Racquet Stringing [RDC vs ERT | String Bed Deflection vs Dynamic Tension]

You know what an RDC and ERT are if you've watched some of my previous videos, specifically on tracking string bed deflection and string tension.
One of the functions of the Babolat Racquet Diagnostic Center (RDC) is to measure string bed deflection, which ultimately is what a player will feel. To achieve the optimum string bed deflection, you must determine the proper reference string tension.
From my experience using the RDC, here's a guideline of the ideal string bed deflection based on the type of string setup.
o Synthetic strings (including multifilament) - 58-64
o Natural gut strings - low 50s to high 60s
o Hybrid synthetic/polyester strings - 54-62
o Polyester strings - 48-54
The ERT700 has been a valuable device for measuring string tension, and I was always curious how it matched up with the current ERT300 model.
Well, I decided to get one.
The ERT300 measures Dynamic Tension (DT) instead of string bed deflection. The ERT300 reading provides a general guideline of the optimum DT according to your playing style and level.
At $250, the ERT300 is well worth the investment.
In addition to measuring DT, here are some valuable ways in which an ERT300 can be used.
* It gives the player confidence that their racquets are strung optimally by getting the most out of
the interaction between the racquet and string.
* It provides the stringer a means to check the quality of work off the machine and track tension
loss over time.
* Allows the stringer to advise customers when to restring their racquets.
* Along with taking ERT300 readings, a record-keeping system will go a long way in providing excellent service. You'll be able to determine if you should use the same reference tension to recreate the same DT value or if you need to adjust the reference tension to optimize the player's DT further.
ERT300 STRING TENSION DEVICE USED IN THIS VIDEO
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REFERENCES
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[@AlexTennisChannel]

Really cool!

[@Javi_C]

Thanks for the comparison

[@AMstringing]

Aloha Javi, Thanks for watching!

[@darrylcaldwell8995]

Head Graphene Touch Prestige Mid MSV Focus Hex Plus 38 1.15mm String: Reference Tension: Mains 53 lbs, Crosses 56 lbs DT 38

[@AMstringing]

Aloha Darryl, Thanks for contributing your string setup. I'll include this on my list! 👍

[@eric4458]

ERT300 works very accurately compared to the set tensile strength of the stringing device. Especially with syn gut and multis. There is sometimes a small difference with polys, especially with thicker polys (1.30mm) Most requested stringjobs for 100in² DT 30-33 Poly 20-22kg DT 33-37 Syn-Gut 22-24kg DT 35-38 Multi 23-25kg Grtz, Eric, Belgium

[@AMstringing]

Aloha Eric, Thanks for contributing your string setups! This is great information! 👍

[@stringmeup2]

I am curious to know 2 things about the RDC as it relates to string bed deflection. First, is there a calibration procedure for this function? And second, is there a lubrication schedule for the mechanism?

[@AMstringing]

Aloha Ed, These are good questions, but unfortunately, I can't answer them. Nothing in the user's manual or technical guide mentions either one of these. I have one of the original models of the RDC and have been fortunate to keep it running for almost 30 years now without any issues. 🤙

[@stringmeup2]

@@AMstringing Thanks for taking the time to check and for responding so quickly.

[@alanvanzee]

You have my setup! My DT is 28.

[@AMstringing]

Aloha Alan, Cool! Funny, according to the ERT300, at the 28DT reading, it's almost "time to restring!" 🤣

[@alanvanzee]

@@AMstringing When I first get my rackets from you Arnulf's ERT300 reads 28. I send them to you when they reach 23, which is almost now.

[@AMstringing]

@@alanvanzee Yes, since you have access to Arnulf's ERT300, you can see how string tension really drops. My ERT700 wasn't always able to measure the tension of your string setup for some reason, but I'm guessing that it was probably at 30/31 DT right off the stringing machine. I'll be able to check now since I have the 300 and will let you know. 👍

[@eric4458]

Tecnifibre T-Fight / Signum Pro Polaris 1.20mm : tension machine 21kg ERT300 dt = 31 fresh ERT300 dt = 30 1day/no play ERT300 dt = 29 2day/no play

[@eric4458]

Prince O3 Legacy 105 Tecnifibre TGV 15L/1.35mm Reference Tension : M & C 24kg ERT 300 : DT 37

[@eric4458]

After 24h : no play : DT 34

[@johnyoungblood]

I question how to interpret DT and RA values as they focus heavily on the properties of the center strings, NOT the entire stringbed. I say this because when I string traditional, say 54 lb mains, 54lb crosses, I get a very similar RA or DT as when I string proportionally with shorter strings being strung at tensions lower than longer center strings. In fact the outermost strings are installed in upper 20’s. The stringbed is clearly not the same. By checking tension on individual strings with a Stringmeter, it’s easy to see there is a dramatic difference, however DT and RA simply does not reflect this difference. So what are these devices actually measuring??? I suspect the measurement skews heavily toward the tension of center mains and crosses vs the entire stringbed.

[@AMstringing]

Aloha John, You bring up an interesting point. However, I'm surprised that when you strung using the proportional stringing method you got similar readings. I would have guessed the readings would be lower than a traditionally strung racquet. As for the tension measured on individual strings with a Stringmeter versus the center of the string bed measured with an ERT300 and RDC, here's an interesting experiment I did with all three devices. I strung two racquets with the same synthetic gut both at 52 pounds. One racquet was a 110 (16x19) and the other was 100 (16x18). RDC reading - 58 units ERT300 reading - 56 pounds STRINGMETER readings - During the stringing process, I took the readings on the two center mains, located at the center of the string bed at the following intervals. Notice the tension listed on the left main (LM) and right main (RM). 43LM/43RM after installing 4 mains 41LM/41RM after installing 8 mains 38LM/38RM after installing 12 mains 37LM/37RM after all mains were installed 39LM/39RM after installing 4 crosses 43LM/43RM after installing 8 crosses 47LM/47RM after installing 12 crosses 51LM/51RM after installing 16 crosses 51LM/51RM after all crosses were installed In the end, the Stringmeter came out with a final reading of 51. In my opinion, this final reading was due to three factors. 1. The natural frame distortion that occurs during the stringing process. 2. The main strings are stretched after the installation (weave) of each cross string as a result of being pushed up and down. 3. The tension reading of the center main strings is tighter due to the surrounding strings that keep them in place. I hope this makes sense. 🤙

[@johnyoungblood]

@@AMstringing All makes perfect sense. I suspect the reason the mains went down with each measurement may have had something to do with frame distortion, but also from stretching those center strings taking readings with the Stringmeter. If you were to perform same setup again, I would not be surprised if you waited to measure until after 12 mains were installed, you might find a reading closer to 43 than 38. And yes, I expected much different readings on proportional vs traditional too.

[@AMstringing]

@@johnyoungblood I'll try that experiment the next time I have the opportunity to do so.