PDA

View Full Version : Why do strings shear - my $0.02


Irvin
08-28-2010, 07:47 AM
I am no structional engineer but I do live close to Georgia Tech and Southern Tech. I always thought that shearing was an excuse for strings breaking but now I am starting to doubt that. I really thought that the reason that poly string shear more than any other string is because they were more brittle. Well now I think that more than ever.

No matter how much tension a string will hold it is no stronger than it weakest point. The weakest point is the point where it bends the sharpest.

As a string goes from one grommet to the next it usually bend at 90 degrees. When the knot bends at 90 degrees think about what happens to the string. The inside of the string is carrying no tension at all (there is a lot of pressure up against the grommet) while the outside of the string is being stretched around the radius of the bend. The sharper the radius the more tension is put on the outside of the string. It starts to shear from the outside in until it completely fails.

If there was someway to increase the radius it would stretch the string less. Power Pads may be just the ticket.

If there is anyone out there that has problems with strings shearing maybe you should try some power pads. Power pads have to increase the radius, and if they were good enough for Pete Sampras, Roger Federer, and other pros they should be good enough for you. They shouldn't cost you any more to have them installedin your racket so what have you got to lose? What is a power pad you ask, these things:

http://i422.photobucket.com/albums/pp304/Irvin44_2008/powerpad.png

I would be very interested if these power pads reduce shearing if you have a problem with shearing.

Irvin

jim e
08-28-2010, 03:26 PM
Hi Irvin:
Most of the shears that I have seen are typically located at the 2 and 4 oclock areas, and every so often at the 4 and 8 oclock areas also.
I doubt that power pads at the throat would help with those spots. The only time I have used those pads were on wooden racquets back in the day, and was usually 1-2 each side on the first few mains to help with those turns in those areas.
To stop the sharp turns, I would think that the racquet manuf. would have to make some design changes. I don't even think of it much, as most shear breaks I have seen the string would most likely need to be restrung anyways just from all the prior use. Once in a while you see a thin poly come back early, and you just know it was a shanked ball, but that happens.

Irvin
08-29-2010, 02:51 AM
Hello Jim,

I agree with you most of the breaks I have seen are on like the 4th to the 6th grommet hole at the top of the racket but I could see it on the outside bottom mains at the throat too. Some manufacturer's put a little rounded hump in their grommets at the bottom of the side strip and in the throat area. Babolat has a more pronounced grommet system with those humps in the woofer system (http://www.babolat.com/#/tennis/en/innovations/18). Here is a picture of some Wilson grommets.

http://i422.photobucket.com/albums/pp304/Irvin44_2008/HPIM3039.jpg

I am not suggesting putting the power pads just in the throat area but anywhere they break. I too used to use them on the old wooden rackets but when the wood went away so did the use of the power pads. Now that poly is here maybe the power pads need to come back too. Just wondering.

Irvin

jim e
08-29-2010, 07:17 AM
You know Irvin, you may have something there, if the maunf. placed a grommet with the rounded hump at the 2, 4, 8 &10 oclock where the majority of the shear breaks are that may cut down on those breaks as the string would not be at such a sharp turn. Seems like the company would have to design the racquet with a channel for the grommet set to accomodate those humps so the string would sit flat on the outside.

Irvin
08-29-2010, 08:49 AM
^^ Yes but until they all do why not just use power pads?

Irvin

jim e
08-29-2010, 11:03 AM
^^ Yes but until they all do why not just use power pads?

Irvin

At the 2 and 4 oclock positions??Thats the most prevalent spots. That would raise the string to high out, look like crap at those positions I would not even want them at 4 and 8 spots. I just don't see much shear breaks right at the bottom throat, and thats about the only place you really can place them.