Warped Hoop - Head Gravity

The recently launched Head Gravity series of tennis rackets are really soft and arm friendly. 

This rare flex got many players on board, especially previous users of the Babolat Pure Drives and Aero Pros.

However, their feedback has been mixed. Some loved the Gravity while many others hated its inconsistency and lack of accuracy.

In stock form, I find the power and stability lacking.

However, it is the incredibly soft hoop that poses the biggest problems. It is almost as soft as the old but very popular Head Prestige.

Maintaining hoop shape while stringing this Gravity is challenging. I received so many badly warped hoops that rendered the racket unplayable.

Take a look yourself at the three videos below...

The stringjob in this first video was done by another stringer. You can see the Head logo stenciled. The hoop was approximately 24.8cm wide.

In the second video below, the hoop width was approximately 25.3cm after the strings were cut and removed.

 

 
The third video showed the width to be almost exactly 25.3cm after I restrung it. No stencil. Almost zero distortion.

Naturally, the player loved the distortion free stringjob.

If you have a Head Gravity playing inconsistently, it could be the stringing. Try measuring the hoop width without and with strings.

PS: Sorry about the lousy video quality...somehow it deteriorated after uploading
 



   

Wilson Clash Customization

The latest Wilson Clash seemed interesting. 

Marketing generated so much hype that even during pre-launch in late 2018, I received many questions from players about its potential to up their game.

It did not take long before both versions were sent in to me for stringing and modifications.

I had a few hits with some that were sent to me strung. Surprisingly, many were strung with poly/multi or full multi. Few were with full poly. 

Dampener or not, the feel was very muted yet included a lot of buzz and trembling. This felt exactly like "hoop wobble" (link). Immediately, this hinted a potentially very soft hoop. Extra care needed when stringing. 

When lacing up the centre main, what struck me was how big the modern grommet holes were. Every hole was large enough to be a tie-off hole. That made threading strings very easy.

My earlier suspicions were confirmed when tensioning the mains. Previous soft hoops I worked on warped more when outer mains like 6, 7 or 8 were tensioned. The Clash started warping significantly from inner mains like 3, 4 and 5. That is a very significant change and carries huge implications.

Crosses start very high and have smaller gaps near 12 o'clock. These gaps almost double near the last few bottom crosses. Another hint of potential erratic stringbed response especially nearer the top quarter or top third which most professional players like to contact the ball at.

When weaving the crosses, the gaps kept reminding me of the earlier Burn series. It was so wide it created control issues for many. And those that could somehow control the ball snapped strings too quickly. Would this happen with the Clash open gaps? (I was later updated by several their strings notched extra fast in the Clash compared to their own 16x19 stringbeds)

As I examined the throat area, I noticed a notched recessed area inside the throat. (Somewhere beside the "o" and "n" of the red "Wilson" wordings) This must be where the racket is flexing on impact. Interesting. Few rackets I can think of, other than wood, flex at such a low and faraway point away from impact point.

Not long after, another Clash came in. Brand new unstrung. For very heavy customizations for a touring professional.

Armed with the feedback from the earlier few Clashes, I took up the challenge. 

It was a challenge because the Clash was marketed as a very powerful frame. Many complained of timing issues and erratic hot spots on the stringbed. And it had very open strings coupled with a very soft flex of about 55. All these pointed to control issues.

To add power or weight meant doubling up on these control problems.

Nevertheless, I did the calculations and it all added up nicely. So I proceeded.

First step, strip the grommets.

Now that you see how much lead tape I am adding, can you understand why I said it was a challenge to add control and keep the ball in? For a professional full time tennis player!

(I scribbled on the lead tape too!)

Grommet installation was very very easy. Took me about 4 seconds. Fastest I have ever reinstalled top grommets after adding lead tape.

For this ease of reinstallation, I have to thank Wilson for this modern grommet design. The centre pieces always cause the biggest obstructions. So they cleverly separated the centre 10 grommets from the bumper guard. And the drilling featured extra large holes for easy grommet installation. Well done Wilson!! And thank you!!

Typical of a new unstrung before racket, the grommets need to be seated properly to ensure a playable string job. Look at the red circles area below, compare the properly seated grommet with the "unseated" one.

Do not assume this happens automatically when you pull tension. I have several strung frames sent in to me with the grommets still "unseated".
 

Until now I do not understand why so many are enamored and mesmerized by silicone in the butt. Everyone I customize for asked for it!

Final checks before handing the frame over to the player. So far the hoop size QC seems very consistent. All Clash and Clash Tour I worked on measured 326mm length and 251mm width for the inside hoop from base of grommet to base of grommet. Zero hoop distortion achieved.

PS: No details of racket weights, specs nor string tensions would be revealed as these players are still actively competing. So please do not ask. 






    

Head Prestige Tour 660

To many racket connoiseurs, the made in Austria Head Prestige Tour 660 is very difficult to string properly.

The challenge stems from its very soft flex and hoop which distorts very easily.

Not my preferred racket to work on too. Many extra precautions to adopt. But, once in a while, I like challenges...

Strung with full poly strings.

New stringjob with full poly on the left while old stringjob with the stenciled head logo on the right. Both done one-piece.

Seems to me the old stringjob compressed the frame narrower.

When I checked my unstrung and strung hoop distortion, mine was out by 0.5mm. Not too bad. I'll take it!

In case you missed it, here's a previous experiment I did with my friends on stringing very flexy frames:

Racket Flex and String Tension Preference

The proud owner of this PT660 couldn't wait to take it out for a game!




     

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. 






     

"Breaking Into" Rackets

Some months back, a junior competitive player asked for advice on how to continue playing with an arm injury.

Then, he was using a Babolat strung very tightly with full poly. Switching to a hybrid or even full multi did not help.

I felt a more flexy racket was necessary. After testing different sticks, he made his choice and stuck with the new racket since. According to published specs, the RA was around the low-60s.

During a recent restring, he started lamenting how the accuracy was still poor compared to his previous stiff Babolat.

I was perplexed.

He has been happily using the four new stick for about four months. Even managed to beat some team-mates he regularly lost to. Why the sudden nostalgia about his old Babolats?

He rang up his coach, passed me the phone and we spoke.

Top on my mind was whether he was "arming or swinging" (link) the new stick. This technique has huge implications on accuracy, especially when one is switching from a stiff flex to something softer. I also asked about his timing.

All seemed well. 

To ascertain, I even dropped in on one of his training sessions to see for myself how he was hitting. And there he was, leaking some forehand shots just a tad right. First serve consistency was not as good as what I recalled.

I borrowed and played a tie-break each with all four of his sticks. Then realised that the flex has changed! The rackets has all broken-in and the graphite has softened!

The pieces started falling into place. Like when he mentioned that he felt he was not able to "load" the strings and "pocket" the ball as much as before. And the reduced spin. And the "not enough time" to shape the ball.

It was finally confirmed after we put the rackets into a Babolat RDC machine. The RA stiffness for all four of them now measured 59, 60, 60 and 61 compared to 63, 64, 63, 65 when new.

To address this, I proposed to:
(1) add some lead tape to increase mass, which would "stiffen" the dynamic flex, &/or
(2) lower the tension of his existing strings, &/or
(3) change to a thinner gauge or softer string.

As it was near an important competition, he selected option (2). It was a quick-fix that addressed most of his problems. His accuracy returned while the arm pain stayed away.

Perfect!




     

Racket Flex and String Tension Preference

Many users of very flexible frames like to string very tight. 

The most common reason was to improve accuracy and that they enjoyed the feel of the racket flex. When strung at normal tensions, these folks claimed the frame stopped flexing.

Out of curiousity, my friends and I tried stringing some very flexy frames (RA 50s) to investigate the flex response.

Tight (75 lbs)
Both the full poly and the full synthetic gut felt like a board. 

The stringbed was so stiff and tight we did not feel any string pocketing at all. 

However, impacts did not feel harsh as we could clearly feel the racket flexing on impact. 

Contrary to the beliefs about stringing it tight for greater accuracy, all our shots suffered some loss of directional control. Some forehands leaked to the right and backhands leaked left. It felt like our timings were slightly late and off.

We tried "swinging" the racket and "arming" the racket. (link) Well connected sweetspot hits felt nicer but it was still boardy, extremely low powered and inaccurate.

Neither could we generate any decent spin. Not even slices.

Serves were pathetic. No power, no pace, no spin, no height and plenty of double faults!


Normal (55 lbs)
This was near our usual tensions so everything felt familiar.

It was comfortable, spinny, accurate although still a tad low powered.

It was interesting to note that when we had sufficient time to prepare, step into the shot before "swinging" the frame, there was a very powerful delivery. The string and racket flex worked in unison.

Even when we were late, on the run and half-muscling through the shot, we were able to partially load the strings before flexing the racket.

After hitting with this, we discovered what and why we did not like about the racket flex earlier with the tight tension. 

Whenever it flexed, power was absorbed by the frame. The energy that was incoming from the ball, and the energy which we threw into the forward swing, was heavily dissipated by the racket flex. 

And before the flex could rebound, the ball has left the strings. Hence the very low power and poor directional control.

Swinging worked much better.


Loose (35 lbs)
For this tension, we chose a stiff poly string and strung it full bed.

The first thing we noticed was the extra huge sweetspot. It was so forgiving we thought we were using an oversized racket!

The second thing that impressed us was the abundance of power and spin. A huge increase over the normal tension.

Along with this was the ability to load and pocket the strings. With the added advantage that the harshness of any off-centred shots would be safely cushioned by the racket flex.

At this tension, the usual downsides were the high rebound angle of the stringbed and some light string buzzing. However, this had nothing to do with the racket flex. It was a common problem across all types of racket frames.

Most distinctly, we did not feel much of the racket flex.


Conclusion
Among the three, we preferred the one lowest tensioned. 

However, for practical play, mainly to mitigate the high rebound angle, we would string somewhere around the mid-40s lbs, depending on strings.

What we unanimously agreed was:
(1) flexible frames felt superior to very stiff frames,
(2) flexible frames are very demanding to wield properly, and
(3) stringing flexible frames loosely made them much easier to use for recreational players as it was much better to load the strings than to flex the racket.