Same racquets, different swing weight

Discussion in 'Racquets' started by aimr75, Mar 16, 2012.

  1. aimr75

    aimr75 Hall of Fame

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    If there are two racquets, same model, static weight and similar balance, but the difference in swing weight is 11 points, e.g. 297 vs 308, would there be a significant difference in how they swing?
     
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  2. li0scc0

    li0scc0 Hall of Fame

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    There would be a difference in how they swing, as well as a difference in the effect on the ball.
    swung at the same velocity, the 308 will have more power than the 297 (assuming both have the same flex).
     
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  3. corners

    corners Legend

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    Big difference in my book. Top players can feel just a couple units difference. Inexperienced player may not notice.
     
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  4. BobFL

    BobFL Hall of Fame

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    I used to have 2 PDRs. The SWs were 322 and 337 so that's 15 points. the difference was MASSIVE.
     
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  5. Muppet

    Muppet Hall of Fame

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    If you're changing the swingweight, don't you have to change the weight and/or balance?
     
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  6. Xizel

    Xizel Professional

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    I suppose it'd be quality control of the manufacturers, so you're not changing it yourself, because then those 2 stats could be subjected to change.
     
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  7. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    Yeah. It is my understanding that SW is based entirely on static weight and balance. I don't believe that the aerodynamics is even taken into account. Off the shelf 2 of the same frame can have somewhat different mass and balance that could result in a different SW. What other parameters would affect the SW?
     
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  8. BobFL

    BobFL Hall of Fame

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    Not necessarily. You can have 2 racquets with the same balance and weight BUT with different sw. For example:

    XXX------XXX

    and

    ---XXXXXX---

    The key here is weight distribution.
     
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  9. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    ^ Thanks, that makes sense. After I posted, I got to thinking that perhaps weight distribution might be a factor. But then I thought, if the mass and the balance location were the same for 2 "identical" frames (same model), could the weight distribution really vary that much off the shelf to account for a difference of 11?

    Or are we talking about 2 similar frames that that have been leaded in different location yet have the same mass and balance location?
     
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  10. aimr75

    aimr75 Hall of Fame

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    I am looking at getting a couple of frames from TW and they quoted those swing weights for two of the same frame with no modification
     
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  11. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    You are not talking about TW's published SWs for the frame? They took 2 frames from inventory and measured them for you!!! Really???
     
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  12. aimr75

    aimr75 Hall of Fame

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    Yes, as part of the $10 racquet matching service, they pick out two with the closest specs (but they currently only have 2 in stock of the racquet i am after) . For $20 per racquet they do proper matching through customisation
     
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  13. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    Wow, that's pretty cool. Have seen variations in weight & balance but would not have expected that much of a difference in SW given that the other 2 parameters were similar.
     
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  14. aimr75

    aimr75 Hall of Fame

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    Yeah a bit surprising, here we're the specs provided:

    1st racquet:
    11.0oz
    12 5/8" Head Light
    297 swingweight

    2nd racquet:
    11.0 oz
    12 3/4" Head Light
    308 swingweight
     
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  15. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    ^ It looks like the swing weights are somewhat consistent with the balance specs. Are these unstrung specs? Are you adverse to adding a bit of lead in the appropriate locations to get the balance specs closer? This change should get the SW of the 2 frames closer as well (if I'm looking at this the right way).

    Alternately, you could string racket #1 a tad bit looser to give it a little bit more power. However, I'd probably go with options #1 if the added mass doesn't bother you.
     
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  16. aimr75

    aimr75 Hall of Fame

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    ^i have done customization as far as static weight and balance, but never really tried working out swing weights. So don't know how accurate I would be modifying the balance to get a desired swing weight.
     
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  17. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    You might not be able to get the SWs to match exactly. In this case, I believe, if you adjust the balance points to match exactly, the SW values would be closer than they are now.
     
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  18. li0scc0

    li0scc0 Hall of Fame

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    The biggest issue between frames is NOT the weight or swingweight or balance, as dramatic as those can be, they can be corrected with lead (although it can drastically add to the weight of the frames to bring them to spec).
    The biggest issue..and the elephant in the room here...is the stiffness. My favorite racquet is the Wilson KBLADE 98. With leather and some lead, that racquet and I simply click. Well, sometimes. Why do I say sometimes? Because when I used this racquet, I had 3....one with a flex of 70, one 67, and one 62. Those are 3 completely different frames. Unusable for me.
     
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  19. BobFL

    BobFL Hall of Fame

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    Not true. There are many situation when 2 racquet cannot be matched with lead tape. That makes them - unusable. The result is pretty much the same.
     
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  20. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    ^^ How does one determine the flex of their frames? Is it trivial to do this or do you need access to special equipment? (I looked a bit around TWU and did not find this info).
     
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  21. BobFL

    BobFL Hall of Fame

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    This.

    10 RDC Machines
     
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  22. li0scc0

    li0scc0 Hall of Fame

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    Read the part I had in parenthesis JUST after what you highlighted. I mentioned you may have to dramatically increase the racquets in overall weight to achieve the same weight, swingweight, and balance between the two. This is what I experienced with my KBLADES, having to get them to 12.5 ounces to get the 3 to the same weight, SW, and balance. And, considering the flex was so dramatically different initially, the point was moot.
     
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  23. li0scc0

    li0scc0 Hall of Fame

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    Exactly. However, support your local tennis shop, and they will happily test them for no charge.
     
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  24. BobFL

    BobFL Hall of Fame

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    No charge? What kind of support is that?
     
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  25. li0scc0

    li0scc0 Hall of Fame

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    I.e. buy your racquets at your local shop, and they will weigh them.
    and/Or
    Get your racquets strung there
    and/Or
    Buy your shoes there
    and/Or

    That is supporting your local shop.
     
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  26. Muppet

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    I think this changes the polarization, and certainly the feel, but not the swingweight.
     
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  27. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    That's what I thought at first. If the weight distribution was irrelevant then you should be able to determine a swingweight knowing the just mass (static weight) and the the balance point (or distance from some reference point on the handle). This does not appear to be the case. Take a look at these links from TWU:

    http://twu.tennis-warehouse.com/learning_center/swingweight_calc.php
    http://twu.tennis-warehouse.com/learning_center/howto_swingweight.php

    It appears that the swingweight is defined as the rotational inertia of the racquet about a given axis of rotation. The Babolat RDC uses 10 cm from the butt end of the racket for the axis of rotation. Given this definition, the rotational inertia would be dependent on the distribution of mass.

    http://www.racquetresearch.com/sevencri.htm#sweet%20spot
    .
     
    Last edited: Mar 19, 2012
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  28. retlod

    retlod Professional

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    BobFL is right--it will change all three. :) Swingweight measures rotational inertia, not just mass, and that inertia has to do not only with mass and balance, but also with mass distribution. If you have two wheels at the top of an inclined plane, both with the same diameter, both made of the same material, and both with the same mass, but one is a solid and the other is a band (think tire-shaped), the solid one will accelerate faster down the ramp when released because it has a lower moment of inertia. Racquets are the same. Polarized frames have higher MOIs and therefore higher SWs.

    Look up the spec differences between Pure Drives and Aero Pros. No misprints there. The APDs have a higher SW because they are more polarized.
     
    Last edited: Mar 19, 2012
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  29. Muppet

    Muppet Hall of Fame

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    Forgive me if I am in error, as it's been many years since I took Physics in college.

    I understand the formula for rotational inertia to be I=ml^2. First I would take the first configuration, --xxxxxx--, and draw a moment of inertia 'l' from the axis of rotation at 10 cm up the grip, and make the I=ml^2 calculation, with m being the total mass of the racquet.

    Next, I would look at the other configuration, xxx----xxx. We notice that for the first three x marks the distance from the axis of rotation is zero and there is no moment for those three x marks. The inertia that is left at the top of the racquet is twice the distance, l, and half the mass, m, compared to the first racquet.

    So I find that half the mass at the top of the racquet holds an equal amount of inertia as all of the mass at the middle of the racquet, rotating about the axis of rotation at 10 cm up the grip.

    I would say that the two racquets would certainly feel different, but they would not resist rotation differently. Thanks for providing this problem for me to delve into.
     
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  30. cellofaan

    cellofaan Semi-Pro

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    you're right that the mass at the top is (about) twice the distance and half the mass, but distance is squared in the formula, so twice the distance means four times as much inertia.
     
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  31. Muppet

    Muppet Hall of Fame

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    You're right. Thanks for pointing that out.
     
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  32. corbind

    corbind Professional

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    That is insane! Same stick, bought same year and that varied of stiffness? TW lists Stiffness: 67 for that stick so you got one perfect, one +2 and one -5 stiffness RA. That makes no sense to me.

    First, how did you determine the flex of the three frames? Second, how can a frame made by a reputable company (Wilson headquarters 20 miles from my home) have such a wild variance in stiffness? :confused:
     
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  33. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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    ^ This is disturbing. I might expect to see slight differences in weight and balance. You would expect, with the cost of a new racquet, that the specs would be fairly consistent. However, we are seeing reported differences of 8 in RA stiffness ratings and 11-15 in SW measurements in this thread alone.

    I might be willing to accept the difference between 70 and 67, but the difference between 70 and 62 just seems to be too much to tolerate. Even if the three "identical" frames had the same rating of 67, it might still not tell the whole story -- they could still feel different even if the other specs were pretty much the same. You would probably really need stiffness ratings at multiple locations to get a more complete picture.

    Some tennis pro shops have a Babolat RDC machine to determine the RA stiffness index and other specs. I assume that TW does as well. Does anyone know if the stiffness index that TW publishes is their own measurement or do they accept the manufacturers stiffness numbers? If TW does measure this spec, how many of each model to they use to determine the specs?

    Here is demo of the Babolat RDC machine used to measure various parameters. (Don't let the ominous face at the start of the video frighten you).

    http://www.youtube.com/watch?v=67ndPgE5ITU
    .
     
    Last edited: Mar 28, 2012
    #33
  34. SystemicAnomaly

    SystemicAnomaly G.O.A.T.

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  35. li0scc0

    li0scc0 Hall of Fame

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    Three purchased at the same time, from the same place!
    Flex tested at local shop on their machine. Tested each frame twice for variance.
    Scary, isn't it?
     
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  36. li0scc0

    li0scc0 Hall of Fame

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    TW tests the frames they get, and thus their numbers differ from reported specs (and also from competitors such as Tennisexpre$$ and Ho1abird)

    Our shop has the Babolat RDC machine, very nice!
     
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