Swing Weight Difference

Discussion in 'TW Questions/Comments' started by udonman, Jul 3, 2009.

  1. udonman

    udonman New User

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    I am currently looking at two rackets. Head Microgel Prestige Pro & Volkl Power Bridge 10 Mid. Prestige Pro weighs 12.1 oz, 7 pt HL with the swing weight of 316. Volkl weighs 12.1 oz, 10 pt HL with the swing weight of 337.

    With the same weight, shouldn't the one with a higher HL balance point have lighter swing weight? But if you look at the above two rackets, the results are the opposite. Can you explain why? Thanks.
     
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  2. TW Staff

    TW Staff Administrator

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    Swingweight will differ depending on how the weight is distributed. For instance, let's say a racquet is even balance. Let's focus on the lower half of the racquet. The half with the handle.

    The balance point is just above the yoke of the racquet.

    The balance point will remain the same regardless of how the weight is distributed for that half of racquet...whether it's at the bottom of the handle, or up near the yoke. The balance point doesn't change.

    Use that same scenario for swingweight. Below the balance point, if the weight is mostly at the bottom of the handle, the swingweight will be different than if the weight was up near the yoke.

    Distribution of mass is the key for swingweight. Not the static weight with balance point.

    Hope that's not too confusing.

    Spencer, TW.
     
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  3. Bud

    Bud Bionic Poster

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    Spencer, how many racquets does TW test in order to determine the frame specs?

    For example, does TW test say 5 frames... taking the average weight, balance and SW of the entire group?
     
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  4. TW Staff

    TW Staff Administrator

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    Bud,

    We will pull 4-6 racquets out of stock, spec them and yes, average those specs.

    Spencer, TW.
     
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  5. jrod

    jrod Hall of Fame

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    Volkl PB10 mid SW????

    Just to add some confusion to the OP's original question, I recently purchased 2 Volkl PB10 mids from TW. I asked for the lightest SW possible on the 1st frame and received it with a measured unstrung SW of 294. A week later I ordered my 2nd frame and again asked for the lightest SW in stock and received a frame measuring 299 unstrung.

    After stringing the estimated SW's for them was 324 and 329, using the TW tools and plugging in the measured #'s supplied by TW staff. Both well under the published 337. While I understand I asked for the lightest SW's in stock, but to get an "average" or even "median" SW of 337, the variance on the weight distribution for this frame must be rather substantial.

    Seriously, it makes me question the accuracy of the published SW of 337. What gives TW guys?
     
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  6. TW Staff

    TW Staff Administrator

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    Question the accuracy? Like you question the RDC machine we use? Or like we're just guessing?.... making an estimate?

    No. we don't do that. We keep our RDC machine calibrated. And we're not pulling numbers out of the air.

    There can be a few reasons this happens.

    As you know, with the exception of Fischer's no tolerance line, all racquets are going to differ in specs...and I'm speaking of each racquet of the same model/style. That being said, one factor is that you did ask for the lightest SW in the batch we have on hand. On top of the fact that coming from the factory, not only each individual racquet will differ slightly, but batches in general can differ.

    But I'm sure you already know this.

    There are times that we will go back and check a spec if we feel it's off.

    Spencer, TW.
     
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  7. jrod

    jrod Hall of Fame

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    Spencer- Hang on a second....When I said "question the accuracy", I was not necessarily insinuating your Babolat RDC machine was uncalibrated or that you were pulling numbers out of thin air.

    There are a number of possible explanations here, including your theory. It's also possible TW provided me erroneous information when I asked them to measure the SW's and send me the lightest. Another possiblity is the TW tool I used is erroneous, or that I am entering the wrong numbers (even though I checked to make sure I was using the numbers you guys provided me). In fact, it's also possible your measurement procedure was compromised and did not draw a representative sample size or sample.

    That said, lets assume your theory is correct. The first frame I received was the "lightest" in SW among 5. The second frame was the lightest among 2. They differed by 5 kg.cm^2. Now it's clear we are pulling frames from the lower tail of the distribution, to some extent. If we assume that the lower SW I received is say, one standard deviation from the mean, and that 337 represents the mean, then there are likely other frames measured with SW's of 342.

    So the question I was really asking was: Is this kind of variation typically observed from Volkl, or any manufacturer other than Fischer? Can you give the observed standard deviation for the PB10 mid, or provide the measured individual SW values for the frames that you used to come up with a SW of 337?

    Just curious....
     
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  8. Bud

    Bud Bionic Poster

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    I recently purchased a Wilson KPS88 from a local vendor that measured 12.8 oz. and 3 pts. HL, strung (should have been 6 pts. HL, strung). Plug those numbers into the TW SW calculator and observe what SW numbers it spits out.

    SW is a very sensitive variable. Within the same frame, it can vary widely, based on small changes of weight and balance (for the most part, we can discount weight distribution when testing the same frames since it's assumed their weight distribution is similar.)

    I like your use of statistics as an investigative tool. There are so many variables that are unknown, however. You'd have to take a much larger sample and conduct the experiment/tests yourself.
     
    Last edited: Jul 3, 2009
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  9. Mansewerz

    Mansewerz Legend

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    Question: Was the 294 unstrung that you requested? Also, how much SW do strings add?
     
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  10. jrod

    jrod Hall of Fame

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    This is what I am trying to understand. I can certainly understand how SW is sensitive to the specified balance. However, I just played around with the Customization and Reverse Engineering tool and entered the initial data for my 1st frame:

    Length: 27 inches
    Unstrung Weight: 331 grams
    Balance: 12.1 inches
    Unstrung SW: 294 (measured by TW)

    Then I entered the weight and placement of the strings (16 grams, 21 inches) to compute an estimated SW of 324.

    Next I went back and changed the balance point, varying it from 1 inch to 27 inches. The SW stayed the same at 324.

    I'm sorry, but I have no idea as to how the SW can remain the same when the balance point changes by so much. It's behaving as if the SW is not a function of the original balance point.

    Not sure I understand what is going on here....
     
    Last edited: Jul 4, 2009
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  11. corners

    corners Legend

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    The racquet customizer does not allow you to perform a balance move. Sure, you can change the balance in the original parameters entered into the calculator, but this is simply the original specs of the racquet. You can't simply alter the balance.

    To actually change the balance you have to add or subtract weight. Now if you added 100g to the butt you might change the balance from 31.5cm to 1cm, but you're not going to do that, and if you did it wouldn't change the swingweight all that much anyway, as swingweight is measured by swinging the racquet 10cm from the butt.

    Swingweight is not a static spec like weight or balance. It is a measurement of how the racquet behaves when swung through space from a position 10cm from the butt.

    I think you got what you wanted, right? Two frames with swingweights below your maximum usable swingweight. I'm surprised as well that Volkl makes frames that vary so much in swingweight. But remember that all this means is that the frames you have don't have as much weight close to the top of the head as the representative 5 or 6 frames that TW measured to get their 337 spec. Maybe they didn't put enough graphite or resin in the top of the mold, who knows? But as your frames have spec balance and static weight they should play similarly to the higher swingweight frames that TW has, but swing easier and have less plowthrough.

    Anyway, you managed to get two low swingweight frames. As for an "official" number - too bad Rush got banned, as I know Volkl does release their target or offical swingweight to their reps, but not to the general public. I'm a bit surprised by the 337, as the last couple Volkl 10 series frames were more around 320, but maybe they are going more toward the old C10, which TW lists at 338. There seems to be a trend toward mid 330s for swingweight on player's frames as well. Check out the new Exos from Prince - very similar static weight, balance and swingweight as the PB10 mid. I wonder with Prince if they figure their O3 frames, being more aerodynamic, allow for faster swing speeds with higher swingweights. I remember reading Roman whatshisname from **** say that Sharapova was able to increase the weight of her frames when she got hold of the O3 racquets.

    Anyway, hope this is helpful.
     
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  12. jrod

    jrod Hall of Fame

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    ^^^ Corners- Very much appreciated. Your explanation makes sense about the tool. Regarding the PB10 mid, I am quite content and the heavier frame I've received has convinced me a little weight goes a long way.
     
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