The Modern Pro Slice: Spin Levels

[stumphges]

Stump,
Another great explanation! But it is true that Rod once said that poly didn't do this. As a true scientist, he revised based on data... but initially there was a school of thought (now extinct I believe) that said it was all an illusion...

My first hybrid convinced me otherwise!

Hi John,

Thanks

Yeah, both Rod and Lindsey, and several ITF-affiliated researchers (Haake, Goodwill) all said for years that copoly didn't give more spin. There were two reasons:

1) The theoretical model for spin generation that they had at the time, which is still valid, predicted that more string-ball friction would not increase spin. Since everyone was saying, until just last year, that copoly strings generated more spin because of more string-ball friction, it didn't make sense that copoly strings could generate more spin.

2) Their lab data was skewed by their experimental setup, as I wrote about in another thread: they were firing balls without spin at clamped racquets. Once they started firing balls with spin at those racquets the difference in spin between strings become clear.

To their credit, once that mistake was caught, Cross and Lindsey pretty quickly reversed their view and started doing experiments to figure out why copoly strings generate the extra spin they were now finding in their experiments. And in two short years they have increased our understanding by leaps and bounds.

Lindsey is committed to figuring out everything about spin generation. The "slippery string" snapback mechanism is pretty well understood at this point, but there remain many interesting questions, shaped/textured strings being one of them. I think they will crack that one soon.

Two recent papers, one by Cross and another by Lindsey, are worth checking out, BTW:

1) Cross' analysis of the kick serve (http://twu.tennis-warehouse.com/lear.../kickserve.php) is very interesting for several reasons. One of them is a spin-generating effect that is quite different from the snapback mechanism. Check out figure 3 in that article, which illustrates how a "closed" raquet-face will compress the top of the ball more than the bottom, which results in topspin. This effect has not been studied very much as far as I know and I suspect that these guys will probably be giving it a closer look. This is probably happening on both serve and groundstrokes and would be maximized with heavy racquets and stiff strings. Think Sampras with his new RPM Blast stringjob strung really tight.

2) Lindsey's most recent spin study (http://twu.tennis-warehouse.com/lear...r/location.php) is on racquets rather than strings. In this one he shows how perimeter weighting of the racquet head both increases spin and changes the spin-levels on impacts at different areas on the stringbed.

[johnyandell]

Stump,
Another great explanation! But it is true that Rod once said that poly didn't do this. As a true scientist, he revised based on data... but initially there was a school of thought (now extinct I believe) that said it was all an illusion...

My first hybrid convinced me otherwise!

[stumphges]

Science also told us that poly did not create any more spin than nylon or gut. Players told us otherwise. Now the same things are being said about copoly, and twisted/textured strings, not giving us any more spin than poly or nylon or gut. Players tell us otherwise.

Who's saying that?

Most people are saying that twisted/textured strings do give more spin than a similar copoly in a smooth texture. Independent lab evidence is not contradicting this. The problem is that there is very little lab evidence to go on. And the results are clear that textured copolys are better than gut or nylon.

Cross and Lindsey have so far only made one direct comparison between two strings of the same composition, one being shaped/textured and the other not, that I'm aware of. That was Luxilon Alu Power vs. Luxilon Alu Power Rough. The difference in spin was very small. Rough gave 1.5% more spin at 50 pounds and about 7% more at 60 pounds. More tests need to be done, and will be done.

And that is the kind of test that needs to be done: the same composition, same coating - identical strings - but in different shapes, compared head to head. We can see from the available data that the same string can generate more spin at 50 pounds than at 60, or vice versa, with no apparent pattern emerging to explain why (so far). So comparing a bunch of strings strung at 60 pounds will tell us which of those strings generates the most spin strung at 60 pounds, but it won't tell you which of those strings generates the most at other tensions. And if that string happens to be pentagon-shaped, it won't prove that pentagon-shaped strings generate more spin than any other shape. It might be some other quality of the string that makes it so great and we wouldn't know.

ITF currently tests every string on the market. They are one outfit saying that shaped/textured strings do not give more spin - they have found no trend suggesting shaped/textured copolys outperformed smooth copolys. However, they may not have looked hard enough, and I can think of several reasons why they wouldn't (and that would bring us into conspiracy land). But their data is not available to the public so we can't check their work.

[stumphges]

Let's stack up spiky shark against bhbr. Let's change the crosses, such as nrg2 and vs gut and vice versa for the mains. Let's change the mass and keep everything else the same, including time inbetween testing to account for static tension loss. Why is this such an obvious line of testing to me, and no one backing it?

I don't think you're going to figure that out on the court, certainly not with a racquet in anyone's hands. As we all say, the player (technique, ability) is the most important variable in spin generation. And for this very reason, any test of strings done on-court, with a player swinging the racquet, will be inconclusive (at best) or misleading.

The level of spin, the trajectory of the outgoing ball and the speed of that ball, are much, much more dependent on the player's swing than on string or racquet. For example, changing the angle of the racquet face, or the angle of the swingplane, by two degrees from swing to swing will result in greater spin variation than between any two copoly strings on the market. Even if you could get a player to swing exactly the same (swingspeed, racquet face angle, swingplane) at two identical incoming balls (speed, spin, trajectory) you'd have a very difficult time even knowing that he'd done it. Wouldn't you need a very sophisticated, and very expensive, 3D motion tracking system to have a chance?

Personally, I think there are very few drawbacks to testing the difference in spin between strings in the lab. It's simple and it's repeatable, which means anyone can check the work of people like Crawford and Lindsey if they have a good ball machine, some clamps or some string to suspend the frame, a high-speed camera, math skills and a scientific calculator.

[GeoffWilliams]

I have just the frames, h22s used by Djokovic when he won the australian against Tsonga, and pt57a used by Soderling. I have a digital scale, to match them by the gram, and they all have silicone in the handles to soften impacts, used by the pros to lessen injury. The problem with poly is injury due to its harshness, and that's one of the main reasons why copolys were developed, softer on the elbow! Many copolys are also teflon inbued to increase slipperiness. It would be really cool to use video, to show the shots, and put up those shots in an article, with the video!

The real exciting measurements would be to compare the spin strings and the flat power strings, as those are the two most sought after game styles, spin and power. The spin strings also should be measured with both 18 x 20 and 16 x 19 patterns, as those are the two most popular, and should show whether or not thinner strings provide more spin, or textured strings, or open vs. closed, or gut vs. copoly.... Three of four top players use the 16 x 19, and Joker alone uses the 18 x 20 for powered control, with the top power/control hybrid there is: vs team/alu power at 61lbs/59lbs. His total mass is 359g. He has a 4.7hl balance point. (1/8 in. past mid pt. in either direction is one point for either head light or head heavy.) Fed is at 364g, Nadal at 338g, Murray at 347g, (he had it at 364g, but hurt his wrist and dropped it back down, using a pt57a with a 16 x 19 open pattern. Same frame as Soderling who uses the 18 x 20 pattern, and has it leaded up to 374g.)

Those tests will be required reading for all top coaches, players, and juniors! An exciting reason to subscribe to and for the site.

An especially interesting comparison would be: vs team mains/alu power crosses and vice versa, to show/prove that gut mains provide 15% more spin than alu power mains: Murray's set up is alu/vs, and feds/joker is vice versa, vs/alu!

Another comparison would be the top textured strings like bhbr/spiky shark/blue gear ultra vs. ashaway kevlar or ace 18g, in a thin string set up versus a 16g set up! Wow.

One of the reasons Murray is not getting the rpms is his lighter frame, and the alu as main. Even if he switched up to vs team mains/alu crosses, I believe he would get higher rpms and more power, as the mains provide 75% of the dynamic characteristics of the bed. So his alu mains are not providing the spin of vs team, nor its power. Nadal also uses a spin string, rpm blast, a shaped string. Its nubs wear off after 1/2 hr., and Nadal is the top string job changer in the mens' game.

What I'd like to know is, why haven't the gut manufacturers made a gut, with a rough texture instead of smoothing it out? Come on Babolat. Give us vs team rough!

[johnyandell]

A friend in Australia is involved in the development of what he thinks is some new super poly. He's asked me to do some tests just like you describe with humans. We can standardize the ball and measure the spin off the court before the hit with my Sports Attack Ball Machine. So if we do that test, why not include some of the other possibilities. Geoff can set up some frames and string combos for that.

[julian1]

An article by Brody referenced

This is where the Cross and Lindsey stuff gets a little confusing for me. IN THE MOMENT when the ball is touching the ground and turning, it is not sliding. (Sorry, Julian. I don't have the book handy right now, but I know I really struggled trying to understand exactly what was going on there.) I can't quite get my head around it. But I think a 5000 RPM slice goes into the ground and loses most of its underspin, but not all of it; the ground should change it by about 3000 RPM. But that would leave it still with underspin. That's what I was suggesting to JY. That 5000 RPM slice will hit the opponents racket spinning with about 2000 RPM on backspin which is a headstart on the topspin going in the other direction; just as an incoming topspin shot is a headstart on spin for an outgoing slice. And I am assuming that is how the 5000 RPM slice was accomplished.

But yes, as JY pointed out, there still is that tremendous amount of absolute rotation on the slice. I was just wondering if there shouldn't be a corresponding immense amount of spin on the topspin return of a slice; but only if the incoming ball started with an awful lot of spin.

don

Don,
you will get an E-mail with two attachments
The first one is about a flat ball ( probably) forehand sliding
and a corresponding topspin generated.
Please note that Brody talks about A FLAT ball-
much simpler situation that addressed above
Regards,
Julian

[GeoffWilliams]

Science also told us that poly did not create any more spin than nylon or gut. Players told us otherwise. Now the same things are being said about copoly, and twisted/textured strings, not giving us any more spin than poly or nylon or gut. Players tell us otherwise. The lab is not the court. I've tried lubricant, silicone spray, not wd-40, and it removed all grab and destroyed control, while the lab tells us that spray increases spin and grab by making the strings slippery so they snap back more. (Too much?) Once again, the court is not the lab. All the tests that tell us textured strings like bhbr, spiky shark, barb wire, ashaway kevlar, or thinner strings like the 1.10mm ace, don't create more spin don't agree with player's experience on the court. With John's video experience, and the 10,000 fps cameras, why don't we prove it on the court? Make this site a world wide draw for those coaches and players who want the real deal on rpms! Seems like an obvious thing to do to me.

Let's stack up spiky shark against bhbr. Let's change the crosses, such as nrg2 and vs gut and vice versa for the mains. Let's change the mass and keep everything else the same, including time inbetween testing to account for static tension loss. Why is this such an obvious line of testing to me, and no one backing it?

I know equipment is not John's subject nor is string, but an rpm comparison, and a velocity comparison, on the court, not the lab is coming from someone, and so why not, John?

[tennis_chiro]

At least you don't have to use up all that film!!

Definitely slice turns to topspin at the bounce.

What Don is refering to is the fact that the ball is rotating in the same direction coming as it does going out with slice.

The interesting question though is what happens on the strings--and that so far as I know hasn't been studied--10,000 frames a second would be nice...

....

Just think, in the old days not only did you have to find a camera that could shoot that fast, but you had to find the money to pay for all that celluloid. Now, you just erase the SD card and start over.

You'd have to do it differently from the classic studies Brody et al did with a fixed racket; someone would actually have to swing, but it would be an interesting study, especially with the variations Geoff is suggesting.

don

[GeoffWilliams]

It would be interesting to test spin strings, and see if the same player produces more spin with one over the other, and with slice over top. Take the five top spin strings: barb wire, spiky shark, blue gear, ashway kevlar, ace 18g, and string them in the same frame/s, same mass, same balance, etc. Same for flat strings: vs team, poly star energy, polyfibre tech, alu power, lux big banger original, big hitter blue rough, and test those for total power: rpm x velocity, before and after the bounce, on all three surfaces, and now that would be an article worth reading! Would also be interesting to change the mass and nothing else, say, from 338g-360g, the common pro range from Nadal to Djokovic.

[johnyandell]

Definitely slice turns to topspin at the bounce.

What Don is refering to is the fact that the ball is rotating in the same direction coming as it does going out with slice.

The interesting question though is what happens on the strings--and that so far as I know hasn't been studied--10,000 frames a second would be nice...

I doubt though that the ball continues to spin on the strings. It probably slows down and stops. The question is how much energy does it take to generate that 3500rpm of underspin versus say 2700rpm of topspin.

Howard Brody once wrote it takes only half as much racket speed to hit a slice groundstroke compared to topspin, but that seems too strong.

One factor that I am going to look at is the angle of the swing plane and make some primitive measurements. For now all I am saying is that there is a hell of a lot of spin on those slices. And I find the values somewhat surprising.

[tennis_chiro]

I think it is all relative

I'm getting confused here...doesn't slice check and turn to topspin once it hits the ground.

This is where the Cross and Lindsey stuff gets a little confusing for me. IN THE MOMENT when the ball is touching the ground and turning, it is not sliding. (Sorry, Julian. I don't have the book handy right now, but I know I really struggled trying to understand exactly what was going on there.) I can't quite get my head around it. But I think a 5000 RPM slice goes into the ground and loses most of its underspin, but not all of it; the ground should change it by about 3000 RPM. But that would leave it still with underspin. That's what I was suggesting to JY. That 5000 RPM slice will hit the opponents racket spinning with about 2000 RPM on backspin which is a headstart on the topspin going in the other direction; just as an incoming topspin shot is a headstart on spin for an outgoing slice. And I am assuming that is how the 5000 RPM slice was accomplished.

But yes, as JY pointed out, there still is that tremendous amount of absolute rotation on the slice. I was just wondering if there shouldn't be a corresponding immense amount of spin on the topspin return of a slice; but only if the incoming ball started with an awful lot of spin.

don

[julian1]

Cross and Lindsey

The increase in spin may be greater than in the past, but I doubt that the increase in spin relative to a forehand is really greater in either an absolute or percentage measure. A maximum backspin of +5000 rpm sounds like a lot, but it is really only an addition of 2000 rpm on a ball that may have already been spinning at over 3000 rpm after the bounce. But for that same ball to be sent back with +3000 rpm on a topspin forehand, the change in spin would be over 6000 rpm. I'm not sure of the numbers, but I don't think that would be that unusual for a heavy forehand from any of today's players with heavy topspin, much less Nadal. On the other hand, the +5000 rpm slice backhand was a bit of an anomaly.

Now someone else can get into some highly technical discussion of how much the ball is actually "spinning" on the strings when the spin is being changed from topspin in one direction to topspin back in the other direction, but that whole section of Cross and Lindsey kind of makes my head hurt.

But let's not get carried away with the idea that there is more spin on a backhand slice than a topspin forehand or serve.

don

Don,
please provide questions,if any, about the above mentioned section
of Cross and Lindsey,
regards,
Julian

[stotty]

A maximum backspin of +5000 rpm sounds like a lot, but it is really only an addition of 2000 rpm on a ball that may have already been spinning at over 3000 rpm after the bounce.
don

I'm getting confused here...doesn't slice check and turn to topspin once it hits the ground.

[johnyandell]

I have to check my notes which aren't here, but yeah probably. Most of the balls coming off the court were spinning with over 5000rpm of topspin. I'll look for some that had underspin on the way into the bounce.