Stringing knowledge from Dr. "String" Love
Our own Dr. Carl Love, Advisory Member of the Board of RSI (Racquet Sports Industry), and member of
the US Racquet Stringers Association, shares his knowledge about stringing in a series of articles to be posted here.
Playability
During the year of 2011 forty-seven racquets were analyzed to assess "PLAYABILITY".
These factors were deemed to make up the major criteria for the term playability:
- Power to keep a high ball speed that lands the ball near the base line on most hits.
- Control to help player feel they can just clear the net or get high lobs, and any in between.
- Comfort which will provide player with reasonable returns on even off center ball contacts.
- Consistency by keeping the ball in play for extended time values.
There are many different kinds of tennis strings for example, Natural Gut, Nylon, Polyolefin,
Polypropylene, Kevlar, Technora, Vectran, and others not in production at this time. As the materials
change so does the performance! A competitive professional can select a combination of two different
types of strings that will improve the playability of any tennis racquet. No single string can provide
such high values of playability as a combination of two. The reason for this is that main strings control
over "80% of what comes off a racquet. Another reason is that few tennis professionals can properly match
hybrid tensions. A HYBRID combination is two different kinds of strings. Of the "Forty Seven Racquets
mentioned above three fourths with hybrid combinations were over tensioned with the stiff string!
In an attempt to help players and tennis stringing professionals be more selective when selecting machine
tension, three bench tests were devised to help select appropriate tensions. Before the bench test data
is brought forth, look what the average tension of the 47 racquets ended up, (some, several months after
stringing), none of the mains were over 45 and none of the crosses were over 32 pounds of static tension.
It is estimated that some of the frames were strung at over "Seventy Pounds of Machine Tension". Today
there are String Shops that can extend the normal tension loss from one month to more than 10 months!
The three bench tests selected to provide an answer to machine tension when two different kinds of strings
are used in a frame are:
- Per-Cent Elongation.
- Slope of the Impact curve in pounds per millisecond.
- Tension change from static tension to maximum impact tension.
The two strings selected for this project were Wilson Enduro Gold 16 g. (Poly) and Babolat Fine Play 16 g. (Nylon).
The machine used was a Gamma 6002 ELS, tension was calibrated @ 50.0 Lbs. See Table 1-1 below.
| Table 1-1 |
Numerical differences in tennis string when subjected to three different types of mechanical tests. |
|
Mechanical Test |
Poly String |
Nylon String |
|
Per-Cent Elongation |
3.6 |
8.9 |
|
Slope of Impact Curve (Pounds/Millisecond) |
16 |
12 |
|
Tension Change On Impact (Pounds) |
54 |
46 |
To obtain the appropriate tension when using different kinds of strings calculate the tension as follows:
Machine Tension = Small Value / Large Value x Machine tension
Using the data from Table 1-1, calculate the typical tension for the Wilson Polyester as main strings and the
Babolat Nylon for cross strings.
Calculations:
- 3.6 / 8.9 = 0.41
- 12 / 16 = 0.75
- 46 / 54 = 0.85
- Add the three values and calculate the average (.41 + .75 + .85 = 0.67)
Therefore the stiff polyester string would be 67 percent of the machine tension. This project, using fifty pounds
as the intended machine tension goal, the poly mains would be installed at 34 pounds and the nylon cross strings
at 50 pounds. Do not hesitate to make this much difference in machine tension with stiff mains and elastic
cross strings. When the cross strings are pulled into the frame, the main strings will increase in tension by
as much as 20.0%. This depends upon how the stringing machines "pre-stretch option of 5.0% to 25.0% is adjusted,
and dwell times are used after pulling to tension.
Happy Stringings,
Carl
