My standard setup for a few months has been VS mains and Xcel 17 crosses at around 50-52 pounds. This was based on TW's friction research showing VS Touch-based hybrids showing low static and sliding friction and Xcel's relatively low static friction, at least for a multi (also tried Recoil but disliked it).
I still recall the first time I tried VS + Xcel. Very comfy and excellent access to spin.
Over the last few days I've had the opportunity to hit with two other VS-based hybrids using the new EXO3 Tour 100 16x18. I've had my EXO3 strung twice based on TW's sliding friction research and the results have been interesting! While it appears both static and sliding friction are important for spin potential other string characteristics clearly enhance or degrade a given string bed's quality regardless of spin potential. However, the following is simply anecdotal (but real world) evidence from one middle aged tennis noob (but one who is a fairly observant geek). So take it with a bucket-o-salt.
HYBRID A
Mains: VS 16 @ 50#
Cross: Hurricane Feel 16 @ 47#
Amazingly easy access to spin (I could even hit "curve balls") but VERY low power, at least for this tennis noob. Stronger, more athletic players could generate more power, but when hitting with lots of spin the ball floated and then only rocketed AFTER hitting the ground. In any case, from a purely spin-potential perspective this is an amazing hybrid. BUT...
Hurricane Feel 16 has the lowest sliding friction value and a very low sliding friction value but a very high stiffness rating in the high 200s. More importantly, after only four hours or so of hitting with this hybrid the string bed exhibited extreme notching and the VS was on the verge of breaking. Not a durable setup to say the least.
HYBRID B
Mains: VS 16 @ 51#
Cross: XR3 17 @ 49#
So, after noticing Hybrid A's low power and extreme notching, this morning I had the EXO3 restrung with XR3 17. Power was perfect for this noob and spin potential was still good. Not nearly as extreme as Hybrid A, but somewhat better than average.
However, as the session wore on, the racquet felt board-like in spite of XR3's low-ish stiffness of roughly 170-180. After a couple of hours I had to switch to my PB10 Mid for relief! Heck, the Hurricane Feel poly felt more comfy!
Then tonight I took a look at the EXO3's XR3 strings and WOW!!! What a mess!!! I never had "string movement" problems with Xcel as in strings moving and then not moving back into place. The EXO3's sweet spot looked like one of those op-art illusions of a grid distorted to resemble a sphere. Every impact point was recorded for posterity in the string bed.
Clearly the XR3 was moving around and its high static friction was preventing it from moving back into place.
THE NUMBERS
So, let's look at the static and sliding friction numbers.
Hurricane Feel 16: Static .089 / Sliding .040
Xcel: Static .120 / Sliding Unknown
XR3 17: Static .159 / Sliding .047
While this is based on the anecdotal evidence gathered by a tennis noob, the results might be interesting, at least for other tennis noobs and fellow geeks!
Given the general patter of relationships between static and sliding friction it's quite likely Xcel's sliding friction falls between Feel and XR3.
It seems then that one might need to consider BOTH static and sliding friction when it comes to overall performance AND stiffness relative to player strength and skill when evaluating a string bed's spin potential.
For this middle-aged noob the VS/Feel hybrid generated insane amounts of spin but lacked the pace needed to be a "keeper". Durability was also an issue and would probably be a BIGGER issue for more athletic hard hitters.
The XR3 generated decent spin and power initially but "non-recovering" string movement seemed to quickly degrade the string bed's performance and comfort.
Meanwhile, the spin-friendly VS + Xcel hybrid in my PB10 Mid and London continue to do outstanding work after many hours of play and with almost no noticeable "non-recoverable" string movement, and certainly no notching.
CONCLUSION:
Static friction appears to impose a limit on a string bed's durability with respect to consistent support for spin potential over time. If too high the SB may become less spin-friendly regardless of a low sliding friction value due to a high static friction value which prevents strings from returning to a "neutral" position.
And while exhibiting outstanding spin potential, hybrids combing stiff polyester and comparatively soft gut may suffer from extremely limited life expectancies due to notching and breakage. For less athletic players polys may also limit power potential thus negating any spin advantage.
Therefore, at least for fellow noobs, there may exist a sweet spot for a spin-friendly string bed based on low static and sliding friction. Spin potential would have to be high enough to tame the power of a less stiff SB. At the same time, that less stiff SB would allow a duffer to hit some pretty heavy balls while accessing the SB's spin potential without fear of over-hitting.
For durability purposes, something important to weekend warriors, the relative stiffness and material qualities between mains and crosses should be such that neither degrades the other's performance through movement across one another.
I still recall the first time I tried VS + Xcel. Very comfy and excellent access to spin.
Over the last few days I've had the opportunity to hit with two other VS-based hybrids using the new EXO3 Tour 100 16x18. I've had my EXO3 strung twice based on TW's sliding friction research and the results have been interesting! While it appears both static and sliding friction are important for spin potential other string characteristics clearly enhance or degrade a given string bed's quality regardless of spin potential. However, the following is simply anecdotal (but real world) evidence from one middle aged tennis noob (but one who is a fairly observant geek). So take it with a bucket-o-salt.
HYBRID A
Mains: VS 16 @ 50#
Cross: Hurricane Feel 16 @ 47#
Amazingly easy access to spin (I could even hit "curve balls") but VERY low power, at least for this tennis noob. Stronger, more athletic players could generate more power, but when hitting with lots of spin the ball floated and then only rocketed AFTER hitting the ground. In any case, from a purely spin-potential perspective this is an amazing hybrid. BUT...
Hurricane Feel 16 has the lowest sliding friction value and a very low sliding friction value but a very high stiffness rating in the high 200s. More importantly, after only four hours or so of hitting with this hybrid the string bed exhibited extreme notching and the VS was on the verge of breaking. Not a durable setup to say the least.
HYBRID B
Mains: VS 16 @ 51#
Cross: XR3 17 @ 49#
So, after noticing Hybrid A's low power and extreme notching, this morning I had the EXO3 restrung with XR3 17. Power was perfect for this noob and spin potential was still good. Not nearly as extreme as Hybrid A, but somewhat better than average.
However, as the session wore on, the racquet felt board-like in spite of XR3's low-ish stiffness of roughly 170-180. After a couple of hours I had to switch to my PB10 Mid for relief! Heck, the Hurricane Feel poly felt more comfy!
Then tonight I took a look at the EXO3's XR3 strings and WOW!!! What a mess!!! I never had "string movement" problems with Xcel as in strings moving and then not moving back into place. The EXO3's sweet spot looked like one of those op-art illusions of a grid distorted to resemble a sphere. Every impact point was recorded for posterity in the string bed.
Clearly the XR3 was moving around and its high static friction was preventing it from moving back into place.
THE NUMBERS
So, let's look at the static and sliding friction numbers.
Hurricane Feel 16: Static .089 / Sliding .040
Xcel: Static .120 / Sliding Unknown
XR3 17: Static .159 / Sliding .047
While this is based on the anecdotal evidence gathered by a tennis noob, the results might be interesting, at least for other tennis noobs and fellow geeks!
Given the general patter of relationships between static and sliding friction it's quite likely Xcel's sliding friction falls between Feel and XR3.
It seems then that one might need to consider BOTH static and sliding friction when it comes to overall performance AND stiffness relative to player strength and skill when evaluating a string bed's spin potential.
For this middle-aged noob the VS/Feel hybrid generated insane amounts of spin but lacked the pace needed to be a "keeper". Durability was also an issue and would probably be a BIGGER issue for more athletic hard hitters.
The XR3 generated decent spin and power initially but "non-recovering" string movement seemed to quickly degrade the string bed's performance and comfort.
Meanwhile, the spin-friendly VS + Xcel hybrid in my PB10 Mid and London continue to do outstanding work after many hours of play and with almost no noticeable "non-recoverable" string movement, and certainly no notching.
CONCLUSION:
Static friction appears to impose a limit on a string bed's durability with respect to consistent support for spin potential over time. If too high the SB may become less spin-friendly regardless of a low sliding friction value due to a high static friction value which prevents strings from returning to a "neutral" position.
And while exhibiting outstanding spin potential, hybrids combing stiff polyester and comparatively soft gut may suffer from extremely limited life expectancies due to notching and breakage. For less athletic players polys may also limit power potential thus negating any spin advantage.
Therefore, at least for fellow noobs, there may exist a sweet spot for a spin-friendly string bed based on low static and sliding friction. Spin potential would have to be high enough to tame the power of a less stiff SB. At the same time, that less stiff SB would allow a duffer to hit some pretty heavy balls while accessing the SB's spin potential without fear of over-hitting.
For durability purposes, something important to weekend warriors, the relative stiffness and material qualities between mains and crosses should be such that neither degrades the other's performance through movement across one another.