Measuring MgR/I

[stoneage]

There has been some discussion about the magic number MgR/I=21.

Since the formula is closely related to the swing time of the racquet, it is fairly easy to measure: Hang the racquet from the butt and measure the time T it takes to swing back and forth, then

MgR/I=39.48/T^2

To get any accuracy it is better to measure the time for 10 swings and divide by 10.

The only problem is that it could be difficult to hang the racquet from the butt without any friction. But you could use the technique of hanging the racquet on one of the strings (as shown here) and transfer the swingtime to the but. You then get the formula:

MgR/I=39.48*g*R/(T*T*g*(H-R)+39.48*H*(2*R-H))

R= distance to the balance point
H= distance to the hanging point
T = swing time
g = 981 if you use cm for the distances

The formula might look messy, but you only need the time and two easily measured distances. But to simplify it I have put a simple calculator at racquetTune.com/MgR_I

I am still interested in knowing why this number is such a good measure? Setting MgR/I=21 means that the swingtime when racquet is hanging from the but should be closely as possible to 1.37 s
I would be very interested in knowing why!

Sten
__________________
Test and tune you racquet with racquetTune for the iPhone

 

[floydcouncil]

Ring, ring......

THERE IS NO MAGIC NUMBER.

 

[Kevo]

I am still interested in knowing why this number is such a good measure?

It's not IMO. It is the conclusion of a single individual AFAIK. I think that different people will favor different numbers based on their own proclivities. It's fun to experiment and try different things. Sometimes you find something you like.

For me though, the best indicators of someone playing good tennis have nothing to do with equipment. The fittest players are most often the best players.

 

[corners]

Hi Sten,

Very cool. Thanks for posting your calculator.

As I understand it, 21 is a magic number for some people. The idea is that, for some people, when the weight of the racquet is distributed such that MgR/I = 21, the relative speeds of the handle of head "match" the swingstyle of that person, making timing the shot easier or more natural.

If you haven't already, search "MgR/I"; author: travelerajm to get into the nitty gritty of this theory.

Trav has speculated that taller people may find that MgR/I < 21 is more suitable, while shorter people may like MgR/I > 21. I'm short and like 21.2 +. Wooden racquets, because they have lots of mass in the throat and handle, typically have MgR/I > 21.5. In my experience, this makes their heads feel quite fast, despite their high static weights and swingweights. This seems to be an illusion created by the timing, however, as I've done informal swingspeed tests and found that the heavier wooden racquets swing more slowly, even though they feel fast. This matches the theory, which predicts the head on these frames would move quicker, but only in relation to the hand/handle. In absolute terms, the heavier, higher-swingweight woodies swing more slowly than lighter, lower-swingweight sticks with lesser MgR/I values, at least for me.

 

[stoneage]

I know there is no magical number, on the contrary I am rather skeptical to the concept. So I wrote the post to see if anyone could come up with an explanation why this is relevant. There were no good ones in the older post as far as I could see.

 

[DEH]

I know there is no magical number, on the contrary I am rather skeptical to the concept. So I wrote the post to see if anyone could come up with an explanation why this is relevant. There were no good ones in the older post as far as I could see.

Here is a post that might help.
http://tt.tennis-warehouse.com/showthread.php?t=330307

 

[stoneage]

Here is a post that might help.
http://tt.tennis-warehouse.com/showthread.php?t=330307

Thanks for the link, I had missed that one. Especially the paper by Cross and Nathan gave some new insights. And the conclusion is that swingweight is a good measure.

However, there is no discussion of MgR/I and no evidence why it should have any value. Except Travelrajm who jumps in says its great.

The problem with MgR/I=21 is that you can easily achieve it with a 3 m long and 10 kg heavy racquet. And how playable is that? The more I think about MgR/I the more insignificant it becomes.

 

[DEH]

Thanks for the link, I had missed that one. Especially the paper by Cross and Nathan gave some new insights. And the conclusion is that swingweight is a good measure.

However, there is no discussion of MgR/I and no evidence why it should have any value. Except Travelrajm who jumps in says its great.

The problem with MgR/I=21 is that you can easily achieve it with a 3 m long and 10 kg heavy racquet. And how playable is that? The more I think about MgR/I the more insignificant it becomes.

I am not smart enough to answer your questions but I have tried it on my daughters Speedport Black and it really seemed to help. I believe he came up with that formula as a measure so that he can look at any racquet with any swingweight and weight and see how it will play. It just puts a number that he can compare. He also came up with that number by looking at some of the great players in history and looking at their specs. One post I read by Travlerjm said he broke down the top 20 ATP player and they had a MgR/I around the 21 mark and player below that ranking number was well below the MgR/I=21. Sorry I could help you out more.

 

[Ash_Smith]

Ring, ring......

THERE IS NO MAGIC NUMBER.

I think you'll find 3 is the magic number...

http://www.youtube.com/watch?v=0irL1M15DH8&feature=related

Ash

 

[floydcouncil]

http://www.youtube.com/watch?v=bl9bvuAV-Ao

I did find a MAGIC BUS!!!!!!!!!!!!!!!!!

 

[corners]

I know there is no magical number, on the contrary I am rather skeptical to the concept. So I wrote the post to see if anyone could come up with an explanation why this is relevant. There were no good ones in the older post as far as I could see.

Simply pick up an old wooden racquet with MgR/I of <21.5 and then a highly polarized modern stick like a Bab Aero Drive (about 20.4). The difference in the feel of the racquet head compared to the handle and the timing of the swing is quite distinctly different. MgR/I is simply a way to characterize the effects of weight distribution on swing dynamics numerically.

The practical implication is that each player may find a value that fits their swingstyle, making strokes easier to time, which might increase accuracy. For me, sticks below 21 feel sluggish, with an odd feeling of disconnect between the head and handle. Sticks above 21.5 swing very smoothly and naturally for me. The feeling and timing are quite distinctly different. If one does find a number that works for them, they can then use it in subsequent customizations to achieve the same feeling and timing, even if going up or down in weight or swingweight. I've found that 21.25 is probably my favorite, and can set up 12 ounce and 13 ounce racquets sharing that number that both feel very similar during the swing, despite the big difference in weight.

It's my impression that Trav's theory is the first coherent attempt to directly relate weight distribution to swing dynamics/timing. This is an area that has always been mysterious, and Trav deserves Kudos for giving us something to work with.

I understand your skepticism, however. But remember that this is a theory or hypothesis that came out of years of innovative racquet customization experiments and was created by a very sharp dude. It would be great if someone would test it properly, but who's going to do that? Before you dismiss it out of hand you should play around with it and see for yourself.

The easiest way is to lead up a frame to a swingweight that is a bit higher than your normal comfort zone. Then progressively add lead at 7" until you feel the frame "come around" easily and naturally. (You can use 2-3 gram fishing weights taped to one of those big rubber bands to make this easier, cleaner and reversible)

I think you'll find there is something to it.

I know one player that has used several frames over the past 20-30 years, each with different specs (moving progressively over the years from heavy, headlight, moderate swingweight to less heavy, less headlight, about the same swingweight), and found that he had unwittingly customized them all to have matching MgR/I, even though they didn't share any other specs. Just an anecdote, but worth something nonetheless.

 

[stoneage]

I am not smart enough to answer your questions but I have tried it on my daughters Speedport Black and it really seemed to help. I believe he came up with that formula as a measure so that he can look at any racquet with any swingweight and weight and see how it will play. It just puts a number that he can compare. He also came up with that number by looking at some of the great players in history and looking at their specs. One post I read by Travlerjm said he broke down the top 20 ATP player and they had a MgR/I around the 21 mark and player below that ranking number was well below the MgR/I=21. Sorry I could help you out more.

Yes I also understood that it was derived from looking at several pro racquets. And that is a good start. And that you were successful is also a positive indication. However, until there is an explanation what the number is describing you can't know under which circumstances it applies and you should be careful in using it. MgR/I is only a description of the massdistribution and is independent of the weight of the racquet. This means that you can add as much weight as you want to a racquet without changing MgR/I as long as you keep the weight distribution constant. So obviously the concept breaks down somewhere, the is question is only when.

 

[(K)evin]

I wanna get this but don't =( maybe I'm just slow today but what is this number supposed to do and how can I achieve it in a brief but simple explanation?

 

[GPB]

It's a measuring stick, like swingweight, used to describe "something" about the racket. (How's that for a simple explanation?)

 

[(K)evin]

It's a measuring stick, like swingweight, used to describe "something" about the racket. (How's that for a simple explanation?)

Are you trying to be sarcastic or mean? Because I really just wanna know what this is about and if it can help me.

 

[GPB]

Hey, sorry I missed your reply. I wasn't trying to be mean. What I was trying to say, is the MgR/I is similar to SW in the sense that it's a measurement that you can use to match rackets.

Some people say "I like a racket that's X grams heavy," or "I like Y for a swingweight." Well, Trav and a few others have this other calculation that works for them.

Notice the end of Corner's post above:
"I know one player that has used several frames over the past 20-30 years, each with different specs (moving progressively over the years from heavy, headlight, moderate swingweight to less heavy, less headlight, about the same swingweight), and found that he had unwittingly customized them all to have matching MgR/I, even though they didn't share any other specs. Just an anecdote, but worth something nonetheless."