Swingweight/Balance question

Discussion in 'Racquets' started by jb193, May 12, 2008.

  1. jb193

    jb193 Rookie

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    I have noticed that certain frame's specs don't coincide with each other in terms of balance being proportionate to swingweight. For instance,

    Volkl C10 Pro - 12.2 oz. - 8 pts. HL - 323 Swingweight
    POG Mid - 12.1 oz. - 8 pts. HL - 328 Swingweight

    OR

    Volkl Tour V Engine Mid - 12.2 oz. - 8 pts. HL - 318 swingweight
    Wilson KSix-One factor 16X18 - 12.3 oz. - 8 pts. HL - 340 swingweight


    The above are just two of many comparisons that intrigues me. I would think that being nearly the same weight and having the same balance that they would have nearly the exact swingweight. If anyone has any insight to why these rackets with nearly the same weight and balance have different swingweight, I would like to hear it. Thanks for any input.....
     
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  2. obnoxious2

    obnoxious2 Semi-Pro

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    More weight in the upper hoop (10-2) regions will result in a heavier swingweight even though they may both way the same.
     
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  3. Bottle Rocket

    Bottle Rocket Hall of Fame

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    This is my grip with those who put lead in only certain locations around the racket head in an attempt to reach a certain swingweight and balance. Its all about weight distribution. The swing weight depends greatly on the shape and the distribution of weight within its shape. It also depends on the point of rotation.

    Picture these two situations:

    1. Imagine a long uniform rigid rod (such as a broom stick). It is made of solid wood and weighs 10 lbs. The balance point is exactly in the center of the rod.

    2. Now imagine an incredibly thin weightless rod with a weight on each end (think of a dumbell). There is one weight on each end and each weight is 5 lbs. This gives a total of 10 lbs and a balance point perfectly in the center of the dumbell-rod-thingie.

    We've now got a situation similar to the racket situation you described above. Both of these contraptions have the exact same weight/mass. They also have the exact same balance point. Do they have the same swingweight? Nope!

    If you were to pick up both rods in the center and tried to twirl them, you would find that the rod with the weights on the end would be significantly more difficult to get into motion. Of course, it would also be more difficult to slow its rotation down.

    Does that make any sense? If you've ever messed around with a stick with a weight on the end, you can probably imagine what is going on here. Picture using a hammer at different ends.

    Its all about weight distribution. You can infer from this that the Volkl has more weight concentrated near the pivot point, while the POG has more weight distributed at greater distances from this pivot point.

    How's that?
     
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  4. jb193

    jb193 Rookie

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    That makes a lot of sense, thanks for the input.

    However, in your explanation, you seem to infer that weight more evenly distributed throughout the racquet is "better" for manueverability in general. Am I correct? Am I also to infer that you have the opinion that racquets with more evenly distributed weight play better overall? One more question. Regarding your scenario with the two different brooms. If I were to add a 3rd weightless plastic broom with 3 pound dumbells at each end, would you still think the all wood broom is more manueverable and would the 3rd broom with 3 ib. dumbells have near the swingweight as the original 10 ib. wooden broom, generally speaking that is? Thanks again for any responses.
     
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  5. fuzz nation

    fuzz nation Legend

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    I've given up on those listed swingweights myself. I honestly wonder if some of them aren't just drawn out of a hat - they can be quite misleading in my experience. Since I'm pretty familiar with the static weight and balance that I like in a frame, I just go with those.
     
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  6. Bottle Rocket

    Bottle Rocket Hall of Fame

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    This is the difference between my analogy and a tennis racket. I didn't do a great job of making this clear, but I did mention "It also depends on the point of rotation." I should have mentioned why. A racket is not pivoting about its center point, as the broomsticks are. Also, a rackets swingweight is taken around the area you hold the handle. Swingweight (the moment of inertia) of a tennis racket is taken at a point about 4 inches or 10 cm from the butt-cap of the racket. For this reason, the farther from this point that weight is added, the greater the increase in swingweight. Lead at 12 o'clock position is the most effective at increasing the swingweight with the smallest weight increase. This, of course, will also give you the greatest decrease in maneuverability. There are always trade-offs, but in general, I'm a big fan of higher swingweight rackets. I never jumped on the SW2 bandwagon for swingweights in the 350's and 360's (units of kg*cm^2, by the way), but I have had my best results and most enjoyment playing with relatively high swingweight rackets.

    Swingweight is one of the most important factors in determining racket performance and each players own perception of racket mobility. A high swingweight racket, even if lighter than a lower swingweight racket, is most likely going to feel less maneuverable. An increase in swingweight also provides a significant increase in power potential as well as stability. If you can handle a higher swingweight, msot of the time, it is going to pay off. Some more (worthless?) information:

    Tennis Definition of swingweight (from TW): Measure of how heavy a racquet feels when swung, i.e. maneuverability.

    Physics definition of swingweight: also called mass moment of inertia or the angular mass, (SI units kg m2, Former British units slug ft2), is the rotational analog of mass. That is, it is the inertia of a rigid rotating body with respect to its rotation. The moment of inertia plays much the same role in rotational dynamics as mass does in basic dynamics.

    If by even, you mean distributed at the center of the racket vertically, no. If by evenly you mean the weight, regardless of a rackets balance, is distributed in a more uniform manner (not concentrated in a few spots) throughout the frame, yes. I am not a fan of Concentrated mass, especially around the hoop.

    I am not sure if your weightless stick with 3 lbs on each end would have a higher or lower swingweight than a solid stick of 10 lbs and equivalent length. I would think intuitively the stick with the 3 lbs on each end would have a higher swingweight (maybe a significant increase?). Its a slow day at work over here, so I should have a chance to do the actual calculation and get you actual numbers. I'll get back to you on that one.

    Here is a nice page I came across which might be of interest to you and anyone else curious about the swingweight of their own frames:

    http://www.usrsa.com/store/learningcenter/lc_swingweight.html
     
    Last edited: May 13, 2008
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  7. Bottle Rocket

    Bottle Rocket Hall of Fame

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    I would probably agree with you.

    A lot of the published specs on rackets are far from reality due to very high tolerances in the racket manufacturing process (especially Wilson!), let alone the fact that there are only 1 or 2 machines being manufactured that can actually measure swingweight. I doubt there is much accuracy in any of these specs. Rarely have the specs I've seen measured by others been consistent with manufacturers claimed specs or TW's measured specs.

    The static weight and balance point are significantly easier to measure, unfortunately, they just don't tell the whole story...
     
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  8. TenniseaWilliams

    TenniseaWilliams Professional

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    I agree that published specs are all over the place, strung vs. unstrung, manufacturing variables, manufacturer scaling, etc. can make it very tough to compare racquets.

    Swingweight can be measured with a decent scale, a stopwatch, a tape measure, and a couple of wooden dowels. The USRSA claims this calculation is within 1% of the machines, and has a nifty online calculator for members. Essentially you are transposing the pivot point from where your hand usually is, to a point just below the second cross. Then you time the period of a pendulum cycle (or 10 and divide), and plug the static mass and overall balance in. Twistweight can be calculated in the same fashion, (without all the axis transposition) and recoilweight can be directly calculated given mass, balance, and swingweight.

    Measuring flexibility is the real problem.
     
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  9. Bottle Rocket

    Bottle Rocket Hall of Fame

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    I found this thread about the method:

    http://tt.tennis-warehouse.com/showthread.php?t=175329

    Post #8 by midlife crisis describes the procedure... I'll give it a shot on one of my frames when I get a chance and see what I get. I had forgotten about that. There is also a link in that thread for a spreadsheet to give a rough estimate of your swingweight knowing a few things that are fairly simple to measure. I am not sure how accurate all of these methods are going to be, especially considering all of the human-induced errors involved, but still interesting information.

    I made it sounds like finding a frames swingweight is nearly impossible, huh?
     
    Last edited: May 13, 2008
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  10. Bottle Rocket

    Bottle Rocket Hall of Fame

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    For this simple little calculation, each weightless stick is 100 cm long. I used 3 grams instead of 3 lbs and 10 grams instead of 10 lbs.

    The "swingweight" of the stick with the weights on each end is 15 (kg*cm^2)

    The "swingweight" of the 10 gram uniform stick of same length is 8.33 (kg*cm^2)

    So there is nearly twice the swingweight for the weight distributed at the tips compared with the solid rod. This is for a pivot point about the CENTER of each rod.
     
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  11. larry10s

    larry10s Hall of Fame

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    bottlerocket EXCELLENT discussion of a subject some people have a hard time understanding.
     
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  12. Bubba

    Bubba Professional

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    Agree. It's not just the balance point, but as been said... the distribution of the weight is the key determining factor. You can see this perspective in several of Babolats frames... its the basis for tapered beams... not only to tapered beams address flex, but they also impact HL balance and weight distribution around the frame.
     
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  13. jb193

    jb193 Rookie

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    That's interesting that the weightless stick with 3 grams at each end has more swingweight. Thanks again for your efforts & insight, I really do appreciate it.

    One more question and this one is subjective. If these two sticks that we are using for our hypothetical discussion were translated into racquets with similar properties, which do you think would be more playable in respect to the following characteristics?

    stability
    Power
    Maneuverability



    I know that this is very subjective and there maybe isn't a correct answer, I am just interested to hear your thoughts.
     
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  14. Bottle Rocket

    Bottle Rocket Hall of Fame

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    This is actually a rather non-subjective subject, which is nice. It isn't like the string pattern debate.

    Anyway, in almost all cases:

    Higher swingweight increases stability (lead at 3 & 9 is popular because it not only increases swingweight and stability longitudinally, it increases lateral stability.)

    Higher swingweight increases power (given the same swing speed as the frame with a lower swingweight). The Wilson kSix-One 95 "X", with a good swing is the most powerful stock racket I have ever used (high swingweight, high stiffness, open string pattern, decent static weight). After using that, the lighter and lower-swingweight Pure Drive's really seem to get "jerked" around by these little fuzzy tennis balls instead of it being the other way around (the way it should be).

    Anyway, An increase in swingweight will always decrease maneuverability. The perception of maneuverability is another issue, but in reality, you cannot increase maneuverability with lead. Guys claiming they added lead to the handle to make their frame more headlight and in-turn more maneuverable are in a dream world.

    Anything that increases maneuverability is going to decrease power and decrease swingweight- most likely decrease stability.

    Like I mentioned before, there are always trade-offs. I think the best case scenario is to have the technical ability and the footwork to handle a frame with a relatively high swingweight (higher than the average stock frame) and a decent static weight. At the lower levels of the game though, I don't think too many people are being held back by their swingweight. I don't think its worth getting caught up in rather than focusing on your technique, but that too is another subject.

    Hopefully I didn't get anything completely wrong here... If I did, I'm sure someone will correct me. And you all are welcome, thanks for the comments. I probably made things much more complicated and drawn out than they need to be, so I apologize for that. There are a whole bunch of extremely knowledgeable guys on this board that will hopefully jump in here and add their insight.
     
    Last edited: May 13, 2008
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  15. ronalditop

    ronalditop Hall of Fame

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    i just put weight to the handle of my raqcuet to make it more headlight (before it as slightly HL). i notice that i can swing faster without losing stability. i´m gonna try it tomorrow to see if my racquet lose a little power, wich is why i do this in the first place.
     
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  16. travlerajm

    travlerajm Hall of Fame

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    Adding weight to the handle increases the swingspeed on groundstrokes.
    This is because your swingspeed on groundstrokes is not simply an inverse relationship between acceleration and swingweight. Rather, your racquetspeed on groundstrokes is governed primarily by the equation for the frequency of a physical pendulum. If you add more mass near the pivot point of a pendulum, it swings faster!

    Also, adding mass to the butt of the handle makes it easier to lift your racquethead into position on volleys, due to the counterbalancing effect.
     
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  17. GasquetGOAT

    GasquetGOAT Hall of Fame

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    Great thread. An educational read.
     
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  18. ronalditop

    ronalditop Hall of Fame

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    this should became sticky.

    well. i tried my racquet with lead tape on the handle and like i supposed, it lose power. now i have more control, its amazing. also I can swing faster.
    so its true that a more HL racquet have more control.
     
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  19. 10nisNe1?

    10nisNe1? Rookie

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    i agree with these, but i've notice a decrease of power (or should i say smaller sweetspot?) in the head area. so in a sense, the increase swingspeed is just compensating for the decrease in power? i dont know, the feel to me is that the racquet flexes more? please help me because i want to make my racquet more headlight by putting weights in the buttcap but i would like to maintain the power (or stiffness?). thanks.
     
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  20. travlerajm

    travlerajm Hall of Fame

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    If your racquet has substantial flex, you can control the amount that the racquet flexes at impact (the dynamic flex) by choosing where you add weight.

    Your racquet has two nodes for the primary vibration mode. One node is in the middle of the handle, and the other node is a few inches from the tip. The distance between these two nodes determines the amplitude of the vibration. And the amplitude of vibration determines how much your racquet flexes at impact.

    If you place lead tape on the butt, it will move the handle node closer to the butt. This will make the distance between the nodes longer. This increases the amplitude of vibration, making your frame feel softer and more flexible. It will also make it feel more spin-friendly.

    On the other hand, you can stiffen the feel of you racquet by placing weight at the top of the handle. Weight here will move the handle node closer to the tip, thereby shortening the distance between the nodes, and reducing the amplitude of vibration. The frame will feel stiffer at impact, and less spin-friendly, but with more power.
     
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  21. in10se

    in10se New User

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    lead at 3 & 9 is popular because it not only increases swingweight and longitudinal stability, which increases lateral stability.

    lead at 10 and 2, what increases ????, that differs from the lead at 3 & 9?


    and finally lead only at 12, to balance a racket hl, can do more unstable part? or only increase the swingweight?

    I have a kpro tour and has to balance very fist, I balance a bit, but trying not to lose maneuverability.

    the best option would be to locate where the lead? between 3 & 9? , At 12? or at 10 & 2?

    Someone I can explain the differences?, The advantages and disadvantages of lead in each of these schedules?

    Thank you!
     
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