***Experience with very different string patterns***

[Technatic]

Because we have the Tension Advisor we get many questions about stringing tensions for the racquets with very different string patters like 18x16 instead of 16x19 before.

If the basic principle of the elliptic stringbed counts for these racquets the tension on the crosses should be much higher than on the mains:

The main strings make the racquet head shorter and the crosses should “pull back” this deformation.

The actual tension in the crosses is much lower because of the friction, and the tension in the mains is higher than the stringing tension, because the crosses stretch the mains.

Therefore there are more crosses than mains needed to eliminate the deformation and the length is larger than the width of the racquet head.

I would like to hear about your experience with these new string patterns.

 

[eelhc]

Interesting analysis but are racquet string patterns actually designed to limit frame deformation/shape retention? I doubt the string patterns were designed with this as the primary goal. Rather, the desired pattern and the frame was designed in concert and the right amount of material + strengthening was added to the stress points. At least I would hope so... but one never knows. It seems there's more going into marketing than development these days. There are other factors to consider as well. For example, grommet friction, especially on the outer grommets where the strings enter at an angle.

However, some shape change/deformation is normal (even for the open pattern frames) and unless it's gross and could cause frame damage, one should string for playability and not worry about it.

 

[Technatic]

I doubt the string patterns were designed with this as the primary goal.

I share this doubt but nevertheless, the elliptic shape is the most logic one for the actual tensions in mains and crosses after stringing. The elliptic shape could also be the result of trial and error.

Or vice versa it did go wrong with racquets with other shaped racquet heads, like the Prince Extenders.

Rather, the desired pattern and the frame was designed in concert and the right amount of material + strengthening was added to the stress points. At least I would hope so... but one never knows.

I am afraid that this thought can only survive because modern racquets are so very strong and modern stringing tensions are so low, in relation to 20 years ago.

Our (very old) Tension Advisor is designed to create as little distortion after stringing as possible.

So we think that the measuring and comparing the length of the stringbed before and after stringing tells if the difference in stringing tension for mains and crosses was right.

It would be interesting to hear if someone with a 6-point machine could get the racquet out after stringing a 18x16 pattern (like the wilson blade 98S) with about the same tension on mains and crosses.

 

[Dags]

I played with the Six.One 95S for about three months, which has a 18x16 string pattern. Always used the same tension on the mains and crosses, usually around 52lbs. No distortion of the hoop was evident.

 

[Irvin]

I've strung many different frames with many varied patterns at many difference tensions. Hybrids and many with different tensions on mains and cross. Sometimes the crosses were tighter sometimes looser. Some manufacturer's frames have more distortion than others but more often than not I see little distortion if any with the strings and or tension. I have experimented with the on line tension advisor and it seems to make sense to me. I believe there is some expert knowledge with tried and true experimention behind it but for the most part it is just too much trouble for very the differences i see. It certainly does not do any harm that' for sure.

Although i like the TA I prefer to use what the racket feels like to me or what the customer asks for. Many customers dont want to be "overloaded" with too much information. If mains and crosses are always strung at the same tension there is also less chance of operator error by not setting / resetting the tension after finishing the mains / cross for the other string or racket.

 

[Technatic]

I played with the Six.One 95S for about three months, which has a 18x16 string pattern. Always used the same tension on the mains and crosses, usually around 52lbs. No distortion of the hoop was evident.

Very Interesting

Did you actually compare Length and width of the string area after stringing with the empty frame before stringing?
Do you have a 6 point machine and was the pressure on the outside supports the same after stringing as you adjusted it before?

Disadvantage" of modern racquets is that they are very stiff, because of the high percentage of carbon, so the distortion is also small and not so noticeable as earlier.

So you have to measure to know, I think.

 

[Dags]

Did you actually compare Length and width of the string area after stringing with the empty frame before stringing?
Do you have a 6 point machine and was the pressure on the outside supports the same after stringing as you adjusted it before?

I had a pair of racquets. First thing I always do with a pair is check they match unstrung: weigh them, check balance point, and put them together to compare length. I then string one, and compare length again with the unstrung racquet to make sure there's no obvious distortion. String the other and check again.

My machine does have 6-point mounting. I can't say I noticed any difference with the pressure of the side supports, but equally I wouldn't know how to measure it other than by feel.

Disadvantage" of modern racquets is that they are very stiff, because of the high percentage of carbon, so the distortion is also small and not so noticeable as earlier.

This is indeed a very stiff racquet. I only played with them for three months because I developed arm problems. I'm not sure how noticeable any distortion would have to be for it to be a concern. If I can't spot a difference when I hold two frames together, that's good enough for me; others may prefer a more scientific approach. ;-)

 

[eelhc]

Isn't flex measured in the z axis (perpendicular to the stringbed) only? Does flex actually translate into racquet deformation (in the X-Y axis)? It would depend on how the graphite fibers are aligned in construction.n Because it's stiff in one direction, it doesn't mean it's stiff in another. For example, it's possible to have a flexible, whippy shaft in golf that's still low torque.

Again... I think this is interesting discussion but in practice, just string for the best playability and don't worry about deformation.

 

[Technatic]

To be able to put this in the right perspective perhaps we can look at this matter in this way.

We compare the same racquet wit 2 different patterns, 16x19 and 18x16.

Let’s assume:

- That the actual tension is 20 % higher in the mains and the tension in the crosses is 20 % lower than the stringing tension.

- That the distortion of the 16x19 is minimum for the same tensions for mains and crosses .

>> This means that the total force of 16 mains on 50 lbs = 16*50*1,2 = 960 lbs

>> Total of all crosses = 19*50*0,8 = 760 lbs

- The total forces in the 18x16 will be:

>> For the mains: 18*50*1,2= 1080 lbs

>> For the crosses 16*50*0,8= 640 lbs

For the 16x19 racquet 760 lbs is needed to eliminate the widening caused by 960 lbs in the mains.

So 200 lbs total tension less than in the mains.

For the 18x16 racquet the difference in total tension is 440 lbs.

I can not imagine that 220 lbs extra in total force does not make any difference for the racquet.

What do you think?

 

[eelhc]

To be able to put this in the right perspective perhaps we can look at this matter in this way.

We compare the same racquet wit 2 different patterns, 16x19 and 18x16.

Let’s assume:

- That the actual tension is 20 % higher in the mains and the tension in the crosses is 20 % lower than the stringing tension.

- That the distortion of the 16x19 is minimum for the same tensions for mains and crosses .

>> This means that the total force of 16 mains on 50 lbs = 16*50*1,2 = 960 lbs

>> Total of all crosses = 19*50*0,8 = 760 lbs

- The total forces in the 18x16 will be:

>> For the mains: 18*50*1,2= 1080 lbs

>> For the crosses 16*50*0,8= 640 lbs

For the 16x19 racquet 760 lbs is needed to eliminate the widening caused by 960 lbs in the mains.

So 200 lbs total tension less than in the mains.

For the 18x16 racquet the difference in total tension is 440 lbs.

I can not imagine that 220 lbs extra in total force does not make any difference for the racquet.

What do you think?

No... Incorrect analysis.

The center mains and crosses pull straight across on but the outside strings the force is spread around the hoop. The grommet guides the string at an angle through the frame. The 2 stress points are where the grommet enters and exists the frame.

Also.... The only frames I know to be identical except for the pattern are the head frames with the interchangeable grommets for closed and open pattern. I suspect the other frames are the same but we can't tell for sure.

 

[am1899]

However, some shape change/deformation is normal (even for the open pattern frames) and unless it's gross and could cause frame damage, one should string for playability and not worry about it.

Couldn't agree more. Seems to be a bit of putting the cart before the horse, no?

 

[Technatic]

No... Incorrect analysis.

The center mains and crosses pull straight across on but the outside strings the force is spread around the hoop. The grommet guides the string at an angle through the frame. The 2 stress points are where the grommet enters and exists the frame.

The matter is not if there are 2 of the same frames with the different string pattern but the huge difference in load on the racquet with the same L/W ratio in case of 16x19 and 18x16 patterns.

The L/W ratio decides how much force in the cross strings is needed to eliminate the widening caused by the mains.

We compare the same racquet wit 2 different patterns, 16x19 and 18x16.

It would have been better if I had said :

“We compare 2 racquets with the same lenght and width of the string area”.

So if the racquet design would be adjusted to the string pattern the L/W ratio should be different.

The stress in the racquet depends on the shape of the racquet head and not of the design of the cross section.

There is not a smart technical solution “inside” the tube that can compensate for the different load between 16x19 and 18x16.

IMO:
If it is the intention of a racquet designer, that the stringing tension is the same for mains and crosses, the racquet head should be adjusted to the pattern.

If the shape is the same the stringing tensions should be adjusted.


Only my 2 cents ofcourse.

 

[eelhc]

IMO:
If it is the intention of a racquet designer, that the stringing tension is the same for mains and crosses, the racquet head should be adjusted to the pattern.

If the shape is the same the stringing tensions should be adjusted.

Only my 2 cents ofcourse.

I highly doubt the intent or the goal of the racquet designer to retain the shape of the head. Your analysis is entirely static and doesn't apply to how the racquet is used.

When the ball is struck with the racquet, the mains do far more "work" and is pulling/tugging on the hoop even more whereas the crosses serve to keep the mains in place. So dynamic analysis taken into account, even on traditional string pattern racquets the mains put more stress on the frame.

Again, this whole discussion is an academic exercise only. In practice, don't worry about it and string for best playability.

One of the most interesting examples of dynamic analysis and engineering is the SR-71 blackbird fueling. As dangerous as it may seem, the fuel leaks out of the fuel tanks because the seals are designed to be loose on the ground and expand tight at speed/flight. Static analysis in general has little bearing in real world applications.