Category Archives: Testing Devices

What’s New?

It has been incredibly busy this winter at Racquet Quest, but that is no excuse to keep you wondering what is here and what is coming your way soon!

You know the new Wilson Ultra series, both the CV and the Tour are in the shop along with the new Head Radical and Head Prestige. I have racquets for your evaluation now.

This website is consumer-centric, but I want to point out some new diagnostic equipment and stringing machines while we are here.

Gosen, one of the premier string manufacturers in the world, sent a GM One Diagnostic machine for evaluation. If you have been to the World Headquarters of Racquet Quest, LLC you have seen several pieces of equipment we use to certify that your racquet is in the very best playing and physical condition.

The Gosen GM One is a swing weight device that has extended the precision to .5 units! And, the included scale measures in the .1 gram range. This is extreme accuracy!




We have the Babolat Racquet Station stringing machine in for evaluation.  A state of the art machine physically and electronically.

We are using this machine to evaluate different string formats, i.e., hybrids with polyester mains/multi-filament crosses, the reverse format, gut/polyester, polyester/gut and straight multi-filament.

The results are exciting and enlightening.

Let’s Talk About This!

I decided to write about this again after reading some posts asking questions, good ones by the way, about string tensions when stringing a racquet.

What we are discussing is not a simple matter, in fact, it is challenging to quantify many things we believe are real.  It is difficult, if not impossible, to tell a stringer how to string a racquet for a new client.  These are the obvious player/stringer questions that need to be answered:
a. What racquet type?
b. What string type?
c. What main and cross string tensions should be pulled?
d. What stringbed (SBS) stiffness is wanted?
e. What racquet weight, swing weight, and CG is wanted?
f. What stringing machine should be used (yes this matters, but is rarely considered!)?

There are also many player-specific questions that are in the mix, including:
a. Do you want more or less power?
b. Do you want more or less control for that power?
c. Do you want to hit with more spin?
d. Do you have any physical problems influencing your play (sore shoulder/arm, elbow, strength, etc.)?

The task/responsibility for a good stringer, or, racquet technician preferably, to his player is quite daunting if the goal is to “string responsibly.”

With answers to these questions, and a stringers plan in place to achieve these goals, one of the most important attributes a stringer can deliver is repeatability. Once a player has settled on a path (racquet, strings, tensions, stringbed stiffness (SBS), etc. you want, as a client and stringer, that customized performance to repeat with every re-stringing. So the stringer must have a process, with metrics, that will guarantee that repeatability. This repeatability is also the foundation for changes from that norm (for example, what happens if I replace my strings with another type, or if I stay with the same strings but switch racquets, etc.)

My comments that follow is the plan I have developed for my stringing process for the players I try to support.

One of the most important influences on how a racquet plays is the stringing machine that is used to string a racquet.

About twenty years ago I developed a machine evaluation procedure for understanding what happens during, and after, the stringing process.

Every machine is treated in the same way. The same racquet, the same string, and the same tension settings, and the same testing devices. I am not going into detail here because it is quite a lengthy path.

Here is what we need to know:
1. When stringing a racquet with main and cross strings, every racquet has a “natural ratio” of the final cross tensions to the final main tensions. That is what the cross string tension is relative to the main string tension of a finished racquet.
2. Nearly every machine tested allowed considerable distortion of the racquet in the three and nine directions. As much as .380 (9.62mm)! You want to minimize that distortion for the final strung racquet.
3. Almost every machine reacted slightly differently when the racquet was removed, i.e., some easier than others.

Why does this matter:
1. Due to the distortion, with the racquet in the machine, every machine produced main string only tensions of about 55% of the machine tension setting. That is the machine is set on 60 for example, and the measured tension is approximately 33 in the middle and increasing slightly going toward the 5th and 6th string. It never reaches 60 with only the main strings installed.

2. When the cross strings are installed, they begin to pull the racquet head back into shape but not significantly until nearing the 11th or 12th cross string.

3. When the racquet is finished and depending a little on the number of strings, it will, hopefully, return to close to the original unstrung shape and dimensions.

4. This “reshaping” can have damaging effects (stress failures) on the racquet.

Here is the question that started this whole discussion again.”

So, do I want to increase or decrease cross string tensions? My opinion is that until you know how the racquet, any racquet, is going to react don’t change tension settings at all. The key here is a responsible stringer wants repeatable metrics first.

We have an “Accuracy Index” procedure for every string pattern, that is the number of main strings and number of cross strings, that calculates the accuracy of the entire string bed based on where the ball is impacting the string bed. The accuracy index is a measure of the ball rebounding normally to a deflected string bed. For example, if a ball were to hit in the geometric center of an elliptical head racquet that was strung with main and cross string tensions that minimized racquet stresses and frame distortion the accuracy index would be 1.0. For the same racquet, if some of the strings were at low tensions (perhaps a break) the accuracy index would be less than 1.0.

Based on “observed breakage locations” we can see the accuracy of that small area of the string bed where most breaks occur.

Most machines I have evaluated will return accuracy indices of 87 to 95 percent.

I have, however, included in this test an “Efficiency Index” which shows me how much the racquet had to “move around” to achieve the accuracy index number and reach some equilibrium. This value is typically in the 70 to 75 percent range! So the racquet is working hard to get back into shape.

If you are a stringer or racquet technician, please note that after the racquet is setup in the stringing machine properly do not make adjustments to the supports during the stringing process. In some cases, the supports will not be in contact with the racquet. Don’t adjust.

Unless the racquet is mounted on a solid annular plate, like the top image, do not restrict the expansion of the racquet by placing a restrictive member across the 3 and 9 o/clock positions which in this image are the top and bottom.  The red knobs are the 12 and 6 o’clock positions

True Tension Professional

True Tension Professional Machine


Wilson Baiardo

Yonex Protech 8 Contact Points

Babolat Racquet Station

Get real!

A lot of players are anxious for new tennis racquets this time of year and have, maybe, asked for one as a gift.  A great idea, of course.

However, be sure the gift giver, or yourself, gets real!  There are some real bargains out there, but the bargains may not get you what you expect.  This can happen to any brand and the more popular the racquet, the more likely there are to be fakes!

Fake Blade 98

This is an image of a fake Wilson Blade 98 compared to a real Wilson Blade 98.

I am showing this image because without seeing this detail the fake racquet graphics will look nearly identical to the real Wilson racquet.

One of the best ways to confirm a fake or real racquet is to “bend” it, that is to check the stiffness of the racquet.  In almost every case the fake will be quite a bit more flexible.  For example, this fake racquet has a stiffness of RDC 41 whereas the real racquet has a stiffness of RDC 63.   If your racquet technician does not have a device for checking stiffness the next best thing is to look at the “insides.”  A qualified racquet technician will know what the insides of the real racquet look like.

Another sign of fakery is the grip pallet.  Most performance racquets will have a foam pallet molded over the graphite shaft or a two-piece pallet that is attached to the racquet shaft.

Fake racquets may very likely have a continuous graphite pallet.  You can quickly look under the first couple of inches of the grip and see if it is foam or graphite.

Clamshell grip pallet

If you are requesting a new tennis racquet be sure you get it from a local business, if possible, or an otherwise reputable source.

If you have any questions at all, please call your local dealer or us (407.491.4755) to be sure you “GET REAL.”

Pictures are Easy!

It is easy for me to post pictures of racquets being made ready for shipment to tournament players. However, there is a lot more work before these can be tagged, bagged and packed!

Paperwork is what I am talking about!  I have included some of the paperwork in this image, so you get some idea of what is involved.  Not many people like paperwork but for this work it is essential!

Every racquet we do has the same “paperwork”, but local customers normally don’t need racquets customized and shipped overnight!  Out of town customers, your racquets are typically prepared as close to the “use by” date as possible.  So these racquets were strung and tweaked this morning and shipped (via overnight) this afternoon.  Most of the customization can be accomplished before stringing but final adjustments, if required,  are the last thing on the list.


The “paper work” on the right is data from the ERECA Balance System, and this information is taken at each step in the customization, and at a “play ready” status.  While I still rely on swing weight as the primary dynamic property I use the ERECA system for very precise static balance, total weight, and a quickly calculated swing weight.

The other “paper” is my standard Racquet Record software data that contains over forty (40) pieces of data that are a permanent record in the customer file.

It sounds like a lot of paperwork, but it is necessary to assure consistency and organization.  Every racquet gets the same treatment.

So, the next time you see pictures remember there is a lot more to it than stringing, bagging, and shipping.


A Visit From Ereca!

I am very happy to have Eric Ferrazzi of Ereca Tennis visiting Racquet Quest!

Eric Ferrazzi-Ereca, France

Eric Ferrazzi-Ereca, France

Eric designs diagnostic equipment for technical tennis shops.  Racquet Quest has been using some of the Ereca designs for several months with great success and acquiring better data.

It is important for us to recognize what we can do with proper equipment, and, take advantage of the technical designs of the Ereca Team.

Ereca has many other designs that are in the “evaluation process” and Racquet Quest is happy to be involved!

Now if Eric could just teach me how to cook French food…

Congratulations, Stan!

First let me get the “shorts” thing out of the way…I like them!  I would like them better with a cool white shirt, but that’s just me.

The next item of business, for me, is the fantastic one hand backhand that serves Stan so well.  It makes me wonder why juniors, and maybe some adults, are being taught (forced?) the two hand backhand?

I think I understand the physics invloved in swinging a racquet and I also understand that you can build muscle memory and pure muscle if you train for that (one hand backhand).

After seeing the effectiveness of the one hander it seems more players would request that technique be taught to them.

I am still in Italy but will be headed back to France in the morning to continue discussions with Eric and Carine of ERECA regarding diagnostic devices and some ancillary equipment.



SBS…What is it?

SBS is “String Bed Stiffness” and is the stiffness of the entire strung area of a tennis racquet.  SBS is not the same as “tension” and this is important to understand.  Why?

When you talk to your racquet technician about “tension” it is, normally, about what number to set on the stringing machine.  This number is usually called “reference tension” and every stringing machine has a way to set how many pounds, or kilo’s, it will pull each string before it stops.

Here is the problem with “reference tension”.  It means different things to different machines!  A “reference tension” of 55 pounds will result in a different SBS when set on different machines.  If you take your racquet to technician “A” who uses a lockout machine it will have a different SBS than technician “B” that uses a constant pull machine .  Over time, perhaps, each technician will arrive at the perfect machine setting to satisfy your requirements.

Why do all of this?  You need to request a SBS!  When talking to your technician you will talk about resultant SBS.  So each time you have the racquet strung it will have the same SBS regardless of what machine it is strung on.  The SBS number will be based on the diagnostic device the technician uses to collect data.  There are three (3) or four (4) devices that will be familiar to all technicians:

Babolat RDC  Babolat RDC

Beer’s ERT 300  Beer's ERT300

Beer’s ERT1000  Beer's ERT1000


FlexFour in Action

FlexFour in Action

The two Beer’s devices will return virtually the same number since they use the same technology.

The Babolat RDC uses, as far as I can determine, a combination of deflection and voltage.  The FlexFour uses a deflection and includes the racquet stiffness..

So, the numbers may be different but it is the variation between tests that are crucial.  If you are serious about your SBS I suggest you get a Beer’s ERT300 (about $180.00) and keep it in your bag.  If the racquet has a SBS of 41 right after stringing you should consider having it strung when the SBS has decreased to about 33.  For any device you should consider a reduction of twenty (20%) percent a reminder to have the racquet strung, soon!

SBS…what is it?

Babolat RDC

Babolat RDC Testing SBS

SBS is String Bed Stiffness.  What this tells us is the “stiffness” of the entire string bed, not just a single string.  You may still hear the term ASPS, Absolute String Plane Stiffness, but that is too many words.  How is this different than “reference tension”?  Reference tension is the number you, the customer, tell your stringer to set the stringing machine to pull each string.

This “reference tension” has been the default conversation between customer and racquet technician for many years.  The problem is that the SBS may not be even close to that number so as a racquet technician we need to know what the SBS is at a given “reference tension”.  A device such as the Babolat RDC shown above can do this but it comes at a hefty price.  The Beers ERT300 is

Beers ERT300

Beers ERT300

FlexFour SBS Device

FlexFour SBS Device in Action

an electronic device that is available for around $150.00 and gives a number in Kg/cm, which can be easily converted to pounds.  The FlexFour is another device that returns valuable SBS numbers.  The point is be sure your racquet technician is using some device to record SBS.  At Racquet Quest we use all three (3) so we can respond to any SBS request.

Why, again?

Without going into what happens to a string and racquet during the install process it is clear that the ball feels the “result” of all the strings acting in concert with one another and the racquet itself.  So it makes sense to know what SBS (stiffness) the ball is “feeling”, and with this SBS number and the racquet stiffness number the “effective stiffness” can be calculated.  Through manipulation of the SBS a “perfect” effective stiffness can be provided to you the customer.

So when you hear the term SBS you can quickly join the conversation and know what you are talking about!  And, that is a good thing!

Quick Trip to String Thing™

I just returned from SanDiego, CA  where Tim Strawn and I met with the StringThing™ team.  A really good group of guys!  Dave, Scott, Stephen, Mike, Steve, and Dr. Norman made us feel like part of the group!

We went to the manufacturing facility (yes, it is the United States!) and it is impressive in terms of taking an idea from concept to market in the short period of time they have done it.

These are tennis players, each and everyone!  They enjoy the sport and it shows in their commitment to this product.

You may have seen my short video on the String Thing™ and there may be other video coming soon.  If you have not seen the video please take a look.  I believe this product is a good one so I wanted to take the trip to SanDiego to meet the people.

If you have any questions about the String Thing™  please let me know.

The String Thing™ is designed to re-align strings that are out of position.


Using the String Thing™

I have been using the String Thing™ for a few months and wanted to post this short video for those that have questions about how to use it.

Please let me know if you have any questions.

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