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-   -   Racket stiffness not the whole story? (http://tt.tennis-warehouse.com/showthread.php?t=447713)

cluelessmoose 12-09-2012 12:01 PM

Racket stiffness not the whole story?
 
Today I took my APD gt and my new head youteck speed pro (18 mm beam) out for a hit. I matched them completely. Same weighting, strings, and grip. I was surprised to find that while they have the same stiffness (70 RA), the speed pro hit quite a bit softer in comparison. It had almost a mushy feel to hit and the ball came off with a bit less spin and pace. Could this have something to do with the difference in beam width or shape despite the frames having the same stiffness?

tennisnut09 12-09-2012 12:37 PM

I am not the expert, still new in tennis but this is interesting to know.

SteveI 12-09-2012 12:50 PM

Quote:

Originally Posted by cluelessmoose (Post 7054648)
Today I took my APD gt and my new head youteck speed pro (18 mm beam) out for a hit. I matched them completely. Same weighting, strings, and grip. I was surprised to find that while they have the same stiffness (70 RA), the speed pro hit quite a bit softer in comparison. It had almost a mushy feel to hit and the ball came off with a bit less spin and pace. Could this have something to do with the difference in beam width or shape despite the frames having the same stiffness?

Yes...........................................

LeeD 12-09-2012 12:53 PM

I don't know.
Is it because they measure the "stiffness" differently?
Is it initial deflection?
Is it longer range deflection?
A thicker beam should be quicker rebounding, while a thinner beam might take more time, with thicker beams usually being more thin walled, while thinner beams can often be made with thicker materials in the walls.

BlueB 12-09-2012 01:02 PM

Quote:

Originally Posted by cluelessmoose (Post 7054648)
I matched them completely. Same weighting, strings, and grip.

But, did you match the SW and ballance? That's more important then physical weight...

cluelessmoose 12-09-2012 01:21 PM

Quote:

Originally Posted by LeeD (Post 7054720)
I don't know.
Is it because they measure the "stiffness" differently?
Is it initial deflection?
Is it longer range deflection?
A thicker beam should be quicker rebounding, while a thinner beam might take more time, with thicker beams usually being more thin walled, while thinner beams can often be made with thicker materials in the walls.

This is also my current thinking on the matter. I think it has to do with the rebound speed of the frame. When stiffness is measured on an RDC machine I believe a set force is applied to the racket the "stiffness" is just a reflection of how far the racket bends when this constant is applied. So, this number would not directly reflect how quickly or efficiently the racket returns to it's natural state after striking a ball.

For those of you unaware of how stiffness is measured, take a look at 1:35 on in this video:

https://www.youtube.com/watch?v=67ndPgE5ITU

...and yes the balance and sw are also matched.

TennisCJC 12-10-2012 10:31 AM

Quote:

Originally Posted by BlueB (Post 7054732)
But, did you match the SW and ballance? That's more important then physical weight...

Yep, SW is huge determinant in how a racket plays while balance can be almost as important.

TimothyO 12-10-2012 11:10 AM

http://www.youtube.com/watch?v=67ndPgE5ITU

The RDC machine tests stiffness by securing the tip and handle and bending the frame in the middle, near the throat/bottom of the head at 6.

So it's only a very broad guide at best like so many other measurements in tennis (eg swingweight is measured as if you're swinging the frame with your wrist).

Other key features which determine how a frame feels in terms of "stiffness" include materials used for construction, thickness at various key points, distribution of weight, head size, and string pattern. All will influence a frame's comfort and perceived stiffness.

A good example is my current frame, the Pure Storm GT. On paper it is at the low-middle end of stiffness around 63. But as others have reported I found it to have some vibration in stock form and play sort of stiff or at least uncomfortable, especially on impacts towards 12. After adding weight to the head and under the grip raising static weight about a full ounce it really does play soft and plush.

By the same token the Pro Staff 6.1 95 is pretty soft on paper but some aspect of the Ampli-Feel technology was very uncomfortable to me. It's designed to increase the feel of the impact which it certainly does!

The softest frame I've used is the Speed 300. It has a low stiffness rating, it is thin beamed, has a large 100" head, and an open string pattern. All of these features provide for a very soft feel but no single feature, including the stiffness value, can be taken to mean a frame is soft or not.

anubis 12-10-2012 12:16 PM

Quote:

Originally Posted by cluelessmoose (Post 7054648)
Today I took my APD gt and my new head youteck speed pro (18 mm beam) out for a hit. I matched them completely. Same weighting, strings, and grip. I was surprised to find that while they have the same stiffness (70 RA), the speed pro hit quite a bit softer in comparison. It had almost a mushy feel to hit and the ball came off with a bit less spin and pace. Could this have something to do with the difference in beam width or shape despite the frames having the same stiffness?

But they're not the same stiffness? Most Speeds are 60, some are 64 and one is 65. The APD gt is 70. that's a huge difference. The speed will hit softer because its a softer racquet, and a softer frame will absorb more shock and power, so less power is transferred to the ball itself. That's why you feel like there's more pace coming off the APD.

This isn't to say you can't hit with the same pace with your Speed, you just need to have a more solid kinetic chain to do so.

El Diablo 12-10-2012 02:44 PM

dear clueless
as TImothy points out the RDC rating of 70 is a meaasurement of stiffness at one point on the racquet. Your two racquets may have completely different flex qualities at every other location along their lengths. So it's incorrect to refer to the RDC number as the "racquet stiffness."

NLBwell 12-10-2012 03:02 PM

I wouldn't say it is "incorrect" to say that an RDC rating measures racket stiffness. It is an approximation that can be measured consistently across different rackets. It will give you an idea of the overall stiffness. It isn't exact, but an EXO 3 Tour 100 will not feel stiffer than an APD.

corners 12-10-2012 03:56 PM

Quote:

Originally Posted by cluelessmoose (Post 7054754)
This is also my current thinking on the matter. I think it has to do with the rebound speed of the frame. When stiffness is measured on an RDC machine I believe a set force is applied to the racket the "stiffness" is just a reflection of how far the racket bends when this constant is applied. So, this number would not directly reflect how quickly or efficiently the racket returns to it's natural state after striking a ball.

Rebound speed is irrelevant. There is not a racquet on the market today that rebounds to it's original or "natural state" before the ball has left the strings. A racquet must be significantly stiffer than anything in production to rebound before the ball has taken off.

MikeHitsHard93 12-10-2012 04:05 PM

We need pvaudio in here to discuss some physics...

corners 12-10-2012 04:11 PM

Quote:

Originally Posted by cluelessmoose (Post 7054648)
Today I took my APD gt and my new head youteck speed pro (18 mm beam) out for a hit. I matched them completely. Same weighting, strings, and grip. I was surprised to find that while they have the same stiffness (70 RA), the speed pro hit quite a bit softer in comparison. It had almost a mushy feel to hit and the ball came off with a bit less spin and pace. Could this have something to do with the difference in beam width or shape despite the frames having the same stiffness?

Someone else asked, but if you want to get to the bottom of this you have to tell whether you matched the swingweights of the two frames. If not, then there is your answer.

You should probably read this article: http://twu.tennis-warehouse.com/lear...csandspeed.php

As you'll read, stiffness has only a little to do with power. In fact, an academic paper published last year showed that you'd have to triple the stiffness (from 60 to 180!) of a racquet to get a measly 4-5 extra miles per hour on your shots. Stiff hoops do tend to have a bit more pop at the tip and sides of the stringbed than flexible, narrow-beam ones, but the differences are quite modest.

HEADfamilydynasty 12-10-2012 06:29 PM

Quote:

Originally Posted by anubis (Post 7056325)
But they're not the same stiffness? Most Speeds are 60, some are 64 and one is 65. The APD gt is 70. that's a huge difference. The speed will hit softer because its a softer racquet, and a softer frame will absorb more shock and power, so less power is transferred to the ball itself. That's why you feel like there's more pace coming off the APD.

This isn't to say you can't hit with the same pace with your Speed, you just need to have a more solid kinetic chain to do so.

The YT Speed Pro has a stiffness of 70.:)

brownbearfalling 12-10-2012 11:20 PM

I have to say that I'm not surprised that you found those racquets to play differently. When you are trying to determine how a racquet feels in play from specifications on paper (like you are doing in your test), generally, you consider swing weight and stiffness as secondary to many other specs. Specs that are better indictor of how a racquet feels are headsize, beam width and balance.

The softness is probably due to the thin beam and smaller headsize. I'm just postulating here but the APD has woofer grommets which will create more power in the string bed and that equals less flex/ torque of the racquet. And the general rule is that thinner beams have more flexability that thicker ones. So there might be something about the SP that makes it test at 70 (possibly the D3O in the throat) but it doesn't acutally play that way.

Marcus2137 12-11-2012 01:56 AM

I have also found that there can be a big difference in feel despite similar stiffness ratings.

There's a couple things I've theorized, but of course have no way to prove without some in depth experiments and complicated tests/machines:

I feel there might be a difference between static stiffness and "dynamic" stiffness. The machine only measures static stiffness, i.e. put the frame on the machine and it slowly flexes the frame and takes a reading. Can we be sure that all rackets that get a reading of RA70 in this test will then flex the same way when a ball strikes the strings? After all, the ball could be traveling as much as 80-90mph even after bouncing after a hard first serve PLUS the returner's racket head speed... the ball will hit the strings/frame pretty hard.

I seem to have experienced this difference in dynamic flex personally with some of my rackets. One great example is that I have a Head PT280, and a Head PT57a. Technically they are the same mold and same racket, but the pt57a is lighter and more flexible as it is a pro stock. When I lightly hold the top of the grip and hit the tip of the head with my other hand, the PT280 resonates slightly higher pitched, indicating that it would be a few points stiffer, but overall they are close.

When I hit with them, they are both soft, but clearly they are different from each other. The PT280 is pillow soft. The PT57a, in contrast, feels springy soft. And even matched, the PT57a also gives me more pop, reinforcing the impression that it is more of a spring while the PT280 is more of pillow that is muted and soft, but also feels like it is soaking up some of the power when you hit. And don't get me started on my Donnay X-Red 94+! The feel of those things are so unique.

As someone else mentioned, WHERE the racket flexes can make a big difference as well. So maybe two rackets are RA70, but one is very stiff in the handle and throat but flexy in the hoop; and the other is very stiff in the hoop but very soft in the throat. When they get a reading of RA70, this is an average, but tells us little more. The 2 rackets I described surely won't feel the same when hitting.

LeeD 12-11-2012 04:06 PM

In the world of windsurfing, we all use carbon masts, of about the same standard diameter.
Thin walled 100% carbon masts cost up to $1,200 each, weigh around 3.5 lbs., have stiffness ratings the same as all masts, but reflex back to original form much quicker.
Thick walled lower content masts cost down to 170 bucks, weigh around 6 lbs., same stiffness ratings, and reflex back to original shape slowly for less response and quickness.
I'd guess we need to measure not only overall stiffness, but it's ability to reflex back to it's original form. Bigger diameter should be quicker.

Miljack 12-11-2012 04:34 PM

Interesting thread, I was just thinking about this topic this morning. I'm going to update my OLLLLD rackets, and have been looking at the stiffness indexes and trying to reconcile my hitting experience with some of these rackets against their "rated" stiffness. My experience is limited as I haven't hit with a lot of rackets in the very recent past, but my overall judgement is to agree with those who have posted that the stiffness index is NOT a great gauge to judge a rackets overall "flex" or power level.
I'm going to try a little more powerful racket (coming from a RA 60 stick) that is a thin beam construction, so not sure where I'll start.
I will say that the straight beam rackets GENERALLY follow their power levels with the RA index number. Obvious exception to me is the Wilson 6.1 rackets seem WAY stiffer than their RA index number would indicate.
I hit with a couple of Babolats and the Pure Storm (straight beam) feels about like one would think an ~20mm beam racket would hit. On the other hand the Aero Storm is a MUCH more powerful racket, even thought the RA scores are very close or the same.
Only other modern racket is a BB V1 Oversize which has a pretty low RA score, but this racket is a very powerful racket, seems stiff for the whole length of the racket.

Keep the comments coming...

MathieuR 12-12-2012 06:59 AM

stiffness measurement
 
an RDC measures the stiffness by measuring the deformation when giving a certain force on the 6 o'clock position, with clamped head and grip.

Does anyone know the exact procedure? The force used? The translation in deformation to a "stiffness". I assume there must be a definition "somewhere" that is translated by the RDC into a measurement.


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