Pre-Stretched Poly

Conventional advice is to tension poly carefully with the slowest pull setting in the machine. That preserves the limited amount of elasticity in the string. (link)

The elasticity of nylon/mutifilaments allow them to stretch about 10-12%, natural gut about 7% and most polys only around 3-4%.

What I could not reconcile with, is that these poly strings, with the worst tension maintenance, is always prescribed for the hardest hitters who break strings frequently. See the dichotomy?

While the string breaking may be taken care of, what about the tension holding? It still becomes unplayable. So, poly users are recommended to restring regularly. 

But how is breaking nylon/multi after a few hours different from cutting out spent poly in the same amount of time?

After two months, a full reel of poly, and deriving only about 4 hours of play per racket, both my big hitter friend and myself got tired of this incessant need to restring.

Against conventional wisdom, and encouraged by positive feedbacks of pioneers online, we pre-stretched the poly string before stringing.

To add a layer of protection from the super-boardy elbow-busting string bed we were anticipating, we hybrid the perimeter with softer synthetic gut, also pre-stretched. And used my arm-friendlier Pro Kennex instead of his stiffer rackets.

Playtest:
- Simple bounce tests after stringing indicated the string bed was about as soft as a brick wall. No pocketing at all.
- The frequency was monitored immediately off the stringing machine and at different intervals.
- After an overnight rest unplayed, the first observation was impressive. String bed frequency dropped by only 9 Hz compared to the usual 40 Hz. This loss was similar to a freshly strung gut/poly hybrid left overnight. Unprecedented for any poly or syn gut.
- On court, the entire first hour played stiff and powerless but NOT boardy at all. The usual break-in after about 20 minutes of rally did not happen. It maintained almost exactly the same tight controlled feel as the initial hits, only softer. 
- Spin was impressive. Very much better than without pre-stretch. Could be the tightness encouraging us to swing away freely. We had fun hitting some new extreme angles previously impossible, and watching the ball curled in.
- We switched to serve practice. Being the weaker hitter, I served first. It was disastrous. There was not enough power to drive the ball even on flat serves. Comparing the slow-motion video frames with my usual strings, I lost about 25-40% ball speed. Clearly reminded myself why I did not like could not use poly. (link)
- However, in the hands of my hard-hitting partner, it was like a dream come true. Alternating with his other freshly strung unprestretched stick, I could see there was absolutely no doubt nor hesitation with the pre-stretched strings. He just let it go full blast. From video reviews, serve percentage, serve speed, placements were all better.
- That took about an hour and we measured the frequency again. It dropped only another 11 Hz, compared to the usual about 30+ Hz.
- Somewhere after 90 minutes of use, I took over the racket for rallies again. By then, the pocketing and sweet spot opened up significantly. There was more proportionate power. Harder hits had deeper pocketing and softer hits less pocketing. Strangely, it reminded me very much of synthetic gut!
- For once, we could even volley decently, with good feel, using this poly string!
- In my partner's words, another distinct difference was that this poly became a "fast string", like natural gut, instead of its usual "slow and sloppy."
- At the two hour mark, it dropped only another 0.8 Hz.
- Immediately, this chap handed me both his rackets to be re-strung. I think we're onto something significant...