Graphs of pre-impact tension vs stiffness and "energy return"

[AlecG]

NOTE: I believe they used a VERY STIFF polyester string here (Black Code?), as some polyester strings have similar stiffness to some nylon strings.

Here are some graphs that were on a talk tennis thread a while ago, from a tennis warehouse article, both of which seem to have since disappeared from the internet. I couldn't find either graph with a reverse image search, but had a copy on my computer. Anyone know why the thread and article were taken down?

The most important take away of the first graph for me is that I can achieve the same stiffness as 25kg nylon by using poly at 12 kg. around what Mannarino uses. I find that polyester at 12 KG has better playability (consistency), durability and comfort than nylon as 25, so I can understand why Mannarino and some other pros opt for low tension polyester for comfort rather than high tension nylon or gut.

The lower "energy return" doesn't seem to make a big difference, probably because a lot of this extra "energy return" goes into squashing the ball instead of accelerating it. As a result *lower* "energy return" seems to be correlated with more power if anything. This makes the second graph somewhat meaningless, or misleading, but the first is very useful.

 

[Kevo]

The lower "energy return" doesn't seem to make a big difference, probably because a lot of this extra "energy return" goes into squashing the ball instead of accelerating it. As a result *lower* "energy return" seems to be correlated with more power if anything. This makes the second graph somewhat meaningless, or misleading, but the first is very useful.

I think that lower energy return is actually correlated with less power if we're talking about ball speed off the strings. I think that is by definition what was measured. In my experience it is quite evident in actual play with poly vs syn gut vs gut. The way gut has such high energy return at higher tension is one of the reasons I didn't really like it except it was amazing on serves. Unfortunately I grew up as an Agassi fan instead of a Stefan Edberg fan. Things could have been so different.

So wether or not you actually want or don't want that higher energy return on a nylon or gut versus a poly will be a personal preference, but it's definitely a factor.

 

[temnik]

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[AlecG]

[deleted]

 

[AlecG]

I think that lower energy return is actually correlated with less power if we're talking about ball speed off the strings. I think that is by definition what was measured.

Energy return wasn't measured by measuring power, which might explain why they seem to have taken down the articles about it.

They acknowledge on their website now that strings with lower stiffness have more power even though they also have less "energy return".

In my experience it is quite evident in actual play with poly vs syn gut vs gut. The way gut has such high energy return at higher tension

This is due primarily to the lower tension. Some of the stiffest polyesters like 4G reported very high "energy return" but are very low in power.

 

[AlecG]

Three things jump out at me:

1. No poly data above 20kg/44lbs? Is this for badminton or something?
2. The "decline" in poly energy return above 20kg is pure fiction: artifact of fitting a 2nd degree polynomial to dataset that doesn't support it.

That's two things. Did you forget one?

No poly data above 20kg/44lbs? Is this for badminton or something?

This is pre-impact tension, not string tension. The real tension of the strings very quickly drops to well below the reference tension after stringing, even before you start hitting, and then it drops even more.

The "decline" in poly energy return above 20kg is pure fiction: artifact of fitting a 2nd degree polynomial to dataset that doesn't support it.

Totally agree, but "energy return" seems a bit meaningless anyway, since they acknowledge on their website that polyester strings with high "energy return" and high stiffness have low power.

 

[Kevo]

Energy return wasn't measured by measuring power, which might explain why they seem to have taken down the articles about it.

Yeah, I think it's complicated. IIRC it was measured with a weight of some sort and not an actual ball. I think that was to eliminate the energy absorption of the ball. So in practice you have to account for the energy from the strings and the loss from the ball. Gut is easily deformed at higher tensions because it's still relatively soft. Even at 70lbs + it's still soft. So I think power may end up being perceived on court as the combination of energy return from strings and the loss from the collision with the ball. So you could certainly end up with less power if you are hitting the ball hard with stiff strings even though the energy return from the stiff strings will be slightly higher than a softer string.

Even trying to talk about these things is difficult because some of the terms are loaded with different meanings.

In any case, I think people have to try things for themselves. These numbers change based on how you hard hit the ball as well and that will make the biggest difference. So two different players will perceive two different things when actually playing with the same setup. In my experience it's actually best to pick your equipment based on feel and not based on any of these reported numbers. I think the numbers are useful for comparison, but in the end you need to actually experience a setup on court to know if it's right for you or not. I don't think there is any formula that works for everyone.

 

[Grafil Injection]

What is the source of the clusters of Nylon and gut strings strung at 25lbs and 35lbs? No one ever does that for tennis rackets.

Looks like the op is comparing a two badminton rackets, rather than Mannarinos stick.

 

[Kevo]

What is the source of the clusters of Nylon and gut strings strung at 25lbs and 35lbs? No one ever does that for tennis rackets.

Looks like the op is comparing a two badminton rackets, rather than Mannarinos stick.

I'm guessing they strung different skus of the material types at the same tension and got clustering somewhere below the reference tension. We'd have to see the original report to know for sure, but since there are so few different kinds of gut, it follows that gut would have the lowest number of plot points. I think it might also explain why the poly is more spread out given the intentional variations in poly materials. ¯\_(ツ)_/¯

 

[temnik]

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[AlecG]

So, if I were to string my poly at a high-ish but reasonable 53lbs, I'd still expect it to be above 44lbs next day or even after 2hrs on court.

Based on data or speculation? The data I've seen shows otherwise. If you check the "Total Tension Loss" box here and click Get Report, you'll see the total tension loss for the first 10 strings is between 13 pounds and 26.5 pounds, with a starting tension of 51 lbs: https://twu.tennis-warehouse.com/learning_center/reporter2.php

This was after just 21 strikes at the force of a 120 mph serve: https://tt.tennis-warehouse.com/ind...ss-vs-stabilization-loss.539585/#post-9511007

That means the first 20 impacts caused a loss of about 1/2 a pound per impact.

In fact, the tension for those first 10 strings dropped 3-8 lbs immediately after stringing, not to mention by the next day.

The 21st strike alone caused a tension loss of about 1/4 of a pound on average, so it's likely to drop a lot more than 9 lbs after 2 hours on court.

This might have to do with energy losses due to tennis ball compressing against stringbed and then expanding again....

Yes, exactly. "Energy return" included all energy that goes into the ball, even if it goes into compressing the ball instead of accelerating it. That's why greater "energy return" does not mean more power. Lower stiffness is a better predictor. But greater tension loss leads to lower stiffness, while lower string friction could also increase power when hitting with any spin.

 

[AlecG]

What is the source of the clusters of Nylon and gut strings strung at 25lbs and 35lbs? No one ever does that for tennis rackets.

Looks like the op is comparing a two badminton rackets, rather than Mannarinos stick.

Mannarino strings at 8-10 kg or 18-22 lbs.
But the tensions on the graph are pre-impact tensions, not reference tensions, and I think they mean immediately before *each* impact, and after previous impacts.

Tension drops 2-12 lbs from the reference tension almost immediately, certainly within the first 60 seconds after finishing stringing.
Then it loses an additional 1/2 pound for each heavy strike for the first 20 strikes, and an additional 1/4 pound for each heavy strike after that. I think the remeasured the tension after each strike.

Even Sinner who strings at 61 lbs is probably hitting at below 40 lbs on some occasions by the time he actually changes racquets.

 

[Roads_to_tennis]

Three things jump out at me:

1. No poly data above 20kg/44lbs? Is this for badminton or something?
2. The "decline" in poly energy return above 20kg is pure fiction: artifact of fitting a 2nd degree polynomial to dataset that doesn't support it.

Are these fitting curves or interpolated rather than actual?