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View Full Version : Is stiffness index subjective or objective?


bruno hau
04-25-2008, 03:11 PM
I have both the Yonex RDS 002 Tour (65 stiffness index) and the Head Microgel Radical Pro (64 stiffness index). With same strings & same tensions, I can tell you the Head Microgel Radical Pro feels MUCH stiffer (jarring even at times) than the Yonex RDS 002 Tour. So how can a 64 feels stiffer than 65?

fuzz nation
04-25-2008, 03:21 PM
The flex rating only tells you the frame's overall flex, but it doesn't tell you if it's a consistent flex, if there's more give in the throat, or more in the hoop. Those differences will often produce dramatically different feel and it would be really great if manufacturers could come up with a simple indication of the different profiles of racquet flex - I like a somewhat soft frame, but if the hoop is too flimsy, it really turns me off.

ollinger
04-25-2008, 03:24 PM
No, the flex rating doesn't tell you "overall flex" as the standard machine measures flex at the throat only.

OrangeOne
04-25-2008, 03:32 PM
No, the flex rating doesn't tell you "overall flex" as the standard machine measures flex at the throat only.

That makes sense for this example too - the 002 Tour felt very "hoop" stiff to me, so maybe the most of the flex it has is indeed in the throat - and it thus measures and plays flexy.

If the MG is more "uniformly flexible", it would come out with a proportionally lower flex measurement, as less of the flex would be in the throat, but it would play stiffer, as some of the flex is further down the lever, if you will.

I'm communicating my thoughts badly there, I could do so much better with a diagram :)

NoBadMojo
04-25-2008, 03:52 PM
I have both the Yonex RDS 002 Tour (65 stiffness index) and the Head Microgel Radical Pro (64 stiffness index). With same strings & same tensions, I can tell you the Head Microgel Radical Pro feels MUCH stiffer (jarring even at times) than the Yonex RDS 002 Tour. So how can a 64 feels stiffer than 65?

. the stiffness test is VERY objective

No, the flex rating doesn't tell you "overall flex" as the standard machine measures flex at the throat only.

this has been discussed over and over and over again and you havent been able to process it properly in spite of being a regular here..it measures the overall average flex.

OrangeOne
04-25-2008, 04:02 PM
NoBad - is there a best thread / location to read into how stiffness is measured?

NoBadMojo
04-25-2008, 04:15 PM
NoBad - is there a best thread / location to read into how stiffness is measured?

no sorry. i dont know of such a place. i suppose it depends upon who you think knows what they are talking about.

Mulligan
04-25-2008, 05:12 PM
No, the flex rating doesn't tell you "overall flex" as the standard machine measures flex at the throat only.

I agree. I checked out the definition from Babolat for their RDC equipment and their definition of frame stiffness is:

Stiffness: Frame stiffness measured longituditional at or about the throat area. This is recognized as the main flex point of a frame during ball contact. The higher the value the stiffer (more powerful) the frame.

It seems like this debate has a long history here so I too am puzzled re: how the flex of a frame is measured. But maybe the above definition is helpful.

SFrazeur
04-25-2008, 05:53 PM
Stiffness: frame stiffness measured at or about the throat area. This is generally recognized as the main flex point of a frame during ball contact. The higher the number, the stiffer the frame. The stiffer the frame, the more power it provides, all other things being equal. This is a relative number but generally, less than 55 is flexible, 55-60 is medium flexible, 60-65 is medium stiff, 65-70 is stiff and 70+ is very stiff. http://av.warehousesports.com/tw/Features/RDC/photo2-RDCflex.JPG
http://av.warehousesports.com/tw/Features/RDC/RDC.html

Whenever measurement is made by a machine the human element is missing.


-SF

NoBadMojo
04-25-2008, 06:46 PM
Stiffness: frame stiffness measured at or about the throat area. This is generally recognized as the main flex point of a frame during ball contact. The higher the number, the stiffer the frame. The stiffer the frame, the more power it provides, all other things being equal. This is a relative number but generally, less than 55 is flexible, 55-60 is medium flexible, 60-65 is medium stiff, 65-70 is stiff and 70+ is very stiff. http://av.warehousesports.com/tw/Features/RDC/photo2-RDCflex.JPG

http://av.warehousesports.com/tw/Features/RDC/RDC.html


Whenever measurement is made by a machine the human element is missing.






-SF






yes that is a picture of an rdc. it illustrates that the fulcrum point for measuring stiffness is at or about the throat area. unless people think that racquets only flex precisely where the fulcrum point is located they would be able to know that the machine measures the amount of resistence to bending <stiffness/flexibility> overall and at places other than the fulcrum point which is on or about the throat area.
There really isnt much of a human element involved. you mount the racquet in the machine and push a button and the machine converts the resistence to bending based upon the formula sored on the chip into the RA number..it's really quite objective..it measures how flexible a racquet is..thats what the test is designed to do

JohnP
04-25-2008, 07:14 PM
The RDC rating is absolutely 100% objective, as NBMJ states.

The problem is that the OP's usage of the words "subjective" and "objective" is slightly flawed. His question is more about whether or not the standard RDC flex rating is an "absolute" measure of flexibility for all practical purposes. Although it is absolutely 100% objective, it is not "absolute" in the context of the OP's question.

It is theoretically possible to have two racquets that flex in much different ways (and therefore play differently, all else being equal) but have the same RDC rating. I have no idea how much variation there really is between racquets as far as that's concerned, so I have no idea if that point is completely moot, but it is what the OP is trying to get at.

bluetrain4
04-26-2008, 01:07 AM
I like a somewhat soft frame, but if the hoop is too flimsy, it really turns me off.


Totally agree. My Hotmelt 200gs have a flex rating of only 60, but feel solid in the hoop which is important to me.

A-Rod6600
04-26-2008, 01:59 AM
Ask your wrist, elbow and shoulder and you'll find the answer!

Rabbit
04-26-2008, 04:45 AM
No, the flex rating doesn't tell you "overall flex" as the standard machine measures flex at the throat only.


The RDC rating is absolutely 100% objective, as NBMJ states.

The problem is that the OP's usage of the words "subjective" and "objective" is slightly flawed. His question is more about whether or not the standard RDC flex rating is an "absolute" measure of flexibility for all practical purposes. Although it is absolutely 100% objective, it is not "absolute" in the context of the OP's question.

It is theoretically possible to have two racquets that flex in much different ways (and therefore play differently, all else being equal) but have the same RDC rating. I have no idea how much variation there really is between racquets as far as that's concerned, so I have no idea if that point is completely moot, but it is what the OP is trying to get at.

And that is precisely why, when measuring a frame, the manufacturers use a machine designed to and used in measuring the flex of skis. It takes measurements for the entire length of the frame at intervals. This is the only true measure of a frame's flex and indication of where the flex is.

And this is also why when evaluating a competitor's frame for the purposes of duplicating it, manufacturers use this method instead of an RDC. This is the true measure of a frame's flexibility and the only way to ensure that it is duplicated from one frame to another.

The RDC measurement assumes that all frames flex the same and in the same area. This was more true during the wood era, but even then after the advent of graphite reinforcements and overlays, manufacturers found ways to make rackets flex differently at different points. Today, it is possible to use the same mold and make two frames play entirely different due to the layup in the frame. Ergo, if the layup and flex pattern is different, the RDC is basically useless. It is only when you have like layups that the RDC is pertinent.

The real use of the RDC then is in matching frames of the same type, not for a valid comparison of one frame being as flexible as another. But yes, the RDC is an objective number although not a valid one in the context of this discussion.

NoBadMojo
04-26-2008, 05:05 AM
The RDC rating is absolutely 100% objective, as NBMJ states.

The problem is that the OP's usage of the words "subjective" and "objective" is slightly flawed. His question is more about whether or not the standard RDC flex rating is an "absolute" measure of flexibility for all practical purposes. Although it is absolutely 100% objective, it is not "absolute" in the context of the OP's question.

It is theoretically possible to have two racquets that flex in much different ways (and therefore play differently, all else being equal) but have the same RDC rating. I have no idea how much variation there really is between racquets as far as that's concerned, so I have no idea if that point is completely moot, but it is what the OP is trying to get at.

The OP using the word FEELS puts the abba dabba on the whole thing. The rdc cant possible consider something like FEEL..maybe that is what SFrazeur was getting at when he mentions the human element. Examples <not pertaining to any one particular poster>;
-If a player miss hits more with one frame than the other and both have the same stiffness, than the frame he is misshitting will FEEL stiffer
-If two frames of the same stiffness have a difference in stringbed density, the one with the denser stringbed is likely to FEEL stiffer all other things being equal. Lots of people confuse stringbed stiffness and racquet stiffness
-Two frames of the same stiffness with one flexing more in the hoop...The one flexing more in the hoop may FEEL more flexy <more flexy than the specs indicate>. The RA measurement doesnt tell you where along the long axis the frame flexes the most or least or how much it flexes at the throat..it just tells you what the overall average flex is..it';s a very useful accurate measurement

kungfusmkim
04-26-2008, 05:12 AM
I say it has alot to do with the Company/ Racquet it self. The technology splut might have alot to do with it. When i first switched from N4to my RDS002 standard i felt that my N4 was alot stiffer then my rds even though they were the same stiffness(65). It could be that the Elastic TI really doesnt exist and that its not a commercial flop like the AS SEEN ON TV stuff. Maybe Flexpoint really does give you a more accurate shot ,if the ball is hit correctly, and maybe the swing weight also effects the stiffness or the feel of it.

WChiang
04-26-2008, 05:16 AM
And that is precisely why, when measuring a frame, the manufacturers use a machine designed to and used in measuring the flex of skis. It takes measurements for the entire length of the frame at intervals. This is the only true measure of a frame's flex and indication of where the flex is.

And this is also why when evaluating a competitor's frame for the purposes of duplicating it, manufacturers use this method instead of an RDC. This is the true measure of a frame's flexibility and the only way to ensure that it is duplicated from one frame to another.

The RDC measurement assumes that all frames flex the same and in the same area. This was more true during the wood era, but even then after the advent of graphite reinforcements and overlays, manufacturers found ways to make rackets flex differently at different points. Today, it is possible to use the same mold and make two frames play entirely different due to the layup in the frame. Ergo, if the layup and flex pattern is different, the RDC is basically useless. It is only when you have like layups that the RDC is pertinent.

The real use of the RDC then is in matching frames of the same type, not for a valid comparison of one frame being as flexible as another. But yes, the RDC is an objective number although not a valid one in the context of this discussion.

Yes, the RDC does assume that the frames flex at the same location and its measurement is the most help when comparing frames of similarity in other areas as you indicated. Good post and it helps to put things in perspective from the "bigger picture". Thanks.

Rabbit
04-26-2008, 05:56 AM
Thanks. From what I understand, it isn't even the mold that is important any more, it is the layup.

For instance, Volkl builds the C10 to be flexible. If they signed Carlos Moya, they could use the same mold and change the layup to make it stiff like a Babolat Pure Drive.

Or, they could "break" the throat area, make it into a V shape and voila! Radek Stepanek is playing with what appears to be a totally different frame, but in reality it is a C10. Even the longer mains don't make any real difference in power, the frame is a C10.

The real deal in rackets is the layup. The real measure of a racket's flexibility then is done across the entire frame. If all things were equal, RDC would be a useful measure. The real value in RDC is when you purchase multiple frames of the same type. Then, you can get a matched set. RDC is also of value when looking at a frame's stiffness after it has some wear on it. By this I mean once a frame has been strung 50+ times, the stiffness may have gone down due to the stress stringing a frame puts on it. For a professional, this becomes important to maintain their gear in perfectly like condition.

NoBadMojo
04-26-2008, 06:15 AM
Thanks. From what I understand, it isn't even the mold that is important any more, it is the layup.

For instance, Volkl builds the C10 to be flexible. If they signed Carlos Moya, they could use the same mold and change the layup to make it stiff like a Babolat Pure Drive.

Or, they could "break" the throat area, make it into a V shape and voila! Radek Stepanek is playing with what appears to be a totally different frame, but in reality it is a C10. Even the longer mains don't make any real difference in power, the frame is a C10.

The real deal in rackets is the layup. The real measure of a racket's flexibility then is done across the entire frame. If all things were equal, RDC would be a useful measure. The real value in RDC is when you purchase multiple frames of the same type. Then, you can get a matched set. RDC is also of value when looking at a frame's stiffness after it has some wear on it. By this I mean once a frame has been strung 50+ times, the stiffness may have gone down due to the stress stringing a frame puts on it. For a professional, this becomes important to maintain their gear in perfectly like condition.

rdc = racquet diagnostics center. think you are meaning RA stiffness

the mold configuration is still very important and can contibute greatly to the stiffness of a racquet

dont think Moya ever used the Pure Drive..think he as always used the Soft Drive, and additionally the racquet doesnt have woofers

stepanek doesnt use a c10. he uses a v-engine frame with an unknown layup. you can tell because it has the v shape in the throat, thus obviously making it a frame which is not a c10. fed uses a frame which looks like a k90 with an unknown layup.

the v-engine configuration purpose is not to give more power because of longer mains. it doesnt, and only 2 of the mains are really any longer and also in an area where the ball isnt usually struck. the purpose of the v-engine is to stiffen the frame in the throat. that is what gives the frame more power. it also increases torsional stability and allows flexier materials to be used in the layup for comfort while providing some additional power. so yes, the mold is very impt

Rabbit
04-26-2008, 06:44 AM
rdc = racquet diagnostics center. think you are meaning RA stiffness

the mold configuration is still very important and can contibute greatly to the stiffness of a racquet

dont think Moya ever used the Pure Drive..think he as always used the Soft Drive, and additionally the racquet doesnt have woofers

stepanek doesnt use a c10. he uses a v-engine frame with an unknown layup. you can tell because it has the v shape in the throat, thus obviously making it a frame which is not a c10. fed uses a frame which looks like a k90 with an unknown layup.

the v-engine configuration purpose is not to give more power because of longer mains. it doesnt, and only 2 of the mains are really any longer and also in an area where the ball isnt usually struck. the purpose of the v-engine is to stiffen the frame in the throat. that is what gives the frame more power. it also increases torsional stability and allows flexier materials to be used in the layup for comfort while providing some additional power. so yes, the mold is very impt

Do you really want to get picayune on this? Do you really want to reduce the discussion to picking fly crap out of pepper? RDC is the general term in use in this discussion. Introducing the above as an attempt to discredit is disingenuous and counterproductive. But, it is so you.

Moya was an example. Tell you what, pick a frame....any frame. The example I cited applies. You can tell it is an example because in the example I said that Volkl, if they signed Carlos Moya could produce any racket he wanted. See, you can tell it's an example because Volkl isn't going to sign any pro.

Stepanek does use a C10. From the man's own mouth in Memphis to my hands here. Have you held his frame? Have you seen inside his frame? Have you seen the model number listed? I didn't think so. I have. The frame is a C10. You are wrong. The difference between you and me is that I admit when I'm wrong. You don't.

Reread the post. I said, quite clearly, that mold isn't the issue. Layup is. The racket that Stepanek uses is the same mold as the C10 save the throat and the same layup. By your logic, any frame not painted like a C10 isn't a C10.

When the V-Engine stuff came out, Volkl indicated that the V also enhanced power and gave a little more pop. The additional stiffness was also a product. But, it is as much marketing as the extra pop. The layup of the frame is the determing factor, not a V-shaped throat. The reality of the V-Engine line was that it was a throwback to Volkl's lineup from the past. The reality is that it didn't succeed. It was a marketing failure and an engineering falsehood. The way to make a frame stiffer is through what the frame is made out of. This said, I liked the V-Engine line and played with the Cat V8. I also think the V10 is 3rd best in the 10 line. But, all that has nothing to do with the V. The V was just cool, nothing else.

Likewise, the Sensor handle is pure marketing. There is no sensor handle. There is a butt cap with two small pieces of foam. The handle of a Volkl, that area under the pallets, is like any other frame. It is a a boxed section of graphite (and other materials).

NoBadMojo
04-26-2008, 06:47 AM
Do you really want to get picayune on this? Do you really want to reduce the discussion to picking fly crap out of pepper? RDC is the general term in use in this discussion. Introducing the above as an attempt to discredit is disingenuous and counterproductive. But, it is so you.

Moya was an example. Tell you what, pick a frame....any frame. The example I cited applies. You can tell it is an example because in the example I said that Volkl, if they signed Carlos Moya could produce any racket he wanted. See, you can tell it's an example because Volkl isn't going to sign any pro.

Stepanek does use a C10. From the man's own mouth in Memphis to my hands here. Have you held his frame? Have you seen inside his frame? Have you seen the model number listed? I didn't think so. I have. The frame is a C10. You are wrong. The difference between you and me is that I admit when I'm wrong. You don't.

nice..make it personal <again>.

i dont think anyone is going to believe that a v-engine frame is a c-10

ohplease
04-26-2008, 07:02 AM
We've covered this ground a million times. The RDC doesn't begin to capture how a racket flexes in play. It doesn't tell you that much about a frame's stiffness along its length - and it tells you NOTHING about a frame's stiffness along its width.

It'd be one thing if we were talking about carbon fiber golf shafts. As tennis rackets also exhibit torque - how they respond off center - even a little bit - matters. And no, the RDC measurement can't tell you anything about that. And yes, it matters, otherwise, people could reasonably play tennis with baseball bat shaped objects. And they don't.

There's nothing more stupid than an inability to understand what a metric actually can tell you, and what it can't. Same with swingweight. Same with mass (is the frame well balanced? Or is all the weight in the head or handle? Or does that not matter either, cause the scale says what it says?).