what is the "si" - is this stiffness rating????

Discussion in 'Racquets' started by jimanuel12, May 14, 2011.

  1. jimanuel12

    jimanuel12 Semi-Pro

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    i bought a wilson profile wide beam racquet and i cannot find the stiffness rating.
    on line i found something about "si" says it is 5.0
    how does that compare to the ratings of 70?
    some specs i found said 2.7 - others say 5.0
    i am confused.
    any feedback?
     
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  2. big bang

    big bang Hall of Fame

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    swing index
     
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  3. VGP

    VGP Legend

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    Actually, Wilson started off using the "si" as stiffness index. IIRC the numbers were determined by how many millimeters down a frame bent when a 5 pound weight was hung from the tip with the handle end clamped down on a table parallel to the floor. The lower the number, the less it bent, therefore the stiffer the frame. The Wilson Profile 2.7 was stiffer than the Profile 3.6, the Pro Staff 7.5 more flexible than the 4.5.

    Then.....Wilson changed it to "swing index" - not how a racket swings, but their scale for the apparent swing style of the player. Say if you have slow swings and want more power you go for a lower number, if you have fast strokes and want more control they suggest you go for a higher number.

    So, it depends on how you look at it and it's two spins on Wilson's marketing strategy from the 80s and 90s. You swing slow and want more power from a stiffer frame - lower number, you swing fast and want flexibility to tame your swing speed - higher number. Both marketing strategies were based on stiffness.
     
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  4. Mick

    Mick Legend

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    this steffi graf racquet has a swing speed index (si) of 7.0. i wonder if wilson has ever made one with a swing speed index of 8.0?
    si would max out at 8.0 according to that chart :)

    [​IMG]
     
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  5. jimanuel12

    jimanuel12 Semi-Pro

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    i have read all kinds of confusing stuff on the net about the wilson profile stiffness rating. some say the lower the number the more stiff - some say just the opposite.
    i read somewhere the stiffness rating is 64 but now i am really confused.
     
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  6. jimanuel12

    jimanuel12 Semi-Pro

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    ok - did some more reseach - looks like the wilson profile is a very stiff racquet even though it weighs about 13.0 oz. it is listed as head light but the stiffness rating i found was 74. that sounds about right from all the reading i have done tonite.
    anyone know for certain?
     
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  7. VGP

    VGP Legend

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    I can see how it can be confusing. The Wilson "si" scale was the lower the number the stiffer the frame. That's a contrast to the now industry-wide stiffness rating done on say a Babolat RDC machine with the stiffness scale of 1-100 with most frames these days in the 50 to 80 range.

    As for what the RDC stiffness of a Wilson Profile, that I don't know. It also depends on the one you mean. There was the gold original which became the Profile 2.7, the silver denser string pattern Profile 3.6, the Aire Shell Profile 3.0, plus the hammer versions.

    Since you mention a Profile of 13 ounces, I assume you're meaning the first ones from 86-89. Remember back then, 13 ounces was considered light. The first thing was to have a stiffer frame, light and stiff came later (Hammer system) and the use of more polarized weight distribution to minimize static weight of frames. I'd guess the 74 you read about might be accurate.....
     
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  8. flashfire276

    flashfire276 Hall of Fame

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    All I know is that the higher the SI, the lower the flex rating is.
    Please correct me if I'm wrong guys. But if I can recall, 5.0 SI rating had an RA of around 70-ish?
     
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  9. jimanuel12

    jimanuel12 Semi-Pro

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    that is correct - that was the stiffest racquet i have ever used. sold the darn thing - my arm almost fell off using that thing - but man - what power!!!
     
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  10. roundiesee

    roundiesee Hall of Fame

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    I agree with VGP; I have always thought Wilson meant it as "stiffness" rather than "swing". Great answer.
     
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  11. retlod

    retlod Professional

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    Back in the early 90's I had a Wilson Graphite Aggressor that was an 8.5 si.
     
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