Do you prefer locked or unlocked strings
- Thread starter Shroud
- Start date
Locked stringbeds are the only thing that hurts my arm. I can play a stiff poly all day and be fine, but if I play full synthetic gut or multi the strings lock quickly and hurt my arm before they break.
My first year playing everything was fine with synthetic gut until I started to improve and hit the ball harder then I developed tennis elbow. I couldn’t figure out why my elbow was never improving until I started playing with poly crosses. My tennis elbow improved quickly and I never had that problem again. I am an advanced player now and tried a full bed of synthetic gut again recently and after 30 minutes of hitting the strings locked up and my elbow started hurting like it did before so I now stay away from locked strings.
My first year playing everything was fine with synthetic gut until I started to improve and hit the ball harder then I developed tennis elbow. I couldn’t figure out why my elbow was never improving until I started playing with poly crosses. My tennis elbow improved quickly and I never had that problem again. I am an advanced player now and tried a full bed of synthetic gut again recently and after 30 minutes of hitting the strings locked up and my elbow started hurting like it did before so I now stay away from locked strings.
socallefty
G.O.A.T.
Like most tennis players, I have no idea what a locked or unlocked stringbed means. I do play decently with VS17 mains/HyperG Soft 18 crosses at 47/44 lbs and my previous hybrid combo was VS/HyperG. You‘ll have to let me know if that is locked or unlocked.
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The purpose of a hybrid is to encourage strings sliding against each other. Eventually every string bed will lock though, but your set up would theoretically delay it.
A side question if you don’t mind. I was thinking about using a similar set up but my stringer discouraged me because the Hyper G with its sharp edges would saw quickly into the natural gut. Do you have any durability issues? How long does a set last for you? Thanks!
socallefty
G.O.A.T.
The poly goes dead before the gut breaks for me meaning that I start feeling discomfort in my elbow/wrist first - so, I restring before the gut breaks. It was about 15 hours for VS/HyperG and is 18-20 hours for VS/HG Soft. I‘ve broken the gut only a few times before that. Usually I play singles for the first ten hours and then doubles after that with my string jobs - when I played only singles with a hybrid string job, the gut tended to break in about 12-15 hours. I play with a Pure Strike Tour at 47/44 lbs.
Your mileage may vary depending on your racquet string pattern, string tension, how hard you hit, how often you mishit, how good your stringer is about not kinking the gut during stringing, the level you play etc.
Thanks a lot! Sounds good!
stapletonj
Hall of Fame
I played some with NG mains and HyperG crosses. I changed to yonex PTP (slippery) in the crosses and like it a lot. (Yonex vcore 100 65/57)
tlm
G.O.A.T.
That what I’m thinking also but I really don’t know. But according to many here they are getting mega snap back that creates big time spin. Still waiting for some proof of this, maybe a lot of rec players do get a lot of snap back that gives more spin I really don’t know.
tlm
G.O.A.T.
Thats what I’m thinking also but really don’t know if rec players are getting enough snap back to make any difference. I can use a Kevlar hybrid with Kevlar main and a synthetic cross that has absolutely no snap back and still produce a lot of spin.
Injured Again
Hall of Fame
Many recreational level players can generate enough racquet head speed and contact the ball with a steep enough angle that the mains move a fairly significant amount at contact. With poly strings that are fairly new, two or three mains will get moved and any restorative force they create acts against the ball in a vector that is below the center of mass. This serves to increase launch angle more than adding spin, as I think the rebound speed of the mains is going to be too slow to add significant spin. If you take a fresh poly stringjob and forcefully pull a main out of position and let go, it slides back into place but at a speed you can easily see. A total ball contact duration is about five milliseconds, so it seem that any snapback would have to happen in 2.5 milliseconds to be effective, which is a vibration frequency of 400 Hertz. If you've ever seen a guitar string that produces that frequency, the string itself is a blur. There's no way that a poly string moves back into place that quickly. So it seems that the poly strings do move back into place, but long after the ball is gone.
I believe experiments have been done where a ball is shot at a stationary racquet contacting the stringbed at an angle and poly strings do produce more spin. I personally believe that's mostly due to other factors than snapback.
tlm
G.O.A.T.
This post make sense. But I know there are many out there that think they are getting this big snap back that is adding mega spin to the ball, even with their 1-2 month old poly strings.
El_Yotamo
Hall of Fame
This is a great post with exemplary critical thinking, and I have a relatively simple explanation which I hope will be satisfactory to you. Essentially, it is a kinematic constraint that the strings do not fully snap back into place while the ball is still in contact with them. In fact, such a phenomenon would decrease spin because the strings fully snapping across the ball would undo their own torque. The critical thing here is that the snap back is only initiated near the end of contact, which allows a more "effective" torque to be applied since the moment arm is bigger. This is the reason that ball-string friction is important. The reason string-string friction is important is that work is lost to friction such that less work is done on the ball by the torque applied by the elastic response of the strings. Hope this makes sense
2nd Serve Ace
Hall of Fame
That is correct. Get a slippery cross on that stringbed and it will feel and perform better.
socallefty
G.O.A.T.
So, I play with a gut/poly hybrid and I’ve noticed that the first time I play with a fresh string job, the strings move a bit and I move them back in place with my fingers periodically. After that, they don’t move out of place at all and I will restring after about 18-20 hours. Does any one know why the strings move slightly only the first time when freshly strung? The strings are VS gut mains and HyperG Soft crosses which is a shaped poly.
I get a tremendous amount of spin and control and like this combo a lot.
I get a tremendous amount of spin and control and like this combo a lot.
Injured Again
Hall of Fame
This is a great post with exemplary critical thinking, and I have a relatively simple explanation which I hope will be satisfactory to you. Essentially, it is a kinematic constraint that the strings do not fully snap back into place while the ball is still in contact with them. In fact, such a phenomenon would decrease spin because the strings fully snapping across the ball would undo their own torque. The critical thing here is that the snap back is only initiated near the end of contact, which allows a more "effective" torque to be applied since the moment arm is bigger. This is the reason that ball-string friction is important. The reason string-string friction is important is that work is lost to friction such that less work is done on the ball by the torque applied by the elastic response of the strings. Hope this makes sense
I'm not sure I understand what you're describing, specifically about the torque.
I think I have a pretty good understanding (or at least conjecture) about why shaped strings have a higher launch angle, and a couple of possible mechanisms which may allow shaped strings to provide greater spin. None of them involve string snapback, so I'd be interested if you could explain again in a different way so I can try to understand what you're saying. Thanks.
The gut moves around in the beginning but after a couple of sessions it starts to lock in place as the intersection with the crosses start to compress and notch.
I fully agree. Reflects my thinking exactly.
El_Yotamo
Hall of Fame
From a mechanical perspective, rotational motion can only be caused by torque (see angular conservation of momentum), and torque is increased with applied force and distance of the force from the central axis of the object that the force is being applied on (moment arm). Think about opening a door, if you apply a force from where the handle is it'll open easily, while if you try to push at the hinge (which in this case is the central axis) you'll have no luck. A door swinging open is rotational motion about the hinge.
Now back to the tennis. Essentially, when the ball makes contact it pushes the strings out of position. At some point the friction stops this and the entire system is static for an infinitesimal split second. Now the strings have an elastic response to their earlier deformation (elastic recoil), and they begin to snap back into place while the ball is now beginning to leave them. Because the strings come into contact with the back/side of the ball, the force exerted by their elastic recoil causes a torque because this force doesn't pass through the central axis of the ball. Remember, the greater the force and the further the force from the central axis the greater the torque and therefore the greater the angular acceleration (more spin).
Now about friction. In grade school we all learned that friction causes energy/work to be lost and this is indeed true in a broad sense. The more friction you have between the strings, the more energy they'll lose during elastic recoil so the less force you can impart at snap back on the ball. On the other hand, the more friction between string and ball, the more energy the ball loses while in contact with the strings. This is actually advantageous because it prevents the ball from "slipping" on the stringbed, an effect which nearly nullifies snap back. Think about car tires: if there wasn't enough friction between the car tires and the road, the tires would slide instead of rotate and you'd completely lose control of your vehicle. The effect is similar with the friction between strings and ball, the ball deforms and rotates on the stringbed which allows for more spin to be imparted at snapback (this is also a version of elastic recoil of the ball).
Since you mentioned shaped strings, I'll give my 2¢ about those too. The edges on shaped strings increase the string-ball friction, while the smooth sides are intended to decrease string-string friction (the latter often fails to happen due to large contact area in viscoelastic deformation, which is a while other can of worms). Based on the principles above, more string-ball friction and less string-string friction cause not only more rotational torque to be applied on the ball, but also more force concentrated beneath the ball which causes your higher launch angle. By the way, these edges sometimes do and sometimes don't come into contact with the ball, which is the cause of inconsistency/erratic response that's often observed with shaped strings (especially odd-sided strings).
I hope I explained it better this time and I recommend you to look up some of the terms I mentioned, it may help you understand what I'm saying better. I have no idea who you are, so it would be silly of me to expect you to know physics beyond a basic high school level (or at all tbh)
LOBALOT
Hall of Fame
I really think the exact opposite. I think that recreational players get a better result and a more comfortable setup with unlocked strings. It does not take much for the below average to average recreational player to deflect the mains when using a slippery cross string. I think more advanced players benefit from a locked setup as they benefit from the control it offers them.
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Injured Again
Hall of Fame
Okay, thanks for writing that. I understand what you were trying to say in your first post.
My conjecture is that what is happening is slightly different than what you describe, and I'll explain why.
First, I think we generally agree on why shaped strings cause higher launch angles. I don't believe it is inconsistency in how the edges contact the ball that causes a perceived inconsistency in performance. I think what is really happening is that launch angle changes with shaped strings are much greater with varying swing trajectories than with round strings, and that when someone experiences what they think is inconsistent launch angle, it is that they swung slightly differently than they thought they did. Photographic evidence over the past couple of decades has shown that the ball significantly flattens out against the strings and that the felt and rubber deform enough to envelope at least half the string. Photographic and test evidence has also suggested that any kind of string has enough friction to fully engage the ball at the point of maximum contact. From this, and from that photographic evidence shows a flattened ball contacts several string intersections, I don't think one string intersection where a shaped string may present a different edge is going to affect the rebound angle of the ball. That rebound angle is going to be generated by the averaged effect of all the strings and string intersections where contact occurs. There is also the local elasticity of the rubber and felt at that one string intersection where the edge contact may be slightly different, and that elasticity will further dampen the effect of a different edge contact. So, I believe it comes down to the most variable link in the equation - that being the human swinging the racquet.
As far as snapback, I again have a slightly different conjecture. Everyone talks about inter-string friction, but rarely is it discussed how inter-string friction varies throughout the ball contact event. First, some history. I was on this forum back in 2004-2006 and had a series of discussions with @travlerajm back in the infancy of scientific based investigation into string/ball dynamics. One of the things I did back then as a test was to use a ball, a series of barbell weight plates, and a digital gauge to measure how much force it took to slide a ball across stringbeds of various materials with different amounts of weight pressing the ball down onto that stringbed. I found that compared to synthetic gut and multifilament strings (I don't recall ever testing gut), that poly strings exhibited a steeper friction slope compared to the other string materials. So both sliding and static friction forces were significantly lower with poly strings with lighter weights but yet increased to roughly the same point with heavier weights as with synthetic gut and multifilament strings, likely more due to the string shape interaction with the felt and the rubber core more than due to the material of the string itself. I never tested inter-string friction because I couldn't think of a way to isolate that effect using any equipment I had that didn't also take into account elasticity of the poly string nor its inherently greater longitudinal stiffness (which would play a part in a strung racquet where string intersections are roughly 1 cm apart). However, I'd assume that poly strings also had lower inter-string friction as well.
So, assuming the previous paragraph is correct, there are some dynamical effects that result. First is that at rest, inter-string friction is less for poly versus other string materials. Anyone can kind of see that. It doesn't take much more effort to start moving a poly string with your fingers, whereas with other string materials, there's a stiction that needs to be overcome where the string creaks/releases and then starts moving. For those non-poly string materials, a greater force is required to initiate string movement, which means that won't occur until further into the ball contact event, at which point the pressure exerted by the ball on the string intersections is also greater than would be the case with poly. As the ball contact event progresses, eventually the pressure exerted by the ball against the string intersections, plus the limits of elasticity of the string, will cause string movement to stop. However, poly, despite its lower elasticity, beings moving sooner and I believe it slides further than a non-poly string material due to its lower inter-string friction, **but only with sufficient racquet head speed** and despite it being less elastic.
At the point of maximum ball compression against the strings, inter-string forces are high and the strings have already been stretched so there is no movement, and there is photographic evidence that the ball and strings are fully engaged with no slippage. At each point where the string is in contact with the ball, the rubber of the ball is stretched underneath the string and compressed above the string. This restitution happens at roughly the same speed as the ball rebounds off the stringbed because these are both inherent to the mechanical properties of the rubber. What I suspect happens is that this restitution occurs and increases the rotational rate of the ball, basically giving the spin rate a boost. With poly strings, due to the lower ball-string friction at lower contact pressures, the ball disengages from the strings at a point sooner than with non-poly strings, retaining the extra rotational rate. Because ball-string friction is higher with non-poly, if the restitution happens and the ball is still statically engaged with the strings, that extra rotational rate is dampened. In both cases, I believe snapback provides minimal additional spin except in the case of pro-level racquet head speeds, where enough string movement is made to occur that the higher restorative force to that greater string movement overcomes the inter-string friction at a point before the ball disengages from the strings.
Shaped strings statically engage the ball with lower ball/string pressures, and thus increase both the amount of string movement and localized deformation of the ball. You get a higher launch angle and the greater restitution of the ball against the strings provide that extra rotation compared to smooth poly strings, and this would be true even with recreational player levels of racquet head speed.
A couple of other minor things. First, I've had poor experiences with triangular strings, and with some softer square strings. I believe especially triangular strings and some of the less axially stiff square strings rotate on ball contact due to the torque exerted on the string edge when trying to impart spin. For instance, take a look at this picture of Volkl V-Square, a soft square string. There's no other way to account for the notch shape other than if the string becomes rotated and cuts into the string with an edge.
I've also seen this effect with triangular shaped strings though not to this same degree. Possibly that's because for the same volume of material, the flat base of a triangle is wider than for a square string and it's harder to tip that string over onto edge. However, the major problem is that sharp triangular strings wear down so quickly that it soon has the shape of just a very thin round string.
This is not proofread at all so apologies for anything that doesn't make sense.
El_Yotamo
Hall of Fame
There's a lot here, so I'll take it but by bit:
It is exactly because you have multiple intersections. The ball doesn't contact each intersection at the same plane/angle and exerts different stresses on different intersections at the same time. The edges are exactly the drivers of this nonlinearity as I explained above and the inconsistency in plane direction brings about inconsistency in local stress distribution which is exactly what brings about different rebound angles. A part of this is also inconsistency in terms of inter-string friction when it comes to shaped strings.
What I sort of understood from this statement is that the compression/restitution process itself is the driving factor in torque which is exactly what causes rotation. This is true, however the amount of restitution you get here is exactly dependent on string-string and string-ball friction. This restitution is also exactly the elastic recoil I was talking about before, you just need to understand that restitution is not a static event and must be triggered by an elastic response which is exactly what snap back is.
The problem with this statement though and the way it is phrased/contextualized is that it may lead one to believe that somehow lower string-ball friction causes more spin, something which has been shown to be wrong many times...
And this doesn't require pro-level swings, however it does of course require big cuts. Elastic recoil requires an initial force, otherwise it of course isn't going to be as effective or prominent...
I don't know if anything I said will convince you however I'm confident that there's still plenty you can take from what I have to say in terms of the physics here
Yes, geometrically edges are a discontinuity in the direction of the string plane. This causes non-linear stress effects which causes more variance with swing trajectories. Nonlinear effects generally cause large differences due to small changes in initial conditions which is exactly what we perceive as inconsistency...
So you agree with me but you don't know it yet
It is exactly because you have multiple intersections. The ball doesn't contact each intersection at the same plane/angle and exerts different stresses on different intersections at the same time. The edges are exactly the drivers of this nonlinearity as I explained above and the inconsistency in plane direction brings about inconsistency in local stress distribution which is exactly what brings about different rebound angles. A part of this is also inconsistency in terms of inter-string friction when it comes to shaped strings.
This is physically wrong. Like, completely wrong. Elasticity does not dampen anything ever, it is viscous/frictional forces that dampen, a purely elastic system will never lose energy.
Well, this is simple to do at least qualitatively. Strings are made of viscoelastic materials such that they don't have a linear relation between normal stress and friction force. Additionally, they don't have any linear relationship between shear stress and friction force. That's what being viscoelastic is all about. In any case, however, the relation is still monotonic such that the greater the stress exerted the greater the friction force.
Did you ever compare these to the average forces in a real impact? I'd be interested to see the results because they may change a few things. By the way, it seems your static friction experiment was a sliding static friction, which unfortunately doesn't describe the physics at contact. You should have measured a rotational static friction which actually describes things. This is especially unfortunate because the static friction is much more of a factor than the dynamic sliding friction...
So for my high-schools thesis (yes I did one of those believe it or not) I chose to completely investigate friction in tennis strings both theoretically and experimentally. I measured string-string friction (both static and dynamic) and string-ball friction (also both static and dynamic). So I know what typical results look like for ball forces around those of a typical impact
This is actually false unfortunately. Due to the stick-slip nature of higher friction contacts, the non-poly strings will usually not slide all the way back into place, but may often slide back and overshoot their original placement. This inconsistency is due to the varying friction on a local scale and the lower stiffness of non-poly strings.
This is inaccurate, because there's always a small degree of slippage which is sometimes difficult to see frame-by-frame. This small amount is significant however, because it is another factor which causes loss of work in the system.
You've been mostly clear up until this point. Here I kinda lost you, not sure what you mean by this or how different string types affect this...
What I sort of understood from this statement is that the compression/restitution process itself is the driving factor in torque which is exactly what causes rotation. This is true, however the amount of restitution you get here is exactly dependent on string-string and string-ball friction. This restitution is also exactly the elastic recoil I was talking about before, you just need to understand that restitution is not a static event and must be triggered by an elastic response which is exactly what snap back is.
This is also something I alluded to originally. If snap back were to happen to completion while the ball is still in contact with the strings you'd get a torque in the opposite direction of the initial torque from the elastic recoil. These cancel each other out and you get less spin.
The problem with this statement though and the way it is phrased/contextualized is that it may lead one to believe that somehow lower string-ball friction causes more spin, something which has been shown to be wrong many times...
Again, see above about elasticity and damping...
Well, you may have finally showed me the real source of our disagreement. There's a reason poly strings are typically recommended for bigger hitters at higher levels. The fact the 3.5ers (and below) on here use poly and claim to reap its benefits in spin comes down not to physics but rather to psychology. I think you can complete the rest...
And this doesn't require pro-level swings, however it does of course require big cuts. Elastic recoil requires an initial force, otherwise it of course isn't going to be as effective or prominent...
Not sure what you mean by this by the way, but in any case localized deformation cannot be caused by pressure because pressure is scalar. It must be caused by stress, which in the case of strings with edges will have a discontinuity at the edge...
I have also never enjoyed triangular strings. They have too long of a flat plane which reduces effectiveness in string-ball friction while their geometry causes their edges to be extremely random which causes huge inconsistencies which imo an advanced player's game can only be hurt from.
This happens for all strings. Torque on the ball is also torque on the strings, so yes strings will naturally rotate at contact. The reason the notches are so defined in the (very nice) picture you have is because of the shape. The edge on a triangular string protrudes more than on other shapes which is what causes such a deep cavity. If you ever get the time, try TB 20 gauge. You'll see the same thing just much much smaller and in a pentagonal pattern.
I don't know if anything I said will convince you however I'm confident that there's still plenty you can take from what I have to say in terms of the physics here
what_army
Semi-Pro
It’s not that hard to figure out but I agree that you have got more pressing matters to worry about.
Morch Us
Hall of Fame
I think the way you asked the question may deviate most to answer "unlocked".
No one likes to keep straightening the strings, but I know for a fact that many actually like the feel of "locked string bed", where the mains does not move as free. Playerss who usually does not like poly as a cross, or players who like the crosses to have higher tension than mains, usually like that locked feel of the string bed. Also players who does a lot of change of directions, sometimes feel more control from a locked stringbed.
Essentially the need to straighten a stringbed is just a consequence, no one likes to do that.
No one likes to keep straightening the strings, but I know for a fact that many actually like the feel of "locked string bed", where the mains does not move as free. Playerss who usually does not like poly as a cross, or players who like the crosses to have higher tension than mains, usually like that locked feel of the string bed. Also players who does a lot of change of directions, sometimes feel more control from a locked stringbed.
Essentially the need to straighten a stringbed is just a consequence, no one likes to do that.
Morch Us
Hall of Fame
I seriously doubt that, it is because most of the folks answered
do you like your strings to stay stright? Or do you like to keep straightening it..
Instead of ...
do you like your mains to move freely, or do you like your mains to stay locked (irrespective of whether or not the strings snaps back into place).
For example an unlocked string bed with rough/sticky multi... the mains won't snap back into place... and that means you have to straighten them. But the string bed can still be "unlocked" if you keep the crosses lose, which allows mains to move freely.
do you like your strings to stay stright? Or do you like to keep straightening it..
Instead of ...
do you like your mains to move freely, or do you like your mains to stay locked (irrespective of whether or not the strings snaps back into place).
For example an unlocked string bed with rough/sticky multi... the mains won't snap back into place... and that means you have to straighten them. But the string bed can still be "unlocked" if you keep the crosses lose, which allows mains to move freely.
Shroud
G.O.A.T.
I have to disagree if you ask someone if they like their means to move freely they will get it wrong. I’ve been on this board for years and when you talk about string movement people always get it wrong. They simply look at the mains and if they are out of position at all they will post something like "my strings are moving all over the place". Or if the mains are straight, they just assume that they are not moving at all. So if you pose it in terms of string movement well you will get the wrong answer most of the time.
and in your example if the mains wont snap back in place then that is a locked stringbed....
Shroud
G.O.A.T.
What are you using? What tension?Well, in an ideal world, I'd prefer my strings to not STAY straight...I'd prefer them to END straight after each swing.
Gamma Live Wire 17 @ 52. I have a super-sensitive arm (recovered tennis elbow and current shoulder something or other), so just staying healthy is more important to me than optimal string performance. A string & tension that stays in alignment yet is soft would be nice, but I have enough areas that I need to work on that I can't blame the strings for too much.
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