Swingweight rule

[Zverev]

Looking through my old personal notebook found this note I made for myself like 7-8 years ago:

1g at 3-9 adds 2g of swingweight
1g at 6 adds 0.5g of SW
10g in the handle adds 1g of SW
it works for any racket

I don't remember how I worked it out, there was probably some heavy math involved like addition and subtraction or even division or multiplication

 

[cellofaan]

Here's the heavy math

swingweight is measured about an axis 10cm from the but.
it's weight, in kg, times the distance to the axis squared.

12 is about 59cm from the 10cm axis. one gram adds 0.001*59^2=3.48

3&9 is about 45cm from the 10cm axis. one gram adds 0.001*45^2=2.03

6 is about 22.5cm from the 10cm axis. one gram adds 0.001*22.5^2=0.51

the butt of the racket, and the top of the handle, are both about 10cm from the 10cm axis. ten grams add 0.01*10^2=1



good cheat sheet!

 

[TimothyO]

cello,

Is there a way to calculate SW without going through the stop wtch process described by TWU? That process always struck me as prone to errrors sp I never tried it.

 

[cellofaan]

Not that I know of.
I don't know exactly how the swingweight is calculated from weight balance and swingtime, but they are all necessary. RDC machines also swing the racket to measure swingweight.

You could use a more precise way of measuring the time, like filming the swinging racket and counting the number of frames, and then divide that by the framerate to get the time in seconds. That should be accurate enough.
There's also an app for the iPhone you could use.



I remember travler and some other posters tried to come up with a way to calculate weight distribution without swinging the racket, but they didn't succeed.

 

[0d1n]

cello,

Is there a way to calculate SW without going through the stop wtch process described by TWU? That process always struck me as prone to errrors sp I never tried it.

The process is not error prone if you're careful when doing the measurements and do as many measurements as your time allows and then average them out.
After you get the SW number you can use the TWU tools to calculate your swing weight depending on where and how much mass you want to add ... without performing the measurements again...

 

[Steve Huff]

Any racket?? Or is that any standard length racket? Wouldn't a longer racket with wt added at 3&9 on a longer racket increase swingwt more than the same wt at 3&9 on a standard length frame? It might be a small difference, but length has to factor into the equation somehow.

 

[shadowshifter]

Any racket?? Or is that any standard length racket? Wouldn't a longer racket with wt added at 3&9 on a longer racket increase swingwt more than the same wt at 3&9 on a standard length frame? It might be a small difference, but length has to factor into the equation somehow.

yes, length is important because you're doing calculations based on how much weight is added and how far away that weight is from the point where swingweight is measured (10 cm from the butt end of the racket)

see cellofaan's post (#2) in this thread

 

[ChicagoJack]

Is there a way to calculate SW without going through the stop wtch process described by TWU? That process always struck me as prone to errrors sp I never tried it.

Hey Tim,

Since you probably already know the published SW of your stock frame, your inquiry (and most everybody elses here at TW) is most likely centered around how adding lead at various positions will affect SW. In addition to the cheat sheet provided by Zverev and cellofaan, and the free ustomization tool here at TW Link 1, the USRSA has a supremely awesome (member only) thingamajiggy called the Racquet Mass Mover Link 2 . The tool predicts how adding lead at up to 3 locations! (wow, that's racket geek/lead head porn) Will affect SW, Recoilweight, Overall mass, Balance, COP. It's effing awesome. I think there are trial memberships available for 1 month, about $10 if memory serves correct.

Note : I do understand the tool is an estimator. I'd really appreciate it if y'all restrained from getting all up in my grill about the most accurate methods and whatnot, thanks!

1 http://twu.tennis-warehouse.com/learning_center/customization.php

2 http://www.racquettech.com/top/tools_toc.html

See Screen Grab Below:

- Jack

 

[corners]

Hey Tim,

Since you probably already know the published SW of your stock frame, your inquiry (and most everybody elses here at TW) is most likely centered around how adding lead at various positions will affect SW. In addition to the cheat sheet provided by Zverev and cellofaan, and the free ustomization tool here at TW Link 1, the USRSA has a supremely awesome (member only) thingamajiggy called the Racquet Mass Mover Link 2 . The tool predicts how adding lead at up to 3 locations! (wow, that's racket geek/lead head porn) Will affect SW, Recoilweight, Overall mass, Balance, COP. It's effing awesome. I think there are trial memberships available for 1 month, about $10 if memory serves correct.

The USRSA Mass Mover is pretty cool, but this tool by TWU (both tools built by the same guy, BTW) allows you to add mass at five locations. It doesn't do COP or Recoil weight, but since that tool was made COP was found to be irrelevant (this is because once you grab the handle the COP moves into the throat of the racquet; the COP location is only relevant to impacts on freely suspended racquets). Recoil weight is a nice feature though.

The TWU also will give you Power Potential (ACOR) after adding mass, at both the center and near 3&9. It will also tell you what your new twistweight will be after adding mass near the perimeter of the head. It will also give you "plowthrough" before and after adding mass.

And unlike the Mass Mover, the TWU Reverse Engineering and Customization tool has you enter racquet length as the first input, so it's accurate for frames of any length, whereas the Mass Mover is only accurate for 27" frames.

 

[Larrysümmers]

Here's the heavy math

swingweight is measured about an axis 10cm from the but.
it's weight, in kg, times the distance to the axis squared.

12 is about 59cm from the 10cm axis. one gram adds 0.001*59^2=3.48

3&9 is about 45cm from the 10cm axis. one gram adds 0.001*45^2=2.03

6 is about 22.5cm from the 10cm axis. one gram adds 0.001*22.5^2=0.51

the butt of the racket, and the top of the handle, are both about 10cm from the 10cm axis. ten grams add 0.01*10^2=1



good cheat sheet!

hey thanks, this will surely come in handy

 

[TennisMaverick]

The USRSA Mass Mover is pretty cool, but this tool by TWU (both tools built by the same guy, BTW) allows you to add mass at five locations. It doesn't do COP or Recoil weight, but since that tool was made COP was found to be irrelevant (this is because once you grab the handle the COP moves into the throat of the racquet; the COP location is only relevant to impacts on freely suspended racquets). Recoil weight is a nice feature though.

The TWU also will give you Power Potential (ACOR) after adding mass, at both the center and near 3&9. It will also tell you what your new twistweight will be after adding mass near the perimeter of the head. It will also give you "plowthrough" before and after adding mass.

And unlike the Mass Mover, the TWU Reverse Engineering and Customization tool has you enter racquet length as the first input, so it's accurate for frames of any length, whereas the Mass Mover is only accurate for 27" frames.

Hey! Hope all is well in China!

Wouldn't it just be easier to give the stick to your stringer and put it in the diagnostic machine?

 

[ChicagoJack]

The USRSA Mass Mover is pretty cool, but this tool by TWU (both tools built by the same guy, BTW) allows you to add mass at five locations. It doesn't do COP or Recoil weight, but since that tool was made COP was found to be irrelevant (this is because once you grab the handle the COP moves into the throat of the racquet; the COP location is only relevant to impacts on freely suspended racquets). Recoil weight is a nice feature though.

The TWU also will give you Power Potential (ACOR) after adding mass, at both the center and near 3&9. It will also tell you what your new twistweight will be after adding mass near the perimeter of the head. It will also give you "plowthrough" before and after adding mass.

And unlike the Mass Mover, the TWU Reverse Engineering and Customization tool has you enter racquet length as the first input, so it's accurate for frames of any length, whereas the Mass Mover is only accurate for 27" frames.

corners - Hey big thanks! I really like many of the advantages of the tool you've linked, and free is always a good price. I'm still on the search for a formula or tool to figure out how lead modifications at various points AND changes in total length of a frame (together) alter swing weight.

 

[corners]

corners - Hey big thanks! I really like many of the advantages of the tool you've linked, and free is always a good price. I'm still on the search for a formula or tool to figure out how lead modifications at various points AND changes in total length of a frame (together) alter swing weight.

My pleasure.

Regarding changes in length, it's difficult to predict. But a good rule of thumb is that reducing length by 1/4" will reduce swingweight by about 12 units. This rule should apply to lengthening a frame also.

Predicting the new balance point is tricky because of the weight of the segment you've removed. Some frames are tailweighted, so removing material from the tail will result in the frame being more head-heavy than you would expect.

 

[ChicagoJack]

My pleasure.

Regarding changes in length, it's difficult to predict. But a good rule of thumb is that reducing length by 1/4" will reduce swingweight by about 12 units. This rule should apply to lengthening a frame also.

Predicting the new balance point is tricky because of the weight of the segment you've removed. Some frames are tailweighted, so removing material from the tail will result in the frame being more head-heavy than you would expect.

corners - Very cool! That rule of thumb you've provided is a good confirmation. I was using a bit of the Parallel Axis Theorum (kinda fancy for a knuckle head jock like myself) to estimate SW changes when lengthening a frame, and arriving at about the same estimates you suggest. Thanks again for your assistance. - Jack

TennisMaverick - The stringers I've used don't have the Bablolat diagnostic machine, If I could find one in my area I'd certainly give your suggestion a go. By the way I've played with many Volkls over the years and really enjoy reading your commentary here.

 

[corners]

corners - Very cool! That rule of thumb you've provided is a good confirmation. I was using a bit of the Parallel Axis Theorum (kinda fancy for a knuckle head jock like myself) to estimate SW changes when lengthening a frame, and arriving at about the same estimates you suggest. Thanks again for your assistance. - Jack

I'm glad my suggested figure is confirmed by your calculations. I remember reading that USRSA article about how to use the parallel axis theorem, backwards, to figure this stuff out years ago. Not easy to do, even with the calculators. I ended up just cutting and hoping for the best.

 

[corners]

Hey! Hope all is well in China!

Wouldn't it just be easier to give the stick to your stringer and put it in the diagnostic machine?

Hey Mav, I find the at-home method of swingweight calculation pretty easy - it takes ten minutes. And it's accurate. And you don't need to worry about whether the diagnostic machine at the shop has been calibrated recently or correctly.

And once I know the weight, balance and swingweight of the stock frame I can use the online calculators to get precise post-mod specs (if I want 'em) at every step of the way. Matching racquets is easy this way.

 

[TennisMaverick]

Hey Mav, I find the at-home method of swingweight calculation pretty easy - it takes ten minutes. And it's accurate. And you don't need to worry about whether the diagnostic machine at the shop has been calibrated recently or correctly.

And once I know the weight, balance and swingweight of the stock frame I can use the online calculators to get precise post-mod specs (if I want 'em) at every step of the way. Matching racquets is easy this way.

Cool. So I take it that you have made the comparison and if the machine is well oiled, that the calculator is close/accurate?

 

[olliess]

A calculated swingweight modification should be perfectly accurate if you measure the positions and the weights correctly, right?

 

[ChicagoJack]

A calculated swingweight modification should be perfectly accurate if you measure the positions and the weights correctly, right?

Hi Olliess

Yes. (with a huge asterisk) There are always going to be variables and a bit of uncertainty on each side of the measurement/calulations fence here. On the measurement side you have the issues of operator error (example: there are at least 8 different ways to simply clamp the frame in to the machine) and calibration. With the calculator tools, some of the numbers will vary slightly due to rounding errors. These rounding errors are so slight that it likely makes no noticeable difference in the actual feel or playability of the frame. When I get my frames measured I'd be happy to post my results here for comparison. I'm expecting slight differences, which I'd be fine with. But of course If there is a huge difference, then I'd be uncertain about both.

- Jack

 

[TennisMaverick]

TennisMaverick - The stringers I've used don't have the Bablolat diagnostic machine, If I could find one in my area I'd certainly give your suggestion a go. By the way I've played with many Volkls over the years and really enjoy reading your commentary here.

Chicago is so huge not to have someone with a Bab diagnostic machine!

Thanks for the Volkl props! I am stringing the new XV1 right now, and taking it out for a hit immediately after. Will report when I get back.