Manually Measuring Swingweight

Curtennis

Hall of Fame
So I’ve been trying to get this right and it’s just over my head. I give up.

edit: quick change of heart. I gave up trying to get it perfectly level and each racquet perfectly aligned. I think it’s good enough and the machine is absolutely dead nuts repeatable in terms of the values it spits out.
 
Last edited:

Curtennis

Hall of Fame
So I’ve been trying to get this right and it’s just over my head. I give up.

edit: quick change of heart. I gave up trying to get it perfectly level and each racquet perfectly aligned. I think it’s good enough and the machine is absolutely dead nuts repeatable in terms of the values it spits out.
So i was being a huge drama queen. got home from a business trip at 10 pm and was excited to open my new toy. It took a little while to get set up and I harped on trying to get the device perfectly level. I was exhausted and took out my anger on the machine.
Fast forward to this morning, i double checked my calibration and got to work.

EYE OPENING. only way to put it. I got all sorts of measurements for my army of racquets that I never would have guessed.

For one thing, some of my RFs were swing weight of mid 320's. I had bought into all the internet hype that they're too heavy and already sort of moved away from them. Maybe they are "supposed" to be, but mine aren't. Yet somehow I convinced myself that mine were too heavy. Sort of like tricking someone into drinking $10 wine telling them it's $100 wine... i just wanted to believe it and I don't know any better i guess...

my two Gravity pros had a 10 pt swing weight difference. I had no clue on that either. one was around 323 the other 333.

my 3 pure aeros were sort of as expected. That one i did good on my mental math, except the heaviest SW one was actually 334.7 which was way higher than any of my RFs, LOL! I never would have guessed that. I knew it was my heaviest Aero, but danggg. In fact even my medium swing weight Pure Aero packed more SW than any of my RFs (i do add tungsten to the PA tho...)

I know this is sort of scatter brained, but i just wanted to share how amazing it is to be able to tell the swing weight. I'm not quite sure it's going to improve my game, but it may have me stop buying racquets unnecessarily. Now that I know what I have and what I like, I don't need to try new things as much. I can throw some tungsten here and there and call it a day.
However i mainly do play with my 3 Pure Aeros (swing weight 323 stock, 328 tungsten, 334 tungsten) and I doubt i'm going to change a thing about them. So is this a valuable tool or not? I guess that depends on what you went into purchasing the BW, or any swing weight machine, for in the first place.
 

PrinceYonex

Semi-Pro
So i was being a huge drama queen. got home from a business trip at 10 pm and was excited to open my new toy. It took a little while to get set up and I harped on trying to get the device perfectly level. I was exhausted and took out my anger on the machine.
Fast forward to this morning, i double checked my calibration and got to work.

EYE OPENING. only way to put it. I got all sorts of measurements for my army of racquets that I never would have guessed.

For one thing, some of my RFs were swing weight of mid 320's. I had bought into all the internet hype that they're too heavy and already sort of moved away from them. Maybe they are "supposed" to be, but mine aren't. Yet somehow I convinced myself that mine were too heavy. Sort of like tricking someone into drinking $10 wine telling them it's $100 wine... i just wanted to believe it and I don't know any better i guess...

my two Gravity pros had a 10 pt swing weight difference. I had no clue on that either. one was around 323 the other 333.

my 3 pure aeros were sort of as expected. That one i did good on my mental math, except the heaviest SW one was actually 334.7 which was way higher than any of my RFs, LOL! I never would have guessed that. I knew it was my heaviest Aero, but danggg. In fact even my medium swing weight Pure Aero packed more SW than any of my RFs (i do add tungsten to the PA tho...)

I know this is sort of scatter brained, but i just wanted to share how amazing it is to be able to tell the swing weight. I'm not quite sure it's going to improve my game, but it may have me stop buying racquets unnecessarily. Now that I know what I have and what I like, I don't need to try new things as much. I can throw some tungsten here and there and call it a day.
However i mainly do play with my 3 Pure Aeros (swing weight 323 stock, 328 tungsten, 334 tungsten) and I doubt i'm going to change a thing about them. So is this a valuable tool or not? I guess that depends on what you went into purchasing the BW, or any swing weight machine, for in the first place.
Before measuring the swingweights, could you tell that the 3 Aeros were pretty different in terms of swingweight? 323 to 334 is pretty big difference. (also with the Gravity's, since you have the same SW difference there also.) In terms of whether the tool helps, hopefully it alerts you to what sort of swingweight you prefer, or what aspects of your game shine with a low 320s SW and which seem to come to the fore at mid 330s.
 

Curtennis

Hall of Fame
Before measuring the swingweights, could you tell that the 3 Aeros were pretty different in terms of swingweight? 323 to 334 is pretty big difference. (also with the Gravity's, since you have the same SW difference there also.) In terms of whether the tool helps, hopefully it alerts you to what sort of swingweight you prefer, or what aspects of your game shine with a low 320s SW and which seem to come to the fore at mid 330s.
Good question.
I knew my 334 SW aero was much heavier than the others. However I didn’t know my 323 was 5 pts lighter than the 328. I sort of thought they were about the same. The real eye opener was that my heaviest aero was way more SW than any of my RFs. I would have told you no freaking way if I didn’t do it with my own two hands. I doubt it’s because of any real feeling I had, 100% just mental.

unfortunately I don’t play the gravity’s enough to really have guesstimated Any of them.

I do have a current gen prestige pro that came in at 331.5. I thought it was pretty easy to swing. I probably would have just guessed 325ish.
 

derick232

Rookie
Question, I'm trying to create my own calibration rod for my own SW machine. I calculated it out to be 97.28kg.cm^2 I followed the equations from this article https://core.ac.uk/download/pdf/42539001.pdf
Can anyone verify my results and see if I made any mistakes? My dimensions are all very accurate, Length = 45.976cm, mass = 0.28042kg, ID = 1.1734cm, OD = 2.6249cm. After calculating the initial MOI I used the parallel axis formula to transfer to 10cm from the base.

Assuming this is correct, my setup has a few moving parts that would obviously effect the actual result and add some built in SW. Can those be determined simply by using the swingTool and calculating the SW of my calibration rod and subtracting the theoretical value from that leaving the built in SW from the fixture itself?
 

Irvin

Talk Tennis Guru
@derick232 the inertia of a rod at COM is ml^2/12 (0.28042*45.976*45.976/12) and the center of your rod is 22.988. PAT for inertia at 10 cm from the end is mr^2 (.28042*12.988*12.988) I believe your calculations are off I get 53.33777 kgcm^2
 

derick232

Rookie
@derick232 the inertia of a rod at COM is ml^2/12 (0.28042*45.976*45.976/12) and the center of your rod is 22.988. PAT for inertia at 10 cm from the end is mr^2 (.28042*12.988*12.988) I believe your calculations are off I get 53.33777 kgcm^2
Just ran your numbers and got the same answer I did as before. Don't you have to add the MOI at COM to the inertia at 10cm?
I1 at COM = (.28042kg * 45.976cm^2)/12 = 49.395 kg.cm^2
I2 at 10cm = I1 + .28042kg*12.988cm^2 = 96.69 kg.cm^2

Is that not right?
 

jmnk

Hall of Fame
Just ran your numbers and got the same answer I did as before. Don't you have to add the MOI at COM to the inertia at 10cm?
I1 at COM = (.28042kg * 45.976cm^2)/12 = 49.395 kg.cm^2
I2 at 10cm = I1 + .28042kg*12.988cm^2 = 96.69 kg.cm^2

Is that not right?
One thing I've learnt - there's a really good chance someone already did it, whatever 'it' is :). In this case there's this very nice Wolfram demonstration that will calculate MOI around an arbitrary axis for a given cylinder: https://demonstrations.wolfram.com/MomentOfInertiaOfACylinderAboutItsPerpendicularAxis/ Sure you can calculate it yourself too - but why would you have to.....
 

jmnk

Hall of Fame
Question, I'm trying to create my own calibration rod for my own SW machine. I calculated it out to be 97.28kg.cm^2 I followed the equations from this article https://core.ac.uk/download/pdf/42539001.pdf
Can anyone verify my results and see if I made any mistakes? My dimensions are all very accurate, Length = 45.976cm, mass = 0.28042kg, ID = 1.1734cm, OD = 2.6249cm. After calculating the initial MOI I used the parallel axis formula to transfer to 10cm from the base.

Assuming this is correct, my setup has a few moving parts that would obviously effect the actual result and add some built in SW. Can those be determined simply by using the swingTool and calculating the SW of my calibration rod and subtracting the theoretical value from that leaving the built in SW from the fixture itself?
It's pretty accurate. The exact value given your measurements is 97.2789 kg*cm^2
 

jmnk

Hall of Fame
Any clue on the assumption that the added swingweight of the fixture would be the difference between the measured SW and calculated?
I'm not sure if I follow what you mean here. The swingweight of an object when measured on RDC-like machine is a function of oscillation period. In idealized theoretical scenario there are two parameters needed for that function: spring constant, and MOI of the device itself. When you use a calibration rods to calibrate your device you end up finding what that spring constant and MOI of the device are.

Then once you measure the SW of a given object on such device the SW you will get based on the oscillation period is the SW of an object + the device. Then depending on how sophisticated user interface of your device is it can display just that - and then the user has to deduct SW of the device itself. Or the device can do it for the user - which is what RDC or SW1 device does.
 

Irvin

Talk Tennis Guru
Any clue on the assumption that the added swingweight of the fixture would be the difference between the measured SW and calculated?
What fixture are you talking about? Does you SW machine have a horizontal or vertical pivot axis?
 

derick232

Rookie
What fixture are you talking about? Does you SW machine have a horizontal or vertical pivot axis?
It's my own device, quite simple and with some inspiration of the SW1. 3D printing really is an amazing tool. At the moment, the axis could go either way. If I can figure out a way to better mount the spring then the axis of rotation will be vertical, till then I will just let it swing with the force of gravity and the axis will be horizontal, being measured by the swing tool
 

derick232

Rookie
Then once you measure the SW of a given object on such device the SW you will get based on the oscillation period is the SW of an object + the device. Then depending on how sophisticated user interface of your device is it can display just that - and then the user has to deduct SW of the device itself. Or the device can do it for the user - which is what RDC or SW1 device does.
This is exactly what I'm asking about, the SW of whatever is holding the racket (fixture, device, whatever you call it) is simply the measured SW minus the calculated SW of the calibration rod. That can then be deducted from the measured SW of a racket to get the actual SW.
 

Irvin

Talk Tennis Guru
This is exactly what I'm asking about, the SW of whatever is holding the racket (fixture, device, whatever you call it) is simply the measured SW minus the calculated SW of the calibration rod. That can then be deducted from the measured SW of a racket to get the actual SW.
Then your specs has a great deal of influence on the SW. any error in the hang point, weight, balance, or friction loss in the pivot is compounded in the final result.
 

ezekiel114

Semi-Pro
@bfroxen
just calibrated and used your device. excellent work! it took me a little bit to level the device but calibrating was pretty straightforward. i appreciate your efforts and love having this extra piece of information. no more matching service for me!
 

bfroxen

Rookie
@ezekiel114 Glad you like it!

Leveling is harder to explain than to actually do. I created a process that I could explain, but basically, you just want to adjust the feet so that the rod doesn't move too quickly when you release it at any position. Calibration will compensate for minor leveling error. With "perfect" leveling, you can calibrate, move the SW1, re-level in the new location, and use it without recalibrating, but it's usually easier to just recalibrate.

I just ran a quick experiment. I calibrated the device with nearly perfect leveling and measured a racquet at 324.82 kg·cm². Then, I raised the rear foot by two full turns (1 mm) and recalibrated. I measured the same racquet (in the same orientation) at 324.99 kg·cm². I expect that the response of the system becomes more nonlinear as it varies from level, so the error would likely be greater if the racquet were further from the larger calibration value (291.2 kg·cm² in my case). But in any case, two full turns off level is quite a bit, and the results weren't much different after recalibration.
 

PrinceYonex

Semi-Pro
There's a lot of discussion about the difference in swingweight between unstrung and strung frames, and the difference that various types and gauges of string make for swingweight. But what about twistweight?

I finally got around to measuring the swingweight and twistweight on an unstrung frame -- my Yonex VCP 310 (2018, blue edition, I've got 3 grams at 10/2). The unstrung SW is 293.8. The unstrung TW is 12.1.
The strung TW (with gut/poly hybrid) was 13.

Have people been measuring twistweights with different string types, noticing any significant differences in value?
 

esm

Legend
Is it possible to have two “matched” racquets with same weight, balance, SW and exact string setup, but possibly with different twist weight, enough to notice?
 

StanAO14

Semi-Pro
Is it possible to have two “matched” racquets with same weight, balance, SW and exact string setup, but possibly with different twist weight, enough to notice?
Probably yes - when racquet 1 is leaded at 3&9 and racquet 2 is not (or something like that). I noticed that recently trying to match racquets and I found the racquet with lead at 3/9 to be somewhat slower despite having the same weight and balance and swingweight ( at least according to the TW matching tool). No I have put the same amount of lead at 6 and 12 and removed the 3/9 and that feels better…
 
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esm

Legend
Probably yes - when racquet 1 is leaded at 3&9 and racquet 2 is not (or something like that). I noticed that recently trying to match racquets and I found the racquet with lead at 3/9 to be somewhat slower despite having the same weight and balance and swingweight ( at least according to the TW matching tool). No I have put the same amount of lead at 6 and 12 and removed the 3/9 and that feels better…
Yes of course, good point. The lead tape placements can contribute to that. I will have to check a few of them out once my SW1 arrives for some experiments. Lol
 

Irvin

Talk Tennis Guru
Is it possible to have two “matched” racquets with same weight, balance, SW and exact string setup, but possibly with different twist weight, enough to notice?
Most ass-u-me the centerline is the center of mass for TW in a tennis racket. The lowest inertia is always found at the center of mass. If the COM is actually off and you measure TW relative you will get a higher than actual reading.
 

esm

Legend
Most ass-u-me the centerline is the center of mass for TW in a tennis racket. The lowest inertia is always found at the center of mass. If the COM is actually off and you measure TW relative you will get a higher than actual reading.
Umm… not sure who are you calling an ass and what is all that in lain English? (Genuine question, thanks)
 

Irvin

Talk Tennis Guru
Umm… not sure who are you calling an ass and what is all that in lain English? (Genuine question, thanks)
Not calling anyone an ass. A saying in the US is when you assume you make as ass out of you and me.

If the COM is not on the centerline and you assume it is you will have an inaccurate reading if you pivot is on the centerline.
 

SozzR

New User
I'm just going to ask hope someone can clarify for me. All the swingweight numbers floating around the Internet are strung swingweight numbers?
 

HitMoreBHs

Professional
For retail racquets, anything over 300 should be a strung swing-weight. There aren't any off-the-shelf racquets that come with 310 320 330 unstrung swing-weights.
This is a good generalisation for 99% of all retail racquets. Crazily, the new Auxetic Prestige Tour seems to be around 340 swingweight strung, which potentially means 310 unstrung! Primed for the USA market, no doubt!
 
I found this website to measure SW with weight, length, and balance point .
-Swingweight Tuner -

I tried it with my racket and compared it with TWU SW calculator method. The result was really close.
Has anyone tried it? Is it accurate ?
 

Irvin

Talk Tennis Guru
I found this website to measure SW with weight, length, and balance point .
-Swingweight Tuner -

I tried it with my racket and compared it with TWU SW calculator method. The result was really close.
Has anyone tried it? Is it accurate ?
You got lucky it is impossible.

EDIT: Go to a couple of rackets in TW and input the specs.
 
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Irvin

Talk Tennis Guru
The Babolat Pure Aero (first racket on TW) specs are 32.99 cm balance, 318 g, and SW of 324. If you use that SW calculator it should be 310 SW.

The first Wilson racket is a Blade. It’s not close either.

The first Head racket a Prestige is only 4 points off, even a blind squirrel finds an acorn every once in a while.
 

gold325

Hall of Fame
I found this website to measure SW with weight, length, and balance point .
-Swingweight Tuner -

I tried it with my racket and compared it with TWU SW calculator method. The result was really close.
Has anyone tried it? Is it accurate ?
Not all that. Sometimes even guesses work especially when there is no real swingweight machine to judge against.

Most racquets the swingweight is close to total weight.. most of my 300SW racquets are just about 300 grams and my 350SW racquets are just about 350 grams. It is a good guess but definitely not accurate.

I have used the TW method with a 120fps (if I had 240 fps I would use that) phone camera to accurately capture the time for 10 and 20 swings. I paid to have a racquet swing weighted as well and was very accurate within 1-3 points of the number I calculated using the TW method. So I am a fan of this method.

I would buy the Briffidi SW1 if it worked with Android.

I now I have many frames at the same specs and despite being very different racquets I am able to switch between them within a few minutes of rallies due to weight, swingweight and balance being very similar.
 
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RobS

Rookie
I found this website to measure SW with weight, length, and balance point .
-Swingweight Tuner -

I tried it with my racket and compared it with TWU SW calculator method. The result was really close.
Has anyone tried it? Is it accurate ?
I've used it but with the head and bottom weight calculations and found it to be accurate on a couple racquets I also measured on a Babolat RDC. Perhaps it was the luck of the draw but regardless of how it compares to an RDC it's a perfectly effective tool when you have 2 or more racquet that you are trying to match up at home.
 

bfroxen

Rookie
it's a perfectly effective tool when you have 2 or more racquet that you are trying to match up at home.
No, it is not effective AT ALL in determining swingweight. It adds nothing beyond just matching mass and balance point. Look at the inputs: mass and balance. Measuring the head weight and butt weight is just another way of determining balance point. Stringway should be embarrassed by it and take it down.
 

RobS

Rookie
No, it is not effective AT ALL in determining swingweight. It adds nothing beyond just matching mass and balance point. Look at the inputs: mass and balance. Measuring the head weight and butt weight is just another way of determining balance point. Stringway should be embarrassed by it and take it down.
I've never used the mass and balance inputs. I have however matched many racquets for swingweight using the head and butt weight calculations, a couple confirmed by RDC and the others with the swingtool app. I wouldn't necessarily use it on a single racquet to hit an arbitrary swingweight value but have no problem using it to match up a pair of racquets.
 

bfroxen

Rookie
I've never used the mass and balance inputs. I have however matched many racquets for swingweight using the head and butt weight calculations, a couple confirmed by RDC and the others with the swingtool app. I wouldn't necessarily use it on a single racquet to hit an arbitrary swingweight value but have no problem using it to match up a pair of racquets.
It doesn't matter whether you use the mass and balance input or the head and butt weight inputs. They're equivalent. Given a racquet with known mass, length, and balance point, one can easily calculate the head and butt weights.

If you're matching the head and butt weights, you're only matching mass and balance. The swingweight may be closer or further from matching. There's no way to know without a dynamic measurement.
 
FWIW, the specs published by TW aren’t very internally consistent. They measure in oz, not grams, so the masses always vary in steps of 3 grams (~0.1 oz). So there’s potentially a 6 gram spread from say a 9.85 oz to 10.04 oz on a fickle machine that only reports to one decimal place.

Throw in the ambiguity of points HL which is *almost* 1/3 of a cm but then I wonder why the balances are usually smack on a whole number (32.0) or a half (32.5) when they do report cm. ???

There’s just not a lot of precision going on.
 

gold325

Hall of Fame
FWIW, the specs published by TW aren’t very internally consistent. They measure in oz, not grams, so the masses always vary in steps of 3 grams (~0.1 oz). So there’s potentially a 6 gram spread from say a 9.85 oz to 10.04 oz on a fickle machine that only reports to one decimal place.

Throw in the ambiguity of points HL which is *almost* 1/3 of a cm but then I wonder why the balances are usually smack on a whole number (32.0) or a half (32.5) when they do report cm. ???

There’s just not a lot of precision going on.
HL / Balance is always difficult to read on the balance board assuming they use a regular balance board unless there is one that gives a special digital reading of Balance.

Weight could be easily more accurate than they report since it is digital scale.

Swingweight could also be messed up slightly depending on how the butt is clamped in I supposed.

I think like anything precision can be overdone. I have bought 5 Price rackets and all have been within 1-2 grams of weight and 1HL of Balance BUT 10-15 swingweight points lighter which ends up working in my favor as swingweight can always be added easily but never removed (Wilson and Head...ahem ahem)

Before self testing I assumed 330-335 was my preferred SW based on TW Racquetfinder.

It was only much later I found out that all the racquets I liked were actually 315-320 since my Princes were under spec with regard to Swingweight.

So their precision or lack of precision doesn't matter in reality. Their MRT service is more accurate and I will never ever buy a new racquet without knowing specs first. 10-15 point swingweight (when excess) is the difference between a killer racquet and a wall ornament atleast for me.
 
Before self testing I assumed 330-335 was my preferred SW based on TW Racquetfinder.

It was only much later I found out that all the racquets I liked were actually 315-320 since my Princes were under spec with regard to Swingweight.
I was in the exact same position. Underspec PStrike 18x20 shoulda been 334 according to TW. Bought a Blade v7 18x20 to get a softer flex at the same swingweight, 334. Got the Blade and it was heavy. Turned out my PS was 325. Many other racquets since are way under TW’s numbers from Prince to Head to Wilson. I take them with a pound of salt now.
 

StanAO14

Semi-Pro
I received my sw 1 / Briffidi last Tuesday. It took about 4 to 5 weeks from ordering to delivery in the Netherlands. Easy to install the app and the machine with calibration. Instruction video really clear. Love to have the opportunity to measure SW now at a great price : ) thank you bfroxen!
 
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