# Why is swingweight calculated 4" from the buttcap?

Discussion in 'Racquets' started by FH2FH, Sep 3, 2009.

?

## The reason is...

Poll closed Oct 3, 2009.

37.5%

25.0%

37.5%
1. ### FH2FHProfessional

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Obviously there was a reason for this. Seems like it would make more sense to calculate it closer to where the racquet actually pivots, say closer to the buttcap or the center of the hand.

How is swingweight calculated for a golf club since they're all different lengths? Are longer racquets calculated still at 4"?

I can like technical stuff, but don't ask me to do formulas. A general statement or two will be just fine.

2. ### CHOcoboProfessional

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i never heard of this 4" from the buttcap thing. the pivot method makes more sense, much more.

3. ### bertrevertHall of Fame

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I've only done the swing method as outlined here at TW, no access to a RDC machine

4. ### cornersLegend

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They needed a standard location. People used to, and some still do, hold the handle for the forehand so that the center of the axis of rotation about the hand (hold racquet and waggle it back and forth), which is roughly between the ring and middle fingers, is approximately 4" from the butt.

There you go.

Now that we have a standard location we can calculate the effective swingweight when holding the handle in any other position, up or down. We can also calculate the swingweight upside down, like if you swing it from the tip. And, you can calculate the swingweight for locations in the body, like the wrist and elbow joints.

Most usefully, a standard location allows us to compare the swingweights of different racquets so we have a better idea of what we like and what we might like to buy.

5. ### FH2FHProfessional

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If the racquet pivots at the 4" point for most strokes they aren't being executed properly. That's why this makes no sense to me.

Having a standard makes sense. I just don't get why 4" is the standard. A 290 gram, head heavy racquet can have the same swingweight as 350 gram head light racquet, and how they FEEL when they're swung is much different that what swingweight suggests. What happens to the ball, and the players body, is also different.

Maybe I'll come up with a way to gauge something like "hit weight" which uses a pivot point closer to the buttcap (or beyond?) and measures "plow through" weight by striking an object at one or more points on the stringbed.

Obviously weight is a good thing here. I guess that's my ultimate point. The measurement of swingweight contradicts that and I feel its misleading. A "plow through" measurement would be more useful in my opinion.

6. ### FH2FHProfessional

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^^^ What I mean by strokes not being executed properly...

Think of the racquet as a lever. Does it make sense for that lever to be longer or shorter? To hit the ball with greater authority it makes sense to lengthen the lever. Only in the case of a volley is the lever shortened.

Therefore, pivoting the racquet further from the point of contact increases velocity WHEN the length isn't so great that the swing slows down.

Hope this makes sense.

7. ### ryushen21Hall of Fame

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This may be a dumb question but how exactly do you calculate swingweight? I've been wondering about this since I have customized my racquets.

8. ### ollingerLegend

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Perhaps it was some French guy, as I believe the standard is actually 10 cm., which is very close to 4 inches (inch = 2.54 cm.).

9. ### cornersLegend

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A plowthrough measurement has been made. Check out TW university for their plowthrough measurements.

You don't need to come up with 'hit weight' either, hitting weight is easily calculated if you know weight, swingweight and balance. You can calculate hitting weight for any point on the racquet face if you also know the twistweight. Check out USRSA calculators for this.

Hitting weight is roughly proportional to racquet inherent power, or apparent coefficient of restitution (ACOR). Other things figure into this, like stiffness, headsize, strings, etc. But hittingweight is by far the largest factor.

In turn, hittingweight is roughly proportional to swingweight. As I mentioned in my previous post, you can calculate swingweight for any place on the racquet if you know the reference swingweight, which is calculated at 4" from the butt. So if you hold your racquet at the bottom of the handle, like many modern players, you can use the USRSA parallel axis calculator to find the actual swingweight for that location - I recommend entering "-5cm" in this case.

You don't need to invent things for this; this is racquet science 101. You can educate yourself on TW University, where there are loads of good articles; at racquettech. com, where you'll find the calculators and other good articles; and you can ask questions on forums instead of posting inane polls.

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11. ### FH2FHProfessional

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Yeah, the poll was inane. I'm just trying to learn something though, not bicker with a TW snob. Just because you are knowledgable about this doesn't mean everyone else is, or have the time to study at TWU. I appreciate your input but the attitude isn't necessary.

A measurement as common as swingweight is obviously lacking. That's really the point of this thread. You say it can be measured at different points, but then it isn't really "swingwight", as defined at 4" anymore is it?

I will go back to TWU and look at some of the information. I checked it a year or two ago and eventually decided to just "play" tennis, not read about this stuff. Like I said, I would like a quick way to do this stuff at home instead of getting online and punching numbers. [How accurate are they and how useful is the measurement anyway?]

In the end though, how much time is wasted discussing this stuff anyway ...in the big picture of life? Probably a lot. Hope you learned something from me too.

12. ### Bottle RocketHall of Fame

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corners is a great contributor to this forum and one of a small number of posters that really "knows his stuff" that still hangs around here and takes the time to respond in threads like this. There is great value in all of his posts and he answered all of your questions in a clear and concise manner. There are a great deal of posters around here that appreciate his contributions and I am one of them.

I think I had a similar reaction to corners when I saw this thread. The way in which you're asking this question implies that this is a subjective topic and, well, not so much...

I don't think corners expects everyone to spend hours studying, but sometimes it says something about one's attitude when there's an apparent lack of previous research. There is a great deal of information out there, on TWU, as well as all over this forum. Some searching will reveal that most of these topics have been covered in great detail. A lot of us have spent a lot of time discussing things like this, including myself.

As an engineer, this gets to me. To say that time is wasted discussing "this stuff" sort of makes me want to rip my face off.

Guess it's ok since no engineering or science has ever made much of a difference in the "big picture of life"...

Last edited: Sep 4, 2009
13. ### Bottle RocketHall of Fame

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Physical measurement must be used to determine the swingweight of a frame. Static measurements or racket specifications are not enough to do a calculation as it depends heavily on the distribution of weight.

Check here for instructions:

http://twu.tennis-warehouse.com/learning_center/howto_swingweight.php

The results aren't real accurate. The best way to determine a rackets swingweight for the sake of comparison is getting it on a Babolat RDC machine, which is the standard for the measurement:

http://av.warehousesports.com/tw/Features/RDC/RDC.html

14. ### sureshsBionic Poster

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In your scale, will there be a situation where for frames 1 and 2, the number for 1 will be greater than for 2, but in the current SW scale, 2 will be greater than 1? Will equal increments in your scale be not equal in the other? If not, it is just a relative number, and it doesn't matter which one you use. You have to explain why your numbers are more suitable, given that the numbers by themselves have no meaning.

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16. ### cornersLegend

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You've got nerve saying 'some people don't have time to study this stuff...', when I've just taken the time to carefully and concisely spell it all out for you. Yeah, it took time to study it, and it took time to distill all of it for your casual consumption. You don't even bother to say thanks when all your questions are answered. Hell, you don't even take the time to realize that all your questions have been answered. The bit about your inane poll was to gently say what I'm saying plainly now.

Finally, you seem like a sharp guy, and I'm saying this to be genuinely helpful: you still don't get it! Please go back and read the two posts I wrote above. There is nothing wrong with the way swingweight is measured or can be calculated for different axes! There is nothing to figure out; there are no discoveries to be made.

You either use a Babolat RDC (or published spec) or the method provided to you by Bottle Rocket to calculate the swingweight at an axis 4" from the butt. Then you can use the USRSA parallel axis calculator to find the swingweight for any other axis. If you hold the racquet at the bottom of the handle, that axis is approximately 2" from the butt rather than 4", so you can plug -5cm into the calculator and presto: you have your number. This number is the effective, actual SWINGWEIGHT for a racquet swung at that location on the handle!

17. ### FH2FHProfessional

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Hey guys, sorry I got so pissy. I was looking for a response that I wanted to hear, not listening. Bottle Rocket, this is why I wouldn't make a good engineer... because I lack the patience! Considering the leaps we've taken, we're lucky to have engineers like youself.

corners, I appreciate your replies. I did read them. The response I was fishing for was that SW (@ 4") isn't the "magic" number its often made out to be (how would you know that?). Anyway, you responded, addressing what I was getting at, and I appreciate that. I had no idea there was already a calculator for it (an adjusted SW at different points). Thanks for taking the time to explain.

sureshs, WTH are you talking about? lol. yes, if I'm reading that correctly, the numbers would be different than current RDC and may reverse; one decreases, one increases ...relatively speaking. I suspect they would be the result of just lowering the 4" point to whatever.

Why do I think that's important? Basically I just want to say that a 9oz, 330SW stick is more likely to get knocked out of someone's hand unless a 100mph+ return is struck perfectly, compared to say a 12oz, 330SW stick, which is obviously more stable. This is something we KNOW, but I'd like a NUMBER besides static weight/balance that says "THIS IS A STABLE FRAME" and
capable of delivering a consistently heavy ball.

Lowering the RDC measuring point below 4" would increase the influence of static weight and reduce the influence of balance. The point of rotation in a swing occurs below the 4" point, and this would be a better guide because of that. Primarily I want to separate the 9oz/HH and 12oz/HL type of sticks. Lowering the point too far makes static weight too important though. A lot of factors come into play, but weight is still very important.

[corners, there was a measurement like this at racquet research, something like "stable power" (versus "quick power," etc.) that I believe produced the kind of result I'm looking for. It was based on several factors I'm sure, including stiffness, which would throw a off any kind of weight/balance based guide.
A "power" measurement I'm familiar with is at Tennis.com. The quick calculation is Headsize X Stiffness X Swingweight. Length is also a factor, but I don't remember how its factored. I don't know if there's a name for this rating/unit of power.

Anyway, I wouldn't expect this magic measurement to be perfect. I'm sure there would be inconsistencies. I'm convinced though that a better measurement is out there than some of the ones we're using, primarily swingweight at 4". Many things come into play - strength, strings, playing style, etc. I'll still keep playing tennis. Just like to think about these things...

Have a good night!

18. ### VenetianProfessional

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This is a cool thread. I have no idea what any of you guys are talking about, but it all sounds very scientific and lovely. It's like watching Star Trek.

19. ### cellofaanSemi-Pro

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Wouldn't the hitting weight calculation of TWU be somewhat of that kind of figure?
Of course hitting weight is different at every spot on the racket, so you get a bunch of numbers for different positions.
http://twu.tennis-warehouse.com/cgi-bin/hittingwtrac.cgi
Example: The Wilson hyper hammer 5.3 has a higher swingweight, but a lower weight, than the kblade tour. The kblade has the higehr hitting weight.

20. ### FH2FHProfessional

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Thanks cellofaan. I played around with some of the TWU stuff, and read finally. I'm not sure what factors are accounted for in the hittingweight calculation here, but the results were not surprising. I feel its fairly accurate as far as power, but lacks the stability factor.

I went back and opened Bottle Rocket's RDC link. I finally know what the acronym stands for! Basically, this link makes my point, that there are descrepancies:

"This can be a little confusing, though, because some lightweight, head-heavy racquets have similar (or higher) swingweights as heavy racquets. Keep in mind that weight and balance influence swingweight."

I also looked at the TWU "at home" swingweight calculator. Is this thing remotely accurate? I was under the impression the racquet would be swung from the other end, but maybe this provides too much room for human error... or friction.

So... I looked up USRSA parallel axis calculator. This thread is the first google link, lol. What I was looking for is here:
http://www.racquetresearch.com/parallel.htm. [At this point I feel like I'm reading The Da Vinci Code or some mystery book.]

corners was spot on as far as knowing a measurement (above) that represented what I was asking; moving the 4" (10cm) swingweight point higher or lower. [He's still a TW snob ...but knowledgable enough to justify it. ]

The problem is determining a useful way to define what I'm looking for... stable power. The racquets that will have this will be heavier and have higher swingweights. How do we get a useful number out of this, without having to make a guess based on several factors?

Last edited: Sep 8, 2009
21. ### cornersLegend

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FH2FH, you're asking some good questions now - some I can answer and some that I can't. No time now, but I'll try to get something up tomorrow.

The parallel axis theorem on racquet research is useless unless you like that math stuff. If you really want to go to town with comparing different racquet classes (heavy & headlight vs. light & headheavy, for example) you'll need to get access to USRSA's calculators. I suggested these the other day, but remember now that the best ones - the parallel axis calculator & the mass mover - require membership. You can join for a month at \$10, which is worth it if your curiosity is driving you to post compulsively here.

22. ### sureshsBionic Poster

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If they reverse for all frames, what have you gained? You just got another scale with the same relative numbers. It is like degrees C and degrees F, if you get what I am saying. A hotter day is higher on both scales.

23. ### JediMindTrickHall of Fame

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The 4" obviously come from the width of the palm which is about 4".

24. ### mtommerHall of Fame

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And I would suspect that the end of the palm in the valley between the thumb and index finger does in fact act like a pivot point and that the fingers wrapping around the grip do not keep the racquet handle completely still. Thus that racquet pivots, though slightly, around the valley.