Calling all Gear Effect experts

[mjstrong]

In one of Trackman's newsletters (http://www.trackman.dk/download/newsletter/newsletter5.pdf), they state that an off center hit, for both irons and woods, will result in a differently-tilted spin axis (no surprise there), but will not result in any change to the launch angle. This goes against existing thinking that the bulge and roll of a fairway wood are there to counter the effects of the tilted spin axis by starting the ball outwards and allowing the gear effect spin to bring the ball back to the middle.

Would not a toe-hit with a driver or fairway wood result in both a more leftward (RH golfer) spin axis and rightward initial launch?

Upon more detailed reading of their July 2009 newsletter, they seem to assume that the opening of the clubface that will happen with the toe hit is included in their clubface measurement/calculation. Their chart is a little misleading.

So, then my question would be: how much of an off-center hit results in how much of a change in face angle/initial launch angle? Are the bulge and roll of clubs designed to balance these effects perfectly? Meaning, would a swing with a 0 face and 0 path, but a toe hit, have it's "opened" face angle and changed spin axis offset each other to end up back at the target?

Just thinking out loud here...

 

[dominicscaife]

Just thinking out loud here...

I agree with you. I suspect Trackman just discounts gear effect for simplicity of calculation.

Let's think this through.

Trackman just measures the ball spin and direction after it hits the club face, the face is not visible so can not be measured so is calculated based on the Trackman model. So the number it gives you has some margin for error which would increase the more roll/bulge involved.

I seem to recall Kevin mentioned that he can fool Trackman with a heel hit. As all D-planers know a specific launch angle, and spin properties can result from an infinite variety of different swing paths/face angles.

So I would speculate there are a few issues that hinder 'doing it right"

1. Models to calculate bulge/roll interactions during impact may not be complete enough.
2. Even if the models were complete. Those models require having accurate friction coefficient data on ball surface, clubface surface, roll/bulge and cleanness of contact between the clubface and ball. (Grass between would change the friction between two). Even 2 different hybrids can have quite different bulge and roll, my old Nike Slingshot had a load of bulge but my new Adams has much less, I think thats why the Adams are favored by so many low handicap golfers.


Presumably Trackman made the call that those factors vary so much, and has such a negligible effect that it's just not feasible to include it.

 

[Frans@France]

So, then my question would be: how much of an off-center hit results in how much of a change in face angle/initial launch angle? Are the bulge and roll of clubs designed to balance these effects perfectly? Meaning, would a swing with a 0 face and 0 path, but a toe hit, have it's "opened" face angle and changed spin axis offset each other to end up back at the target?

I have trouble understanding the question due to the mixing of both horz. launch, vert launch bulge and roll.

If hit on the toe, due to bulge you are hitting it on the area of the face that is open. So while it's center has a 0 degree face angle the toe has an open angle. That open face will correct the fligth offset to the left due to gear effect. The final result between the open face forcing the ball to go to the right and the gear moving it to the left will generate a ball the will return to the target line.

Using a driver without buldge would bring to ball to far to the rigth of the target due to gear effect.

 

[Frans@France]

Even 2 different hybrids can have quite different bulge and roll, my old Nike Slingshot had a load of bulge but my new Adams has much less, I think thats why the Adams are favored by so many low handicap golfers.

Bulge is a calculation based on the position of the cog. If a club has less bulge it means that the cog is closer to the front of the face.

 

[wulsy]

I have trouble understanding the question due to the mixing of both horz. launch, vert launch bulge and roll.

If hit on the toe, due to bulge you are hitting it on the area of the face that is open. So while it's center has a 0 degree face angle the toe has an open angle. That open face will correct the fligth offset to the left due to gear effect. The final result between the open face forcing the ball to go to the right and the gear moving it to the left will generate a ball the will return to the target line.

Using a driver without buldge would bring to ball to far to the rigth of the target due to gear effect.

Hi Frans

I was a bit confused about your last comment about the ball going to the right if there was no bulge.

Does this mean that the gear effect (toe hit causing ball to curve left) is dependent on bulge being present?

Thanks, wulsy

 

[natep]

This link may have some useful info:

All about Gear Effect - 3

 

[ggsjpc]

Yea, there are some serious mistakes in some of the above posts.

 

[Frans@France]

Hi Frans

I was a bit confused about your last comment about the ball going to the right if there was no bulge.

Does this mean that the gear effect (toe hit causing ball to curve left) is dependent on bulge being present?

Thanks, wulsy

Confused by your statement because I have not stated that the ball will go right if there is no bulge.

This is what I wrote

"the open face forcing the ball to go to the right " and "gear moving it to the left "

If there is no bulge the face it not open and there is only gear effect present to move it the the left.

arggg.....re-reading everything again.......... I also wrote "Using a driver without buldge would bring to ball to far to the rigth of the target due to gear effect"

that should read "Using a driver without buldge would bring to ball to far to the left of the target due to gear effect"

 

[Frans@France]

Yea, there are some serious mistakes in some of the above posts.

Which ones? besides the last sentence with the right left error.

 

[Frans@France]

Does this mean that the gear effect (toe hit causing ball to curve left) is dependent on bulge being present?

Yes, bulge is only there to counter-act the gear-effect. The calculation of the correct radius is based on the center of gravity

 

[ggsjpc]

Which ones? besides the last sentence with the right left error.

Yes, and it was corrected.

 

[ggsjpc]

In one of Trackman's newsletters (http://www.trackman.dk/download/newsletter/newsletter5.pdf), they state that an off center hit, for both irons and woods, will result in a differently-tilted spin axis (no surprise there), but will not result in any change to the launch angle. This goes against existing thinking that the bulge and roll of a fairway wood are there to counter the effects of the tilted spin axis by starting the ball outwards and allowing the gear effect spin to bring the ball back to the middle.

Would not a toe-hit with a driver or fairway wood result in both a more leftward (RH golfer) spin axis and rightward initial launch?

Upon more detailed reading of their July 2009 newsletter, they seem to assume that the opening of the clubface that will happen with the toe hit is included in their clubface measurement/calculation. Their chart is a little misleading.

So, then my question would be: how much of an off-center hit results in how much of a change in face angle/initial launch angle? Are the bulge and roll of clubs designed to balance these effects perfectly? Meaning, would a swing with a 0 face and 0 path, but a toe hit, have it's "opened" face angle and changed spin axis offset each other to end up back at the target?

Just thinking out loud here...

As a non trackman owner, I will try to answer. I think because trackman calculates face angle, a square sweetspot position with a ball hit on the toe (of a club with bulge) would register as an open face on trackman. Also if above or below the sweetspot the launch angle would be represented by the shape of the face at the impact location. It isn't registering an open face because of the twisting. It's measuring an open face because the toe side points more right than the sweetspot(for a right handed club).

Just guessing here, but I think trackman may be saying that the twisting that results from off center hits happens after the balls direction has been determined and has no effect on the launch conditions.

 

[Frans@France]

Yes, and it was corrected.

ah... well my english is no good but I did see the use of some plural?

"Yea, there are some serious mistakes in some of the above posts." or was that a mistake

 

[ggsjpc]

ah... well my english is no good but I did see the use of some plural?

"Yea, there are some serious mistakes in some of the above posts." or was that a mistake

Another was lost in translation and turned into a misunderstanding on my part.

 

[mjstrong]

Just guessing here, but I think trackman may be saying that the twisting that results from off center hits happens after the balls direction has been determined and has no effect on the launch conditions.

I think you're right.

I've also found a few of my own answers. It's been reported (don't ask me to quote my source's sources) that: an off-center hit of 1/2", assuming a typical bulge radius of 12" for a driver, would result in a change in face angle of approx. 2.4°. So, a square sweetspot, combined with a 1/2" toe hit, will result in a 2.4° open face reading. If the path was also square, that same 1/2" mishit should (according to Trackman's newsletter) experience a hook-tilting of its spin axis by 20°. This would still be a pretty severe hook though, definitely not ending up near the target. Either one of those calculations is wrong, or golf clubs aren't made with enough bulge (which I think they are). Hmm...again, just thinking out loud...

John, weren't you asking for a more "complete" model of the D-Plane earlier, to include off-centre (Canadian spelling) hits? Rhetorical question, I know you were. I think that it is possible to calculate all of this, and even to have a fairly trustworthy model. It would be very calculation-heavy, but I think it could be done. An earlier poster made some good comments about having to know the coefficients of friction involved and such, but it can all be calculated...

(Do I use too many "..."'s in my posts?)

Thanks guys.

 

[Frans@France]

It's been reported (don't ask me to quote my source's sources) that: an off-center hit of 1/2", assuming a typical bulge radius of 12" for a driver, would result in a change in face angle of approx. 2.4°. So, a square sweetspot, combined with a 1/2" toe hit, will result in a 2.4° open face reading. If the path was also square, that same 1/2" mishit should (according to Trackman's newsletter) experience a hook-tilting of its spin axis by 20°. This would still be a pretty severe hook though, definitely not ending up near the target. Either one of those calculations is wrong, or golf clubs aren't made with enough bulge (which I think they are). Hmm...again, just thinking out loud...

I would not worry the bulge, it's formula is know for a long time and don't think that after the spalding reseach any head released had not the correct bulge.

Important part of the trackman newsletter is that the data presented has a horz. launch angle of 0 degree. So either the test was done using a head without bulge or the data is recalculated to explain the deviation when having a horz. launch angle of 0 degree.

IMHO it is clear that it was a recalculation to explain also the reason behind the bulge...just read this part of the newsletter.

If you impact as much as half an inch towards
the Toe, the dispersion will be 35 yards left of the target on
a 250 yards carry!

Luckily the club manufactures have added a curvature to the club
face (the bulge) on woods and drivers. This means that when you
impact the ball on the heel your face angle at the impact point will
most likely be closed, hereby starting the ball more left and tilting
the D-plane towards a draw spin. The net effect will be a much
straighter shot compared to the zero face angle situation.

 

[wulsy]

If you impact as much as half an inch towards
the Toe, the dispersion will be 35 yards left of the target on
a 250 yards carry!

Luckily the club manufactures have added a curvature to the club
face (the bulge) on woods and drivers. This means that when you
impact the ball on the heel your face angle at the impact point will
most likely be closed, hereby starting the ball more left and tilting
the D-plane towards a draw spin. The net effect will be a much
straighter shot compared to the zero face angle situation.

My understanding of this quote wound be that they ignore bulge on the grounds that it "cancels out" the gear effect, ie they use the alignment of the whole clubface independent of bulge as if there was no bulge. No?

 

[dominicscaife]

I think you're right.

I think that it is possible to calculate all of this, and even to have a fairly trustworthy model. It would be very calculation-heavy, but I think it could be done. An earlier poster made some good comments about having to know the coefficients of friction involved and such, but it can all be calculated...

(Do I use too many "..."'s in my posts?)

Thanks guys.

...'s are fine by me... they show an enquiring mind right? I probably do the same.

I think the point is that the benefit in terms of increased accuracy of doing those complicated calculations and measurements necessary to do it right just doesn't make sense versus the cost involved.

Trackman's a great tool as is. Would there be a real benefit from having to spend a bunch of time measuring clubs over and above the current situation.

I doubt it.

Certainly the rave reviews from Trackman users on this forum suggest Trackman is at a pretty nice sweetspot of maximizing benefits for teaching golfers how to optimize their swing.


Wulsy, yes that was my conclusion above as well.

 

[Frans@France]

My understanding of this quote wound be that they ignore bulge on the grounds that it "cancels out" the gear effect, ie they use the alignment of the whole clubface independent of bulge as if there was no bulge. No?

I have trouble understanding your question, the data presented is either from a head without bulge or from a head including bulge and then recalculated like there is no bulge. They only did that to explain gear effect. So the 20Degree spin axis tilt is if there is no bulge.

The data presented can not be measured using a bulged driver head as it is impossible to hit it towards the heel or toe and still have a horz. launch angle of 0, if path, face and attack are 0.

 

[Dan44GT]

Trackman does measure impact face angle (regardless of where on the face you hit the ball). It is simply a measurement of what is being introduced to the golf ball. I do not believe that bulge makes up for gear effect, although it does give you a fighting chance. One reason it could not be a perfect fit is that ball speed plays a role in how much the ball ultimately curves. I would venture a guess that there is one specific ball speed that would bring any shot back to the sweet spot implied direction, no matter the severity of mishit. But only one specific speed would land it back on that line. Too slow would not curve the ball back enough, and too much speed would over-curve the ball.

As for the original post question, launch angle (horizontal or vertical) is strictly based on face angle (spot of contact, not necessarily sweet spot) and true path.