# Thread: Why +2lbs On The Cross?

1. ## explanation on why 2 more lbs on the cross.

here i offer an explanation why we need 2 more lbs on the cross string. actually quite trivial and i wonder why no one has brought it up.

the first pound.

let imagine the situation in which we have a good 6-pt machine.

we weave and tension mains string first, and then we weave and tension the cross string. when we tension the main string, the strings are a straight line when tensioned. without loss of generality, let say we first tension the mains to 20lbs.

then we weave and tension the cross at 20lbs. notice now that after the tensioning, the mains are no longer straight as they are weaved with the cross. the result of the mains being displaced and since the frame isn't moving, the tension will have to go up. by how much is anybody's guess, but my guess would be say 1 lb?

now, if the mains goes up by 1lb, then we have to increase the cross tension to 21lb to compensate for the difference.

the second pound.

i believe if we have good support, 1lb or so is all we need. many have said that if we have a machine with no support, we need 2 pounds to compensate the distorted frame. i think that is a legitimate argument.

collorary:

what else can we find from this?

well, one observation i can see is that, if we tension, eg. 20/22, the resultant mains tension is actually higher than 20. and imho, more like 21 or so.

does that make sense?

2. ## Re: explanation on why 2 more lbs on the cross.

Originally posted by kwun
here i offer an explanation why we need 2 more lbs on the cross string. actually quite trivial and i wonder why no one has brought it up.

the first pound.

let imagine the situation in which we have a good 6-pt machine.

we weave and tension mains string first, and then we weave and tension the cross string. when we tension the main string, the strings are a straight line when tensioned. without loss of generality, let say we first tension the mains to 20lbs.

then we weave and tension the cross at 20lbs. notice now that after the tensioning, the mains are no longer straight as they are weaved with the cross. the result of the mains being displaced and since the frame isn't moving, the tension will have to go up. by how much is anybody's guess, but my guess would be say 1 lb?

now, if the mains goes up by 1lb, then we have to increase the cross tension to 21lb to compensate for the difference.

the second pound.

i believe if we have good support, 1lb or so is all we need. many have said that if we have a machine with no support, we need 2 pounds to compensate the distorted frame. i think that is a legitimate argument.

collorary:

what else can we find from this?

well, one observation i can see is that, if we tension, eg. 20/22, the resultant mains tension is actually higher than 20. and imho, more like 21 or so.

does that make sense?

1) Restore raquet to original shape
2) Original shape more difficult to restore because of weaving and tension diffence on crosses.

3. Makes perfect sense kwun Perhaps you should sticky it in FAQs or something.

Yodums

4. G'day Kwun,

For a long while after reading, I was like ->

Then I guess after the beer has worn off, I did a big ->

Good post! And makes perfect sense!

5. let me just say this. if you can string a racquet without needing to adjust the mains and crosses to look neat upon completion (by stringer, not by player after use) then you can skip this whole 2lbs / 10% diff on the crosses. but no real harm generally if still practiced.
if not then stick to the 10% rule is all i can say to the average stringer.

6. +10% rule if the desired end result is to have similar tension for both cross and main. those are what i call regular tension.

7. ## Just Curious

Hi, I wanted to ask whether 2lbs difference is the recommended difference on iso shapped racquets?
Well, jus read the post from mr.lok from a forum where he strung racquets for pros, and he strund Kim's racquet at 27lbs mains, and 21lbs cross... not only was the cross not 2lbs higher than the mains, its way lower..

Just hope to find an explanation before restringing my racquets.. all of them are quite loose at the moment and i need them redone soon..
cheers

Hi, just a question, whether it will do any harm to the racquet or any change in performance if the cross is strung lower than the mains?
in one forum, it was stated that Kim DM played with 27 mains, 21 cross, is that ideal?

Hope to get an explanation

9. Originally Posted by benibeni
Hi, just a question, whether it will do any harm to the racquet or any change in performance if the cross is strung lower than the mains?
in one forum, it was stated that Kim DM played with 27 mains, 21 cross, is that ideal?

Hope to get an explanation
I believe that's a mis-typed information because a 6 pound difference could potentially damage the racket. I think it should be like 27x31, which is close to the tension that Koreans prefers in Olympics.

27x21.....the racket will become a full circle .

10. That's not mistyped information. Mr. Keen has special attachments that allows all sorts of tension and tension-ratio combination.

Originally Posted by bluejeff
I believe that's a mis-typed information because a 6 pound difference could potentially damage the racket. I think it should be like 27x31, which is close to the tension that Koreans prefers in Olympics.

27x21.....the racket will become a full circle .

11. How is the tension measured? I don't string my own rackets, and I was just wondering.

12. Originally Posted by benibeni
it was stated that Kim DM played with 27 mains, 21 cross, is that ideal?
Hope to get an explanation
I'm not sure that 27x21 is KDMs normal tension setup.
The impression I got was that on that particular day his racquet just felt wrong and he had to keep changing it. Eventually, after several restrings, when it got to 27x21 it felt OK.

13. Originally Posted by kwun
then we weave and tension the cross at 20lbs. notice now that after the tensioning, the mains are no longer straight as they are weaved with the cross. the result of the mains being displaced and since the frame isn't moving, the tension will have to go up. by how much is anybody's guess, but my guess would be say 1 lb?
As we've been talking about Main v Cross tension a bit recently, I thought I'd have another look at this. I don't claim to be an expert. Thse are just thoughts and observations.

From measurements on a strung racquet, I calculate that the mains are stretched by about 0.027mm per cross string. This is for 0.7mm diameter string.

Centre mains are 24cm, or 240mm
Stretched length becomes 240.6mm
An increase of about 0.25% (maybe 0.5% for the side mains)
Small enough to be ignored (in my opinion. 0.5% of 20lb = 0.1lb )

So any increase in mains tension as a result of stringing the crosses may be mostly due to the frame changing shape during stringing.

Another reason for increasing tension on the crosses may be that when you pull the crosses, friction from the mains reduces the effective tension that the string experiences. How much by, I dunno, but we should be able to find out by attaching some string to some scales. Weaving it through some tensioned mains, and pulling tension. Compare what the string machine is set to pull and what the scales read. Probably easiest to do on a drop weight.
I'll have a go next time I string.

14. Originally Posted by bluejeff
27x21.....the racket will become a full circle .
Maybe he wants an oval shaped titanium head-heavy racquet...
jl
PS maybe there is a better racquet out there than the cab30ms :P

15. Originally Posted by Neil Nicholls
......

So any increase in mains tension as a result of stringing the crosses may be mostly due to the frame changing shape during stringing.

....
compared with highlight as bold blue

Quote:
Originally Posted by kwun

then we weave and tension the cross at 20lbs. notice now that after the tensioning, the mains are no longer straight as they are weaved with the cross. the result of the mains being displaced and since the frame isn't moving, the tension will have to go up. by how much is anybody's guess, but my guess would be say 1 lb?

I thought during racket stringing that if you use a 6-point support stringing machine, the supporting system is able to hold the frame of the racket more or less in its unstring shape.

16. Originally Posted by leehsim
compared with highlight as bold blue

Quote:

I thought during racket stringing that if you use a 6-point support stringing machine, the supporting system is able to hold the frame of the racket more or less in its unstring shape.
actually, we are talking about the same thing. what you quoted was my first part which assumes a 6pt machine that holds the frame in place. the second part explains the 2nd lbs of tension which assumes no support which is what Neil assumed also.

17. Originally Posted by kwun
actually, we are talking about the same thing. what you quoted was my first part which assumes a 6pt machine that holds the frame in place. the second part explains the 2nd lbs of tension which assumes no support which is what Neil assumed also.
Thanks to your clarification. Help to confirm my understanding.

Some more thought.

Thought 1: During stringing of racket on a 6-point, the frame in sahpe but the tension of main may increase due to weaving of crosses.

Thought 2: After the the racket is dismounted from the stringing machine, the frame of the racket may change due to the reaction of the tension on the mains and crosses.

Any misconception of my thoughts?

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