String Tension and Effect on Racket Stability

In the past few weeks, more than a few very good players have asked me to add more lead to their racket hoops. 

All wanted a little more stability, especially when dealing with heavy balls, or when returning hard first serves.

Most of these folks already have their swingweights in the 320s to 340s region. So I thought it was decent enough.

After reviewing some of their shots in question, it seemed to me that the problem was a little more string related than racket.

Most were using stiff frames of RA68 and above. All were strung with full poly above 50 lbs. To me, that was the problem.

Let me explain...

Playing tennis is managing a series of collisions between stringbeds and a tennis ball. When both the racket and stringbed is very stiff, and the ball is new, hard and bouncy, where does the energy dissipate?

Some of the impact energy would be absorbed by the racket, stringbed or tennis ball. But not all. So the racket, deflects backwards or twists and turns. And the ball compresses too.

I have posted this slow motion video of Federer's racket wobbling on impact. Here it is again. Take a look at 1:16 in the video below. That's the racket flexing and absorbing the energy on impact. 

Stiff frames with tight strings would always be less stable than softer frames, or when strung looser.

To prove the point to an unbelieving player, we beefed up his stiff racket (with tight strings) to 365 swingweight, total weight about 360 grams and balance 32.5 cm. Then got him to try returning first serves from his coach.

Same twisting. Same instability.

Eventually, he moved a gauge up to a slightly thicker string to compensate for a slight drop in tension and obtained his desired stability.

Some may claim the thicker string added weight as well.

Yes it did.

Merely 2 grams. 






     

Fastest Way to Increase Spin

Almost everyone wants more spin!

If I were to estimate, among all those whom I have worked with, about 80% wanted more spin. 

About 15% asked for comfort as top priority since they had some sort of pain in their arms.

Only a few (<5%) asked for more power or more control.

What these spin-obsessed folks did not realise, was how paramount power was to generating spin.

Let me make this statement boldly:
To achieve more spin, you have to obtain more power first!

The very nature of hitting topspin is inefficient. Compared to a flat shot, topspin robs power. 

And in many low to intermediate players' quest for more spin, they end up swiping the racket almost 60-70 degrees upwards. That further reduces the amount of forward drive they put into the ball.

Sometimes they get a lot of spin, but it is a sitter. It does not kick forward.

A simple visit to the physics classroom to understand the resultant force under "Vectors" easily explains why. (link)

If you search youtube videos of Federer or Nadal, or any other pro player, you will see their follow through is only about 30 degrees upwards. That's all they need to achieve their 3000+ rpm on their forehands.

If you observe carefully, their shots usually land near the service line and then kicks all the way to the baseline. Average net clearance was only about 60cm or so.

So how should amateurs and wannabes like us hit topspin?

Simply:
- keep the net clearance low (max 60 cm)
- smack the ball hard with a shallow 30 degrees follow through

Of course many other factors play a part, including:
- string type,
- string tension,
- racket flex,
- racket hoop size,
- racket string pattern,
- type of balls,
- court surface,
- swing timing, 
- footwork, etc

From my observations and experiments, power is the most critical and most neglected factor.

Specifically, swingweight.

When matched with the player's strength and abilities, this single variable has the most direct and strongest correlation with how much offensive kicking topspin he can generate.

All other spin factors have a poor correlation.




     

Heavy Rackets Again: 400 grams

For at least about 100 years, between the 1870s to the 1970s, tennis was most commonly played with wooden rackets. (link)

At that time, 13 to 14 ounces rackets (368-400 grams) was the norm. Everyone who wanted to play, had to get used to the weight, including women and children.

The last time I used very heavy rackets (370-390 grams) was about 2 years ago. (link) I stopped after injuring my wrist.

Now, with a better understanding of my limited capabilities, plus knowing how to tweak the racket weights and strings, I thought I should give this another try...

This time, I kept swingweight down to "only" about 365 kg/cm².

Air swings after the final adjustments felt good. The swing speed was definitely slower than lighter rackets, but the heavy plow felt really nice, and familiar.

Surprisingly, the first two sessions on court was very good. It did not take me long to get in tune with the weight and timing. It was like bumping into an old friend on the street, and continuing exactly where we left off last time.

However, my partners suffered. Both LOVED receiving heavy balls. So I did not hold back and let it all out.

The first partner showed no emotions throughout. After the session, my partner showed me the red and swollen index finger base knuckle. Apparently, my shots had been pushing back my partner's stick every impact and the hand bore the brunt of the shock.

The second partner uses a racket about 90 grams lighter than mine. Almost all my shots were returned to me very short. Just barely passing the net a meter or so. I had to tone down to get a decent rally going.

At another session with another partner, the outcome was totally different. He was initially surprised by how heavy and spinny the ball was (see ball fur pic above). But got used to it in about 10 minutes.

Instead of blocking my shots, he took compact back swings with full follow-throughs, just like return of serves, and simply re-directed my pace back at me. I do not recall ever seeing him hit such fast paced shots and so deftly placed. He was using MY energy!

I switched back to my normal racket and immediately saw him struggle to generate pace. His balls fell so short it did not even clear the service line. Or they flew out due to loss of control. In the end, he reverted back to flatter shots hit straight to me.

What was unexpected, was that the change back to a lighter stick was much more difficult to adapt than when picking up a heavier stick. My timing became too fast, my footwork wrong, control became very poor, spin levels dipped and volleys were suddenly so unstable!

If you have never tried heavy sticks and think this is ridiculous, you could have missed the point. There are reasons why top pros insist on such heavy rackets. And these heavy sticks are not as unwieldy nor cumbersome as most people think! 

Don't believe me? 

Take a look at how fast and easily these 10 to 12 years old kids adapted to a male tour pro's heavy racket, and with no warmup:
https://www.youtube.com/watch?v=CCw2gZM-eNg
https://www.youtube.com/watch?v=9d07GAyQuuY
https://www.youtube.com/watch?v=WMeXWXzoJqs
https://www.youtube.com/watch?v=JugXpLT3EVI
https://www.youtube.com/watch?v=-uSl3UycOoo

For me, the acid test is when I meet "M" and pit it against his nuclear powered stick. (link) That would be the "Clash of the Titans!"


5th November 2015 update:

Mission accomplished. 

Happy to cross swords with the 200G now!


     

Nuclear Powered Softie - Dunlop Max 200G

For a few years now, an old friend, "M", has been searching for his long lost "old love" - the Dunlop Max 200G. The one from the 1980s used by John McEnroe and Steffi Graf. (link1)(link2)

When I saw one put up for sale, I bought it immediately! Since it was from the 80s, to be fair, I brought my 80's stick (ProStaff 85) to pit against the 200G.

Although the 200G was a graphite racket, it played incredibly soft. With a flex of RA 40+, it is probably the softest graphite racket ever made. That flex is almost on par with wooden frames!

I thought it would be a challenge to wield the 365 grams racket. Maneuverability would be pathetic. Not to mention that meagre 84 square inch head size. And that 18x20 dense stringbed...

But I was very very wrong!

While I cannot say the racket was fast, it played extremely well! Effortlessly well. And it had a HUGE sweetspot! Much easier to handle than the PS85. More comfortable. More powerful. And oh so comfortably SOFT!!!

Usually, when I bring out my PS85, I was the bully. The beefed up heavy swingweight of almost 350 kg/cm² meant very few could push me around. Even their hardest shots could easily be returned or simply blocked back deep with a compact swing.

Against the stock 200G, I was the victim!

I took full loopy swings and flattened out my swing path. Smacked the back of the ball directly forward with mere inches of net clearance. 

But I could do no damage to my heavily-armed opponent. 

My partner took a leisurely swing and returned ALL my power into the ball right back at me. I did not have to run. I had enough time to swing, load up and step into the shot. Despite that, I could not sustain the VERY heavy impacts.

By the fourth or fifth of each rally ball, I was spent. My shots became shorter and slower. Then my timing went. Out of about 10 balls we used, 9 eventually hit the tape or went into the net.

The change from bully to victim was demoralizing. This is simple physics. Sir Isaac Newton explained:

Force = Mass x Acceleration

No one can defy this physical law. The one who can wield the heavier stick prevails. Why else would professional tennis players use such ridiculously heavy rackets with high swingweights?

Luckily, my partner could only handle the 200G for brief moments of about 10-15 minutes. So we could take turns to rule the court and dictate play!




     

ProKennex Black Ace 98 (2009) BumperGuard Removed

Two years after I acquired this racket (link), (or a tennis buddy left it or gave it to me I could not remember), I am still discovering interesting aspects of this racket.

Other than strings, I wanted this stick to move a little faster, especially for return of serves against huge bombers!

The bumper guard is removable and is touted to reduce about 15 swingweight points when taken off. So I tried it...

Checking the weight strung.

Weight unstrung.

Bumper guard weight.

Playing both rackets on court, one with bumper, one without, gave me a very quick feel and conclusion how they differed.

Undoubtedly, this racket's weight is polarized. Although the stock swingweight is a sizeable 331 kg/cm², when the bumperguard is removed, the mid-section felt too light and hollow to provide enough power and stability.

While I could move the head much faster, there was little I could achieve as I could neither send it back deep nor re-direct the ball confidently away from my partner. I felt like I only dinked the ball back, then got punished by a passing shot my partner effortlessly returned.

Feel wise, the feedback was completely lost. The strings felt hollow and boardy, like I was unable to load it. No spin either.

Comments from my partner who received my shots with both sticks echoed the same sentiments.

As a quick test that the culprit was the missing swingweight, I stuck two dampeners totaling 5 grams right at 12 o'clock and played with the racket. Everything came back.

I'll have to install the bumper guard back in.




  

Mysterious Arm Pain and Hyper Hammer 4.0 Overhaul

A playing partner asked if there could be any explanations why only a particular racket caused elbow pain when playing.

Both were strung with full synthetic gut around 55 lbs. Both specs were very close, but only the Wilson always resulted in pain after play, whereas the Head TiS6 never caused any discomfort.

Looking at the string wear in the sweetspot of the Wilson (above left picture), there was absolutely no doubt on the consistency of sweetspot impacts. So I ruled out pain due to framed shots.

Then I compared their specs:

	Wilson HyperHammer 4.0 OS	Head TiS6 OS
Weight	249 grams	252 grams
Balance	9 pts head heavy	8 pts head heavy
Swingweight	308	318
Length	27.75"	27.75"
Flex	RA 70	RA 75
Headsize	110 sq inch	115 sq inch
String Pattern	16 x 20	16 x 19

Ironically, the TiS6 was 5 points stiffer on the RA scale compared to the Hammer. So it ought to have been the more damaging stick instead!

After much probing, dry-fitting and testing, similar to what I attempted here two years ago, the culprit pointed towards two things:
(1) the very low swingweight of this Hammer, and
(2) the very extreme weight polarization (9 points head heavy)

When there was sufficient time to prepare and swing, every shot felt good for both frames, for forehands and backhands, groundstrokes and volleys. 

But when I was late, or on the run to retrieve a well-placed corner shot, the abbreviated compact swing made the racket feel very inadequate. It was powerless.

The extended length allowed me to reach the ball, but the feeble swingweight worked against me, and allowed only a very miserable pathetic tap against the full velocity of the ball. 

As a result, instead of me swinging the racket to hit the ball, it became the reverse - the ball pounding hard on the racket, which in turn twisted or deflected my wrist/arm backwards. 

With the racket weighing only a mere 250 grams to bear the impact, my arm became the shock absorber! I played with it, in stock form, for only about 10 minutes before I had to set it aside.

Literally, I had to beef up the racket by adding weight to improve its swingweight, vibration dampening and simultaneously reduce the extreme weight polarization.

The original handle was entirely hollow all the way up to the hoop. 

Most of the racket's weight was concentrated on the tip of the head, near 12 o'clock. This encouraged vibrations to travel down the hollow frame towards the handle, which was the lightest part of the racket. And then up our hand, wrist and elbow.

After stuffing one side of it, I tapped around the frame and measured the vibrations via frequency. I stopped when about 70% of the "bad vibes" were removed or reduced.

Then the old strings were cut and restrung.

A little lead was added around the grip pallet as well. And about 4 grams were added to the hoop at 4 & 8 o'clock to add about 7 swingweight points. Placing the lead any higher would worsen the weight polarization so lower was better.

Here's how it looked completed.

While some aspects, like vibrations, total weight, balance and swingweight were easily quantifiable, the most important variable - player feel/preference, remained entirely subjective.

The only way to take this further, is for my friend to make minor adjustments and fine-tune after each session of play.

Whatever the outcome, the general consensus about "light and stiff" rackets stand - that they are hazardous to our arm health.


11May2015 update:
- For those with tennis elbow or wrist injuries, just a few hits with an unfriendly frame usually flares up the pain very quickly. 
- After I handed the modified Wilson to the owner, she gave it a few air swings and proceeded to rally. I watched intently the ball impact locations on the stringbed, the amount of prep time and the magnitude of back swing.
- Added weight usually visibly slows down a player. Ironically, it enhanced this partner's swing timing. Immediately, I knew the racket had been too light earlier.
- Coupled with the extreme weight polarisation, it actually hindered her from taking a free swing as the heavy head's momentum ended up "pulling" her arm instead.
- The average pace of her shots increased. Directional control improved. 
- What she admitted readily, was the absence of any pain or discomfort. The frame felt cushioned and friendly. But she did not believe that her ball speed increased and felt heavier to me. 
- So I told her to keep this modification to herself. Then play with her usual doubles group and see what those three regular partners would say after their two hours session.
- I was updated later, that just during their warm-up rally prior to the game, her partners already remarked about her improved hitting depth, power and control. Even asking if she had been working out in the gym to achieve all that!
- Needless to say, she sent me a message, saying:
"Thanks again for resuscitating my racket... It keeps me grinning the whole day..."

  

A Hidden Function of Dampeners

Among my playing partners, three simply do not like to use dampeners. No matter what racket or strings was used.

They like the raw feedback of the ball impacting the strings. But I don't. When I test their rackets, I put on a dampener so I could better compare their sticks with mine.

Most of the time, we would forget about the dampener as the rackets go back and forth.

After hitting with one for a while, and then removing it, these friends started wondering if something was missing. And it was not the vibrations!

It was the swingweight difference!!!

A small dampener, like the yellow face or red ring (above pic) weighs 2 grams. The Babolat, Dunlop and Wilson dampeners weigh 5 grams each. And the tennis ball dampener, 7 grams.

When placed at the strings above the throat of the racket, every gram adds approximately one swingweight point. At the top of the stringbed, one gram adds about three swingweight points.

How perceptible would a few swingweight points be?

Very!!! The difference in weight of using 1.22mm strings versus 1.30mm strings could be felt by most. And that difference is merely 3 to 5 grams.

Keep in mind, the racket is swung with an axis about 10cm from the butt. When the racket is in motion, the dynamic feel of the weight difference is highly magnified, compared to the tiny extra few grams when it is stationary. 

Another important thing to note, is the trend of heavily polarized racket weights. That leaves the middle of the racket light and hollow, and very prone to vibrations.

They ended up adding a few grams of lead tape at the hoop.

Wilson PS95s again...

Both Z and I have unfinished business with this frame. (link1)(link2)

In online forums, this racket is notoriously difficult to string.

Specifically, it is the combination of:
(1) very low swingweight of about 300 kg/cm²,
(2) very flexible hoop and throat, and
(3) open 16x15 string pattern.

Conventional wisdom dictates: 
(1) Low swingweight = low power 
So lower tensions or soft and powerful strings like gut or multifilaments are recommended.

(2) Flexible hoops affects accuracy and requires stiff strings or a very high tension to provide impact stability. But that reduces power and pocketing, which in turn reduces spin.

(3) Open strings require stiff and thick poly strings or thick (1.40mm or more) nylon strings for durability, but these strings inhibit spin and are low-powered as well.

Professional players who use the PS95s like Dolgopolov or Dimitrov (link) focus on control and spin. It is rumoured they lead up their swingweights to 360+ kg/cm² so power is a non-issue. Neither is durability relevant since they restring so often.

But what about mere mortals like Z and I? How do we balance the traditional stringing variables of comfort, spin, control, power and durability?

Something must be sacrificed. For the premium price paid for this "heavy spin" model, and with marketing targeted at "spin chasers", spin cannot be compromised.

Power and control are already lacking, and Z absolutely loved the comfort of synthetic gut. So what could we achieve by sacrificing durability alone?

See the dilemma now?

After some deliberation, I decided to increase both swingweight and total weight to add power, ball pocketing, stability and also "stiffen" the dynamic flex of the racket. 

Once the low swingweight and flex problem can be dismissed, stringing would be a little easier. Moreover, I felt a heavier racket could improve Z's timing, considering how fast, strong and fit he is.

After calculating the desired numbers, the previous 6 grams I added was re-positioned. Another 11 grams was added under the butt cap to keep balance at about 31.5cm. Swingweight should now be around 325 kg/cm² and total weight about 345 grams.

Still being new to this 16x15 string pattern, I aligned the PS95s on top of my ProStaff Classic to understand just how open it was.

The above picture had some parallax error. So I took two closer snapshots from directly on top of the head and throat of the rackets.

Both the first and last cross string of the PS95s are about 1cm nearer the centre of the stringbed than the ProStaff Classic. 

Total distance from first cross to last is 24cm for the PS95s and 26cm for the ProStaff Classic. So it seems quite evident, that the open strings are not really THAT open after all.

After establishing that, I decided to use Z's favourite syn gut again. To minimise the string variables so that we can better feel the effects of the weight modifications, I strung using the same modified proportional stringing as before. 

Let's see how this would turn out...


Playtest:
- Z's first comments were "I can feel the pocketing and bite". I could see he was very comfortable with syn gut.
- However, the added weight slowed down his swing prep and timing. From my side, I could see he was late in hitting for a lot of balls.
- When he got the timing right, both power and spin came across strongly, especially those ankle-high fast-skidding @#$%^&* unreturnable backhand slices.
- Getting the ideal swingweight and total weight takes several sessions. I advised him to move the lead around and keep trying.
- For the few shots I hit, both spin and power increased significantly from previous setups due to the extra pocketing from the added weight.
- Feel wise, the racket is getting very close to how a traditional ProStaff usually feels like.
- The hoop also seemed to flex less and was a little more stable on off-centre hits.
- String movement was minimal but ball fur adorns the stringbed after playing, as usual, showing how much the strings were biting...

Adding Swingweight

Since the last time I posted about how addictive a heavy swingweight can be (link), I still hold the same opinion, that swingweight remains the most important factor for any tennis racket.

Swingweight for pros varies around 330-360 kg/cm² while recreational players use mainly between 300-330 kg/cm². The higher the number, the more powerful that racket is.

What I have not been able to narrow down, is exactly how much to add. Too much and the racket becomes clumsy and unwieldy. Too little and it makes almost no difference at all.

So far, what seemed to work well for me, is to add only as much as my "weaker" strokes can bear comfortably and consistently. Those weaker strokes would be my backhand and second serve.

The forehand enjoys a much wider arc of shoulder rotation, so power is easy. On the contrary, the backhand requires muscles less used in daily activities. Even the backhand preparation needs support from the non-dominant (left) hand as well, so it makes no sense to add swingweight based on the stronger wing.

Compared to the forehand or backhand, the serve is even more sensitive to swingweight changes. It is the only stroke in tennis executed with the elbow straight and arm in full extension. That places the racket furthest away from the centre of our body rotation. 

During the serve motion, the wrist rotates the racket through almost 270 degrees from start till completion (link). Naturally, the serve is the first to suffer deterioation after racket changes or weight adjustments.

1 gram added inside the hoop at 12 o'clock adds about 3.3 kg/cm². Whereas 1 gram added at 3 or 9 o'clock adds about 1.8 kg/cm². Just add up whatever you add to the stock swingweight of your racket model and keep that below 330 kg/cm².

Use small weight adjustments. Protect your wrists and enjoy the plusher plowthrough, stability and better bite for spin!

Swingweight Addiction!

Whenever I see someone examining a new racket, the first, and almost the only aspect they talk about, is weight.

There seem to be a wrong association between a racket's weight and performance. 

To me, swingweight is paramount. Not only in tennis, but baseball bats, golf clubs and hockey sticks as well!

Swingweight determines power, affects racket flex, stability, string tension, plowthrough, impact feel, pocketing, racket balance, swing timing and many more.

Here's two excellent articles I found online:
1. Swing Weight of a Bat (Why MOI matters more than weight)
2. Tennis Racquet Weight. Does it Matter?

As a recreational player, I mainly play topspin from the baseline. Occasionally, I would change styles and do some serve and volley plus drop shots. I play both singles and doubles friendly games.

Naturally, as a baseline-basher, I like heavy sticks. Most of my preferred rackets are about 370g. A few are just shy of 390g.

It's not a conscious act. I did not go out to search for heavy sticks nor add lead till I hit my "target". There was no target weight in the first place. It was all based on feel.

So I gradually increased lead until I felt it was a little too heavy, then I backed off, removed a few grams and stopped there. It's something like the swingweight1 and swingweight2 concept. (link)

However, I did not test out my adjustments thoroughly enough. What worked well for baseline-bashing was disastrous for doubles volleys. And my heavy sticks tend to make me hit too hard for drop shots, turning them into sitting ducks in mid-court!

During crunch time, attempts to hit faster serves resulted in the racket swinging my hand instead of my hand leading the stick! And in very fast doubles volley wars, my wrist bears the full wrath from off-centre hits!

TFCC (link) crept-in. It was painful and I had to stop. Fortunately, I detected it very very early. Recovery was very fast. I was up and running in two weeks.

If you are baseline basher and like the powerful plowthrough of heavy rackets, remember to have a lighter setup for those other tennis shots you rarely play.

In case you are curious, the average swingweight of my baseline bashing sticks is about 375 kg-cm². I have since brought it down to about 340-350.

High swingweight is extremely addictive! Please play with care!

Strings: Determining Tension (Part 2)

Other than the style of players and type of tennis balls used, the racket specs play an important role in choosing string tension.

Rackets specs vary in many factors. What I found to affect my decision in string tension are (from most influence to least):
- Stringing pattern (ie 16x18 or 18x20)

- Head Size (eg 85, 95 or 100 sq inch)

- Swing weight

- Balance point

- Total weight

- Flex / Stiffness

A dense stringing pattern like 18x20 in a small 65sq inch head size (like "Woody") will play much stiffer than a similar pattern in a larger head size. If the head size is similar, then the more open stringing pattern will always play softer than a denser pattern at the same tension.

While many have heard of swing weight, not many that I've spoken with understand it's implications. A heavy swingweight provides better plow through the ball. For me, I can feel the strings grip the ball much better with a higher swingweight. When stringing a low swingweight racket, I usually drop a few pounds of tension to liven up the stringbed.

I used to wonder how could Pete Sampras generate power with his 85 square inch Pro Staff 6.0 strung at 75lbs. Much later, I realised he had so much lead tape on the hoop that his racket balance is moved to become even. If his racket was 10 points headlight originally, that's at least 30g of lead taped to the top of the racket! His racket swingweight increased tremendously to help generate power even at ridiculously high tensions! I think even he would struggle if I string 75 lbs for him in a 9oz (255g) racket.

So while we sometimes want to emulate our favourite tour players, we need to pay attention to the customisations they made as well rather than just racket brand and string tension.