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String Test: Iso-speed Energetic 1.30
Iso-Speed is a little-known manufacturer in the USA, but Head string users have known their products for years (ever since the popular RIP series strings surfaced). They’ve been selling strings under their own label for some time now, and I decided to take a look at one of them: Iso-Speed Energetic.
Specifications
Energetic is one of Iso-Speed’s groundbreaking polyolefin ribbon string designs, but with a little twist: while it’s technically a multifilament design, it does have a center core. The core is comprised of 280 polyamide fibers covered by an “outer core” of 600 polyester fibers, and an outer wrap of polyolefin ribbons. All of the filaments are pre-stretched to aid in tension maintenance, about which we’ll see later (I’m always skeptical about promises of tension stability). It’s a classic 16 gauge, measuring 1.30mm in diameter. Elongation percentage tested out at 7.24%, and it surprisingly exceeded 80 lbs. on the knot strength test. My proprietary Power Potential Index is 1.87, a slightly low number. Our test set of Energetic measured out at 40‘8”, which should allow you to string pretty much any frame on the market. Its gold color is quite normal, and shouldn’t cost any sales over the “ick factor”.
You can expect Iso-Speed Energetic to have an installed “street price” in the $27-33 range.
Stringing
I installed Energetic in the Wilson HTour test racquet at a reference tension of 55# on the Babolat Star 5 machine, and received a Dynamic Tension reading of 38 on the Beers ERT700 Tenniscomputer, the same as Head IntelliTour (an Iso-Speed manufactured string, if I remember correctly), Luxilon Alu Power and Alu Power Fluoro, RAB Monoflex, and Ashaway Dynamite. This dropped to 34 after 24 hours of unused time, a 10.53% tension loss, and not a good start for Iso-Speed’s claim of tension maintenance. The Babolat RDC measured an initial string bed stiffness (SBS) of 59, dropping to 52 after 24 hours, or an 11.86% loss. The other RDC ratings were: Power of 44(B), control of 57(B), and maneuverability of 63(A).
By contrast, IntelliTour lost the same 4 DT units on the ERT700, while Alu Power and Alu Fluoro lost only 3 units, as did Monoflex. Dynamite’s Zyex fibers lost only 1 unit after 24 hours, which is as good as it’s going to get on tension maintenance. After one week of no play, Energetic had lost one more DT unit, and 3 SBS units, while Alu Power, Alu Fluoro and Monoflex lost one DT unit, and Dynamite had remarkably stayed the same.
I’m not so sure I’m going to like a multifilament string that doesn’t hold tension better than polyester. We’ll see how the string holds tension during play.
I also strung Energetic in my personal Prince Diablo XP MidPlus frame at 42.5#, receiving the same DT reading of 31 that I got from Gamma TNT2 17, Ashaway Dynamite 17, and Wilson K-Gut 16 (all strung at 40#), and Bow Brand Championship Gut 17 (strung at 41#). I got an SBS reading of 41 on the Babolat RDC, the same as Tecnifibre Multifeel 125 strung at 40, and 1 unit less than TNT2 17, also at 40#. The other RDC readings were as follows: Power rating of 55(B), control of 41(B), and maneuverability of 75(A). Swingweight was increased by 31 units – about normal --, and racquet weight was increased by 20g, also within the norm.
It was quite easy to install this string, with very low coil memory and little worry over kinking. The clamps didn’t bother it at all, weaving was a breeze, and knots cinched up nicely. All in all, Iso-Speed Energetic was one of the easier “soft” strings I’ve worked with lately.
In Play
Iso-Speed Energetic has a remarkably soft feel, absorbing almost all unwanted shock and vibration. It also doesn’t leave much ball feel behind, but this may not trouble many folks with sore elbows. A slight bit of “extra feel” off hits high on the string face went away after the first couple of hours’ play, leaving the entire strung area of the racquet feeling shock-free.
Unfortunately, power was not a strong point of Energetic, as it was harder to generate pace than I would’ve liked, especially once the balls were used for a set or so. This may cause some of us to swing harder than our arms would like, and take away some of the string’s shock absorption benefits. String movement wasn’t bad, as I only had to do moderate straightening after long topspin rallies.
At the end of the test period (about 15 hours of use), the DT had dropped from 31 to 25, a 19.4% dip, and more than I would’ve hoped for. The RDC reading went from 41 to 32, a huge 22% drop. This is not good tension maintenance, and there’s just no way to sugarcoat it: this stuff doesn’t hold tension well. The durability aspect of the string also jumped up and bit me a little.
Brilliant Observation
I’m not what you would call a major string breaker, but I was starting to notice quite a bit of fraying in Energetic’s outer wrap after less than 10 hours of play (mostly on the teaching court). I wish my camera was of high enough quality to show you what happened, but the shots weren’t clear enough to share with you here. Suffice it to say that I found it odd to see a gold string fraying white in some areas, but it was enough fraying to make me take notice and have a spare racquet in the wings.
In Conclusion
I think that, if you’re at all recognized for breaking strings, you would want to steer away from Iso-Speed Energetic. Also, if you need power with your forgiveness, you might try one of many other strings (Wilson NXT, Tecnifibre NRG2 or Gamma TNT2) that are noted for soft feel with higher levels of power, even if you have to spend a little bit more. I will not be adding this string to my inventory due to these problems.
But, if you don’t want any extra power, this string can offer you a shock-free string face without excessive string movement. Just be prepared to restring more often due to the tension loss and fraying.
Accumulated Data:
Manufacturer: Iso-Speed Model: Energetic Gauge: 16 (1.30mm)
Construction: Center core of 280 polyamide fibers; outer core of 600 polyester fibers, polyolefin ribbon outer wrap. All filaments are pre-stretched.
Elongation Percentage: 7.24% @ 60# Knot Strength: >80#
Power Potential Rating: 1.87 (low of 0.5, high of 6.73)
Power Rating: 1 2 3 4 5 6 7 8 9 10
Control Rating: 1 2 3 4 5 6 7 8 9 10
Comfort Rating: 1 2 3 4 5 6 7 8 9 10
Durability Rating: 1 2 3 4 5 6 7 8 9 10
Cosmetic Rating: 1 2 3 4 5 6 7 8 9 10
Tension Maintenance Rating: 1 2 3 4 5 6 7 8 9 10
String Movement Rating: 1 2 3 4 5 6 7 8 9 10
Expected Installed “street price”: $27-33
Recommended Player Type: High Power Moderate Power Low Power
Sore Arm Average Arm Healthy Arm
Full Swing Medium Swing Short Swing
Recommended Racquet Type: Stiff Medium Flexible
Coming soon!
Reviews of:
*Ashaway Dynamite
*Bow Brand Championship Gut
*Gamma TNT2
*Tecnifibre Multifeel
*Prince O3 SpeedPort Black
*Plus: Mondo Grip Test Returns!!
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