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newyorkstadium 03-26-2013 03:56 AM

Questions for corners
 
I've read through TW Professors posts on the dead strings article thread.

Quote:

Originally Posted by corners (Post 6956865)
Basically, their tests make the copolys lose more tension than they would in the real world - basically they are testing them "dead"

In addition, if we're clever we can still use the test data to compare the stiffness and energy return, string deflection and dwell-time, of a poly to a nylon string, or a poly to a natural gut. The String Performance Database allows us to sort results by "actual tension" - the tension is really at after the tension loss protocol has been carried. If we do this we can compare a nylon strung at 50, which might have an "actual tension" of 40 pounds, with, for example, a poly strung at 60 but, after tension loss, that is now also at an actual tension of 40 pounds. This way, we can compare them both at 40 pounds and get a pretty decent apples to apples comparison of their dynamic stiffness, energy return, deflection, dwell-time, peak force, etc. Then, we can use those actual tensions to compare the nylon at 40 pounds to the same poly at 30 pounds, which might be a good reflection of those strings after they've been played with for 10 hours or so, since we already know that the poly will lose about 10 pounds more tension than the nylon will in real life. Hope that makes sense.

Is it still a good idea to follow this procedure, after the TW Professor's recent revelations?

Thanks

corners 03-26-2013 12:19 PM

Quote:

Originally Posted by newyorkstadium (Post 7303847)
I've read through TW Professors posts on the dead strings article thread.



Is it still a good idea to follow this procedure, after the TW Professor's recent revelations?

Thanks

Oh, I don't know. What I usually do when comparing two strings of different materials - a nylon vs. a copoly - is to choose all three tensions at fast swingspeed. Then sort by actual tension. Then I can try and compare them at the same actual tensions, or I can try and make an adjustment. So we know from real world tension loss data that copolys lose about 15 pounds of tension by about 8-10 hours and syngut loses a little more than half that. So if I can compare a copoly at 45 pounds actual tension to a syngut at 52 pounds actual tension I can get a pretty rough idea of the stiffness, energy return, deflection and dwell time (which are the four that I focus on most) that those two strings will have after playing with them for 8-10 hours.

I'm usually doing this to figure out what tension I would like, let's say, a gut/ZX stringjob that I'm thinking about, as compared to a gut/copoly string setup that I have experience with. So if I thought that, at hour 8, the deflection of the main strings was giving me what I wanted in terms of spin and rebound angle I might be able to replicate that performance by getting the tension of gut/ZX just right, or close enough.

I think your focus is different, though, but I still don't know what that focus is.

Anyway, remember that I'm just a guy that's made a hobby out of fiddling with and obsessing about racquets and strings, as well as other things tennis-related. But I've got no professional training in this area, so take everything I babble about with one or more grains of salt.

newyorkstadium 03-27-2013 01:24 AM

My focus was also to compare strings, to assist in picking a tension. Thanks for the explanation.

Quote:

Originally Posted by corners (Post 7304822)
So we know from real world tension loss data that copolys lose about 15 pounds of tension by about 8-10 hours and syngut loses a little more than half that.

Just to be clear, this is the thing I didn't understand. Where did you find this out? I've been searching the forums for similar info. How do you know the nylons don't stop losing after 8-10 hrs of play? Thus the nylons are also partially "dead".

The recent TWU article has got me re-thinking the importance of tension loss anyway. Is it worth comparing just the tension loss of strings, when increased COF can negate tension loss. Isn't it best to just use your method of observing stiffness, energy return, deflection and dwell time?

I've just realised that a lot of the questions I asked you on ChicagoJacks thread, you had already answered. Sorry for going round in circles a bit. I've been waiting for a pair of reading glasses to arrive, so my reading comprehension was a bit rubbish. The reading glasses have arrived now and your posts are no longer a blurry haze :).

corners 03-27-2013 07:11 AM

Quote:

Originally Posted by newyorkstadium (Post 7306640)
My focus was also to compare strings, to assist in picking a tension when changing strings. Thanks for the explanation.



Just to be clear, this is the thing I didn't understand. Where did you find this out? I've been searching the forums for similar info. How do you know the nylons don't stop losing after 8-10 hrs of play? Thus the nylons are also partially "dead".

What do you mean by "dead"?

One source of real court data is stringforum.net's DT database: http://stringforum.net/dtdb.php

These are records of static stringbed stiffness, but they give a good indication of tension loss over time.

Quote:

The recent TWU article has got me re-thinking the importance of tension loss anyway. Is it worth comparing just the tension loss of strings, when increased COF can negate tension loss. Isn't it best to just use your method of observing stiffness, energy return, deflection and dwell time?
Yeah, I'm not so sure tension loss is that important. I mean, all things being equal, I'll pick a string that holds tension well over one that doesn't, but I'm more interested in stiffness, energy return, COF, deflection and dwell time.

Quote:

I've just realised that a lot of the questions I asked you on ChicagoJacks thread, you had already answered. Sorry for going round in circles a bit. I've been waiting for a pair of reading glasses to arrive, so my reading comprehension was a bit rubbish. The reading glasses have arrived now and your posts are no longer a blurry haze :).
No problem. I put up with you because I can relate to your curiosity. :)

newyorkstadium 03-27-2013 07:28 AM

Quote:

Originally Posted by corners (Post 7304822)
So we know from real world tension loss data that copolys lose about 15 pounds of tension by about 8-10 hours and syngut loses a little more than half that.

I dispute these figures, corners. I had some time to kill, so I looked at 20+ nylons and 30+ poly's on stringforum. Here are my findings:

1) The average total loss for nylons after 8-10 hrs was 21.8 DT.

2) The average total loss for poly's after 8-10 hrs was 24.2 DT.

3) The dynamic tension loss after 8-10 hrs hitting for nylons ranged from 0.5-7 DT. The average is 3.

4) The DT loss after 8-10 hrs for polys ranged from 1-12 DT. The average is 4.4.

5) Poly and nylons seem to slow down at a similar point of around 23DT. This challenges the idea that poly's lose more tension.

I would estimate that for the TWU nylon data, total loss averages 12lbs. For the TWU poly data, I would estimate the average total loss is 23lbs. So the TWU tension loss appears to be too low for nylon, rather then too high for poly. So poly's stiffness

Taking all of this into account, I'm not sure you can conclude that copolys lose about 15 pounds of tension by about 8-10 hours and syngut loses a little more than half that

Quote:

Originally Posted by corners (Post 7304822)
Another thing to consider is that all of these stiffness numbers are taken post-tension loss. The nylons lose much less tension than the copolys, so the numbers make the copolys look pretty soft. But I believe TWU's procedure for tension loss measurement is too aggressive. Basically, their tests make the copolys lose more tension than they would in the real world - basically they are testing them "dead" (although I don't believe strings go dead in the way people believe them to). Adjusting for that, the copolys are probably about 10-15% stiffer than they appear in comparison to the nylons.

In light of everything I've revealed, do you still think co-polys are 10-15% stiffer? I think, looking at the stringforum data, maybe the TWU nylon figures are too soft.

I'm also not sure the TWU nylon tension loss data is useful, as it is less then half the stringforum numbers. So, we don't know which strings will have lost the most by the 8-10hr mark for the TWU data. Also julianashaway's post's seems to indicate dynamic stiffness is the first thing you should look at for tension loss, anyway.

corners 03-27-2013 03:14 PM

Quote:

Originally Posted by newyorkstadium (Post 7307142)
In the sense that the string has all but stopped losing tension. How do we know the nylons haven't stopped losing by the end of the TWU test's, just like the poly's. Thus the qoute below would be false. How do you convert stringforum's static stringbed stiffness loss to tension loss?

Well, if you define "dead" as a string reaching a point where tension loss is no longer happening to a significant degree then that would mean that "alive" means the string is in the process of losing tension.

What is the significance of that distinction?

Why is it important?

Why is it important to you?

I'm actually getting pretty tired of fielding these questions with no clear idea of what you are after. If you spell out what your objective is maybe I can help you, but I'm starting to think you don't have an objective and that you're just asking questions that won't lead anywhere. Can you see how that would be unsatisfying for me. I hear that young people are starting to treat other human beings as though they are computers. Is that what's going on here?

newyorkstadium 03-28-2013 11:10 AM

Sorry, my post was unfinished. I intended to edit it but got sidetracked. In the future, I won't post half-complete posts. I will put an unfinished post in a word document, or in an email draft. Sorry for any stress deciphering my post may have caused. I will finish editing it today.

I try to treat all people I encounter as decent human beings. I've definitely never treated another person as a computer. But it does scare me the amount of technology the youth of today are engaged in.

I am extremely grateful to talktennis for the help they've given me. You and travlerajm, in particular, have been a valuable source of help and knowledge. I was in a tennis rut before I signed up here. My game wasn't what I wanted it to be, and I wasn't improving. It's improved tons since I started soaking up all the info on here.

newyorkstadium 03-28-2013 04:27 PM

Right, I've edited my post. I'm not sure what it all means though.

newyorkstadium 04-03-2013 11:06 AM

Quote:

Originally Posted by newyorkstadium (Post 7307142)
Quote:

Originally Posted by corners (Post 7304822)
So we know from real world tension loss data that copolys lose about 15 pounds of tension by about 8-10 hours and syngut loses a little more than half that.

I dispute these figures, corners. I had some time to kill, so I looked at 20+ nylons and 30+ poly's on stringforum. Here are my findings:

1) The average total loss for nylons after 8-10 hrs was 21.8 DT.

2) The average total loss for poly's after 8-10 hrs was 24.2 DT.

3) The dynamic tension loss after 8-10 hrs hitting for nylons ranged from 0.5-7 DT. The average is 3.

4) The DT loss after 8-10 hrs for polys ranged from 1-12 DT. The average is 4.4.

5) Poly and nylons seem to slow down at a similar point of around 23 DT. This challenges the idea that poly's lose more tension.

I would estimate that for the TWU nylon data, total loss averages 12lbs. For the TWU poly data, I would estimate the average total loss is 23lbs. So the TWU tension loss appears to be too low for nylon, rather then too high for poly. So poly's stiffness

Taking all of this into account, I'm not sure you can conclude that copolys lose about 15 pounds of tension by about 8-10 hours and syngut loses a little more than half that

Quote:

Originally Posted by corners (Post 7304822)
Another thing to consider is that all of these stiffness numbers are taken post-tension loss. The nylons lose much less tension than the copolys, so the numbers make the copolys look pretty soft. But I believe TWU's procedure for tension loss measurement is too aggressive. Basically, their tests make the copolys lose more tension than they would in the real world - basically they are testing them "dead" (although I don't believe strings go dead in the way people believe them to). Adjusting for that, the copolys are probably about 10-15% stiffer than they appear in comparison to the nylons.

In light of everything I've revealed, do you still think co-polys are 10-15% stiffer? I think, looking at the stringforum data, maybe the TWU nylon figures are too soft.

I'm also not sure the TWU nylon tension loss data is useful, as it is less then half the stringforum numbers. So, we don't know which strings will have lost the most by the 8-10hr mark for the TWU data. Also julianashaway's post's seems to indicate dynamic stiffness is the first thing you should look at for tension loss, anyway.

Okay. I've finished editing my question now. That's the longest post I've ever written on here, by far.

newyorkstadium 04-08-2013 07:56 AM

I've edited the questions again to add more. Apologies if this all a bit banal, corners. I'm just trying to work out how to best utilise the TWU string tool.

corners 04-09-2013 10:59 AM

Quote:

Originally Posted by newyorkstadium (Post 7331741)
I've edited the questions again to add more. Apologies if this all a bit banal, corners. I'm just trying to work out how to best utilise the TWU string tool.

First of all, I just want to know what your objective is. Answering your questions feels like working for an unknown company, without getting paid, with no idea of why I'm doing the work.

About your edited post, could you include the units for all the numbers? I can't tell if those are DT (static stringbed stiffness), tension loss (in pounds), percentage lost (%).

Regarding Julian and dynamic stiffness, yes, TWU also sees dynamic stiffness as most important. But keep in mind that even if the stiffness does not change much with changes in tension, the dwell time and deflection does. Do a comparison with the TWU String Database on a natural gut string strung at 40, 51 and 62 pounds. You'll see that the dynamic stiffness of natural gut is more of less the same at each tension (which is NOT the case with nylon and copoly strings; zyex is more similar to gut in this respect), but the dwell time and deflection is very different at each tension.

So even though the dynamic stiffness of Monogut ZX doesn't change much when it drops tension, the deflection and dwell time will increase. And as the TW Professor found in his recent paper on "going dead", changes in deflection are probably a big factor in the control problems people experience with "dead" strings.

Incidentally, this is why, with natural gut (and to a lesser extent with ZX), I think it makes sense to string very tight. At high tensions the stiffness and energy return are more or less the same as at low tensions, so the power (ACOR) will be very similar. But at high tension the strings will deflect less, providing more consistent rebound angles on shots hit at various places on the stringbed. At low tension you don't really get much out of the deal except longer dwell time and increased comfort, at the expense of directional control.

newyorkstadium 04-10-2013 12:22 AM

Quote:

Originally Posted by corners (Post 7334134)
First of all, I just want to know what your objective is. Answering your questions feels like working for an unknown company, without getting paid, with no idea of why I'm doing the work.

About your edited post, could you include the units for all the numbers? I can't tell if those are DT (static stringbed stiffness), tension loss (in pounds), percentage lost (%).

Regarding Julian and dynamic stiffness, yes, TWU also sees dynamic stiffness as most important. But keep in mind that even if the stiffness does not change much with changes in tension, the dwell time and deflection does. Do a comparison with the TWU String Database on a natural gut string strung at 40, 51 and 62 pounds. You'll see that the dynamic stiffness of natural gut is more of less the same at each tension (which is NOT the case with nylon and copoly strings; zyex is more similar to gut in this respect), but the dwell time and deflection is very different at each tension.

So even though the dynamic stiffness of Monogut ZX doesn't change much when it drops tension, the deflection and dwell time will increase. And as the TW Professor found in his recent paper on "going dead", changes in deflection are probably a big factor in the control problems people experience with "dead" strings.

Incidentally, this is why, with natural gut (and to a lesser extent with ZX), I think it makes sense to string very tight. At high tensions the stiffness and energy return are more or less the same as at low tensions, so the power (ACOR) will be very similar. But at high tension the strings will deflect less, providing more consistent rebound angles on shots hit at various places on the stringbed. At low tension you don't really get much out of the deal except longer dwell time and increased comfort, at the expense of directional control.

They are all DT loss. I've edited them now. Does stringing gut and ZX at high tensions increase the COF? You also get a little less durability at high tensions, which could be an issue for some.

Firstly, I wish to know if DT loss is the same as TWU's tension loss. This way I can try to compare the stringforum data and the TWU data. It would be easier to ask questions if I know the answer to this question.

I'm basically questioning your assertions that:

1) Copolys lose about 15 pounds of tension by about 8-10 hours and syngut loses a little more than half that.
2) Co-polys are 10-15% stiffer then the TWU figures. The stringforum data I've posted suggests poly and nylon lose similar tension (see point 5) and at similar rates. So it is the nylons that are too low in the TWU data.

I'm also not sure the TWU nylon tension loss data is useful, as it's less then half the stringforum numbers. So, we don't know which strings will have lost the most by the 8-10hr mark for the TWU data, the point of relative stabilisation.

fgs 04-10-2013 01:14 AM

if you read the methodology of the twu measurements you will find out that they measure tension loss on a single strand of string pulled at a certain tension. while this may be indicative for the performance of the material itself, it has nothing to do with stringbedstiffnes (dt).

the stringforum-data is mostly stringbedstiffness. also bear in mind that if we both play the same stick, the same string at the same tension, strung by the same stringer and measuring off the stringer the same stringbedstiffness, due to different stroke mechanics it is most probably that by the end of a session in which we have hit the same amount of strokes the stringbedstiffnesses will differ, as due to our stroking motions (for instance flat hitter vs. extreme topspin-hitter) the forces applied to the stringbeds will be quite different.

the tension losses i have compiled over time with the racquettune-app indicate that polys generally lose more tension at the beginning and then seem to plateau off and only lose a little bit more. for instance i had 8% settling loss within 24hrs off the stringer with no playing activity. then, after the first 2hrs session the reading was another 6% lower while the next three times out (2hrs sessions each time), the loss would only be in the 2-3% range, always relative to the last tension measured!
with syngut or multis i have experienced a lower settling loss but somewhat larger losses after each session. needless to say that i hardly make it to the end of the second session with most of them in fullbed, some have broken even within the first session, so i could not do any measurement at all, as i did not measure on court.

copolys are not stiffer nor are synguts softer than the twu-measurements as long as you understand the methodology. of course the stringbed of a stiffer string will be much stiffer than the stringbed of a softer string, but if you simply try to extrapolate you will reach false conclusions.

the stringbedstiffness itself is just a part of the equation. you can string a poly and a syngut at different tensions and have identical readings in matters of stringbedstiffness. the dynamic behaviour of the stringbed itself will be vastly different though because you will get completely different deflection values, dwell time and all of this "assorted candy", including launch angles etc. you will have different energy returns and you will have a completely different stringbedbehaviour in terms of evolution in time.

newyorkstadium 04-11-2013 09:56 AM

Although I laboured to reach my point initially, it's all becoming clearer now.

Quote:

Originally Posted by fgs (Post 7335464)

the stringforum-data is mostly stringbedstiffness. also bear in mind that if we both play the same stick, the same string at the same tension, strung by the same stringer and measuring off the stringer the same stringbedstiffness, due to different stroke mechanics it is most probably that by the end of a session in which we have hit the same amount of strokes the stringbedstiffnesses will differ, as due to our stroking motions (for instance flat hitter vs. extreme topspin-hitter) the forces applied to the stringbeds will be quite different.

There is a point of relative stabilisation, where the tension loss all but slow's down to a halt. I think it is around 23DT for both nylon and poly's.

Why does the TWU figures have nylon losing half as much as poly, yet the stringforum data has them losing similar amounts of DT after 8-10hrs?

Quote:

Originally Posted by fgs (Post 7335464)

the stringbedstiffness itself is just a part of the equation. you can string a poly and a syngut at different tensions and have identical readings in matters of stringbedstiffness. the dynamic behaviour of the stringbed itself will be vastly different though because you will get completely different deflection values, dwell time and all of this "assorted candy", including launch angles etc. you will have different energy returns and you will have a completely different stringbedbehaviour in terms of evolution in time.

All of these things are influenced by tension loss though. So you will know if you a string will become a "rocket launcher" by looking at the TWU tension loss value. Although, the increase in COF does counterbalance this.

corners 04-11-2013 10:13 AM

Quote:

Originally Posted by newyorkstadium (Post 7338096)
Although I laboured to reach my point initially, it's all becoming clearer now.



There is a point of relative stabilisation, where the tension loss all but slow's down to a halt. I think it is around 23DT for both nylon and poly's.

Why does the TWU figures have nylon losing half as much as poly, yet the stringforum data has them losing similar amounts of DT after 8-10hrs?

I don't know. But as fgs mentioned, DT (static stringbed stiffness) and tension are not the same thing. Each material is different (for example, gut will show very similar DT measurements as copoly straight off the stringer, but we know that gut is half as stiff as copoly dynamically). In my opinion the ability to determine tension using the RacquetTune app makes DT measurements obsolete. fgs cited some RacquetTune figures. It would be good to start a thread purely for RacquetTune tension loss records.


Quote:

All of these things are influenced by tension loss though. So you will know if you a string will become a "rocket launcher" by looking at the TWU tension loss value. Although, the increase in COF does counterbalance this.
What do you mean by that?

newyorkstadium 04-11-2013 10:29 AM

Quote:

Originally Posted by corners (Post 7338124)
In my opinion the ability to determine tension using the RacquetTune app makes DT measurements obsolete. fgs cited some RacquetTune figures. It would be good to start a thread purely for RacquetTune tension loss records.

What do you mean by that?

Stringforum has RacquetTune down as also being DT. Is this wrong?

I will quote the TW professor to explain what I mean't:

"The increasing static and/or sliding coefficients of friction will decrease the amount and efficiency of the sideways main string movement and snap back. This, in turn, decreases spin, lowers launch angle, and stiffens the stringbed parallel to the strings. This is perceived as a loss of power and spin as well as an increase in stiffness, harshness, and pain, especially if the player starts swinging even faster to compensate."

lawrencejin 04-11-2013 10:41 AM

NY Stadium, while I applaud your curiosity, I feel like your questions are too broad, too scattered, and simply too many to be answered effectively in a forum like this.

A forum (as well as emails, etc) is an effective means to exchange simple information quickly... but it becomes radically inefficient when we start dealing with long texts and large information. That's because people tend to be sloppy and imprecise when writing here, which makes it very time-consuming to read everything, clarify ambiguities, and respond accurately.

As I said, I do think it's great that you're fascinated by this topic. But you should also keep in mind that science behind tennis is still relatively unexplored from an academic point of view. It helps to think simple.

newyorkstadium 04-11-2013 10:51 AM

lawrencejin, usually my questions are concise and short. I let my standards drop with this thread.

Honestly, this thread wasn't so much a bunch of questions, as it was challenging a few things corners said in another thread. I don't doubt that corners is more intelligent and knowledgable then me. But I felt this was worth bringing up.

I disagree with you that it's wrong to ask questions on here. There are some really intelligent people on this forum, and through questioning the science, or experimenting, we are able to improve the scientific knowledge of tennis. I have no scientific background, just curiosity. So, I do sometimes make mistakes with the terminology.

corners 04-11-2013 11:03 AM

Quote:

Originally Posted by newyorkstadium (Post 7338142)
Stringforum has racquettune down as also being DT. Is this wrong?

My understanding is that Racquetune can give you both static stringbed stiffness (DT or equivalent) and tension. Tension is what should be focused on, IMHO.

Quote:

I will quote the TW professor to explain what I mean't:

"The increasing static and/or sliding coefficients of friction will decrease the amount and efficiency of the sideways main string movement and snap back. This, in turn, decreases spin, lowers launch angle, and stiffens the stringbed parallel to the strings. This is perceived as a loss of power and spin as well as an increase in stiffness, harshness, and pain, especially if the player starts swinging even faster to compensate."
Yes, but one thing that could vary from this description is rebound angle. The Professor writes that the launch angle will be lower with increased inter-string friction. But that would happen if the friction is large enough to prevent lateral sliding and stretching of the main altogether. But if the mains slide laterally but then get stuck, and so fail to snap back with the ball, the rebound angle would increase, as has been demonstrated in several of the Professor's experiments in other papers. This could compound the "rocket launcher" effect that might result from tension loss and increased dwell time/deflection, rather than counterbalance it.

newyorkstadium 04-11-2013 11:05 AM

Thanks. There is a measurement called RA that the Babolat RDC measures, and a measurement called DA that the Pacific Multi test Computer measures. Are these also obsolete, in comparison to the Racquetune app. I will start a new thread comparing the data to the TWU data.


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