/-0.1. Third, the spin rate increases with increasing club speed, 660 rpm on average."

I think they are saying the increased spin and decreased launch angle effects are caused by increased clubhead speed. But the relationship between spin and launch angle is inverse as you've stated.  Whether that would hold true for two balls of different spin characteristics struck at the same speed is another question.  The data is questionable too in the sense that the setup was different at different swing speeds so that the strike was comparable.  Those differences could have impacted spin and launch angle.  Interesting though.

The delta of 0.7* per 660 rpm is not large.  For Tom, it doesn't seem likely that the spin differences would account for the low launch of old balatas that you saw.  Unless of course those long hitters of yore were creating 5,000 or 6,000 rpms with their drivers.  

[TEPaul]

"I don't think Tom said he saw any data.  He said they speculated that you'd get similar distances.  Why do you think the balata ball would be the same?  Clearly the Pinnacles were longer than the balata balls back when."

That's right. I didn't see data. What I'm talking about were conversations. My arrangement is very simple---it's that I can ask general questions about the physics and dynamics involved in golf ball aerodynamics and ball performance in a general sense. I don't ask about the USGA Tech Center's specific statiistical test data. I'd assume that's probably somewhat classified for obvious reasons. I don't ask about USGA I&B future policy or even present policy. If I ask a question that's not appropriate in this kind of simple conversation context I don't get an answer. Very simple really. Plus there is no real reason for me to start asking technical mathematical questions about the reasons why some of these things work, perform or happen as they do for the simple reason I wouldn't understand them anyway. I'm definitely not mathematically or technically minded like you two guys are.  

Oh, by the way, when you two guys finally come to an agreement in your discussion on launch angle, spin rate, horizontal speed, lift, drag and the inverse secrets of the Bernouilli Effect would you mind explaining it all to the USGA Tech Center so they can get on with the job of understanding golf club performance characteristics and golf ball aerodynamics?  

[TEPaul]

"Indeed all balls have to pass the initial velocity test.  Does that mean they are all exactly maxed out to the limit?  And what about distance performance below or above the test speed? Are you suggesting that all the manufacturers' work in the last 5 to 10 years on materials, cores, mantles, covers, etc hasn't in some way created balls like the Pro V1 with COR's that are higher than the Titleist balata balls?  Aren't Pro V1's just a Pinnacle at the core with a marshmallow cover for short game spin?  Weren't Pinnacles longer than balatas?"

That's right. As I understand it all conforming golf balls have to pass the initial velocity test and four other specification tests. In that overall context to be conforming they have to pass the USGA's ODS test which is essentially a "pass/fail" line on overall distance.

Since almost all good and high swing speed players used the high spin three piece ball up to around a decade or so ago the question became where were those high spin three piece soft balls in relation to that ODS "pass/fail" line and also compared to say the 1990 Pinnacle? And where was that old Pinnacle in relation to that ODS "pass/fail" line? My sense is that a ball like the Pinnacle was right on it and the old high spin three piece ball was somewhat below it. The question is by how much?

I did ask that question once of Frank Thoms but I didn't get an answer. Maybe there isn't one. Maybe they didn't keep that comparative data or maybe it was classified for manufacturing reasons. All he said was the ODS was a "pass/fail" line and the mph protocol of 109 (now 120) was an arbitrary selection that they thought was representative enough for golf generally. He just said the high spin three piece ball passed as did the low spin two piece Pinnacle type ball. Where either ball was distance-wise in relation to the ODS "pass/fail" line wasn't the point. The point was did they pass or didn't they?

[Bryan Izatt]

Tom,

Oh sure, I'm going to go tell those USGA PhD's, who work on this full time every day, how the physics works.  I'm not quite that vain    I'm sure they know much more than any of us.  Too bad they can't share;  and, when they do, some on here are inclined to tear apart their methodologies.

Here's a piece of logic - not mathematically or experimentally supported - re the Pinnacles, the Balatas and the ODS.  Seems everyone agrees that Pinnacles were longer than the Balatas.  Let's assume that was true uniformly across the swing speed spectrum.  (I don't recall in that era anyone claiming the Pinnacles were shorter for them.)  

So, if we took a bunch of people who swung at the the ODS speed limit of 109 mph and had them hit the two kinds of balls, I'd expect the Pinnacles would have uniformly come out longer.  The most likely cause would be a difference in initial velocity, probably from different COR's.  If the Pinnacle met the initial velocity standard then the Balatas must have been below it.  It's my theory and I'm sticking to it (despite it's obvious flaws) because the people who might know (the USGA), are not talking.

[TEPaul]

Bryan:

I don't think there is any question the Pinnacle was longer than the old balata a decade and more ago. Tech seems to suggest it was a matter of trajectory giving the Pinnacle greater carry distance. I doubt they'd know if that was true across the swing speed spectrum because they never tested that. They tested at 109mph.

For distance almost all the high swing speed players used the wrong ball. But the real question is---did the low swing speed players use the wrong ball? The Pinnacle may not have been the best ball for distance with lower swing speed players. They all used low spin rocks like the Pinnacle. Perhaps they should've used higher spinning balls to create more lift.

Since almost all high swing speed players (good players) back then used high spin rate balls and almost all higher handicappers and lower swing speed players used low spin rate rocks like Pinnacles back then, it really would be pretty ironic if both groups of players were using the wrong ball for them for distance.  

[Brent Hutto]

Driver distance isn't the only distance that matters and driver carry distance isn't the only kind of driver distance that matters.

For a low clubhead speed player who doesn't compress the ball well, high spin giveth driver carry distance and high spin taketh away iron carry distance.

So it could be argued that an 80's-vintage handicap golfer with a weak swing should have been playing a distance ball. With a low-spin ball they'll get back in roll and straightness at least as much distance as they lose on driver carry (and for driver carry+roll is probably as important than pure carry for weaker players) while maximizing carry distance with irons where it matters most.

That's certainly why I play a low-compression distance ball. As long as the cover is soft enough not to totally play like a rock with wedges and chips, the 3-5 extra yards of carry my low-80's driver swing gets with a high-spin ball can't possibly make up for curving more plus being shorter with the irons. Unless of course I have a 180-yard forced carry off the tee on a cool day, then I'm well and truly screwed (ask Sean Arble).

[TEPaul]

"...and high spin taketh away iron carry distance". (from the low swing speed player).

Are you sure about that and if you think you are what empirical evidence are you basing that on?

[Doug Siebert]

Brent,

Some further info that sort of supports your contention.  It's from the USGA's Dr Quintavala's much maligned report on the EFFECTS OF CLUBHEAD SPEED ON DRIVER LAUNCH CONDITIONS.  It's empirical data from their testing of launch conditions at various driver speeds.

The preamble to the results table states:

"Some basic trends can be observed from this data. First, a clubhead speed increase of 39% results in a ball speed increase of about 37% in all cases. This is due to the declining coefficient of restitution with impact speed, as discussed in the next section. Second, the launch angle decreases with increasing impact speed, about 0.7 degrees +/-0.1. Third, the spin rate increases with increasing club speed, 660 rpm on average."

I think they are saying the increased spin and decreased launch angle effects are caused by increased clubhead speed. But the relationship between spin and launch angle is inverse as you've stated.  Whether that would hold true for two balls of different spin characteristics struck at the same speed is another question.  The data is questionable too in the sense that the setup was different at different swing speeds so that the strike was comparable.  Those differences could have impacted spin and launch angle.  Interesting though.

The delta of 0.7* per 660 rpm is not large.  For Tom, it doesn't seem likely that the spin differences would account for the low launch of old balatas that you saw.  Unless of course those long hitters of yore were creating 5,000 or 6,000 rpms with their drivers.  

I think what you are quoting does support Brent's position.  As increased clubhead speed in Quintavala's tests causes more spin, it also causes a slightly reduced launch angle.  660 more rpm and 0.7 degrees lower launch angle.

[Bryan Izatt]

Doug,

It's indicative, but not conclusive.  Where it comes up short, is in demonstrating that that launch angle is inversely related to spin at the same swing speed.  That wasn't what they were trying to determine in their experiment, so the data doesn't conclusively make Brent's point.

Brent,

Good points about roll needing to be considered too.  The long hitting pros of today want to play an aerial game with minimum roll (to keep from rolling into trouble).  They don't need the extra roll distance.  For the handicap golfer who are often offline anyway, more distance is helpful, however achieved.

The conditions would also dictate the preferred approach - all carry or carry and roll.  I can carry the ball 230.  In the spring I get zero roll.  In the summer I can get up to 70 yards of roll.  In the spring I want a ball to optimize carry.  In summer on some holes I want a ball that will maximize roll and total distance.