New (3-14-11) at TWU: Spin and String Stiffness

Check out the new experiment:

http://twu.tennis-warehouse.com/learning_center/spinandstiffness.php

Spin increases with stiffness. Spin increases with lateral string movement...up to a point. Then spin decreases and launch angle increases. Stiffness is the moderator between just enough and too much string movement. In dense, high tension stringbeds, stiff, slippery strings (low coefficient of friction) are required for efficient, timely string movement and snap-back to produce spin.

Here are some examples of what you don't want if you want spin:


Check out the article to see why.

And look at the spin from the 16x10 60 lb setup! Yikes.

Great stuff, by far the best yet. Really like your discussion this time.

Would add that this data also indicates that swing speed matters. The same string set up will perform differently depending on impact forces. Maybe people will stop copying the pros....doubt it.

Thanks a lot for this one, very informative.

Great stuff!!!

Nice work, good read. Time will tell how many threads about 16x10 setups pop up... heh

Wow. :shock:

Lots of great info. Thanks.

I'm going to try this 16x10 setup!

It seems to me that mains string snapback gives extra spin on groundstrokes while crosses snapback will contribute to serve spin. I put Babolat elastocross on my full poly setup and I have been getting more spin on my serves because the crosses are not locking on the abrasion notches. I'd like to see some spin experiments with the racquet in the vertical position.

Interesting results.

But Kevlar at 60 lb??? my elbow hurt just by reading that...

treo said:

I'm going to try this 16x10 setup!

It seems to me that mains string snapback gives extra spin on groundstrokes while crosses snapback will contribute to serve spin. I put Babolat elastocross on my full poly setup and I have been getting more spin on my serves because the crosses are not locking on the abrasion notches. I'd like to see some spin experiments with the racquet in the vertical position.

Click to expand...

Be careful of warping your frame! When you decrease the number of cross strings you need to up their tension, or lower the main strings' tension to equalize the forces on the frame.

Others, please correct me if I'm wrong, but I look at this way:

If you've got a 16 x 19 and string it up at 60 pounds the total tension on the frame would be:

Mains: 16 x 60# = 960
Crosses: 19 x 60# = 1140

If you reduce the crosses from 19 to 10, but keep tension on both mains and crosses at 60# you'd have:

Mains: 16 x 60# = 960
Crosses: 10 x 60# = 600

Doing it like this will probably squash your frame from tip to butt. How about 35# for the mains instead?

Mains: 16 x 35# = 560
Crosses 10 x 60# = 600

The difference between crosses and mains is now pretty much the same as with the 16x19 at 60#.

But now your mains are pretty loose, which this study suggests is sub-optimal for spin because the loose strings are not stiff enough to snapback in time. (But as Consolation suggests above, this will depend on your swingspeed - players with slower swings can string lower.) I've tried it like this and it gives a high launch angle but not so much spin.

Two options: 1) Increase to even higher tensions, like 50 mains and 75 crosses, but then you'd be putting a lot of stress on the frame and might damage it. 2) Switch out the mains for a stiffer string, like Kevlar. Kevlar is more than twice as stiff as a stiff poly like RPM Blast, so you can still string it at 35# and it will be as, or more, stiff than poly at 60#.

This is what Travlerajm did here: http://tt.tennis-warehouse.com/showthread.php?t=347846

corners said:

Be careful of warping your frame! When you decrease the number of cross strings you need to up their tension, or lower the main strings' tension to equalize the forces on the frame.

Others, please correct me if I'm wrong, but I look at this way:

If you've got a 16 x 19 and string it up at 60 pounds the total tension on the frame would be:

Mains: 16 x 60# = 960
Crosses: 19 x 60# = 1140

If you reduce the crosses from 19 to 10, but keep tension on both mains and crosses at 60# you'd have:

Mains: 16 x 60# = 960
Crosses: 10 x 60# = 600

Doing it like this will probably squash your frame from tip to butt. How about 35# for the mains instead?

Mains: 16 x 35# = 560
Crosses 10 x 60# = 600

The difference between crosses and mains is now pretty much the same as with the 16x19 at 60#.

But now your mains are pretty loose, which this study suggests is sub-optimal for spin because the loose strings are not stiff enough to snapback in time. (But as Consolation suggests above, this will depend on your swingspeed - players with slower swings can string lower.) I've tried it like this and it gives a high launch angle but not so much spin.

Two options: 1) Increase to even higher tensions, like 50 mains and 75 crosses, but then you'd be putting a lot of stress on the frame and might damage it. 2) Switch out the mains for a stiffer string, like Kevlar. Kevlar is more than twice as stiff as a stiff poly like RPM Blast, so you can still string it at 35# and it will be as, or more, stiff than poly at 60#.

This is what Travlerajm did here: http://tt.tennis-warehouse.com/showthread.php?t=347846

Click to expand...

This is a very good point! The last experiment even strings the 16 x 10 pattern with Kevlar at 60 lb mains and Polyester at 30 lb crosses - that's crazy!

Prince synthetic gut produces 25% more spin that Lux Alu Rough and 13% more spin than RPM blast at 30lbs???

The Alu Rough / RPM crowd are going to love that.....

Extrapolating that graph, that would suggest that Prince synthetic gut would produce as much spin as Lux Alu Rough and RPM Blast at 45lbs. That surely can't be right.....

X1 is also absymal for spin at any tension according to those figures.

I love reading these articles, but I wish the experiment was done with patterns that are commonly used. Say 16x19 and 18x20. Given the example above by corners, I am not sure too many will try to experiment skipping holes on their frames.

corners said:

Be careful of warping your frame! When you decrease the number of cross strings you need to up their tension, or lower the main strings' tension to equalize the forces on the frame.

Others, please correct me if I'm wrong, but I look at this way:

If you've got a 16 x 19 and string it up at 60 pounds the total tension on the frame would be:

Mains: 16 x 60# = 960
Crosses: 19 x 60# = 1140

If you reduce the crosses from 19 to 10, but keep tension on both mains and crosses at 60# you'd have:

Mains: 16 x 60# = 960
Crosses: 10 x 60# = 600

Doing it like this will probably squash your frame from tip to butt. How about 35# for the mains instead?

Mains: 16 x 35# = 560
Crosses 10 x 60# = 600

The difference between crosses and mains is now pretty much the same as with the 16x19 at 60#.

But now your mains are pretty loose, which this study suggests is sub-optimal for spin because the loose strings are not stiff enough to snapback in time. (But as Consolation suggests above, this will depend on your swingspeed - players with slower swings can string lower.) I've tried it like this and it gives a high launch angle but not so much spin.

Two options: 1) Increase to even higher tensions, like 50 mains and 75 crosses, but then you'd be putting a lot of stress on the frame and might damage it. 2) Switch out the mains for a stiffer string, like Kevlar. Kevlar is more than twice as stiff as a stiff poly like RPM Blast, so you can still string it at 35# and it will be as, or more, stiff than poly at 60#.

This is what Travlerajm did here: http://tt.tennis-warehouse.com/showthread.php?t=347846

Click to expand...

That's not how it works.

With the mains in the racquet, there's an expansive force on the hoop in the lateral direction. The crosses help to minimize this, but racquets are made such that they are still well within the structural limits of the frame even without any crosses.

The racquet hoop is mostly constrained from deformation by the stringers mounting mechanism. If you put no crosses in, it would deform when you removed it. Even a few well placed crosses can maintain shape though. 10 crosses is plenty to completely maintain head shape, and while the average force on each string will be higher than the 19 cross situation, the difference is pretty minimal as the total expansive force is not that high.

You have to get really funky to ever put a compressive lateral force on a racquet (like stringing crosses first). Hoops are designed to be relatively flexible vertically, and stiff laterally. Even fairly dramatic differences in tensions (with crosses much higher than mains) still results in an expansive lateral force.

Torres said:

Prince synthetic gut produces 25% more spin that Lux Alu Rough and 13% more spin than RPM blast at 30lbs???

The Alu Rough / RPM crowd are going to love that.....

Extrapolating that graph, that would suggest that Prince synthetic gut would produce as much spin as Lux Alu Rough and RPM Blast at 45lbs. That surely can't be right.....

X1 is also absymal for spin at any tension according to those figures.

Click to expand...

So instead of all these polys, multis, guts, hybrids, etc. we should all just play cheap syn gut at 45 lbs. ???? !!!!

NLBwell said:

So instead of all these polys, multis, guts, hybrids, etc. we should all just play cheap syn gut at 45 lbs. ???? !!!!

Click to expand...

Not my view. Lab tests simply don't represent real world conditions. Everyone knows polys generate more rpm and movement on the ball at normal range of tensions.

It does make me chuckle though when people say X-1 is good for spin.

... explains why PSG is still ranked among many players favourite strings including myself but yah a full poly allows more spin and control for sure. (no way stringing every other cross is gonna be playable with PSG). I agree with the X-1 observations and other polyurethane infected string - less spin and launch angle was messed up. Drove me bonkers and felt stiff due to the lack of string movement.

TW Professor - I wonder if these results would also translate over to 18x20 string pattern?

I might try 18x10 and see how that goes. For one thing, it would save me about 10 minutes weaving the crosses since I am slow at weaving.

parasailing said:

For one thing, it would save me about 10 minutes weaving the crosses since I am slow at weaving.

Click to expand...

LOL, that's the first thing I thought after reading the article! heheh!!! Also, get 4 sets of crosses from 1 pack of poly!!! hmmmmm, very tempted.... :twisted:

JT_2eighty said:

LOL, that's the first thing I thought after reading the article! heheh!!! Also, get 4 sets of crosses from 1 pack of poly!!! hmmmmm, very tempted.... :twisted:

Click to expand...

That's another reason to give this setup a try. Too bad you can't cut down on the mains either otherwise natural gut might actually not be too bad in cost .

parasailing said:

That's another reason to give this setup a try.

Click to expand...

You surely can't be serious? 16x10 will be absolutely horrendous for directional control. No point having spin if the ball doesn't go anywhere near where you want it.

I tried 16x10 last night...

I was curious about the results and since I have my own stringer AND plenty of poly, I decided to try the 16x10 pattern in a Prince TT Warrior OS (normally a 16x19 pattern).

It did, at times, provide LOTS of topspin, but was very inconsistent and the directional control was a huge problem.

A good example of when lab testing doesn't work in reality. I can see how it produces the greatest amount of spin, but you just can't play with it. Trust me.

Remember guys, the point of the lab test was not to advocate the use of 16x10 or 18x10 patterns.

Recall if you will (quoted from article):

"Many factors have been offered as influencing spin: string material, tension, gauge, pattern, stiffness, texture, shape, ball-to-string friction, and string-to-string friction. Many of these theories have been addressed elsewhere at TWU (see String Comparison menu above). Here, we will consider the role of string stiffness (as determined by material, tension, and pattern) in spin production."

[lab tests, data, more explanations, etc]...

"The optimization rules for spin appear to be "Goldilocks Principles": the stringbed must be not too soft and not too stiff, not too closed and not too open, and not too rough and not too smooth. You can have too much or too little of each. Stiffness helps keep movement in check in open patterns and helps to overcome friction in tighter, higher friction environments. But stiffer materials and higher tensions also create greater inter-string friction and may too severely constrain lateral string movement, thus not getting the maximum spin benefit."

"We thus can't make any categorical rules about spin. We can't say, for example, that stiffer, slipperier, or more open always creates more spin. It depends on "compared to what?" If you are already getting too much string movement, changing to a setup that gives more movement will give you less spin. And if you don't have very much movement, changing to a stiffer, tighter, stickier setup isn't going to help."

I think most of us were joking about saving some string and time weaving. This is but one piece of the large puzzle. Take from it what you will, but stringing up 16x10 wasn't the proof being made.

So lets just look at the 16x19 data and ignore the crazy stuff.

Very cool article. When are you guys going to make a robotic swinging arm though? Like the golf ones:
http://videos.howstuffworks.com/discovery/30237-some-assembly-required-ping-man-golf-test-video.htm

JT_2eighty said:

Remember guys, the point of the lab test was not to advocate the use of 16x10 or 18x10 patterns.

Recall if you will (quoted from article):

"Many factors have been offered as influencing spin: string material, tension, gauge, pattern, stiffness, texture, shape, ball-to-string friction, and string-to-string friction. Many of these theories have been addressed elsewhere at TWU (see String Comparison menu above). Here, we will consider the role of string stiffness (as determined by material, tension, and pattern) in spin production."

[lab tests, data, more explanations, etc]...

"The optimization rules for spin appear to be "Goldilocks Principles": the stringbed must be not too soft and not too stiff, not too closed and not too open, and not too rough and not too smooth. You can have too much or too little of each. Stiffness helps keep movement in check in open patterns and helps to overcome friction in tighter, higher friction environments. But stiffer materials and higher tensions also create greater inter-string friction and may too severely constrain lateral string movement, thus not getting the maximum spin benefit."

"We thus can't make any categorical rules about spin. We can't say, for example, that stiffer, slipperier, or more open always creates more spin. It depends on "compared to what?" If you are already getting too much string movement, changing to a setup that gives more movement will give you less spin. And if you don't have very much movement, changing to a stiffer, tighter, stickier setup isn't going to help."

I think most of us were joking about saving some string and time weaving. This is but one piece of the large puzzle. Take from it what you will, but stringing up 16x10 wasn't the proof being made.

Click to expand...

Well said.


So, I'm interested in more spin capability from a racquet with

- a 16x19 or 18x20 string pattern in a 95" head
- strung with a nat gut/syn gut hybrid (no poly)

Can anyone advise me on tension(s) for the mains and crosses? (And any other factors to consider besides tension?)

Keifers said:

Can anyone advise me on tension(s) I should use for mains and crosses? (And any other factors to consider besides tension?)

Click to expand...

Just look at every other thread on this sub-forum. Or better still, experiment yourself on a tennis court.

Lab conditions with a fixed clamp and a fixed ball angle are hardly going to replicate real playing conditions.

And spin of itself means nothing if it has a detrimental effect on other areas of play.

brb trying my POG mid with 14x9 at 65 lbs.

Torres said:

Just look at every other thread on this sub-forum. Or better still, experiment yourself on a tennis court.

Lab conditions with a fixed clamp and a fixed ball angle are hardly going to replicate real playing conditions.

And spin of itself means nothing if it has a detrimental effect on other areas of play.

Click to expand...

Excuse me, but do you have nothing more to offer than these supercilious bromides?

I mean...it's OK if you keep them to yourself and let the rest of us carry on. Really it is!

Sheesh... :roll:

^ Oh, c'mon for chrisakes.

Who is able to suggest a tension for you? What works for one person isn't going to work for another.

Just try a tension in the 50s and adjust up and down depending on your preferences. There are loads of threads about this.

But the only person who is able to tell you what the best tension is, is YOU, based your results on court, your racquet and the way that YOU hit!

JT_2eighty said:

Remember guys, the point of the lab test was not to advocate the use of 16x10 or 18x10 patterns.

Recall if you will (quoted from article):

"Many factors have been offered as influencing spin: string material, tension, gauge, pattern, stiffness, texture, shape, ball-to-string friction, and string-to-string friction. Many of these theories have been addressed elsewhere at TWU (see String Comparison menu above). Here, we will consider the role of string stiffness (as determined by material, tension, and pattern) in spin production."

[lab tests, data, more explanations, etc]...

"The optimization rules for spin appear to be "Goldilocks Principles": the stringbed must be not too soft and not too stiff, not too closed and not too open, and not too rough and not too smooth. You can have too much or too little of each. Stiffness helps keep movement in check in open patterns and helps to overcome friction in tighter, higher friction environments. But stiffer materials and higher tensions also create greater inter-string friction and may too severely constrain lateral string movement, thus not getting the maximum spin benefit."

"We thus can't make any categorical rules about spin. We can't say, for example, that stiffer, slipperier, or more open always creates more spin. It depends on "compared to what?" If you are already getting too much string movement, changing to a setup that gives more movement will give you less spin. And if you don't have very much movement, changing to a stiffer, tighter, stickier setup isn't going to help."

I think most of us were joking about saving some string and time weaving. This is but one piece of the large puzzle. Take from it what you will, but stringing up 16x10 wasn't the proof being made.

Click to expand...

And to add to what JT_2eighty quoted, here are a couple more:

"Extreme ends of the spectrum were chosen in terms of both movement and stiffness to make sure that any string behavior of interest would be observable and would exhibit significant change over the range of test conditions. Such extreme pattern setups would also allow us to see string behavior as if through a microscope — allowing us to see things that might be hidden under more "normal" situations."

"But is this a viable pattern to play with? Or is a similar but slightly different setup better? Is there enough control, consistency? As the eA column in Table 5 shows, power is essentially the same for all setups, the difference mostly being from slight variations in impact location on the racquet. But, still, is it playable?"

"For the purposes of this experiment, the answer to that question does not really matter. Comparing the data from that setup with others has revealed processes that would be difficult to identify and measure otherwise, and the setup also helped us to see what wasn't happening in certain circumstances with other setups."

So, the 16x10 was only a means to an end in the experiment. However, it would be interesting if some players do try it and like it. One person has already told me he loves it . . . and there are bound to be others like him.

But, again, that is not the point. The pattern allows us to see on a macro level what is more hidden on a micro level ("regular" setups). It helps us discover processes and develop explanations of how string affects spin in normal setups.

Perhaps racquet manufacturers would test other setups, particularly with the number of crosses.

Torres said:

^ Oh, c'mon for chrisakes.

Who is able to suggest a tension for you? What works for one person isn't going to work for another.

Just try a tension in the 50s and adjust up and down depending on your preferences. There are loads of threads about this.

But the only person who is able to tell you what the best tension is, is YOU, based your results on court, your racquet and the way that YOU hit!

Click to expand...

So you would trash at least half of the threads here. Because people ask for advice about strings and tensions all the time. But... when they do that, NO-ONE expects to be told exactly what to do. Most replies -- certainly the best ones -- are in the form of "Well, I did this... and ended up with these results..."

But let's get to the real issue here. I'm only guessing, but it seems to me you're frustrated somehow at the science that TW Prof has presented here. You think that lab measurements in no way correlate with "real playing conditions."

Well, that's your pov, isn't it? And apparently it's not shared by many here. They see potential value in the work that TW Prof has done -- and they feel confident they can make the translation from lab results to things they might try or experience in real life. (Just as I feel I can make the translation from people's advice/experience with gut/syn wrt spin to my real life.)

But instead of voicing your concerns about the string lab test results and engaging TW Prof and the others in a direct debate, you choose to go off on me for asking my questions. That's a little pathetic, isn't it?

Like I said, I'm only guessing... but I wouldn't be surprised if this is what's happening.

If I'm right, step up, mate. Challenge them head on. Who knows, you might change minds -- and shape TW Prof's future research.

Awesome stuff. The geek in me giggled lol

Keifers said:

Well said.


So, I'm interested more spin capability from a racquet with

- a 16x19 or 18x20 string pattern in a 95" head
- strung with a nat gut/syn gut hybrid (no poly)

Can anyone advise me on tension(s) I should use for mains and crosses? (And any other factors to consider besides tension?)

Click to expand...

It's more complicated than that.

You can't even look at the results of this paper and draw conclusions on how the string/patterns tested would perform for you.

The take away is there seems to be a certain combination of several factors that results in maximal spin. Those factors will change depending how how you individually hit the ball. The best spin set up for one person may be terrible for another.

If anything, I think the biggest thing this paper shows is how personal results are. The first thing you should think when you read a string review is whether the person reviewing hits the ball like you. If she doesn't, it's probably not worth reading it.

Bravo!
This is a great article, professor.
I had tried a 16 x 10 set up at 30 lbs in the Kevlar mains and 60 lbs in the Poly crosses.

The result was a bit disappointing. The spin increase did not seem that noticeable, but the launch angle was so extreme that it made the racquet uncontrollable on volleys and other shots with low racquethead speed, especially if the incoming ball had high rpm.

Now I see that I should try upping the tension quite a bit. I'll try 50 lbs in the mains and 70 lbs in the crosses in my 16 x 10. I use different tensions to help balance out the overall forces pulling on the frame.

Consolation said:

It's more complicated than that.

You can't even look at the results of this paper and draw conclusions on how the string/patterns tested would perform for you.

The take away is there seems to be a certain combination of several factors that results in maximal spin. Those factors will change depending how how you individually hit the ball. The best spin set up for one person may be terrible for another.

If anything, I think the biggest thing this paper shows is how personal results are. The first thing you should think when you read a string review is whether the person reviewing hits the ball like you. If she doesn't, it's probably not worth reading it.

Click to expand...

She doesn't. So I usually don't... It's one of those relationships.. (Just kidding!)


Seriously... thanks for your remarks. Not thrilled to hear them, but they make sense.

I guess I'll have to try different things for myself and report back to this forum. WHICH I will do because you're intimating that that's the way to go. NOT because that other fellow said so. (JUST to be clear.)

travlerajm said:

Bravo!
This is a great article, professor.
I had tried a 16 x 10 set up at 30 lbs in the Kevlar mains and 60 lbs in the Poly crosses.

The result was a bit disappointing. The spin increase did not seem that noticeable, but the launch angle was so extreme that it made the racquet uncontrollable on volleys and other shots with low racquethead speed, especially if the incoming ball had high rpm.

Now I see that I should try upping the tension quite a bit. I'll try 50 lbs in the mains and 70 lbs in the crosses in my 16 x 10. I use different tensions to help balance out the overall forces pulling on the frame.

Click to expand...

That will be interesting. Optimization of such an open pattern to get increased spin and an acceptable launch angle will definitely depend on altering tensions. The experiment shows that higher tensions are certainly required for spin in this pattern.

What was the effect on a slice?

TW Professor said:

That will be interesting. Optimization of such an open pattern to get increased spin and an acceptable launch angle will definitely depend on altering tensions. The experiment shows that higher tensions are certainly required for spin in this pattern.

What was the effect on a slice?

Click to expand...

TW Prof,
Hitting a slice from the baseline has the same problem as a volley -- it's a shot where the racquet is not moving very fast, so the spin energy in the incomming ball effects the rebound trajectory a lot.

It's the same reason that the best string setups for volleying are ones that have minimal bite.

On the other hand, I really, really loved serving with the 16 x 10 setup. The serve is the opposite of the volley in that all of the energy of the collision comes from the racquet.

Serves had extra explosiveness (both spin and power) compared to a normal stringbed, and control was fine since I was hitting a ball that isn't rotating.

You might want to take a closer look at Figs. 4b and 5b of:
GOODWILL, S. R. and HAAKE, S. J. (2004). Ball spin generation for oblique impacts with a tennis racket. Experimental mechanics, 44 (2), 195-206.

On the plots of rebound angle vs incoming spin, you'll note that the slope of the curve for 40 lb string (closed symbols) is significantly steeper than the slope for 70 lbs string (open symbols).
This indicates that the lower tension is more sensitive to the rpm of the opponent's shot. (I believe this is the primary reason for the old refrain of "higher tension for more control").

One question:

Have you tried doing some of these string spin experiments while attempting to adjust the racquetface angle to maintain constant rebound angle?

I think this would be a more directly applicable way to compare spin for different stringbeds. If the increased "bite" of the stringbed causes the rebound angle to change, but the spin and rebound speed stays constant (as in the 40 lb vs 70 lb tension comparison in the article referred to above), it might lead to misleading results if only the racquet frame of reference is used.

But if you hold the rebound angle constant (thereby using the court frame of reference rather than the racquet frame of reference), a higher rebound angle (on a topspin shot) due to looser strings means that the player needs to close the face more to compensate. Closing the face more would almost certainly result in increased spin (and increased rebound speed too). I found it surprising that Goodwill and Haake concluded (incorrectly I believe) that tension has no significant effect on spin or power level.

travlerajm said:

TW Prof,
Hitting a slice from the baseline has the same problem as a volley -- it's a shot where the racquet is not moving very fast, so the spin energy in the incomming ball effects the rebound trajectory a lot.

It's the same reason that the best string setups for volleying are ones that have minimal bite.

On the other hand, I really, really loved serving with the 16 x 10 setup. The serve is the opposite of the volley in that all of the energy of the collision comes from the racquet.

Serves had extra explosiveness (both spin and power) compared to a normal stringbed, and control was fine since I was hitting a ball that isn't rotating.

You might want to take a closer look at Figs. 4b and 5b of:
GOODWILL, S. R. and HAAKE, S. J. (2004). Ball spin generation for oblique impacts with a tennis racket. Experimental mechanics, 44 (2), 195-206.

On the plots of rebound angle vs incoming spin, you'll note that the slope of the curve for 40 lb string (closed symbols) is significantly steeper than the slope for 70 lbs string (open symbols).
This indicates that the lower tension is more sensitive to the rpm of the opponent's shot. (I believe this is the primary reason for the old refrain of "higher tension for more control").

One question:

Have you tried doing some of these string spin experiments while attempting to adjust the racquetface angle to maintain constant rebound angle?

I think this would be a more directly applicable way to compare spin for different stringbeds. If the increased "bite" of the stringbed causes the rebound angle to change, but the spin and rebound speed stays constant (as in the 40 lb vs 70 lb tension comparison in the article referred to above), it might lead to misleading results if only the racquet frame of reference is used.

But if you hold the rebound angle constant (thereby using the court frame of reference rather than the racquet frame of reference), a higher rebound angle (on a topspin shot) due to looser strings means that the player needs to close the face more to compensate. Closing the face more would almost certainly result in increased spin (and increased rebound speed too). I found it surprising that Goodwill and Haake concluded (incorrectly I believe) that tension has no significant effect on spin or power level.

Click to expand...

Yes, the backspin will make friction last longer, slowing the parallel speed of the ball on the stringbed, thereby making the rebound/launch angle higher. Also, the backspin helps to move the mains forward, thus pushing the normal force offset further forward, again increasing the angle.

I have not done experiments keeping the rebound angle constant. I don't really know how I would do that, since it is an output, not an input. But you probably have something else in mind. Either way, yes it can be confusing talking in the racquet frame of reference. Of course, explaining a frame of reference transformation gets confusing too. But I will give that some thought going forward.

I think in that article, they said that tension effects rebound speed but not spin, with the 40 lb setups rebounding the ball faster. As to spin, it is tempting to agree with you that, for the 23 m/s impact anyway, it looks like the lower tensions had more spin, but then it was more random at 31 m/s. As Figure 3 in my experiment shows, tension definitely mattered in the 16x10 pattern but the results were mixed in the 16x19 material depending on the relative roles of friction, tension, and stiffness in the individual setups. I think the 16x10 results shows that tension does matter, but how much and under what circumstances gets more difficult to determine as you add more strings and friction into the mix. Then the spin pluses and spin minuses start adding and subtracting from each other in more complicated ways.

Torres said:

Not my view. Lab tests simply don't represent real world conditions. Everyone knows polys generate more rpm and movement on the ball at normal range of tensions.

It does make me chuckle though when people say X-1 is good for spin.

Click to expand...

Pay attention. According to Tennis Warehouse X-one has the highest friction http://twu.tennis-warehouse.com/learning_center/COFreporter.php there is a reason why they chose X-one in their testing. As far as strings sliding X-one is the worst. The reason why so many people find X-one helps with spin is its friction against the fibrous fluffy felt on a tennis ball. It grips like no other.

Lambsscroll said:

Pay attention. According to Tennis Warehouse X-one has the highest friction http://twu.tennis-warehouse.com/learning_center/COFreporter.php there is a reason why they chose X-one in their testing. As far as strings sliding X-one is the worst. The reason why so many people find X-one helps with spin is its friction against the fibrous fluffy felt on a tennis ball. It grips like no other.

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I think you're the one who needs to 'pay attention' since you seem to have misunderstood the content of the very articles that you've linked to. Friction in the context of those TW articles are a reference string to string friction. The same series of TW articles you quote from say string surface and shape make little or no difference to the strings 'gripping the ball'. So, please do get your facts right.

Anyone who's played with X-1 knows that its utter crap for spin compared to poly.

A court surface can be viewed as a textured string. Like clay courts. We all know how clay alters the way the ball performs compared to grass. So I think texture matters when it comes to spin. This new sliding of the strings is just another way to produce spin. Inevitably this will come down to what feels right to the player.

Lambsscroll said:

I think texture matters when it comes to spin.

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If believing that makes you happy, then believe away!

TW Professor doesn't - he wrote an article which that which you clearly haven't read.

And the rest of us that live in the real word know from experience that X-1 is crap for spin compared to poly. The difference is night and day.

Torres said:

If believing that makes you happy, then believe away!

TW Professor doesn't - he wrote an article which that which you clearly haven't read.

And the rest of us that live in the real word know from experience that X-1 is crap for spin compared to poly. The difference is night and day.

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Like i said court surface is like a textured string. It cant any simpler than that.

Lambsscroll said:

Like i said court surface is like a textured string. It cant any simpler than that.

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Court surface is not really like the stringbed because the impact angle of the ball on the court is much shallower than on the stringbed. At the shallow angles of impact between the ball and the court the friction of the court surface is important. If the court surface has very high friction the ball will slow down more, come off the court with more topspin and rebound at a higher angle. If the court surface is very slippery the ball may slide throughout impact, which results in less spin after the bounce, lower rebound angle and more of the original ball speed remaining after the bounce.

But this is only true for those shallow impact angles. For realistic impact angles on the stringbed, all strings have sufficient friction to stop the ball sliding. The moment the ball stops sliding is known as the moment the ball "bites" the strings. The only time the ball will fail to bite is if the impact angle is very extreme - like in a topspin lob with the racquet swung extremely fast. On other shots, even on Nadal's heavy topspin shots, for example, the ball will still bite the strings before the ball rebounds off the stringbed, regardless of string type.

This is why researchers have said for years that friction between ball and strings doesn't matter to spin production. It's not actually that it doesn't matter - friction between ball and string is still the most important factor in spin production - but that all strings have enough friction with the ball to stop it sliding and therefore impart the maximum amount of spin attributable to ball/string friction. Check out the TW Professor's books - The Physics and Technology of Tennis and Technical Tennis - if you'd like to look into this further.

TW Professor's most recent research, however, suggests that high ball/string friction might play a role during the "snapback" phase. But then you have to figure out what's more important, low string/string friction vs. high ball/string friction. Looking at the lab results, it's pretty clear that low string/string friction strings, like the copoly family, produce more spin than high string/string friction strings, like X-1 biphase. Further, lubricating these strings results in even more spin, which strongly suggests that low string/string friction trumps high ball/string friction by a fairly large margin.

I strung up some X-1 one time and thought that it gave pretty good spin. But there are all sorts of things going on out on court that feed into our perception of the way we are hitting the ball. A significant factor is probably the way the ball feels on the stringbed. A high friction string like X-1 will give a different feel of the ball as it slides across the string than a low-friction string. The ball will also stop sliding sooner (at least in theory) than with a slippery string like RPM Blast. That it stops sliding sooner will not result in more spin, but it may give the player the perception that the strings are "biting" the ball better. The player doesn't know that that feeling of quick "bite" doesn't actually result in more spin, but he may feel that it does.

The results in this study also show that X-1 Biphase launches the ball at a significantly lower rebound angle than do the copolys tested. A low rebound angle might require that the player take a steeper swing to achieve the same depth. The steeper swing will generate more spin. So there are lots of things happening on the court that could lead a player to believe that X-1 Biphase is a good string for spin. And for his swing, he might be right (or he might be wrong). But in the lab, objectively, it is not.

Effect of Vibration Dampeners on Spin?

Just now I was thinking about stiff-material vibration dampeners. Do they limit movement of the mains to some degree?

I don't really remember my physics, but I think a stiff dampener under the bottom cross string would reduce the effective length of the two center mains, much like fretting a string on a guitar, albeit only to a small extent. At this point I'm not so much talking about vibration as I am about string movement and its effect on spin. Does this translate to less string movement? In other words, when a ball hits the string bed with a dampener in it, do the two center mains have more difficulty "opening up" or "spreading apart"? I imagine that the more the strings can spread apart, and then snap back, the more spin there is. But again, only to a very very small extent...

TW Prof:

Thanks again for your nice analysis in the article.

I'd like to point out a couple of thoughts that might simplify the explanation for why a 16x10 60lb setup seems so much superior to the 16x10 30lb setup.

1. A stiffer stringbed is advantageous not only because it reduces the energy losses that you point out, but for another important reason:

A stiffer stringbed increases ball flattening. The more the ball is flattened, the more the radius can grow as it decompresses. Due to conservation of rotational momentum, the more the radius grows during decompression, the more the ball's surface will accelerate, resulting in overspin. To take maximum advantage of this overspin, it is important for the main strings to be able to snap back upward beyond the equilibrium position (following the ball's surface as it overspins faster than the stringbed).

2. If the rebound angle is taken into account, and it is assumed that a player hitting a topspin shot would compensate for the steeper launch angle by closing the face, then the 16x10 30lb setups rate 2nd best of the 4 groups and not 4th. I believe using the tangential coefficient of restitution (which translates better to the court frame of reference) gives a better overall measure of spin performance than outbound spin in the racquet frame of reference. (Also, I believe the values for tangential e in the table should be calculated using rad/s units for omega rather than rpm?).

While the 16x10 30lb setup has relatively high tangential e value, much of the force is converted to a change in rebound angle. In contrast, the stiffer 16x10 setup is more efficient at converting the high tangential e value to spin rather than rebound angle.

It would appear from your test using the Kevlar/Poly hybrid (which gave higher spin numbers than the 5 other string types tested) that an even stiffer 16x10 setup might work even better. I wonder how 60 lb kevlar mains and 80 lb poly crosses would fare?