What is the spread of DTs across stringers?

#1
I like to read threads on the forum about specific string setups and how they perform. Often folks will comment with a certain tension they like. I can string up my racket with the same setup and tension and compare their observations to my own experience... but how do I know we're really talking about the same tension? Even if it's the same number set on the machine, the effective DT could be way off. There are so many variables that affect the actual string bed stiffness other than the number punched into the machine (type of stringing machine, mounting system, clamp drawback, stringing and knot technique, time before clamping, etc).

Consider the following experiment. Let's say I bought 100 PS85 frames, 100 sets of ALU Power 16, and 100 ERT 300 dynamic tension readers. I mail these out to 100 TalkTennis users at random, asking them to string the racket at 52 lbs with their normal process, and measure the DT 24 hours later. What would the data set look like? Assuming it's a normal distribution (big assumption), what would the variance and standard deviation look like? What would be the highest and lowest value?

Similar question: In a TT thread, if user Dave says he likes his stringbed at 52 pounds, and Larry chimes in saying he likes it more at 50, what are the chances that Dave's stringbed is actually stiffer than Larry's? Certainly not 100%. Maybe it's closer to 50%.

Just trying to get a handle on how wide the spread is. I'm starting to doubt the validity of any conversations regarding tension. I suspect my 50 lbs is actually another man's 57!
 
#2
That's why you try to eliminate some of the variables with stringing. Use the same stringer, who uses the same stringing machine. Hopefully, his/her technique is consistent. If you used 100 different machines with a 100 different stringers, you'd have results all over the place unless you had top-notch stringers with good, electronic equipment. Then, your variation would most likely be less.
 

norcal

Hall of Fame
#3
Dropweight with floating clamps probably strings much looser than good machine w/fixed clamps.

I string at 63ish (with the former setup), comes off the stringer at 55.xx (according to racket tune) and within a couple weeks or so I'm playing in the high 40's, after a month about 46lbs (15% loss). Then I cut them out if the syn cross has not broken yet (18polyM/17synX).

So yeah my numbers are way different from 'stringing at' to 'playing at'. I am very consistent though!

Be interested to see the difference for those of you with 'good' machines (especially guys who string for the pros) - does "string it at 52" mean it comes off the machine at 52?
 
#4
Dropweight with floating clamps probably strings much looser than good machine w/fixed clamps.

I string at 63ish (with the former setup), comes off the stringer at 55.xx (according to racket tune) and within a couple weeks or so I'm playing in the high 40's, after a month about 46lbs (15% loss). Then I cut them out if the syn cross has not broken yet (18polyM/17synX).

So yeah my numbers are way different from 'stringing at' to 'playing at'. I am very consistent though!

Be interested to see the difference for those of you with 'good' machines (especially guys who string for the pros) - does "string it at 52" mean it comes off the machine at 52?
RacquetTune can be great for tracking relative progress over time, but for absolute numbers it's not the greatest. For instance, my last job was 55 lbs and RacquetTune tells me 64.1 right off the stringer (and 59.9 24 hours later). I suspect my string jobs end up on the tighter end of the distribution, but even so, we can't compare our results. I could've selected a string factor that results in these high readings, a different choice would land them lower. Maybe if we both used the exact same string and same string factor setting, we could get a useful comparison.
 
#5

This graph has haunted me since I first saw it. The takeaway here - Timing really matters! Letting a string dwell under a constant pull tension head for 30 seconds will produce a string with 7 or 8 pounds higher "final" tension than one which is clamped almost immediately. I believe a basic nylon string was used in the experiment. This graph is taken from the book The Physics and Technology of Tennis.

In my experience, a dropweight with fixed clamp produces the stiffest bed, especially if you take your time fiddling with the tension arm.

Embarrassing story: When I first started stringing, I used to think time spent with the string clamped was "dangerous" (as if the clamps might be slipping) and time spent with the string tensioned by the dropewight was "safe" (ie, you can divert your attention briefly, the string is safely being kept under tension). I couldn't have been more wrong! Now I know, when the string is being tensioned, that is the critical time, and it needs to be kept to a minimum. No sips of beer, no looking up string patterns, and certainly no chatting with the girlfriend. The string is stretching here, people! Just a beat or two, then clamp and move on. As others have mentioned, a quick pace is a good way to be consistent.
 
Last edited:

uk_skippy

Hall of Fame
#6
I replicated the experiment above albeit with 2 rqts, but I think the results work with the 2.

This info is taken from a previous post I made

I strung 2 identical racquets, Babolat Flow recreational racquet, 16x19 pattern, with Babolat N.Vy synthetic gut string at 55lbs.

The 1st racquet (rqt 1) was strung using a delayed method. After every pull I waited until the machine beeped a second time. The 1st beep is when the tension-head initial reaches the desired tension. The time between each beep is 1 minute. Time taken to string the racquet ~40minutes.

The 2nd racquet (rqt 2) was strung using a normal method and therefore took ~17 minutes.

DT was measured using an ERT directly after each racquet was strung, and then 24 hours later.

Racquet 1 had an initial DT of 41, and a DT of 40 after 24 hours; racquet 2 had an initial DT of 42, and a DT of 40 after 24 hours. FYI, an ERT reading has a tolerance of +/- 1

Conclusion

For this string, tension, frame there is no difference between how quickly the racquet was strung. The DT readings are within the acceptable tolerances, and backs up the conclusion

In isolation, this experiment confirms the that speed doesn't affect the tension/DT drop both after initial stringing and after 24 hours. However, due to the number of types of strings available and the choice of tension for each player, this experiment would need to repeated for different strings & tensions. But this experiment lays a foundation for what would be expected.
 
#7
I replicated the experiment above albeit with 2 rqts, but I think the results work with the 2.

This info is taken from a previous post I made
Fascinating... Thanks. Your results are both comforting and concerning.

It leaves me wondering, what's the "magnitude" of one DT unit? If you strung that same racket with the normal method, once at 50 lbs, and another at 55 lbs, what would the DTs be after 24 hours? 39 and 40? Or closer to 35 and 40?

Another way to ask the same: How different can two stringbeds be, while both ending up at 40 DT? Would a racket strung at 53 and one at 55 both end up at 40 DT? Your conclusion is that there is "no difference" after 24, but I'd say there's no measurable difference.

RacquetTune is nice insofar as it presents stiffness in terms of lbs, which is easier to comprehend.

Anyways, thanks for the hands on data. Practice trumps theory every time.
 
Last edited:

uk_skippy

Hall of Fame
#8
1 DT unit is normally consider to be ~2lbs, which in theory is a lot. However, an ERT isn't that acute as it only shows whole numbers. IMO, I think it rounds up or down. So if it could read 40.4 it would show 40, if it read 40.6 it would show 41. This would show up more if you strung several rqts with the same string at the same tension; and the ERT readings bounced between 2 numbers with 1 DT apart. Thats why we allow the tolerance of +/- 1.

For 50lbs, I'd think I get a reading of 37/38 after stringing; so after 24 hours it should be 36/37.

With 1 rqt strung at 53lbs, and a 2nd at 55lbs. I would expect a different DT of 1 or 2.

I agree with your point @ba4x about measurable difference since we'd need something more accurate than an ERT; although using an ERT helps to show a difference.

An ERT should be used to check initial SBS, and tension loss over time; and is easier to use than RT particularly in a tournament environment.
 
#9
Sort of beside the point but I have 4 ERT devices, an ERT-300, an ERT-700 and two ERT-1000. They are not calibrated the same. The 700 produces the lowest readings, the 300 is a couple notches higher and the 1000's a couple notches above that. So typically I could get readings of 38, 40, 43 on the 3 different meters.

When it comes to leaving a tension head pulling, even if someone had conclusive proof that it was beneficial I would probably not do it. Not because of the amount of time but because of the amount of heat. My machine has the motor mounted externally. It gets hot.
 
#10
10shoe, are ERT-1000 and ERT-700 older generations of the same tool? Could you please post a picture of all three side by side? I only saw (and own) and ERT-300. I am very curious to see the other models.
 
Top