MgR/Io=21 Formula for frame/pro balance points/moment of inertia/total mass gravita.

[GeoffWilliams]

MgR/Io=21


This formula is supposedly a common set up used on pro frames, given, M=total grams (kg) x g=gravitational acceleration 980.5 cm/s2 R=distance in cm from end of handle to balance point (where frame will start to tip over ie, off the edge of a table or a ruler balance point) Io: moment of inertia= swing wt + (20MR) - 100M

So if your frame is 360g, and swing weight is 355g, and balance point is 31.5cm, the formula would be .360 x 980.5 x 31.5/ 355 + (20 x .360 x 31.5) - 100 x .360 11118.87/355+226.8 -36 11118.87/545.8=20.37, which would be close to 21.


"Supposedly if the MgR/Io = 21, the swing of the racquet acts most naturally with the swing of the arm, giving the most effortless use of power and most consistent angle of racquet head at the point of contact." The purpose of which is to allow the hitter the most well balanced, effortless pendulum arm on the balance point based on the average arm length. (Io)

MgR/Io = 21 is easily obtainable by using lead tape.

The formula would be affected by a longer arm, and to adjust the balance pts, if the swing wt is too high, we add lead at 7" up from the butt, to neutralize rather than at the bottom, the moment of inertia, being too head heavy which would make us late on returns. Soderling has a metal rod in the handle to compensate his heavy lead under the entire capped grommet, rather than lead only at 7". His specs: 379g, 384g sw, bal pt. 33.75 or 21.05





"If you'd assume the arm and racquet to act as a double pendulum, than the racquet part will swing faster for a higher MgR/Io, but the arm part of the double pendulum may swing slower because of the weight difference between the original and the MgR/Io improved version."

Federer's frame showing power pads, and string a lings. He strings at 48.5/45.2 vs team/alu power rough (Both types of alu only come in 17g)


"There is some ideal 'angle' between your arm and the racquet at the point of impact (depending on how the player hits a ball). If the MgR/Io value is exactly right, then the racquet will automatically be at that angle at the point of impact. If MgR/Io is lower than ideal, it will be at that angle a little after the point of impact, thus you'd need to force it to come around quicker, probably using your wrist. If MgR/Io is higher than ideal, the racquet will be at the ideal angle before the point of impact, and pass it before the ball is hit. In that case you would need to slow it down in order to get it right.", or shank a lot of returns!

"The less you have to help your racquet to get to the ideal 'position', the easier it is to get it right, and that will (or should) increase your consistency, and make it feel 'effortless'."

"I'm not sure how two racquets of the same static weight and SW, but different balance (for different MgR/Io) would affect your stroke as a whole, speed-wise."

Fed's numbers: 357g total mass, 32.2 cm bal., 355g swing wt.= 20.68
Nadal's numbers for clay court play: 336g total mass, 33.5 cm bal., 355 swing wt.=20.19 old numbers
Nadal's new numbers for this hard court season: lower sw: 336g, 33 cm, 344 sw:=20.43
Soderlings numbers: 379g mass, 33.75 bal. pt., 384 sw=21.05
Djokovics numbers: 360g, 32 cm, 371 sw= 20.0 flex RA: only 51

So, even though they have radically different frames, and way different masses, the constant is within 1.0

Swing wt: manually without an rdc machine: http://twu.tennis-warehouse.com/lear...wingweight.php


1. Materials

* Two Pencils
* Heavy book or weight
* Meter/yard stick or tape measure
* Stop watch
* Table edge
* Racquet
* Weight and balance (if don't know, see bottom of page)

Measure distance to top string

2. Measure To Top String

* Measure distance from end of the handle to the bottom of the top string (or whatever string you hang from).
* The finer the measurement the better (mm or 1/32").
* Swingweight measurement is very sensitive to small changes. Even 1 millimeter will affect the results.

Hanging Racquet

3. Setup: Hang Racquet

* Hang the pencils over the table edge and place the book on top for support.
* Hang the racquet by the top string on the pencils.
* Evenly space the pencils on either side of the center.
* Do not let the pencils rub on any main strings.

Tapping Handle

4. Tap or Push Handle

* Tap or push handle to set racquet in motion.
* A very small push will do.

Swinging Forward

5. Swinging Racquet (1)

* Swing need only be 1-2 inches either side of center.
* Too large a swing will introduce error into the calculation.
* One swing equals one back-and-forth.

Swinging Backward

6. Swinging Racquet (2)

* Let racquet swing a couple of times to settle in.
* Find or place a mark on floor against which to count swings.

Swing Viewed from Above

7. Count and Time Swings

* Stand over racquet to observe swings.
* Start stop watch just when swing reaches your mark (where it reverses direction) — count=0.
* Count for each time the racquet edge stops at your viewing mark.
* Adjust your viewing position slightly as swing decreases to keep view mark at apex of the swing.

Stoppin the Stop Watch

8. Stop Time

* Stop the watch exactly on the 10th swing. Or let it swing 20 x and divide by 2.
* Time to one hundreths of a second.
* Write down the time.
* It is best to perform test 2-3 times and take the average.
* Be very precise: swingweight is very sensitive to the time.

Calculator Screen Shot

9. Enter Into Calculator

* Go back to the Customization calculator if you were in middle of customizing.
* Go to the Do-It-Yourself Swingweight calculator if you are simply measuring swingweight.
* Enter your measurements.
* Voila! There is your swingweight.

Quick and Easy Balance Measurement
View of Balancing Racquet

Procedure

* Tape a yard/meter stick to the top of a table.
* Place the "zero" end at the edge of the table.
* Move the racquet until the butt of the handle just comes off the table.
* Read the measurement at the handle butt.
* That is your balance point.
* NOTE: It is best to create a "T" along the edge of the table by placing something of equal height as the yardstick on either side of that yardstick. Otherwise you might not be able to balance the racquet accurately.

[tennis_chiro]

Fascinating

Geoff,
you asked in one of your earlier threads, before you got much of a response, if anyone read your threads. I think they are great.

I am very much an old school kind of guy who thinks players coming up spend way too much time, energy and money worrying about their frames, strings and tensions. I tell them to find something they like and feels good and get used to it and stay with it. It usually took me more than a month to get adjusted to a new frame if I changed. When I bought rackets I tried to get 4 or 5 that had the exact same weight and balance (once I had decided I liked the frame). The only reason I changed was companies discontinued and I didn't have a storehouse full like Sampras. I would go to a match with 3 frames, maybe 4 but rarely, and have those as interchangeable as I could get them so if one broke, I could pick up a replacement without hesitation (of course, you always have a favorite). I didn't mess with my strings a lot except to try to keep them the same once I found the tension I liked. When I go to look for new frames because I can't find the one I'm using anymore, I check the swingweights, etc on TennisWarehouse and try to look for a frame that has similar characteristics to what I've been using and find a few models close to that and try them out before I commit. I don't play much anymore so I only need a couple at a time, but I still hate changing.

I probably have strung less than 10 frames in my lifetime. (And 6 of those were one night in '68 at Van der Meer's Incline Village summer camp when someone had to string a bunch of T2000's. No one knew how. I was the engineering student. We had a manual. And I was playing with it. First one took me well over an hour. Strung all night and by the end of the night I could do it in about a half hour... and maybe strung 1 or 2 more frames the rest of my life!) So I relied on stringers to do the work for me. Sure, we all did the Nastase-dance on the strings and whatever else, but strings usually lasted for well over 20 hours of play, probably more like 40. Especially when we were still using real gut. A couple of years ago when I had a lot of nationally ranked junior players, they would snap a string job almost every lesson. It seemed ridiculous to me.

These kids are watching the pros change rackets on change of balls. So, of course, they need to change theirs constantly too. I routinely hand them my racket to "feel" the ball because they are bazookeeing the ball all over the place. Or maybe I'll pull out an old wood racket so they get the idea of what it is like to feel the ball. Yes, I know the game has changed, but these kids that can't hit three balls in a row to a spot shouldn't be bankrupting their parents with unreal expectations that a new string job is going to change the outcome of a match they lost 6-2, 6-3. Tie-breaker in the third, maybe, but it shouldn't be about that.

So that gives you a little bit of an idea of where I come from on all this stuff about picking the right string, tension, pattern, ect. I do believe the guys on the ATP Tour can recognize these differences (and also afford to spend to get what they need in their frames...in fact, can't afford not to).

But all that being said, I am fascinated by some of the stuff you post on stringing. I think I need an education. I would like to understand exactly what you are talking about. No, I don't want to string. I don't have time. But I'd like to be able to understand this conversation a whole lot better than "tighter for control; looser for power".

What are some good sources for reading to get a better idea and understanding of the whole science (and you do seem to try to make it like a science, although I expect it is more of an art)? I need some framework just to follow some of the stuff you are putting up here. I really don't like the idea that I feel ignorant about an important part of this game.

thanks,
don

[GeoffWilliams]

Thanks so much for that thoughtful reply! (It's thousands of string jobs for me!) And it's not even an area you agree with. You are right about the art aspect, although, it's a science as well, as the top customizers are paid big bucks by the top pros for their artful science. Where can you go for more info? Right here. Too many sources, pleading too many aspects, such as : grand slam stringers, Joes string forum, tw forum, etc. I am gleaning many opposing view points, and their opposing goals, and posting them for anyone who has the interest/patience to try out new methods. But those are some sites that will overload you with tons of useless posts/data/methods.

As an old school guy, who like me grew up with wood and vs imperial gut, you know that all this new tech is a bunch of bs, unless, you are a high level player. Racquet manufacturers don't make frames for those people, due to the fact, they make up only a tiny percentage of the people playing and buying. They make them for people who don't care about the frame/string/etc. they use. While the truth is, they lie about which frames their pros are using, and it's a bald faced lie much of the time! Ie, Nadal uses an apd orig., painted to look like a cortex frame. Here is a real cortex next to the apd orig., painted to look like the cortex, with Nadal's john hancock..

I don't buy that. Any player can play better with frames/string to match their game, that's balanced up to pro standards, and not just a little better, a lot better. Even with such hugely different frames and equipment, the top guys match out very closely when you look at the balance/mass/gravitational Io/swing wt compared to the other top pros, and that is not an accident at all. (Soderling at 379g, strung, gripped, etc., Fed at 357g, Nadal at 336g, with hugely different bal pt., stiffness RA, etc, yet, they are very close in one aspect: how the frame comes through inertially.) joker lead tape

Fed has lead under the bumper guard at 10-2, which varies 2" or so frame to frame, (see the pic from p1) to achieve this balance, due to manufacturing imperfections. Nadal has 8.5g at 12 under his bumper and 2.5g at 7" in the handle. Djokovic has four pieces of lead from the seventh cross down, to 1" below the last cross down, bringing his bal. pt. downwards. Even with Soderlings' custom made pallet, which has a deformation for his pinky finger, and a lead rod in his handle, his frame is at 21 pts.
soderling pallet

http://www.youtube.com/watch?v=Eql8Jnpa9Bs

Ie, only the top pros are changing every 8 games, due to affordability issues. Doubles guys only string a frame per match or the whole tournament! Why, they make less money, and can't pay, that's why.

[klacr]

Geoff,

I love and read your articles as well. I find them extremely informative. I have strung thousands of frames, most not willingly, but as a teaching professional at an active club it comes with the territory. I, much like you, am traditional in my views with racquets and the overall game of tennis. But my fantasy of being tennis commissioner is for another forum post.

I'm amazed at how few players care to know about their racquets and/or strings. I'm also intrigued by the ways Professionals customize their racquets. I've been known to tinker with my frames

(Head Prestige Mid YouTek. Luxilon Big Banger Rough 56lbs/VS Natural gut 60lbs. 385 Grams. Lead tape at the
12 3,9 positions and 5 strips around handle. I also have a built up handle near butt cap a la Soderling)

I think you should collect all your articles on stringing, racquet customization, player quirks and racquet specs and have John Y devote a tab for player equiptment and all your knowledge. Think about it. We have stroke archives, advanced tennis, famous coaches, tennis history, music videos, strategy and mental game. Why not add another section-title it Equiptment, or something in that context. That would be great. keep up the great work Geoff and thanks for sharing all your info. That's one reason I love tennisplayer.net so much. Without a doubt, I learn something new every day from this site.

Sincerely,

Kyle LaCroix USPTA

[GeoffWilliams]

Wow, great post for a solid thread! Thanks so much for that response, as I have suggested that to John, and he replied, "That's not my favorite subject." I don't think he likes or agrees with the topics premise: that your equipment makes a huge dent against your game, or for your game, depending on not just how it matches your skill/temperament/style/court positioning/mind positioning, but how much it matches you for spin/power/control/arm/depth/angle/touch. Anyone like you who has the experience you do, can vouch the truth: folks don't care about their strings, even though strings are the soul of the frame, and the frame is just the body. Whether that body is too fat, too skinny, too slow, too fast, too powerful, not powerful enough, depends entirely on the individual alone! It is a science, and an art, to match the strings not just to the frame, but to the client. I would like to see this site achieve its rightful place as an experts site, in that area, in all areas of the game, including equipment. Imagine if you were a junior, able to learn how to do exactly what the pros are doing, but in your own home?

385g, head youtek, lead at 3, 9 and 12, and five strips on the handle, that is some serious plow through! I'd say your swing wt. is about 404g, balance point about 32 cm. That would put you at about 19.7. To achieve 21: your Io would have to be 575 instead of 611, if the bal. pt and sw is right, but I am guessing on those. Take some lead off 3,9,12 and put it at 7" above handle to see what that does to the sw. (Just a guess.)

vS gut and bb rough is a great combo, and I won a 4.5 in carmel with that, but I had it strung at global gut mains/60 and bb rough 56 on cross, in a pt57a. I lost the first set, to a home town guy, in a tie breaker, and changed frames 3 x, until I found the one with the right balance for the angle of trajectory (shots were going long off groundies and volleys) off the gut/hybrid, and was able to win after going down 3-0 in the second set! It's not just our games we have to adjust when losing, it's our frames as well.

[tennis_chiro]

Adjusting frame and strings for your opponent

Wow, great post for a solid thread! Thanks so much for that response, as I have suggested that to John, and he replied, "That's not my favorite subject." I don't think he likes or agrees with the topics premise: that your equipment makes a huge dent against your game, or for your game, depending on not just how it matches your skill/temperament/style/court positioning/mind positioning, but how much it matches you for spin/power/control/arm/depth/angle/touch. Anyone like you who has the experience you do, can vouch the truth: folks don't care about their strings, even though strings are the soul of the frame, and the frame is just the body. Whether that body is too fat, too skinny, too slow, too fast, too powerful, not powerful enough, depends entirely on the individual alone! It is a science, and an art, to match the strings not just to the frame, but to the client. I would like to see this site achieve its rightful place as an experts site, in that area, in all areas of the game, including equipment. Imagine if you were a junior, able to learn how to do exactly what the pros are doing, but in your own home?

385g, head youtek, lead at 3, 9 and 12, and five strips on the handle, that is some serious plow through! I'd say your swing wt. is about 404g, balance point about 32 cm. That would put you at about 19.7. To achieve 21: your Io would have to be 575 instead of 611, if the bal. pt and sw is right, but I am guessing on those. Take some lead off 3,9,12 and put it at 7" above handle to see what that does to the sw. (Just a guess.)

vS gut and bb rough is a great combo, and I won a 4.5 in carmel with that, but I had it strung at global gut mains/60 and bb rough 56 on cross, in a pt57a. I lost the first set, to a home town guy, in a tie breaker, and changed frames 3 x, until I found the one with the right balance for the angle of trajectory (shots were going long off groundies and volleys) off the gut/hybrid, and was able to win after going down 3-0 in the second set! It's not just our games we have to adjust when losing, it's our frames as well.

Geoff, I agree with Kyle above. We could use a whole section on equipment. Part of John's reluctance to do that might be that it is not something you can back up so easily with video or scientific studies. Your knowledge seems voluminous, but how does John determine who to give this platform to "officially" by putting it in a Tennis Player tab at the left there.

I'm getting better just by trying to follow your descriptions in your posts. Still think I need something basic like a manual. There is a lot in the Lindsey, Cross, Brody book on Physics and Technology of Tennis. I'll have to try to wade through that.

But aside from all that, the idea that you should have an arsenal of different weapons when you go on the court with different tensions and swingweights to deal with the ball your opponent gives you is a facet I don't think many people have really given much consideration to. But it makes sense you would need a different weapon to deal with Nadal or Soderling or worse yet, the Frenchman, Fabrice Santoro. I know I always had trouble with a soft ball hitter. I couldn't get ahold of the ball, ... or so it seemed. Adjusting the racket specs and string specs could have helped.

Perhaps you should consider fleshing out an article for John like that: how you would adjust your racket and string specs for different opponents. You ought to be able to get the companies to sponsor that kind of information; it would lead to them selling more equipment.

don

[llll]

geoff
my racquet weigh 354 grams. balance 312mm swingweight 326
am i close to 21???

[GeoffWilliams]

Assuming your bal. pt. is 31.2 cm, you're at 21.19! Just a little over Soderlings 21 mark. That's fine.

[GeoffWilliams]

I don't think John wants the big companies mad at him for exposing their lies to the subscribing public! Don't just change a losing game, change a losing frame, would be a good campaign for the stick companies! I would love a whole section to equipment, but there's the rub, who does John trust, with which info, and how does he distance himself from the fall out, due to manufacturer anger over exposure ala Tiger Woods ball? It's worse in tennis, and very bad to fool the people, and it's not widely known at all among the lower skilled, less informed, about just how wide spread the paint jobs are, and even sometimes shoes, strings, are lied about as well!

[klacr]

Geoff,

Great to see this thread is picking up some momentum.

You are right. My racquet does have some heavy plow through. But as I said in my previous posts I like to tinker. I will certainly try your suggestion and put some at 7''. thanks.

I do think equipment and customization is a huge and very integral part of the game, just like forehands and backhand. Imagine if every player had to use the same exact racquet. Say, a Head Pro Tour 280 (old Thomas Muster Racquet) for all matches. Just one racquet, one size fits all. Players racquets, specs, and their equipment quirks and requests are just as fascinating as their strokes. Don't get me wrong, I'm still a technical geek still in search of hitting that "perfect" forehand. But stringing and customization is, much like a player's strokes, totally unique and always interesting.

Kyle LaCroix USPTA

[GeoffWilliams]

Geoff, I agree with Kyle above. We could use a whole section on equipment. Part of John's reluctance to do that might be that it is not something you can back up so easily with video or scientific studies. Your knowledge seems voluminous, but how does John determine who to give this platform to "officially" by putting it in a Tennis Player tab at the left there.

I'm getting better just by trying to follow your descriptions in your posts. Still think I need something basic like a manual. There is a lot in the Lindsey, Cross, Brody book on Physics and Technology of Tennis. I'll have to try to wade through that.

But aside from all that, the idea that you should have an arsenal of different weapons when you go on the court with different tensions and swingweights to deal with the ball your opponent gives you is a facet I don't think many people have really given much consideration to. But it makes sense you would need a different weapon to deal with Nadal or Soderling or worse yet, the Frenchman, Fabrice Santoro. I know I always had trouble with a soft ball hitter. I couldn't get ahold of the ball, ... or so it seemed. Adjusting the racket specs and string specs could have helped.

Perhaps you should consider fleshing out an article for John like that: how you would adjust your racket and string specs for different opponents. You ought to be able to get the companies to sponsor that kind of information; it would lead to them selling more equipment.

don

Soft ball hitters depend on you missing long, due to a failure to create your own power, and a steep angle of trajectory off the bed, from too short in the court, so you go long too much, on shots that you would not go long on a power hitter. They gloat over how many of your shots are going out, and act as if they are better than you, when you are just using the wrong equipment/mind positioning on the match. You have to stand inside the baseline, and go into the net off short shots, and also back up if they hit deep, and use a stiffer bed type string like poly, strung a little tighter, and a frame a little more flexible, and a little lighter, to drop the angle down, so you don't go as long on your shots.

The frame companies are not selling to people like us who are more aware of strings/tens/frames than the gen pop. We are only 1% of the buyers and are not a viable market. Just as the courts are always dominated by the same gen pop, in public, so are the frame companies dominated by who buys their wares. And so is John, as well, as he can't afford to have them come down on him.

[tennis_chiro]

Soft ball hitters depend on you missing long, due to a failure to create your own power, and a steep angle of trajectory off the bed, from too short in the court, so you go long too much, on shots that you would not go long on a power hitter. They gloat over how many of your shots are going out, and act as if they are better than you, when you are just using the wrong equipment/mind positioning on the match. You have to stand inside the baseline, and go into the net off short shots, and also back up if they hit deep, and use a stiffer bed type string like poly, strung a little tighter, and a frame a little more flexible, and a little lighter, to drop the angle down, so you don't go as long on your shots.

Geoff,
Certainly, I did take the ball early, usually out of the air, but I never thought to have an extra frame strung a little tighter just to deal with the pushers. I don't think many other players do either, even today. And it makes a lot of sense.
don

[GeoffWilliams]

Not only a little tighter, but stiffer string, which cuts down on depth, which is what you need against a short hitting soft ball hacker. Cowardly way to win, that style, but you are allowed to win with any style, even the style of a coward! I don't enjoy playing them either. No fun to practice with them but you have to acclimate yourself to that style if you are facing it in a match before the match occurs. That's why the pros hire "shadow" players, like Fed did in Dhubai, with the lefty college kid, to duplicate Nadal's lefty strokes. You see that in team sports as well, in football, where they try to duplicate the opposition's tactics in practice against the scout team.

[GeoffWilliams]

"No one would subscribe to this site if they weren't looking for improvement, or the "perfect forehand". This is a site for not the normal type at all, but the type who wants to know and learn everything they can to gain the most knowledge they can, and improve not only their game, but their belief in their own game!"

Stringing is interesting only in so far as it improves your own game/or clients game. It's not too fun to string a lot of frames, for folks who don't appreciate the extra time you take to ping out the mains, to let the poly settle before you clamp off at least 5 seconds, to adjust the tensioner for knot loss, to manually tie off knots instead of using the tensioner, etc. Not even the top pros stringers take that kind of time, due to the fact they have too many frames to string, in too little time, so they average about 17 minutes.
The point I was making was to change the sw, to achieve a better balance, by switching some of the lead from the 3,9, and 12, without changing your total mass, to the 7" position, to see if that improved your Io, or inertial swing through, so that it lined up better with your natural inertial contact point. That would depend on the bal. pt., and the existing sw, which I guessed at!

How is Boca? Saw your pic online. You look like a bruiser.

This thread is approaching a level of awesomeness not usually seen!

Geoff,

Great to see this thread is picking up some momentum.

You are right. My racquet does have some heavy plow through. But as I said in my previous posts I like to tinker. I will certainly try your suggestion and put some at 7''. thanks.

I do think equipment and customization is a huge and very integral part of the game, just like forehands and backhand. Imagine if every player had to use the same exact racquet. Say, a Head Pro Tour 280 (old Thomas Muster Racquet) for all matches. Just one racquet, one size fits all. Players racquets, specs, and their equipment quirks and requests are just as fascinating as their strokes. Don't get me wrong, I'm still a technical geek still in search of hitting that "perfect" forehand. But stringing and customization is, much like a player's strokes, totally unique and always interesting.

Kyle LaCroix USPTA

[klacr]

I'm glad this thread is reaching a higher level of awesomeness for you. Hopefully I am contributing to it. WINNING!

I do understand what you mean when you talk about stringing frames for the sake of stringing. But to go the extra mile and give the extra details is something the weekend warrior or club hot shot has no clue about. Then again, I don't expect them to as it is not an area of expertise. I do expect the vast majority of tennis teaching professionals do know, or if not, educate themselves on this subject. I'm glad you are here to educate us further into the dimension of stringing, customization, and general frame enhancement.

Racquet manufacturers do use some tricks to help the bottom line. It's unfortunate, but it is a business and a competitive one at that. It is a bit of a coincidence that the hottest racquet technology each season seems to be a surplus of technology from the aerospace industy. Perhaps there is something to that as well.

Boca Raton is busy. Boca Raton is beautiful. Boca Raton is tennis crazy.

I'm a bruiser? I guess. Compared to alot of the guys on tour I now seem to be normal. But yes, being 6 feet 6 inches tall has its advantages. serve, volley and backhands are my friends, my height still can't help me hit a forehand though!

Take care and keep posting.

Kyle LaCroix USPTA