TW swing weight DIY

corners

Legend
Hey, I've used it several times. It's pretty quick and easy once you get the hang of it. 5-10 minutes, depending on how many timed runs you decide to do (the more the better).

I can't vouch for accuracy of the method, as I've never had opportunity to put my results up against an RDC machine.

However, I did notice a post from the Professor, from about a month ago, where he wrote that the TW machines needed recalibration and the pendulum/DIY method was used to help calibrate the RDC machines.

As long as you follow the protocol, I think the results are as accurate as you're gonna get.

I make sure to only let the racquet swing 2" in one direction, max - so the total swing distance is no greater than 4", but I try for 2".

I also time 20 swings instead of 10, and then divide the result by 2 for greater precision.

Last time I did it, I timed 6 sets of 20 swings, dropped the high and low outliers and then averaged the middle 4. I reckon the number I got out of that is pretty solid.

I did notice that the swingweight number spit out by the calculator is pretty sensitive to your balance point measurement. An error of 1mm in your balance measurement will result in a change in swingweight of 2.
 
Maybe if works fine, but I'm never going to use that method. Pencils, phone books, stopwatches, not gonna do it.

Out of curiosity, and perhaps boredom, I conducted an extensive internet search to find a formula for racket swingweight. I found sites that had sw calculators for fly rods and golf clubs but not much for tennis rackets. The racket stringers association supposedly has a sw calculator but one has to be a member to use it.

I found one site, racquetscience, that has a simple formula that supposedly closely approximates racket swingweight. Devised by a guy named Avi Wiezel who is an engineering prof at Arizona State Univ. I cannot vouch for the formula's accuracy but maybe one of the resident sw geeks can.

SW (kg.cm^2) = 10 x racket length in cm + racket weight in grams
- 690 (constant?) +5 x balance points (+ number for head heavy points, - number for head light points)


Swing Weight:

Example: A 3 points Head Heavy racquet 70 cm long racquet weighting 265 g has a swing weight of 10*70 + 265 - 690 + 5 * 3 = 290.

How to remember the number 690? Think of it this way: a 69 cm long balanced racket of 300g has the swing weight 300 kg·cm²



According to our friend Avi, my 408 gram, 11 points head light, customized PT280 would have a sw as follows:

10 x 69 + 408 -690 + 5 x -11 =

690 + 408 -690 + -55 =

408 -55 = 353

Sound right?

If one is using 27 inch (68.58cm rounded to 69cm) frames, it seems to me you could lose a couple of terms in Avi's equation and it would come out the same; the 690's cancel and the formula simplifies down to racket weight in grams - 5 x balance points (+ for hh balance points, and - for hl balance points)


Edit: Having compared Dr Wiezel's simplified SW formula to some real world actuals, it seems his formula doesn't hold water.

Anyone here know for certain what factors influence SW? Length, balance, total weight, all yes. How about head size?

If anyone knows a better formula that works in practice, post away.
 
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corners

Legend
Maybe if works fine, but I'm never going to use that method. Pencils, phone books, stopwatches, not gonna do it. ;o)


Edit: Having compared Dr Wiezel's simplified SW formula to some real world actuals, it seems his formula doesn't hold water.

Anyone here know for certain what factors influence SW? Length, balance, total weight, all yes. How about head size?

If anyone knows a better formula that works in practice, post away.


2 pencils, phone book, stopwatch (online stopwatch), ten minutes.
 

Bud

Bionic Poster
Hey, I've used it several times. It's pretty quick and easy once you get the hang of it. 5-10 minutes, depending on how many timed runs you decide to do (the more the better).

I can't vouch for accuracy of the method, as I've never had opportunity to put my results up against an RDC machine.

However, I did notice a post from the Professor, from about a month ago, where he wrote that the TW machines needed recalibration and the pendulum/DIY method was used to help calibrate the RDC machines.

As long as you follow the protocol, I think the results are as accurate as you're gonna get.

I make sure to only let the racquet swing 2" in one direction, max - so the total swing distance is no greater than 4", but I try for 2".

I also time 20 swings instead of 10, and then divide the result by 2 for greater precision.

Last time I did it, I timed 6 sets of 20 swings, dropped the high and low outliers and then averaged the middle 4. I reckon the number I got out of that is pretty solid.

I did notice that the swingweight number spit out by the calculator is pretty sensitive to your balance point measurement. An error of 1mm in your balance measurement will result in a change in swingweight of 2.

I like your scientific method/approach.

**
Can you post a set of your results prior to dropping high/low? <---

Thanks!
 

sunnyIce

Semi-Pro
Hey, I've used it several times. It's pretty quick and easy once you get the hang of it. 5-10 minutes, depending on how many timed runs you decide to do (the more the better).

I can't vouch for accuracy of the method, as I've never had opportunity to put my results up against an RDC machine.

However, I did notice a post from the Professor, from about a month ago, where he wrote that the TW machines needed recalibration and the pendulum/DIY method was used to help calibrate the RDC machines.

As long as you follow the protocol, I think the results are as accurate as you're gonna get.

I make sure to only let the racquet swing 2" in one direction, max - so the total swing distance is no greater than 4", but I try for 2".

I also time 20 swings instead of 10, and then divide the result by 2 for greater precision.

Last time I did it, I timed 6 sets of 20 swings, dropped the high and low outliers and then averaged the middle 4. I reckon the number I got out of that is pretty solid.

I did notice that the swingweight number spit out by the calculator is pretty sensitive to your balance point measurement. An error of 1mm in your balance measurement will result in a change in swingweight of 2.

corners i do the exact same thing and it works quite well. but usually i find 3 trials of 20 swings is enough. the most anal i get is with the balance measurement. i go decimal points on this one.
 

sunnyIce

Semi-Pro
Maybe if works fine, but I'm never going to use that method. Pencils, phone books, stopwatches, not gonna do it. ;o)

Out of curiosity, and perhaps boredom, I conducted an extensive internet search to find a formula for racket swingweight. I found sites that had sw calculators for fly rods and golf clubs but not much for tennis rackets. The racket stringers association supposedly has a sw calculator but one has to be a member to use it.

I found one site, racquetscience, that has a simple formula that supposedly closely approximates racket swingweight. Devised by a guy named Avi Wiezel who is an engineering prof at Arizona State Univ. I cannot vouch for the formula's accuracy but maybe one of the resident sw geeks can.

SW (kg.cm^2) = 10 x racket length in cm + racket weight in grams
- 690 (constant?) +5 x balance points (+ number for head heavy points, - number for head light points)


Swing Weight:

Example: A 3 points Head Heavy racquet 70 cm long racquet weighting 265 g has a swing weight of 10*70 + 265 - 690 + 5 * 3 = 290.

How to remember the number 690? Think of it this way: a 69 cm long balanced racket of 300g has the swing weight 300 kg·cm²



According to our friend Avi, my 408 gram, 11 points head light, customized PT280 would have a sw as follows:

10 x 69 + 408 -690 + 5 x -11 =

690 + 408 -690 + -55 =

408 -55 = 353

Sound right?

If one is using 27 inch (68.58cm rounded to 69cm) frames, it seems to me you could lose a couple of terms in Avi's equation and it would come out the same; the 690's cancel and the formula simplifies down to racket weight in grams - 5 x balance points (+ for hh balance points, and - for hl balance points)


Edit: Having compared Dr Wiezel's simplified SW formula to some real world actuals, it seems his formula doesn't hold water.

Anyone here know for certain what factors influence SW? Length, balance, total weight, all yes. How about head size?

If anyone knows a better formula that works in practice, post away.

dude..this absolutely does not seem to work
 

OrangePower

Legend
Maybe if works fine, but I'm never going to use that method. Pencils, phone books, stopwatches, not gonna do it. ;o)

Out of curiosity, and perhaps boredom, I conducted an extensive internet search to find a formula for racket swingweight. I found sites that had sw calculators for fly rods and golf clubs but not much for tennis rackets. The racket stringers association supposedly has a sw calculator but one has to be a member to use it.

I found one site, racquetscience, that has a simple formula that supposedly closely approximates racket swingweight. Devised by a guy named Avi Wiezel who is an engineering prof at Arizona State Univ. I cannot vouch for the formula's accuracy but maybe one of the resident sw geeks can.

SW (kg.cm^2) = 10 x racket length in cm + racket weight in grams
- 690 (constant?) +5 x balance points (+ number for head heavy points, - number for head light points)


Swing Weight:

Example: A 3 points Head Heavy racquet 70 cm long racquet weighting 265 g has a swing weight of 10*70 + 265 - 690 + 5 * 3 = 290.

How to remember the number 690? Think of it this way: a 69 cm long balanced racket of 300g has the swing weight 300 kg·cm²



According to our friend Avi, my 408 gram, 11 points head light, customized PT280 would have a sw as follows:

10 x 69 + 408 -690 + 5 x -11 =

690 + 408 -690 + -55 =

408 -55 = 353

Sound right?

If one is using 27 inch (68.58cm rounded to 69cm) frames, it seems to me you could lose a couple of terms in Avi's equation and it would come out the same; the 690's cancel and the formula simplifies down to racket weight in grams - 5 x balance points (+ for hh balance points, and - for hl balance points)


Edit: Having compared Dr Wiezel's simplified SW formula to some real world actuals, it seems his formula doesn't hold water.

Anyone here know for certain what factors influence SW? Length, balance, total weight, all yes. How about head size?

If anyone knows a better formula that works in practice, post away.

It's just not possible to devise an accurate mathematical formula for swingweight with easily-measured variables as input. This is because absolute weight and balance don't specify exactly where mass is located.

As an example, consider a standard length racquet that is 12oz and exactly evenly balanced:

It could have 5oz concentrated at 12 o'clock on the head, another 5oz right at the buttcap, 1oz evenly distributed over the rest of the lower half of the racquet, and 1oz evenly distributed over the rest of the upper half of the racquet. This would result in a very very high swingweight.

You can picture it looking like this in terms of weight distribution: XXX--------------XXX

Alternatively, it could have 10oz concentrated right in the middle of the racquet, and then 1oz evenly distributed over the rest of the lower half of the racquet, and 1oz evenly distributed over the rest of the upper half of the racquet. This would have a much lower swingweight.

You can picture it looking like this in terms of weight distribution: -------XXXXXX-------

Fortunately it's relatively easy to determine swingweight by observing and measuring the rotational momuntum of the racquet, which is what RDC machines do and effectively what the TW method does.
 

corners

Legend
Can you post a set of your results prior to dropping high/low? <---

Thanks!

Sure:

US K90 strung with Cyberflash 17 mains/Cyberblue 16 crosses

Timed trials (20 swings/2):

1) 27.32/2 = 13.66 (high outlier - dropped)
2) 27.18/2 = 13.59
3) 27.19/2 = 13.595
4) 27.13/2 = 13.565
5) 27.09/2 = 13.545 (low outlier - dropped)
6) 27.12/2 = 13.560

Average of 2,3,4,6 = 13.5775 seconds for 10 swings

Info entered into TW University DIY Swingweight calculator:

Weight: 360 grams
Balanced point: 31.5 centimeters
Distance from handle to hang string (hung from 2nd cross): 62.5 centimeters
Time for 10 swings: 13.5775 seconds

Swingweight given by calculator: 331



The method is really simple, so for those having trouble making it work - most likely you're making a 'doh!' error somewhere. Check your work, (and make sure your pencils can't move on the table).
 
The morning after my post above, I emailed the good Dr. Wiezel and informed him that his simplified swingweight formula doesn't work but he hasn't replied.

I would think you could probably come out with a formula that approximates swing weight given it is a function of weight, balance, head size and length but it would never be spot on like a RDC. Since there is an abundance of data of actual rackets, one could probably derive a workable formula from the data that would work with most rackets.

Interestingly enough, his research indicates most people can't tell a difference in racket weight until the difference exceeds 10 grams. (I assume the balance is unchanged between the rackets.)

Update: He did eventually reply to my email and stated the his model assumes equal mass distribution throughout the racket. That is a false assumption and renders his model inaccurate.
 
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djinni999

New User
The morning after my post above, I emailed the good Dr. Wiezel and informed him that his simplified swingweight formula doesn't work but he hasn't replied.

I would think you could probably come out with a formula that approximates swing weight given it is a function of weight, balance, head size and length but it would never be spot on like a RDC. Since there is an abundance of data of actual rackets, one could probably derive a workable formula from the data that would work with most rackets.

Interestingly enough, his research indicates most people can't tell a difference in racket weight until the difference exceeds 10 grams. (I assume the balance is unchanged between the rackets.)

Update: He did eventually reply to my email and stated the his model assumes equal mass distribution throughout the racket. That is a false assumption and renders his model inaccurate.

so, if we were to know the typical mass distribution, say for players type frames as opposed to the OS, game improvement or granpa sticks, then the above formula could be tweaked to produce results consistent enough with actual RDC data regarding this type of frame.
 
D

Deleted member 25923

Guest
When I try to measure balance, I find it difficult since I have a large grip and thin beam.
 
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