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View Full Version : Equal Strung Weight and Balance doesn't equal equal SW, why ?


jangpyo
04-15-2006, 11:14 AM
I hope someone can explain this for me.

My limited understanding of racquets says that when comparing two racquets that have equal or very close strung weight and balance the swing weight of the two racquet should also be equal or close. Is this right ?

To be more specific based on TW specifications, comparing LM prestige MP to RDX 500 mid, both have very close strung weight as 11.9oz. and 11.8oz respectively. Also the balance is the same.
But, the swing weight is very different, 325 vs. 318. I have both racquets and when I swing the racquets I can empirically feel the difference in sw.
There is got to something that I am not understanding correctly or missing.
Could the experts on this board help me understand ?

imadeulook
04-15-2006, 11:19 AM
aerodynamics maybe? i dont really know:mrgreen:

snoflewis
04-15-2006, 11:26 AM
this may be a question that most people won't be able to answer.....maybe the 0.1 oz counts for the 7 pt SW differenece...but that doesnt seem too likely

rich s
04-15-2006, 11:39 AM
the weight distribution within the two frames is different.

as an example: the lm prestige mp may have 5.95 oz of mass 11" above and below the balance point whereas the RDX may have 5.90 oz of mass 8" above and below the balance point. Because the lm prestige mass is further from it's balance point it will have a higher swingweight.

These numbers are not exact nor are they are not to be constued as acutal they are for exampletory purposes only.

Davai
04-15-2006, 11:42 AM
I hope someone can explain this for me.

My limited understanding of racquets says that when comparing two racquets that have equal or very close strung weight and balance the swing weight of the two racquet should also be equal or close. Is this right ?

To be more specific based on TW specifications, comparing LM prestige MP to RDX 500 mid, both have very close strung weight as 11.9oz. and 11.8oz respectively. Also the balance is the same.
But, the swing weight is very different, 325 vs. 318. I have both racquets and when I swing the racquets I can empirically feel the difference in sw.
There is got to something that I am not understanding correctly or missing.
Could the experts on this board help me understand ?

SW is the numerical indication of how the masss is located on the racket (rod). It's basically rotationla inertia around the end point. You can use the same weight of materials, but not necessarily the same materials. Moreover you can distribute them at different locations at different amounts to a achieve the same center of mass (balance). Thus achieving different SWs.

In simpler terms: the two rackets have their masses located at different places on the racket, with the prestige, respectively, having more proportional mass towards the head. An isolated example would be look at the encompassing, heavier bumper guard on the prestige and the short, lighter bumper guard of the rdx.

I hope that wasn't too confusing. If you wish to understand it better grab a Physics book and read the section about rotationla Inertia.

J D
04-15-2006, 11:50 AM
Rich S is correct, swingweight will vary according to weight distribution among frames of the same mass and balance. Also, measuring swingweight is a not an exact science for a couple of reasons. The equipment used is very sensitive and gets out of calibration very easily. It must constantly be calibrated for accurate results. And, to further complicate matters, small temperature changes can cause a SW reading to vary by as much as 10 units.

Jangpyo, 7 units is not that much difference in swingweight. I would wager that some players can't even tell a difference in SW until it gets to over 7 units.

jangpyo
04-15-2006, 12:20 PM
Thanks for the help.

But as Davai puts it if the distribution of materials at different location along the racquet can account for the different SW, wouldn't that also make the balance be different between the two racquets ? But the balance is shown to be the same. Just a thought.

snoflewis
04-15-2006, 12:37 PM
Thanks for the help.

But as Davai puts it if the distribution of materials at different location along the racquet can account for the different SW, wouldn't that also make the balance be different between the two racquets ? But the balance is shown to be the same. Just a thought.

yeah...if there was more mass towards the head compared to the RDX500 mid, then the two rackets would have different balances

jangpyo
04-15-2006, 01:10 PM
aerodynamics maybe? i dont really know:mrgreen:


As Imadeulook says it could be the aerodynamics of the racquet that makes the LM prestige feel heavier (SW) than RDX 500. The design of the LM prestige causes more resistance or drag as it cuts through the air when you swing the racquet.

I don't want to get too technical because I am definitely not an expert in this field. But just wanted to understand what I experienced playing with both racquets.
Despite being close to equal on strung weight and equal on balance LM prestige really felt heavier(?) moving through the air than the RDX.
Of which puzzled me !!!
I would have thought they would feel quite similar in SW.

This goes to show you how actual demoing a racquet can't substitute going by the specification alone.

Davai
04-15-2006, 02:15 PM
Thanks for the help.

But as Davai puts it if the distribution of materials at different location along the racquet can account for the different SW, wouldn't that also make the balance be different between the two racquets ? But the balance is shown to be the same. Just a thought.

Think about this way: You have a rod you put two weights in the middle of the rod vs. two weights on the endpoints. Balance is the same as well as weight but which one is easier to rotate? SW is different. Similiarly you can distribute weight on a racket and keep the balance the same.

jangpyo
04-15-2006, 04:54 PM
Think about this way: You have a rod you put two weights in the middle of the rod vs. two weights on the endpoints. Balance is the same as well as weight but which one is easier to rotate? SW is different. Similiarly you can distribute weight on a racket and keep the balance the same.

Davai ! appreciate your continued effort in trying to explain it.
I think I am starting to understand it a little. Based on your example, the two rods would be of equal strung weight (if they were racquets !) and the balance would be even. right ?

Therefore for a racquet to be 8pts headlight, the upper half of the racquet need to be 8pts headlight compared to the bottom half. In the same way, for two racquets to be 8pts headlight but be different in terms of sw, the weights(material,composition etc..) in the upper half of two racquets is distributed (positioned) differently but retains the 8pts headlightness compared to bottom half of the racquet.
I hope this makes sense !

Two Fister
04-15-2006, 05:09 PM
Anyone wishing to understand more about the physics of tennis racquets should consider this book required reading. It's actually a very easy read.

http://www.tennis-warehouse.com/descpage-TECHTENNIS.html

dcreasy55
04-15-2006, 06:10 PM
This is funny because I just had a dynamics test on moments of inertia. :)

J D
04-15-2006, 10:58 PM
To clarify even more, a racquet with the same mass and balance point as another frame but with a higher SW would usually have more weight in the head AND in the handle but less weight in the throat. The extra mass further away from the handle makes the swingweight higher. The extra weight lower in the handle balances out the extra head weight, keeping the balance point the same.