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

Discussion in 'Racquets' started by travlerajm, Jul 5, 2011.

  1. Mig1NC

    Mig1NC Professional

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    Yeah. I know what you mean. It's like I can max out the configuration for serve, but my forehand suffers.
     
  2. AlpineCadet

    AlpineCadet Hall of Fame

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    Bump! So if I am 5'9" and using an IG Radical MP, my MgR/I value should be at 21.1, but how would I figure out lead tape placement?
     
  3. corners

    corners Legend

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    Do you know how to use the formula to figure out the MgR/I of your current stick? If you find that it is less than 21.1 you can add lead at the top of the grip. If you find that you're over 21.1 you can just leave as is (high MgR/I doesn't really seem to be a problem) or add a gram at 12. If you're comfortable with the MgR/I formula you can measure your new specs after adding any lead (or use the TWU Reverse Engineering page to figure out your new specs) and then run the numbers through the formula. 21.1 might not be your magic number or anything either, but for players shorter than 6' it seems to be preferred.
     
  4. AlpineCadet

    AlpineCadet Hall of Fame

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    Thanks for the reply. I have no idea how to use the forumla... the only data I have is that my frame is stock, except for the leather grip (which probably added 15 grams and made the frame 2-3 pts more headlight.)
     
    Last edited: Feb 6, 2012
  5. corners

    corners Legend

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    Missed your last post...if your frame is close to the TW measured average for the IG Radical MP, you specs would be about:

    320 grams, 33.3 cm balance, 320 swingweight. Adding the 15 grams for the leather replacement and overgrip, you'd have:

    335 grams, 32.2 cm balance and 320 swingweight. MgR/I on that would be 21.1, so you are right about there. And this is also a good place to experiment with this theory. If you add a gram at 12, MgR/I will drop to 21.0. The head will probably feel a bit slower coming around. If you instead add 5 grams at the top of the grip MgR/I will go to 21.2 and the head may feel faster.
     
  6. ptb5021

    ptb5021 Guest

    Is there a single location where all of this is explained? I started sifting through threads and realized that I keep opening new ones...
     
  7. AlpineCadet

    AlpineCadet Hall of Fame

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    Corners, thank you! That's amazing. I tried 4 inches of 1/4 inch lead at 12 and the frame felt solid on serves, but a bit sluggish on volleys. I removed the lead and applied it to the top of the handle and the frame played horribly--too whippy, hard to time my shots, and I was just inconsistent on feel.
     
  8. Mig1NC

    Mig1NC Professional

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    Well, it has been said all along that once you get close to your ideal, that you would need to fine tune it.

    Try adding only 2 inches instead of 4 inches and see how that plays.

    Or try adding 2 inches at each point. There are endless variations.
     
  9. ChicagoJack

    ChicagoJack Hall of Fame

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    I am not corners, but I did stay at a Holiday Inn last night. There's a whole lot of racquet between 12:00 and the top of the handle. Sounds like you were really close to golden with lead at 12:00, you should try a few baby step adjustments. Give 10-2 a try, or my favorite for volleys and serving, 3 and 9. Your volleys will be more stable, your racquet will be less sluggish (than lead at 12), and your serves will still have some added oomph.
     
    Last edited: Feb 21, 2012
  10. sstchur

    sstchur Hall of Fame

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    Trying to follow all this...

    Trying to follow all this and apply it to my Fischer Pro One 98

    Stock specs on that are:

    weight: 335g
    balance: 12.625cm
    swingweight: 317

    I had been playing with a leather grip + overgrip, and I believe that adds about 22g to the handle (let's say at about 3.5in, since the handle is roughly 7in)

    I used the TW customization worksheet to fiddle around and try to arrive at an MgR of about 385 (I believe that was what the OP stated as the optimum?) and and aiming for a swingweight of about 360?

    But what is this mysterious I? What is the value? How does one find it? If I can tune to get an MgR of 385 and a swingweight of 360, why do I need the I? If I is a constant, why does it matter?

    I'm about 5'9" like someone else who posted, so I worked backwards from another poster's comments, and arrived at an I value of roughly 16.46. I then took the values I got after customizing and plugged in that for I and ended up with an MgR/I of about 24, which sounds way way too high.

    Any help on this?
     
  11. travlerajm

    travlerajm Hall of Fame

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    I is the physics symbol most commonly used for rotational moment of inertia. I have used it to represent the swingweight about the butt end of the racquet.

    You can calculate I using the following formula (based on the parallel axis theorem):

    I = SW + 20MR - 100M
    SW = swingweight about the 10cm axis (measured using either RDC or TW swingweight tool).
    M = mass in kg.
    R = distance from butt to balance point in cm.

    PS. For the formula to work for you, you need to get yourself a scale and measure the swingweight. Each racquet can vary significantly from the specs. For example, if you switch from syn gut to poly of the same gauge, it will add about 2g in weight and about 4 SW units, which is enough to throw off the formula.
     
    Last edited: Feb 21, 2012
  12. sstchur

    sstchur Hall of Fame

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    Oh, well that makes a difference. Without a tool to measure swingweight then, this sort of customization is out of reach of the average person, is it not?

    EDIT: I tried the TW swingweight tool, and ended up with a swing weight of about 224. That seems very very wrong.
     
  13. travlerajm

    travlerajm Hall of Fame

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    Follow the instructions carefully. Or tell us what your measurements were, and we'll tell you where your error is.
     
  14. sstchur

    sstchur Hall of Fame

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    Racquet is standard 27" and it measures as such, spot on. I input 68.58cm for this (2.54cm in an inch)

    I have a leather grip + overgrip, and I already has 2g of lead at 12 o clock, bringing my total weight to 349g

    The distance from the handle to the top of the string on which I rested the pencils was 24 15/16in (63.34125cm)

    And I measured the balance point to be 12 1/8in (30.7975cm). And actually, this is an adjusted (and I believe more accurate) balance point than the balance point I used when I replied a few moments ago.

    The tool now tells me the swingweight is 209

    The times I got for 10 swings (I did it 3 times) were:

    12.34
    12.34
    12.25

    I used the mean of 12.31
     
  15. travlerajm

    travlerajm Hall of Fame

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    Based on what you tell me, I conclude that your SW is ~311.

    (You are only counting 9 oscillations).
     
  16. sstchur

    sstchur Hall of Fame

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    Ok, so I'll trust you are correct there (311 seems a reasonable swingweight number).

    Now how to do I move forward applying the MgR/I

    Is g force due to gravity (9.8 m/sec squared)? I haven't heard anyone in any of the threads talking about it -- it almost seems as if the g is being ignored by most commentors doing any sort of math (unless I'm just missing it)
     
  17. sstchur

    sstchur Hall of Fame

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    Not sure if I'm doing it right, but using 311 as the SW, I get

    I = SW + 20MR - 100M

    I = 311 + (20 * .349 * 30.7975) - (100 * .349) = 491.06655

    If I then use g = 9.8m/sec^2, or 980cm/sec^2, I can plug in

    MgR/I = .349 * 980 * 30.7975 / 491.06655 = 21.449966

    So that's at least a reasonable number, based on what I've been reading.

    Now, what I still don't know is:

    A. Did I do that right?
    B. What is my optimal MgR/I number? I'm about 5'8", maybe 5'9"
     
  18. ART ART

    ART ART Semi-Pro

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    Again,

    can you comment this specs travlerajm ?

    Thnaks
     
  19. klementine

    klementine Hall of Fame

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    I've read through all of Travelarjm's posts and I would like to take the time to thank him for some great detective work.

    I understand that the point of this experiment is to isolate all the variables involved in a tennis swing and focus on the constant (racquet) in order to stabilize the other ever complex variables.

    I've always tried tuning my racquet based on feel. Always opting for weight placed high in the handle and at the 3&9 o'clock positions of the frame.

    I want to give this experiment a shot. I'm 6'1". What would my optimal MgR/I value be?
     
  20. corners

    corners Legend

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    Maybe 21.0 based on your height. Spec out your frame and go from there. Once at 21.0 you can play around with 5 grams or so at the top of the grip to raise it to 21.1 or a gram or two at twelve to lower below 21. For someone like you, with experience with lead, the fun part is tuning it until it feels just right.
     
  21. corners

    corners Legend

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    Hey Art,

    I do believe that Trav thinks that tuning MgR/I is more important than the 380 rule. The easiest way for you to get to 21 is to either remove some lead at12 or repoition it to 3&9. Alternatively you could add 15 grams at the top of the grip but that is a pretty big addition. On the other hand, some people find that high static weight isn't so bothersome when MgR/I is in their preferred range. Adding at the top of the grip would also keep you in the 380 "club" :)
     
  22. klementine

    klementine Hall of Fame

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    ^Thanks. That's what I thought. Don't understand how/why height has any relevance. Seems like arm length is more relevant.

    I guess the logic is taller=longer arms. This is not always the case though.
     
  23. travlerajm

    travlerajm Hall of Fame

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    Yes. The taller=longer arms was my logic.

    I also noticed that the racquets I tuned for myself seemed to work great when friends who were my size tried them, while really short guys couldn't control the ball at all.

    Then when I compared average MgR/I values of WTA players to ATP players, it lent support to the shorter = higher MgR/I story.
     
  24. klementine

    klementine Hall of Fame

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    ^travlerajm?

    I've always wanted to ask you your opinion of John Cauthen.

    Were your theories (before being defined by physics and empirical data) at all influenced by him?
     
  25. TheLambsheadrep

    TheLambsheadrep Professional

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    travlerajm, is achieving MR^2 to be = 385, or MgR/I to be = 20.7-21.1 more desirable?

    And I'm working on comparative data based of Jura's 2005 pro data. As of now, Excel says the average STRUNG weight (I added 22 grams to every racquet mass given, since the mass difference of my racquets of strung-unstrung is always around 22g) is 360.7g. This is interesting, because you can see from my summer posts, I just made all my rackets 360g. The thing is, to achieve a MR^2 of 385 with a racquet of 360g, the balance needs to be 5.003pts head light. I thought pro rackets would have been a little more head light than that...
     
  26. travlerajm

    travlerajm Hall of Fame

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    I read his posts with curiosity. And he was one of a couple of posters (along with MackSamuelHustovisics) that inspired me to start experimenting myself.

    I must admit that it took me several years of experimenting before I finally felt like I figured out how the physics of how adding lead works.

    At first, I was fascinated that adding as little as a gram or 2 could make such a huge difference to my racquet, even when I added it to the handle.

    Adding a gram to the butt seemed to reduce power (I couldn't fully understand why at the time), while adding a gram to the the top of the handle seemed to increase it in some cases.

    More than John Cauthen, reading all of the papers by Cross, Brody, Lindsey, Goodwill, etc. really helped me get a base for the impact dynamics. And the MgR/I stuff (i.e., swing dynamics) I figured out myself after lots of fiddling both with my racquets and with excel spreadsheets with logs of my various racquet specs.

    Once you can isolate the effects of swing dynamics from the effects of impact dynamics, tuning a racquet gets a lot easier.
     
    Last edited: Feb 29, 2012
  27. klementine

    klementine Hall of Fame

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    ^Impact dynamics seems even more intriguing to me but we have very little control over that. Except for string tension and gauge. Plasticity (flex) and different materials are beyond our control.

    Although, pt630 once told me the flex of a racquet can be tampered with. But, I'm not willing to drill holes in the shaft of my racquet, so swing dynamics it is! :smile:
     
  28. travlerajm

    travlerajm Hall of Fame

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    Impact dynamics can be tuned with lead also. That is, the flex and dwell time of your frame can be tuned independently of the strings. And independently of the weighting specs.

    For a very stiff frame it is less important, but it still matters.

    There are two primary bending nodes - one midway up the handle, and another about 2/3 of the way up the hoop.

    Any time you add lead between the nodes, it will stiffen the frame. Adding lead to the throat just beneath the bridge will have maximum stiffening effect. It won't test any differently on an RDC, but it will play stiffer.

    Adding lead to the butt (below the bending node) will tend to make the frame play more flexible. Adding lead at 12 will make a big difference on how dead the upper hoop feels.

    For a given mass, balance, and swingweight, their are infinite weighting combinations - some stiffer than others.

    For example: Let's say you want to add 15g at 3&9 plus 5 grams in the butt to achieve a certain mass, balance, and swingweight. You could alternatively reach the same specs by adding roughly 8g at 12 plus 12g at the top of the handle.

    The latter weighting will play much stiffer than the former, even though less weight is added to the hoop. Why? It's because of the mass added at the top of the handle, between the nodes.

    If I want a racquet to play stiffer (at the same weighting specs), I move the hoop weight further north (which means less hoop wieght, but more counterweight between the nodes). If I want it to play more flexible, with more dwell time for more spin, I move the weight south more toward 3&9. It's what happens with the counterweighting that affects the stiffness.
     
    Last edited: Feb 29, 2012
  29. travlerajm

    travlerajm Hall of Fame

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    I think the keys are:
    1. MgR/I needs to be tuned to your personal swing.
    2. Swingweight needs to be high enough for stability (at least 350).
    3. Swingweight needs to be low enough to be able to serve big for an entire match (less than 380).

    I think the 385 MR^2 optimum is simply a convergence of the 3 factors above.
     
    Last edited: Feb 29, 2012
  30. TheLambsheadrep

    TheLambsheadrep Professional

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    So a "performance #" of 385 is the better racquet quality to achieve...?

    I do need to calculate swingweight, it's about the only thing I haven't done to my racquets. and my optimal MgR/I would be 21.0 since im right about 6 feet tall, but do you mean something else when you say "needs to be tuned to your personal swing?"
     
    Last edited: Feb 29, 2012
  31. klementine

    klementine Hall of Fame

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    Interesting. Verifies what I've experienced from experimenting on my own.

    If this aspect of adding weight and it's effects on impact dynamics can't be measured by an rdc machine, it can surely be measured by some more sophisticated means.
     
  32. travlerajm

    travlerajm Hall of Fame

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    It can be measured by vibration frequency.
     
    Last edited: Feb 29, 2012
  33. travlerajm

    travlerajm Hall of Fame

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    21.0 is just the starting point - you really need to find a wall and patiently tune the racquet while hitting against it to to get the most out of this.

    Somewhere in these threads I posted a how-to on wall tuning, but I don't recall exactly where...
    Edit:
    http://tt.tennis-warehouse.com/showpost.php?p=5859118&postcount=17
     
  34. TheLambsheadrep

    TheLambsheadrep Professional

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    ok. so from your "It's my belief that the optimal MR^2 zone of ~385 arises due to circumstance, because those pros that have both high swingweight (>350) and optimized MgR/I value (~21.0) tend to have racquets with MR^2 of about 385," you're saying you have to optimize MgR/I before MR^2...?

    hypothetically, if you had to say that finding one was better in general, which would you choose (unless MgR/I and MR^2 are worthless without each other)?
     
    Last edited: Feb 29, 2012
  35. DeShaun

    DeShaun Banned

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    Dear Travelerjam,

    I'm really sorry, I cannot do math. Learning calculus is on my bucket list though.

    Would you please tell me where this racket falls on your spectrum:
    27inch
    416 grams
    balance- 30.9cm from butt?

    I'm 5'8"

    Thank you
    Sincerely,
    DeShaun
     
  36. TaihtDuhShaat

    TaihtDuhShaat Semi-Pro

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    Deshaun- you will need to provide the SW to get a response for the MgR/I, but your racquet does check in at a very powerful 397 MR^2.
     
  37. corners

    corners Legend

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    Yeah, you need your swingweight and it needs to be precise, but once you have that you can use this spreadsheet posted yesterday by pbbrommer: https://docs.google.com/spreadsheet/ccc?key=0AgowZT0_5hPGdHhfMTd5d1FXTHJHNWZYZ251b04ydWc#gid=0
     
  38. TaihtDuhShaat

    TaihtDuhShaat Semi-Pro

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    FWIW, I'm 5'10" and my perfectly tuned MgR/I tested across many racquets is ~20.93.

    But, I use only head frames with their little extra buttcap flair, so my grip is ever so slightly choked up where the pinky ends a few mm's north of the end of the butt cap, compared to a wilson which is easier to hold at the end of the buttcap.
     
  39. dmcb101

    dmcb101 Semi-Pro

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    I have looked for the answer to this question and could not find it. I am about 5'8-5'9 and I have seen that my optimal number is about 21.2. A racquet that I am considering getting has a number that is 21.24. My question is, how much does a 100th of a number effect this whole pendulum stuff? Would 21.24 be fairly close or not that close? Just wondering the effect of the numbers. Thanks for the great information by the way. This thread literally opened my eyes to what I thought I knew about racquet customization so thanks!
     
  40. TaihtDuhShaat

    TaihtDuhShaat Semi-Pro

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    Every little bit has an effect when you are close the that tuned spot. 1/8 of a gram of lead transferred from the hoop to the upper grip can be felt. But, when you are within a 10th, that's close enough for practical purposes.
     
  41. dmcb101

    dmcb101 Semi-Pro

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    Ok cool. I am not looking to get pro on this or anything but its really neat to kinda see what racquet suits what type of person. In stock form the new PS 6.1 95 BLX theoretically should suit my game. Thats implying that the specs are the same as the TW website of course, interesting non the less though.
     
    Last edited: Mar 1, 2012
  42. travlerajm

    travlerajm Hall of Fame

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    I would agree with this.

    Also important to note that it's possible to tune your racquet more accurately than how accurately you can measure MgR/I (assuming normal measurement tools like stopwatch, ruler, and digital scale). It's tough to measure MgR/I more accurately than +/- 0.03. That's why I find it important to tune against the wall after I get it close using measurements and spreadsheets.
     
  43. ptb5021

    ptb5021 Guest

    Rod Cross' Technical Tennis: worth the read to get more on this stuff?
     
  44. TennisCJC

    TennisCJC Legend

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    my volkl o10 295 is customized to 343 grams, 12.875 HL (5 pts HL), and SW 336 and the magic mgr/i number is 20.90. I paid no attention to this magic number during customization. Just tweaked it a few times until it felt right. I am a bit under 5'10" and think 20.90 is in the good range according to some of the post above. Trial and error got me to the same point as science and math. I tried the racket at one point with about 3-4 grams in the head and it was no where near as good. Much better when I increased the weight in the head.
     
  45. corners

    corners Legend

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    Well worth it, and their first book "The Physics and Technology of Tennis" is much more extensive. Cross' co-author, Crawford Lindsey, also happen to be the Tennis Warehouse University Professor and has written a bunch of articles and constructed even more tools that are very useful:

    Racquet articles: http://twu.tennis-warehouse.com/learning_center/articles.php#racquets

    TW University: http://twu.tennis-warehouse.com/learning_center/index.php

    But what this thread is about - racquet weight distribution and timing of the double stroke pendulum - is not something these authors have gotten into much. Travlerajm's MgR/I ratio is really the first attempt to sort this stuff out, at least the first attempt that's made it to the public. Although, Rod Cross did look at the double pendulum of tennis strokes in this recent paper, also on TWU: http://twu.tennis-warehouse.com/learning_center/doublependulum.php
     
    Last edited: Mar 3, 2012
  46. Xizel

    Xizel Professional

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    How does an extended length racquet and a grip lower on the handle affect this concept?
     
  47. Racquet-Priority

    Racquet-Priority Rookie

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    Travelerajm, could you post the players who are used for this experiment?
     
  48. travlerajm

    travlerajm Hall of Fame

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    The sources for the list are provided in the OP. All players with Top-200 career-best ranking from were included in analysis.
     
  49. Xizel

    Xizel Professional

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    Edit: wrong thread.
     
  50. Racquet-Priority

    Racquet-Priority Rookie

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    Yes I saw but I tought you might have a list with names and the calculated swingweights. Thanks in advance!
     

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