The most underrated spec - how to improve your volleys instantly

[travlerajm]

When a ball hits your strings on the volley, your racquet begins to pivot about the balance point. This starts to happen even before you feel the impact.

The magnitude of the resistance to this movement is determined by the rotational moment of inertia about the balance point (Ic).

Because of this, Ic is the most critical spec when determining a good volley racquet. It is more important than swingweight, static weight, or balance alone.
And it is even more important than twistweight.

Luckily Ic can be easily calculated if you know the SW, static weight and balance using the following formula:

Ic = I - M*(R - 10)^2

Ic = moment of inertia about balance point
I = specified SW about 10cm axis
M = static weight in kg
R = distance from butt to balance point in cm

I have done some checking, and to my knowledge, every single serve-and-volleyer or doubles specialist on the ATP tour plays with an Ic of roughly 180 kg-cm^2. Roddick, in contrast, plays with an Ic around 165.

In general, this formula can be used to compare which stock racquets are most stable for volleys, just based on specs alone!

 

[jace112]

It's true. This inertia moment reflects the force you feel when hitting the ball. It's more critical on volleys of course, but it's also true everywhere else.

BTW travlerajm, I like your topics. Even if they appear a bit weird at the first sight (or too much physics oriented instead of focusing on the practice), your explanations rock.

 

[Deleted member 6835]

Ic = I - M*(R - 10)^2

Ic = moment of inertia about balance point
I = specified SW about 10cm axis
M = static weight in kg
R = distance from butt to balance point in cm

Question: whats I supposed to be? whats SW about 10 cm axis? is it the SW per every 10 cm of the racket? so for example, for a 69 cm (27 in) racket, it would be the SW divided by 6.9?

cuz i tried that formula for my racket (check sig) and got 44. something

 

[Greg Raven]

FWIW, this is also referred to as the recoil weight.

 

[louis netman]

travlerajm: 1) due to my grip mods, my frames don't fit into the Bab SW machine. Any way to derive SW from BP and static wt? 2) still waiting on that revised formula with target SW. 3) can you do the formulas in metric measurement as grams and mm are more precise than ounces inches.......
Thanx very much!!!

 

[Court_Jester]

travlerajm: 1) due to my grip mods, my frames don't fit into the Bab SW machine. Any way to derive SW from BP and static wt?

I'm not travlerajm but I'll take a crack at this. Yes, it's possible to determine the SW but in addition to BP and mass, you'll also need the racquet's period of oscillation or time to complete one swing when suspended on a peg and the distance of this peg from the BP. That's I how I do it and I notice that in a lot of cases, my measured values are within a few points (< 5) of what TW has measured. I even set it up on a spreadsheet program so that when I type in a set of values for a racquet, I will get the SW instantly.

Anyway, the formula goes like this:

SW = M[(PT^2/40.28 ) - (P^2/1000) + (Y^2/1000)] (in kg-cm^2)

where:

• M = static mass of the racquet in grams
• P = distance from the balance point (BP) to the point where the the racquet is suspended in cm
• T = period of oscillation in seconds
• Y = BP - 10.16 (measured in cm) NOTE: 10.16 cm is 4" from the butt cap

This is the equation that I use.

 

[Court_Jester]

Question: whats I supposed to be? whats SW about 10 cm axis? is it the SW per every 10 cm of the racket? so for example, for a 69 cm (27 in) racket, it would be the SW divided by 6.9?

cuz i tried that formula for my racket (check sig) and got 44. something

Sorry but the SW calculation doesn't work the way you're suggesting. The "I" is supposed to be your racquet's swingweight. But with your lead mod, the SW will increase by about 10 points. Try the calculation again with the corrected SW value.

 

[noah]

Can we Have a Real Calculation

Take Roddicks racket and input the numbers in the formula:

Ic=I-M*(R-10)^2

I think this will make it easier to understand.
I still do not understand how to calculate SW about 10 cm axis.

thanks, Ken

 

[AdvocateTDV]

RDC Swingweight

Swingweight is something that is measured, and you need certain instrumentation to do it.

Tennis Warehouse publishes the swingweights about a 10 cm axis from the buttcap on their website. In short, there is nothing for you to calculate (with respect to swingweight) if the racquet specs are known from TW or some other reliable, accurate, and precise source.

 

[sureshs]

In general, this formula can be used to compare which stock racquets are most stable for volleys, just based on specs alone!

And the winner is?

 

[Deleted member 6835]

Sorry but the SW calculation doesn't work the way you're suggesting. The "I" is supposed to be your racquet's swingweight. But with your lead mod, the SW will increase by about 10 points. Try the calculation again with the corrected SW value.

alright, thanks

i did the formula and got 156.21 (rounded of course). i guess the results vary between people because some people are a lot shorter like me, so the "mass" you need in your racket to be solid for volleys is less. oh well, all i know is, i like volleying with my frame, so its all good

btw travlerajm, this is a very useful formula. thanks for finding it out

 

[Court_Jester]

Swingweight is something that is measured, and you need certain instrumentation to do it.

Like a scale and a stop watch.

Tennis Warehouse publishes the swingweights about a 10 cm axis from the buttcap on their website. In short, there is nothing for you to calculate (with respect to swingweight) if the racquet specs are known from TW or some other reliable, accurate, and precise source.

To a point. You're assuming that the racquets are in stock form. Most likely, players have added things like dampeners and lead strips, thus changing the swingweights values from those published by TW and others.

 

[AdvocateTDV]

Wilson nPS 95

Haha...I just performed the calculation for a Wilson nPS 95...and it came out to be 149.15 kg-cm^2

Now we quantitatively know why that racquet is on its way out...besides the P/L sheet. Oh, and it is light with respect to staticweight as well.

And Court Jester, yes...I didn't think about it that fundamentally. Haha...my bad! I was totally thinking of the actual device itself. But yes, all one needs is a stopwatch and a scale.

 

[Court_Jester]

Yeah, I know that machine you're referring to. It's this one. No way any of us could afford this.

 

[AdvocateTDV]

Oh yeah, that's the one. Yes, quite a bit on the pricey side - I'm sure.

Hell, the Babolat stringers are quite pricey. :|

 

[noah]

I did the math..check it out

I used the following stats:

Even balance (distance from butt to BP is 13.5 inches or 34.29 cm)
324 sw
327 static weight (.327 kg)

Ic= I-M*(R-10)^2

Ic = 324 - .327(34.29 -10)^2
Ic = 324 - .327(24.29)^2
Ic = 324 - .327(590)
Ic = 324 - 176
Ic = 148

Does this seem correct for an even balanced racket with a sw of 324 and stat weight of 327?

 

[noah]

If I read this formula correctly
Ic= I-M*(r-10)^2

Then if eveything on two rackets were the same.EXCEPT that racket "A" was 8 point head light.. then racket 'A' would have a higher Ic that racket 'B' which had identical specs to racket A other than being even balanced Vs. 8 points head light for "A"

Do you agree

 

[Deleted member 6835]

If I read this formula correctly
Ic= I-M*(r-10)^2

Then if eveything on two rackets were the same.EXCEPT that racket "A" was 8 point head light.. then racket 'A' would have a higher Ic that racket 'B' which had identical specs to racket A other than being even balanced Vs. 8 points head light for "A"

Do you agree

yes

 

[Court_Jester]

Then if eveything on two rackets were the same.EXCEPT that racket "A" was 8 point head light.. then racket 'A' would have a higher Ic that racket 'B' which had identical specs to racket A other than being even balanced Vs. 8 points head light for "A"

Sounds right. I guess that why headlight racquets are more desirable because of their larger recoilweight.

 

[travlerajm]

Sounds right. I guess that why headlight racquets are more desirable because of their larger recoilweight.

High recoil weight gives you better depth control.

But there might be a tradeoff - for maximum control on groundstrokes, it's also important to make sure MR^2 > 355 kg-cm^2. If you go much lower than that, you're giving up a lot of directional control.

So you want high MR^2 and high recoil weight. Which means that for best performance you should play with the highest swingweight that you can handle.

The right racquet for each player is a delicate balance of these specs.

 

[KFwinds]

Ok; I'm interested in this, but can someone explain it in simpler terms and possibly give some examples of racquets that fit the "prime" specs for volleying? (and yes, I did understand the aspect that it will vary slightly from person to person...)

 

[travlerajm]

Ok; I'm interested in this, but can someone explain it in simpler terms and possibly give some examples of racquets that fit the "prime" specs for volleying? (and yes, I did understand the aspect that it will vary slightly from person to person...)

If you go to racquetresearch.com, there is a list of many racquets ranked roughly in order from highest recoil weight to lowest. The POG OS tops that list. The NXG OS would rank even higher if it were on the list. Adding a few grams of lead at 3 and 9 to any of HL racquets that top the list makes for a very good volley racquet.

 

[Redflea]

Aieeeeeee! What is this, did I walk in on an honors physics final?!?

Please, be considerate, and remember that there are liberal arts majors hanging around here who are very easily frightened by complex equations!

 

[travlerajm]

Aieeeeeee! What is this, did I walk in on an honors physics final?!?

Please, be considerate, and remember that there are liberal arts majors hanging around here who are very easily frightened by complex equations!

The bottom line is that a good volley racquet has lots of weight both in the handle and in the hoop. If you start out with a HH racquet like an O3 Silver, adding an ounce along the handle will make it much better for volleys. Or if you start out with a HL player's racquet, it probably needs more weight in the hoop to make it better for volleys.

 

[TheNadural]

High recoil weight gives you better depth control.

But there might be a tradeoff - for maximum control on groundstrokes, it's also important to make sure MR^2 > 355 kg-cm^2. If you go much lower than that, you're giving up a lot of directional control.

So you want high MR^2 and high recoil weight. Which means that for best performance you should play with the highest swingweight that you can handle.

The right racquet for each player is a delicate balance of these specs.

Can you elaborate on how higher recoil improves depth control and why a r^2 of 355 is an important line for directional control? Is there a simple general rule of thumb for going from r squared to SW?

Would you alter this in anyway based on any advances in racket tech?

 

[MasterSlice74]

The best way to improve your volleys is to practice them... and maybe get a coach to look at them... I know the point of the thread is to take the physics/rackets perspective but just going to say this if anyone needs to hear it