# New Spin Potential Measurement

Discussion in 'Strings' started by TW Professor, May 3, 2012.

1. ### TW ProfessorAdministrator

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The new TWU String Finder (http://twu.tennis-warehouse.com/learning_center/stringfinder/stringfinder.php) introduces a new measurement called "Spin Potential". The number is actually a ratio of the ball-to-string COF to the string-to-string COF (COF = coefficient of friction). A higher COF indicates higher friction and a lower number lower friction. The ideal combination is to have high ball-to-string friction and low string-to-string friction. Such a combination would mean the main strings will easily move sideways and snap back, and during snap-back, the strings will grab the ball and spin it.

That is what a high spin potential ratio indicates.

That is not all there is to spin. The other ingredient is stiffness. A stiffer string will tend to create more spin. So if you have two spin ratios that are almost equal, the one with greater stiffness probably has the greatest potential.

A couple caveats. First, theoretically, you could have "false positive," meaning that a string could have a very high ball COF and a very high string COF compared to other strings, but the ratio is still high, even though the strings don't slide on each other. Fortunately, that doesn't occur, at least for strings that we know about. You can see the ball and string COFs by clicking on the table cell with the spin potential ratio in the "Compare Strings" and "Similar Strings" views. In this way you can determine if the ratio is suspect for a given string.

Second, the ratio is only measured using the string-to-string COF for a string sliding on itself. So, there are no hybrids represented. Further, you cannot assume that a string that slides easily on itself will also do so on another string. Maybe, maybe not.

Also, the string sliding ability of any string depends on whether it is a main or cross. Strings can have a different inter-string COF with other strings depending on whether it is sliding parallel or perpendicular to the other string. That is why a hybrid using gut in the mains and poly in the crosses can be the slipperiest combination of hybrid, but if you reverse them, it can be among the worst.

The spin potential ratio also does not factor in changes in COF with wear, notching, etc. These may enhance or inhibit spin. But they also change stiffness, energy return, etc. The stringbed changes over time. But, still, we are light years ahead of where we were just a year or two ago with regards to predicting the spin potential of a string.

We have done some hybrid measurements of inter-string friction. Those can be found using the String Friction Tool: http://twu.tennis-warehouse.com/learning_center/COFreporter.php.

Also, spin experiments for ball and string friction can be found here:
http://twu.tennis-warehouse.com/learning_center/stringballfriction.php
http://twu.tennis-warehouse.com/learning_center/COF.php

2. ### rdis10093Hall of Fame

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that is so sick

3. ### TorresBanned

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A nylon multifilament like [K]Gut and a basic Volkl synthetic gut have more spin potential than a whole host of polys including Luxilon Alu Rough, BHBR, and Tornado?

Anyone who has played with those strings knows that that simply isn't true.

That table is throwing up alot of anomalies already....

Last edited: May 3, 2012
4. ### fortun8sonHall of Fame

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To be fair, the Prof does admit that there are limitations and possible anomalies in using just those factors to compute spin potential.
It is a step in the right direction, however.

5. ### arche3Banned

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Yes.... I would like to thank Prof5 as well. Good job. Good job.

6. ### pvaudioLegend

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As I said in the other thread, I respect the scientific approach. I cannot possibly agree with the justifications made. The numbers simply contradict the deductions: Volkl Syn Gut has higher spin potential than Polystar Turbo. Prince Synthetic Gut Org. has higher spin potential than Solinco Barb Wire. Gamma TNT has an entire point more spin potential, not decimal point, but 4.5 vs. 3.5, than Kirschbaum Spiky Shark. So I mean, I guess I respect the willingness to measure these parameters, but the results just don't make sense.

7. ### retlodProfessional

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Friction between two surfaces depends upon more than just the coefficient of friction. In elementary physics, it's F = uN, just that easy. In the real, physical world, not so much. I would take these numbers with a grain of salt.

8. ### pvaudioLegend

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:shock: I had forgotten what your real-life profession was, retlod. It's safe to say we can trust his opinion on all things engineering

9. ### kiteboardLegend

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Ball is gone from bed after 4/1000th/sec. All that feel is short in time. Any wonder why so many have such different tastes? We feel what we feel, do what we do, and see what we see in a shorter time, than it takes you to blink your eyes by a factor of 32. (1/3 sec.) Although I have a degree in electricity, it still does not add up to me, that the vibrations we feel in that time are what they are.

10. ### olliessSemi-Pro

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In their previous work they have noted that the coefficient of friction is not constant with normal force.

11. ### fortun8sonHall of Fame

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Transferred from other thread without the L-tec stuff. It belongs here, too.

12. ### NoobWannabeRookie

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I think the way they calculate spin potential is over simplified, flawed and misleading, ignoring other factors such as texttures, shapes, thinness, etc. Therefore, base your decision of strings solely on these results is not recommended.

13. ### WuppyProfessional

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Hey at least it's a start. Better than a bunch of dudes saying "wow this is the best string I've played with OMG!!"

14. ### NoobWannabeRookie

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lol, to me it's about the same, but yeah it's start. one question, i dont see a whole lot of strings do they only cover what they sell?

15. ### TW ProfessorAdministrator

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The friction numbers that compose the spin potential number (i.e., ball-to-string coefficient of friction and string-to-string COF) factor in those elements. The only significance of textures, shape, and gauge is to influence friction. The way you determine the influence of these characteristics on spin is to measure the change in COF by altering any of these.

Other factors influence spin: stiffness, pattern, tension, for example, and of course stroke factors like tip speed, swing angle, racquet tilt, incoming ball speed and spin and angle. All of these are held constant, except stiffness which is an actual property of the string and which the String Finder shows along with the Spin Potential. All of these other factors depend on the player and the setup the player uses. We test under the conditions of "all things being equal or the same" except the string itself.

The string-associated factors in spin production are presented here:

http://twu.tennis-warehouse.com/learning_center/stringmovementPart2.php

16. ### Don't Let It BounceHall of Fame

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Ball CoF List?

The String Finder compares ball-to-string friction to string-to-string friction. The latter is listed on this TWU page.

Is there also a TWU page that lists the former?

17. ### sansaephanhProfessional

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They ARE a warehouse. Using what they have in stock would be more cost effective then buying everything they don't have.