Question of the Day: Perusing Strings By Stiffness

TENNIS.com gear editor Justin diFeliciantonio and his technical advisers answer your equipment questions each day. Click here to send in a question of your own.

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In a recent article, you recommended searching for string based on the United States Racquet Association’s 2012 String Survey. Do you know what the last three columns of the tables mean? (I think the second last column is the 'stiffness’.) I use Luxilon M2 currently, but have been experiencing pain in the knuckle area of my index finger. I figured I’d go for a softer poly such as Head FXP Tour. Do you recommend that?—Piyush

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Thanks for your question, Piyush. To reiterate, I do think the USRSA’s String Survey is a very good resource for players looking to buy or switch string—in short because it lists all major strings on the market in order of their type and stiffness. How stiff a string plays—which depends on its material, gauge, and construction—has a lot to do with the string’s feel and playability; and so players would do well to pay attention to it. (Natural gut, for example, is much more pliable than polyester or nylon, which accounts for gut’s unique playing characteristics, such as its high-energy return and low shock.)

To answer your question, the last three columns of the survey—from left to right—are the string’s gauge (in mm), stiffness (in lbs./in.), and tension loss (in lbs.). Dave Bone, of the USRSA, explains the testing procedure for these three variables as follows:

“All strings were tensioned to 62 pounds and allowed to sit for 200 seconds. Then the string was hit five times with a force equivalent to hitting a 120 m.p.h. serve. The tension loss represents the total amount of the relaxation over both time and impact. The stiffness value is a calculation derived from the amount of force created at impact to stretch the string. Lower values represent softer strings and lower impact forces. Higher values represent stiffer strings and higher impact forces.”

In response to your final question, it’s of course reasonable to look for more arm-friendly strings when dealing with a nagging injury. (Even more reasonable is to seek physical therapy and/or take a break.) The Head FXP Tour would indeed be a good, soft choice. (Disclaimer: I strung it in my crosses throughout my college tennis days). If you want to get technical though, FXP Tour isn’t entirely a polyester; a multifilament wrap surrounds the string’s monofilament core. Honestly, if you’re looking to quell a nagging injury, it might be best to go even softer. How about hybridizing a pliable poly, like Babolat Pro Hurricane 18, with natural gut?