NEW TWU (4-17-13): Dead Strings Part 2

Discussion in 'Strings' started by TW Professor, Apr 17, 2013.

  1. TW Professor

    TW Professor Administrator

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    #1
  2. Readers

    Readers Semi-Pro

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    I know this is prob too much to ask, but can you consider making videos?

    As I (and likely many others)really have a hard time reading though this huge amount of highly technical text.
     
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  3. TimothyO

    TimothyO Hall of Fame

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    From TW Prof's report:

    I believe this might be why I'm enjoying pre-stretched Focus Hex crosses so much.

    As I noted in another thread I feel like the VS Longevity / pre-stretched Focus Hex setup has lots of welcome "pop" compared to 4G, plenty of comfort, and yet is very controllable and extremely spin-friendly.

    I hit with my son and a friend this evening (the friend is an A-level doubles/ALTA player) and after several hours of hitting with this hybrid in 80 degree weather I still had tons of spin and very controllable and comfortable power.

    The only delta between my experience and TW Prof's report is in friction. After several hours of hitting (at least!) my gut mains slide perfectly over the pre-stretched Focus Hex crosses. They slide much better than over the 4G and spin is very much "casually accessible". The Focus Hex crosses remain smooth and un-dented by the gut mains. By this time the 4G crosses would have been dented and scuffed by the gut mains providing less access to easy spin (but still spinny compared to full gut or full poly).
     
    Last edited: Apr 17, 2013
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  4. Tight Lines

    Tight Lines Professional

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    From TW Prof's report:
    Well, I think that basically settles the debate about pre-stretching a poly string. If better tension maintenance comes at the cost of producing less spin due to more friction between strings, then you are probably better off not pre-stretching.

    The one issue that the TW Profs did not cover is durability of the pre-streched string. In my opinion, any type of home made device for prestretching will cause a severely weakened spot in the string as it is logical to think that most stretching will occur at the weakest spot in the string. So, that is a double whammy against pre-stretching.

    Harry
     
    Last edited: Apr 19, 2013
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  5. TennezSport

    TennezSport Hall of Fame

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    Nicely done......

    Thanks for the paper, and I really like the analogies to help in understanding. For those who understand this they may get a better reasoning for why strings perform the way they do and dont last forever. Thanks again.

    Cheers, TennezSport :cool:
     
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  6. corners

    corners Legend

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    I didn't read it that way. A pre-stretched string essentially acts like a string with better tension maintenance strung at higher tension. So if you found that stringing your normal copoly 5 pounds tighter than normal results in less spin, then yes, prestretching that string might result in less spin. But the other side of the coin is that prestretching that string and then stringing five pounds looser than normal will give you about the same spin performance as at your usual reference tension, but tension maintenance will be better.

    I'm not saying that pre-stretching is necessarily a good idea, but any slight increase in string-on-string friction due to a tighter string or a slightly stiffer string is easily compensated for by adjusting reference tension. The increased string-on-string friction resulting from pre-stretching would be the same as you would encounter if you strung a normal string tighter, in other words.
     
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  7. db10s

    db10s Hall of Fame

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    I'm printing this up and showing it to some friends (and my old-school father) since they don't believe me that poly goes dead and doesn't break.... More stringing business for me.
     
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  8. Tight Lines

    Tight Lines Professional

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    I admit I didn't read the article that carefully. I will try to read it again tonight. In the meantime, are you saying that if I normally string the poly at 40 lbs and if I pre-stretch and then string it at 35 lbs, the resulting spin performance would be equivalent?

    Harry
     
    #8
  9. corners

    corners Legend

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    The five pounds was just a ballpark, but yes. The Professor pre-stretches most strings he tests in the lab. The data on pre-stretched copolys shows that, in general:

    If a particular copoly is strung at 60 pounds it might have 200 stiffness and return 90% of the energy in an impact. It also might lose 15 pounds of tension, settling in at around 45 pounds of tension.

    If you pre-stretch that same string and then string it to 60 pounds it might show 230 stiffness and return 93% of the energy in an impact. It will also lose less tension, maybe 12 pounds.

    So if you want the pre-stretched string to play like the normally strung one you could string it at 55, at which tension it might have 200 stiffness and 90% energy return and lose only 12 pounds, settling in at 43 pounds of tension. Since the stiffness is now equivalent to the regular string strung at 60 it will play the same when fresh but will lose less tension and so maintain its playing characteristics for a longer period of time.

    Again, though, these are all ballpark figures. Previous research that the TW Professor has done has shown that string tension is important to spin, but probably more important is maintaining a smooth, slippery string surface. When that smooth slippery surface is lost to denting, notching or scuffing, the main strings stop snapping back and so stop generating the extra spin that copolys are famous for. And when that happens they play much stiffer too. So now you've got loose strings that don't give much spin but that feel stiffer than when they were new. It turns out that this is what we call "dead" strings.

    And keep in mind that pre-stretching a string might make it slightly more fragile (according to some reports by people who have been experimenting with extreme pre-stretching over the past two weeks), so do it at your own risk.

    It's important to note too that this paper is not really about pre-stretching. The professor "pre-stretched" a piece with hundreds of impacts, then re-tensioned that piece of string to its original tension, and then "pre-stretched" the string with several hundred more impacts, and then repeated this cycle several times. He did this not to test the effect of pre-stretching, but in order to test the hypothesis that copoly strings die because their internal structure becomes fatigued by repeated impacts and that this fatigue results in a loss of elasticity or resilience. But his experiments showed that this does not happen. If anything, the string "improved" slightly after these cycles of repeated impacts, tension loss, and re-tensionings.

    The two "going dead" papers will lead to a complete paradigm shift in the way we view copoly strings and how we might get them to play well for longer periods of time.


    It's very cool, too, in my opinion, that these two papers were written kind of in response to questions raised by posters on this forum. TW is really doing us players a great service by providing us, for free, TW University.
     
    Last edited: Apr 20, 2013
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  10. travlerajm

    travlerajm Hall of Fame

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    This article agrees 100% with my findings from my first experiment with pre-stretching a poly.

    My pre-stretched poly played with much improved playing characteristics than any un-stretched poly I have used. It felt soft, but the dwell time was shorter, and energy return seemed noticeably higher than any un-stretched poly. "feel' was enhanced. It was converted into a completely different type of string (without any of the negatives that I associate with poly).

    It felt like I imagine natural gut would feel like if gut had a slippery surface (Ashaway ZX monogut felt a little like this, but I'd say the thoroughly pre-stretched Prince Tournament Poly felt even more gut-like at impact than the ZX, even though the ZX stretches more like gut when I string it).

    It seems like tension loss and energy return are essentially inverse properties - the more you pre-stretch a string, the less energy is lost during impact to polymer interchain friction, and the more it plays like a perfectly elastic material.

    The only downside I found to pre-stretching was that the string became more fragile (broke in less than an hour when strung at 45 lbs as a cross with kevlar mains in a mid). My first test was with a 70-lb, 90-minute pre-stretch. I think I'll try a gentler 20-lb pre-stretch next time, and maybe let it hang under tension for a few days and see it I can reach the same degree of creep that I reached on my 70-lb pre-stretch (1.4% creep elongation).
     
    Last edited: Apr 20, 2013
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  11. travlerajm

    travlerajm Hall of Fame

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    I've just done a comparison of creep behavior of Prince Tournament Poly 16g vs Ashaway Kevlar 18g. According to the USRSA string database, the kevlar string had greater tension loss (27 lbs loss) than the poly (24 lbs loss) in their test (which combined impacts and relaxation over time).

    But my creep test (using my home-built constant tension pre-stretch device comprising a pulley-and-weight system) suggests that the kevlar string has much better tension stability than the poly:

    [​IMG]

    My on court experience is that kevlar loses tension initially during a 1-2h break-in period, then holds tension extremely well thereafter, with a plateau of nice playability and stable tension maintenance until it breaks (which can be 100h of play or more).

    In contrast, all poly strings tend to gradually lose tension over time until the performance drops off and becomes intolerable (for me, I only like poly in the first several hours).

    It seems to me that the tension loss numbers in the USRSA database are misleading because strings like kevlar that actually have low creep might test poorly because they behave with a "break-in period.".

    When I cross kevlar mains with poly crosses, the difference in creep behavior between the two strings gets amplified because the faster creep of the poly causes the racquet to squash over time, reducing the stress on the mains. When I cut out the strings after being in the racquet for awhile, the kevlar has nearly 1-cm gaps between cut ends, while the poly has no gap, suggesting minimal remaining tension.
     
    Last edited: Apr 21, 2013
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  12. jackcrawford

    jackcrawford Professional

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    The Luxilon String Expert takes a dim view of this article, despite his respect for its source. He begins, "So I began reading, eagerly at first but with a growing sense of disappointment the further I read. Not because it slaughtered any string-sized sacred cows or forced me to rethink any of my own, personal theories or beliefs, but simply because of the growing sense that the testing, reporting and reading of the article had been a complete waste of everyone's time." http://www.protennis.us/ExpertDetail.asp?id=3197
     
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  13. mikeler

    mikeler G.O.A.T.

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    Somebody teach the Luxilon guy about paragraphs for heavens sake!
     
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  14. fgs

    fgs Hall of Fame

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    he is a behavioural psychologist mikeler, try a little understanding.:)
     
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  15. Readers

    Readers Semi-Pro

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    So you are saying he doesn't actually want anyone to read it? :confused: :evil:
     
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  16. jackcrawford

    jackcrawford Professional

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    Since Lux is used by 65% ATP pros, you'd think their advice column would have better formatting - it's not as advanced as TW's software.
     
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  17. JT_2eighty

    JT_2eighty Hall of Fame

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    It's funny, because after reading the Luxilon "String Expert's" article, I also felt like I completely wasted my time! He offered no alternative theory or ideas, just some banter about why he didn't like the TWU tests. Yea, he needs someone to proof and parse his articles into readable format; talk about making your eyes bleed...
     
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  18. corners

    corners Legend

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    Oh, but he did offer an alternative hypothesis. He claims that "going dead" is all in our heads:

    Frankly, I could have saved [TW University] a lot of trouble. Having the advantage of having studied behavioral psychology as well as more scientifically-based subjects, I constantly take account of the 'human' factor in evaluating a player's perspective when involved with such a physically and mentally complex and demanding sport as tennis. We have all experienced the 'great' days when everything goes right and the ball flies true and deep. We have all experienced those frustrating days when we can't win a point to save our lives. There has to be a reason for it, doesn't there? We are still the same person so it must be our equipment. How often have you seen a player looking intently at his racquet - trying to devine what evil is lurking therein to explain some woeful performance? It happens to the best of us... It is clear from how players describe their racquets "going dead" that it is simply a question of perception rather than of physics or mechanics. Players report quite contradictory effects of string aging - some report a lack of power, others too much. Some report stiffer strings, others softer. Some lose control, others feel more confidence. Some like it, some don't. And that, folks, is the bottom line.... Jeff

    So there you have it. TW University should never have bothered to go looking for the real reason(s) why strings go dead, because there are no reasons. Luxilon strings are so wonderful that they may seem to go dead but they really don't. In reality, only inferior and crazy players delude themselves into thinking that strings go dead. There you have it, folks, the bottom line.
     
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  19. fgs

    fgs Hall of Fame

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    readers,

    no, he wants as many as possible to read it in order to see the behaviour afterwards. psychologists work with little stimuli they exert and your reaction (ie behaviour in this case) is what is of interest.

    the conclusion he drew is that this going dead stuff is just in our minds (he is obviously a psychologist), sort of like looking for excuses for a bad performance - you know, i lost today 'cause my string went dead.

    the guy is funny, i wonder if he plays tennis and if he doesn't just imagine (ie that is also just in his head) that his strings never go dead. you know, some people can't see colours, maybe this person has other issues.
     
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  20. Don't Let It Bounce

    Don't Let It Bounce Hall of Fame

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    I wonder if the gentleman "took account of the human factor" in examining his own ego reactions to the TWU article... I wonder too if there was a draft of his article that contained the phrase "all that high-falutin' book larnin'"?

    It would be an amazing discovery to learn that while players' good performance days correlate with new poly string jobs, and their bad performance days correlate with old poly string beds, there is no causation whatsoever in the correlation.

    *******************
    Thanks for putting the time and work into the article, TW Prof. It is much appreciated, as is TW's willingness to provide this information free of charge.
     
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  21. siata94

    siata94 Rookie

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    and top pros changing rackets for fresh strings every 8 games, he must think they're complete idiots...
     
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