Optimum Racquet Balance for Performance II - MgR/I Data for ATP Pros

[travlerajm]

Originally Posted by stoneage

I have said several times that my main complain is that MgR/I is the frequency of a single freely swinging pendulum and nothing, I repeat nothing, more. Now you tell me "you see it is a pendulum"!!!!!! Yes, it is the frequency of a pendulum, if you hold the racquet at the but end between your thumb and forefinger MgR/I=21 means that it will swing with 0.73 Hz. But only if the swings are small and you don't move your hand.

I repeatedly ask for some kind proof that you can apply this formula everywhere like you do, and you reply by telling me to take the physics 101! After a number of years of research and teaching at the post doc level, including helping several student to their PhD:s in mechanical engineering, I think I know my physics 101.

You have obviously seen Rod Cross writings about the double pendulum (I recognize some of the statements, even if you write as if they were your own findings). You probaly saw the word "pendulum" and then you found a formula somewhere on the net that also said "pendulum" and used that without understanding what you did.

Rod Cross model includes some radical simplifications, like one that you don't use your wrist, and should be used carefully. But since you re so attached to it lets assume that it is a perfect description. Then behavior of the racquet involves solving eq A10a and A10b in A double pendulum model of tennis strokes. And I can assure you that the result won't be MgR/I.

As to your hilarious statement that you need to take the variation in gravity into account. The air resistance of the racquet has a much greater influence than the gravity, shouldn't you include the air pressure and temperature as well?

There are a lot of helpful people at this forum and if you had chosen so you could have received help from them (me included) and maybe made this into something useful where you know how and when to apply it. Instead you have the attitude that you know it all and can apply it everywhere, even when it obvious that you don't have a clue what you are talking about. Pity.

Since you not are interested in any feedback except praise of your great finding I won't bother you with comments any more.

/Sten
________________________________
Ph.D. (Aerospace Eng.), M.Sc. (Eng. Physics)

Look, buddy.
I have a degree from Stanford in Biomechanical Engineering.
I have a PhD in Chemical Engineering from the largest research university in the world.
The reason I'm in Vienna this weekend is to receive the highest international award in applied science innovation in my field.
I've read every tennis-related article by Lindsey, Brody, Cross, Haake, and Goodwill, and I have respect for their work.
And I've spent enough years of careful experimentation with racquet customization that I am quite certain I know more about how lead tape affects racquet than any of them. The reason I continue to discuss the MgR/I concept is because it works, and because it's an essential tool for anyone interested in optimizing the performance of a tennis racquet. I'm in the process of preparing a comprehensive book on racquet customization in my spare time, which will more formally present the concept, along with other key concepts. I plan to use Lindsey as editor. Until I see something more useful than venom from your posts, I don't have any intention of consulting your help.

[Power Player]

Stoneage i have to say your app is so great that it automatically lends you a ton of credence on this board. I would not worry about it as many of us question a lot of the ideas presented in this thread and what you are saying is legtitimate to me.

[Mig1NC]

I have a bachelors degree in Computer Information Systems... Which means I have no idea what half this means...

But I will say that regardless of the scientific validity of the formula, it does work for me. I have found when I tune my racquets using this formula (and then fine tune) they just feel right. It just clicks.

[jmnk]

Originally Posted by Mig1NC

I have a bachelors degree in Computer Information Systems... Which means I have no idea what half this means...

But I will say that regardless of the scientific validity of the formula, it does work for me. I have found when I tune my racquets using this formula (and then fine tune) they just feel right. It just clicks.

two questions:
1. Have you done any 'blind test' to verify that 'it just clicks'?
2. If you need to 'fine tune' some more - does it mean you end up with MgR/I --not-- being equal to 21.0? if so, doesn't that mean that 21.0 is not any magic number? It's like saying that the 'best' weight for a tennis racket is 290 grams - but you have to fine tune it to suit you. For a player A he will fine tune it to 310gr. Other will tune it to 280 gr. the rackets will feel great for a respective player. Does that mean that the 'best' weight is 290 gr, or not?

Look, if it makes you play better with believing that your racket should be at MgR/I=21.0 than by all means use it. I believe I play better in blue shorts and black wristbands. But let's not claim there's some scientific proof or evidence that racket with MgR/I = 21.0 is 'the optimal one'. No one showed that, including travlerajm.

[Ramon]

Originally Posted by Power Player

Stoneage i have to say your app is so great that it automatically lends you a ton of credence on this board. I would not worry about it as many of us question a lot of the ideas presented in this thread and what you are saying is legtitimate to me.

You got that right! I have Sten's apps on my iPhone. They work great and he constantly keeps them updated.

RacquetTune and SwingTool are the best apps of their kind for tennis players. If you customize your racquets or really want to know how much tension your strings are losing, you need to get these apps!

[Circa 1762]

Originally Posted by jmnk

two questions:
1. Have you done any 'blind test' to verify that 'it just clicks'?
2. If you need to 'fine tune' some more - does it mean you end up with MgR/I --not-- being equal to 21.0? if so, doesn't that mean that 21.0 is not any magic number? It's like saying that the 'best' weight for a tennis racket is 290 grams - but you have to fine tune it to suit you. For a player A he will fine tune it to 310gr. Other will tune it to 280 gr. the rackets will feel great for a respective player. Does that mean that the 'best' weight is 290 gr, or not?

Look, if it makes you play better with believing that your racket should be at MgR/I=21.0 than by all means use it. I believe I play better in blue shorts and black wristbands. But let's not claim there's some scientific proof or evidence that racket with MgR/I = 21.0 is 'the optimal one'. No one showed that, including travlerajm.

I think you're misconstruing travlerajm's argument. Each person, the theory goes, has an ideal MgR/I, but this ideal MgR/I depends on things like arm length. Therefore, each person's ideal MgR/I is going to be slightly different. Travlerajm has looked at the specs of pro's rackets, and based on the assumption (I think) that pros are likely to have MgR/I's close to their ideal, found that the pros cluster around an MgR/I of 21.0 (although again, there are variations due to things like height). As a result, he's suggesting (travlerajm, correct me if I'm wrong) that you might want to start with your search for your ideal MgR/I around 21.0. He is not saying that your ideal will necessarily be 21.0.

Based on a series of blind tests - for example, setting up two rackets with the same weight and swingweight but different balance, leading to different MgR/I's - I've concluded that my ideal MgR/I is around 21.2. I'm shorter than the average pro (5'8"), so this isn't too surprising. And these were blind tests with the exact same racket model and on the same day, so I'm pretty sure the differences I felt were real. So basically, don't just set your racket up to MgR/I = 21.0 and call it a day. If you have two rackets, set one to 21.0 and one to 21.1, and see which you like better (you should feel a difference). Say you like the 21.1 racket better. Next, leave that one the same, but set the other one up to MgR/I = 21.2. If you still like the 21.1 racket, you can be pretty sure your ideal is around 21.1, and almost positive it's between 21.0 and 21.2. You can continue to do blind testing like this until you zero in on your ideal.

[travlerajm]

Originally Posted by Circa 1762

I think you're misconstruing travlerajm's argument. Each person, the theory goes, has an ideal MgR/I, but this ideal MgR/I depends on things like arm length. Therefore, each person's ideal MgR/I is going to be slightly different. Travlerajm has looked at the specs of pro's rackets, and based on the assumption (I think) that pros are likely to have MgR/I's close to their ideal, found that the pros cluster around an MgR/I of 21.0 (although again, there are variations due to things like height). As a result, he's suggesting (travlerajm, correct me if I'm wrong) that you might want to start with your search for your ideal MgR/I around 21.0. He is not saying that your ideal will necessarily be 21.0.

Based on a series of blind tests - for example, setting up two rackets with the same weight and swingweight but different balance, leading to different MgR/I's - I've concluded that my ideal MgR/I is around 21.2. I'm shorter than the average pro (5'8"), so this isn't too surprising. And these were blind tests with the exact same racket model and on the same day, so I'm pretty sure the differences I felt were real. So basically, don't just set your racket up to MgR/I = 21.0 and call it a day. If you have two rackets, set one to 21.0 and one to 21.1, and see which you like better (you should feel a difference). Say you like the 21.1 racket better. Next, leave that one the same, but set the other one up to MgR/I = 21.2. If you still like the 21.1 racket, you can be pretty sure your ideal is around 21.1, and almost positive it's between 21.0 and 21.2. You can continue to do blind testing like this until you zero in on your ideal.

Nicely summarized! This post might also be useful:
http://tt.tennis-warehouse.com/showp...8&postcount=17

[stoneage]

Originally Posted by travlerajm

Look, buddy.
I have a degree from Stanford in Biomechanical Engineering.
I have a PhD in Chemical Engineering from the largest research university in the world.
The reason I'm in Vienna this weekend is to receive the highest international award in applied science in my biomechanics-related field.
I've read every tennis-related article by Lindsey, Brody, Cross, Haake, and Goodwill, and I have respect for their work.
And I've spent enough years of careful experimentation with racquet customization that I am quite certain I know more about how lead tape affects racquet than any of them. The reason I continue to discuss the MgR/I concept is because it works, and because it's an essential tool for anyone interested in optimizing the performance of a tennis racquet. I'm in the process of preparing a comprehensive book on racquet customization in my spare time, which will more formally present the concept, along with other key concepts. I plan to use Lindsey as editor. Until I see something more useful than venom from your posts, I don't have any intention of consulting your help.

Let me begin by saying that I am not out to spread venom and I apologize if you get that impression. As I already said I have been intrigued with the concept and I have spent many hours trying to find out what it really means, and got a little annoyed of the lack of solid information. I must admit I am a little surprised by your reply, with a background like that you should be able to give better answers to the questions asked by me and others.

You (and others) are often referring to the fact that the concept works in practice and as I have said I have never doubted that. With all your additional requirements you end up with a fairly heavy, head light racquet with rather high swingweight. Not a radical concept for stable play, and it is not surprising that people like. No problems there.

But beyond that you are claiming that the formula is describing a lot of things in a tennis swing. You didn't have to do that to make your tuning specs creditable, it would have been enough to refer to experience and your collected data. But you are making those claims and then it is your call to give evidence that they are true. You have not given one single shred of evidence. You say that you could feel how MgR/I works. Feelings are fine and probably more important than physics for a good tennis game. But physics isn't based on feelings, so if you present something as a physical fact it must be based on math and/or solid measurements. You have given neither.

Lets just pick one example (of many): "The point is that tuning the racquet's natural swing frequency to match the natural swing frequency of the arm will significantly improve control by ensuring that your racquetface naturally stays perpendicular to your target as it passes through the hitting zone". This is a very specific claim of the natural swing frequency of the racquet, i.e. MgR/I, being connected to the swing frequency of the arm (whatever that is). This problem is possible to analyze and a proof could be given that is more than just words. If you can't do that don't make the statement. I might sound negative when I express my doubts, but if you had described how you reached that conclusion I or someone else might have been able to give more constructive critique, or just applauded your result.

Maybe you are saving it for your book, then I will read it with great interest (honestly).

[stoneage]

Originally Posted by Ramon

You got that right! I have Sten's apps on my iPhone. They work great and he constantly keeps them updated.

RacquetTune and SwingTool are the best apps of their kind for tennis players. If you customize your racquets or really want to know how much tension your strings are losing, you need to get these apps!

Originally Posted by Power Player

Stoneage i have to say your app is so great that it automatically lends you a ton of credence on this board. I would not worry about it as many of us question a lot of the ideas presented in this thread and what you are saying is legtitimate to me.

Guys, thanks for the positive feedback.

And I probably shouldn't have gotten into this discussion, it won't lead to anything

[Mig1NC]

Stone, make your apps for Windows Phone so I can try them out

[jmnk]

Originally Posted by Circa 1762

I think you're misconstruing travlerajm's argument. Each person, the theory goes, has an ideal MgR/I, but this ideal MgR/I depends on things like arm length. Therefore, each person's ideal MgR/I is going to be slightly different. Travlerajm has looked at the specs of pro's rackets, and based on the assumption (I think) that pros are likely to have MgR/I's close to their ideal, found that the pros cluster around an MgR/I of 21.0 (although again, there are variations due to things like height). As a result, he's suggesting (travlerajm, correct me if I'm wrong) that you might want to start with your search for your ideal MgR/I around 21.0. He is not saying that your ideal will necessarily be 21.0.

Based on a series of blind tests - for example, setting up two rackets with the same weight and swingweight but different balance, leading to different MgR/I's - I've concluded that my ideal MgR/I is around 21.2. I'm shorter than the average pro (5'8"), so this isn't too surprising. And these were blind tests with the exact same racket model and on the same day, so I'm pretty sure the differences I felt were real. So basically, don't just set your racket up to MgR/I = 21.0 and call it a day. If you have two rackets, set one to 21.0 and one to 21.1, and see which you like better (you should feel a difference). Say you like the 21.1 racket better. Next, leave that one the same, but set the other one up to MgR/I = 21.2. If you still like the 21.1 racket, you can be pretty sure your ideal is around 21.1, and almost positive it's between 21.0 and 21.2. You can continue to do blind testing like this until you zero in on your ideal.

That's nicely stated. Note however that this is no different than saying that each person has ideal mass of the racket, balance and swingweight - which very well may be true. In fact, as stoneage pointed out, combining those three values in some sort of equation (like MgR/I) and implying that that particular equation should result in some sort of particular number (or range) for the racket to be perfect is counterproductive. This is because even though one may have a particular optimal racket, balance, and swingweight (as in one optimal value for each) you lose that fact when you multiply the values. Please read this post by stoneage http://tt.tennis-warehouse.com/showthread.php?t=352140 when he nicely explains (with numbers, not feelings) that there are (quoting) "infinite number of very varying solutions making it impossible to use [MgR/I) as a design criterion". There was also a post somewhere that noted that $15 Walmart racket has MgR/I~21.0 while Head Prestige, widely regarded as one of the best rackets ever, was nowhere close to that value.
But again, you can read into it whatever you believe.

[Bartelby]

So it will already work for the new edition of ios or will it need an upgrade?

Originally Posted by stoneage

Guys, thanks for the positive feedback.

And I probably shouldn't have gotten into this discussion, it won't lead to anything

[kaiser]

Originally Posted by stoneage

Let me begin by saying that I am not out to spread venom and I apologize if you get that impression. As I already said I have been intrigued with the concept and I have spent many hours trying to find out what it really means, and got a little annoyed of the lack of solid information. I must admit I am a little surprised by your reply, with a background like that you should be able to give better answers to the questions asked by me and others.

You (and others) are often referring to the fact that the concept works in practice and as I have said I have never doubted that. With all your additional requirements you end up with a fairly heavy, head light racquet with rather high swingweight. Not a radical concept for stable play, and it is not surprising that people like. No problems there.

But beyond that you are claiming that the formula is describing a lot of things in a tennis swing. You didn't have to do that to make your tuning specs creditable, it would have been enough to refer to experience and your collected data. But you are making those claims and then it is your call to give evidence that they are true. You have not given one single shred of evidence. You say that you could feel how MgR/I works. Feelings are fine and probably more important than physics for a good tennis game. But physics isn't based on feelings, so if you present something as a physical fact it must be based on math and/or solid measurements. You have given neither.

Lets just pick one example (of many): "The point is that tuning the racquet's natural swing frequency to match the natural swing frequency of the arm will significantly improve control by ensuring that your racquetface naturally stays perpendicular to your target as it passes through the hitting zone". This is a very specific claim of the natural swing frequency of the racquet, i.e. MgR/I, being connected to the swing frequency of the arm (whatever that is). This problem is possible to analyze and a proof could be given that is more than just words. If you can't do that don't make the statement. I might sound negative when I express my doubts, but if you had described how you reached that conclusion I or someone else might have been able to give more constructive critique, or just applauded your result.

Maybe you are saving it for your book, then I will read it with great interest (honestly).

Hear, hear!

[stoneage]

I don't want hijack this thread so if you have more question regarding racquetTune please mail me privately.

Originally Posted by Bartelby

So it will already work for the new edition of ios or will it need an upgrade?

You mean iOS 6? Since it isn't out yet I don't know
However, I don't think it will be a problem from what I have seen in the beta-version.
But I will check as soon as it is launched and do updates quickly if needed.

Originally Posted by Mig1NC

Stone, make your apps for Windows Phone so I can try them out

I have started a cooperation with a partner concerning Android. We are starting with another app (sprintTimer), but hopefully there will be a racquetTune for Android eventually.
Windows Phone, however, is not on the horizon I am sorry to say.

[floydcouncil]

Originally Posted by travlerajm

Look, buddy.
I have a degree from Stanford in Biomechanical Engineering.
I have a PhD in Chemical Engineering from the largest research university in the world.
The reason I'm in Vienna this weekend is to receive the highest international award in applied science innovation in my field.
I've read every tennis-related article by Lindsey, Brody, Cross, Haake, and Goodwill, and I have respect for their work.
And I've spent enough years of careful experimentation with racquet customization that I am quite certain I know more about how lead tape affects racquet than any of them. The reason I continue to discuss the MgR/I concept is because it works, and because it's an essential tool for anyone interested in optimizing the performance of a tennis racquet. I'm in the process of preparing a comprehensive book on racquet customization in my spare time, which will more formally present the concept, along with other key concepts. I plan to use Lindsey as editor. Until I see something more useful than venom from your posts, I don't have any intention of consulting your help.

GIVE THIS MAN A COOKIE!!!!!!

[TaihtDuhShaat]

I have extensively tested Travlerajm's MgR/I formula on mine and others' racquets over the last 1 1/2 years, and have proven it's truth many times over.

I'm sure MgR/I could be modeled in a lab using a pendulum of known mass with a freely rotating joint attached to a tennis racquet with a MgR/I matched to the pendulum, and measuring the acceleration over many points of the racquet tip to the acceleration of the freely rotating joint of the pendulum over 1 period.

The formula's worth can even be proven visually. Maybe I'll try to post a video, but if I compare a perfectly tuned racquet to one that has a MgR/I that is too low or 'slow' and 'shadow' swing my forehand very slowly from backswing to follow through with a loose wrist, the racquet head with the 'slow' frequency will lag behind my hand after the backswing and through the contact zone. The tuned one will stay in the same plane with my loose wrist joint all the way through. This works as well using a continental volley grip and tracing a 'U' in front of your body. The tuned one's stringbed will stay in a constant angle to the wrist while the 'slow' one will fall behind the hand while tracing down the 'U' on both sides. The same can be applied for the 2HBH once well tuned, and even the beginning of the serve motion.

IMO, naysayers can prove it to themselves with enough dedication (since there is a learning curve). It took me a few months of testing at a wall and shadow swinging slowly in front of a mirror to even know what to feel for by following the procedure Travlerajm linked to above.

My ideal happens to be close to 21 for my semi-western FH (20.93 if I use a western FH) and around 22.5 for my 2HBH. I am 5'9" with average length arms. These values are tuned for me using any weight of racquet, as long as the balance and SW are changed to meet these values. I just also happen to prefer the effortless power, stability, spin, shot directionality regardless of incoming angle/pace/spin, and repeatability of shot that the high SW gives me. Because of this, I must then also use a high weight racquet with HL balance meeting the MgR/I requirements if I want my racquet head to be synched with my wrist. To use a frame with a SW in the 365 range really just means that 30 or so grams must be added to the top of the handle (of a prostock or light starting frame) if I want my frame to swing synched with my wrist, and this ends up making the SW much easier to wield. Thus, there really are no tradeoffs for me by using a frame like this. What I have learned has just corroborated and given further credence to Travlerajm's discoveries.

[Power Player]

^^^

I hope you know that sounds insane.lol.

If my racquet was not "tuned", I would be too early or late on my shots. And yes, I experiment with lead when I buy sticks.

[ART ART]

@travlerajm:

check this post with Novak racket specs:
http://tt.tennis-warehouse.com/showthread.php?t=441393

Specs strung+overgrip+dampener, are:
Mass: 360gr
Balance: 33cm
SW:371

So the MgR/I = 20,35 and MR^2= 392

Far away from the ideal MgR/I = 21,0 and MR^2= 385

Any comments about it ?

[travlerajm]

Originally Posted by ART ART

@travlerajm:

check this post with Novak racket specs:
http://tt.tennis-warehouse.com/showthread.php?t=441393

Specs strung+overgrip+dampener, are:
Mass: 360gr
Balance: 33cm
SW:371

So the MgR/I = 20,35 and MR^2= 392

Far away from the ideal MgR/I = 21,0 and MR^2= 385

Any comments about it ?

Remember, the 21.0 number is not the ideal for every player. It is a good starting point for most players when tuning; but many factors, such as arm length, grip type, whether you use an overgrip, and wrist band use can shift the optimum for the particular player.

The longer the arms, the slower the naturally swing speed of the arm, and the lower the optimum MgR/I value. Shifting the grip more toward western also shifts the optimum MgR/I lower. And a wrist band adds several ounces of weight to the arm pendulum, slowing down the hand through the downward gravity-powered first portion of the forward swing and thus shifting the optimum MgR/I lower. Using an overgrip also shifts MgR/I optimum slightly lower by shifting the grip position almost a millimeter up the handle.

Given Djokovic's slightly taller than average height, longer than average limbs for his height, nearly western grip, and large wrist band, his MgR/I value is right where I would expect it to be.

[kaiser]

So what about big vs small hands, wide vs narrow wrists? Aren't your theory and equations suggesting far more accuracy and preditive power than they really have?