Please check my MGRI calculations using TW worksheets (pics inside)

Pp3355

Rookie
Hello

I would like someone with more understanding than I to check on these results -- I am new to racket customisation... @TW Staff @TWE Staff @Ranc feedback would be welcome

Problem 1
I have a Gravity Pro with the current measurements (strung)

Length: 27 (standard)
Weight: 332g
Balance: 32.4cm
SW: 325 (measured as average of 3 measurements using the DYI TW method)

Using this calculator, the MGRI is: 20.80

mgri-gravity-unmod.jpg




Now, I want to keep the SW and balance close to what they are and add weight to the racket to raise the MGRI -- I understand that doing so between 7" and 8" would achieve this, while also keeping the handle free of mods.
The why is in the below steps:

1. First I worked out I need to add around 13 grams of weight to get the MGRI above 21 keeping all things equal (I will use a combination of Babolat 3g and Technifibre 2g lead tape).
Note: I aimed to get a bit above where I wanted because I knew adding weight would slightly change balance/SW and affect the actual MGRI

mgri-gravity-weight1.jpg


2. Then I worked balance and SW numbers from there using the TW customisation worksheet adding the weight just at the end of the handle (7.9")

mgri-gravity-custom-WS.jpg



Putting the re-calculated balance and SW numbers back in the first calculator gives an MGRI of 21.09

mgri-gravity-weight2.jpg







Problem 2
I am also ordering an Angell TC100 v4 70RA and would like to have an MGRI above 21 with no mods.

The unstrung specs are:
Lenght: 27
Weight: 330g
Balance: 31 cm
SW: 297-299

My assumptions are:
- Strings will add 17g weight (Luxilon natural gut 1,25mm)
- Balance will move up 10mm once strung
- Swing weight will increase about 30 points

If I put these in the calculator I get an MGRI range of 21.08/21.16 (depending on unstrung swing weight)

angell.jpg



Does this all sound about right?
 
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Irvin

Talk Tennis Guru
Now, I want to keep the SW and balance close to what they are and add weight to the racket to raise the MGRI
Good luck with that. Adding mass raises Inertia no matter where you add it and if you want to maintain balance you need to add it at the balance point. If you divide that weight equally and add some weight above and below the balance point Inertia goes up even more.
 

t_pac

Semi-Pro
Problem 1 - adding weight at 7" won't leave your balance unaffected, that's why your mgri result came back higher than expected

Your mgri calc for the TC100 is about right

And Irvin is right, what you want isn't possible. To get the mgri up you have to add weight and this will change the balance (make it more head light) and increase SW marginally
 
Last edited:

Pp3355

Rookie
Good luck with that. Adding mass raises Inertia no matter where you add it and if you want to maintain balance you need to add it at the balance point. If you divide that weight equally and add some weight above and below the balance point Inertia goes up even more.

Thanks -- if you see I expect those numbers to be affected (as shown in the TW customization screenshot, however the amount they are affected by does not really add much (1kg to swingweight and a bit lower balance) while achieving the target MGRI, if that makes sense? (see my line under point 1 in the steps)

Problem 1 - adding weight at 7" won't leave your balance unaffected, that's why your mgri result came back higher than expected

Your mgri calc for the TC100 is about right

And Irvin is right, what you want isn't possible. To get the mgri up you have to add weight and this will change the balance (make it more head light) and increase SW marginally

See answer above -- I'm happy to affect balance and SW slightly, I know it is not possible to leave it unaffected, but I have accounted for that in the calculations (I think?) :)
 

Irvin

Talk Tennis Guru
Thanks -- if you see I expect those numbers to be affected (as shown in the TW customization screenshot, however the amount they are affected by does not really add much (1kg to swingweight and a bit lower balance) while achieving the target MGRI, if that makes sense? (see my line under point 1 in the steps)
You made a long post and I not sure if the TW Calculator is correct or not. Let me just say this, to calculate I (SW or inertia) you must know the RW and you can get that from the SW, mass, and balance Using the parallel axis theorem.

SW = RW + (mr^2)
325 = RW + (mr^2)
325 - (mr^2) = RW
158.42 = RW

Now to get the inertia at the butt you need to use the Parallel axis theorem again. I = RW + (mr^2) but the time the r value increase by 10 because you’re not using The 10 cm pivot but the 0 cm pivot.

Now you want to add mass and not change the balance, so you need to add mass at 32.4 cm. So for every gram you Inertia goes up by 32.4x32.4x.001 or 1 kgcm^2. If you want to separate that mass by dividing it in half and placing equal amounts at equal distance from the center of mass you RW also goes up by I = mr^2 so you can add another 1 kgcm^2 by placing 1/2 g at the butt and another 1/2 g at 64.8 cm.

You can’t maintain balance AND inertia by adding mass it is impossible. You can maintain balance but never inertia and balance.
 

Pp3355

Rookie
You made a long post and I not sure if the TW Calculator is correct or not. Let me just say this, to calculate I (SW or inertia) you must know the RW and you can get that from the SW, mass, and balance Using the parallel axis theorem.

SW = RW + (mr^2)
325 = RW + (mr^2)
325 - (mr^2) = RW
158.42 = RW

Now to get the inertia at the butt you need to use the Parallel axis theorem again. I = RW + (mr^2) but the time the r value increase by 10 because you’re not using The 10 cm pivot but the 0 cm pivot.

Now you want to add mass and not change the balance, so you need to add mass at 32.4 cm. So for every gram you Inertia goes up by 32.4x32.4x.001 or 1 kgcm^2. If you want to separate that mass by dividing it in half and placing equal amounts at equal distance from the center of mass you RW also goes up by I = mr^2 so you can add another 1 kgcm^2 by placing 1/2 g at the butt and another 1/2 g at 64.8 cm.

You can’t maintain balance AND inertia by adding mass it is impossible. You can maintain balance but never inertia and balance.


Thanks for this -- understood

I'm ok with changing the balance slightly
 

esm

Legend
Thanks for this -- understood

I'm ok with changing the balance slightly
hopefully it will all work out for you.
just wanted to mention that you must be lucky to have a low strung SW Pro @ 325SW.
both of mine (2019 version) came at 338SW and 339SW strung with fullbed of syn gut.
 

tomkowy

Rookie
Buy "Racket Tune" app on your smartphone (costs pennies). You can easily add weight there on a nice interface.

No way you can have the same balance and SW without affecting swingweight. If you add the weight around the throat, you raise the SW without changing the balance. If you add weight in the handle, you lower the balance.

To lower MGR/I you need to add mass around the balance point. This means mainly throat and bottom of the hoop. 4 grams on the bottom of the hoop, 4 grams inside the throat, 2 grams on the top of the handle. This way you get to 342 grams, 329 sw, 32,3 balance, 21,00 MGR/I
 

Pp3355

Rookie
hopefully it will all work out for you.
just wanted to mention that you must be lucky to have a low strung SW Pro @ 325SW.
both of mine (2019 version) came at 338SW and 339SW strung with fullbed of syn gut.

wow that's crazy

I have 2 others on order with racket matching service + will measure with a machine everything again next week or so...
 

tomkowy

Rookie
Buy "Racket Tune" app on your smartphone (costs pennies). You can easily add weight there on a nice interface.

No way you can have the same balance and SW without affecting swingweight. If you add the weight around the throat, you raise the SW without changing the balance. If you add weight in the handle, you lower the balance.

To lower MGR/I you need to add mass around the balance point. This means mainly throat and bottom of the hoop. 4 grams on the bottom of the hoop, 4 grams inside the throat, 2 grams on the top of the handle. This way you get to 342 grams, 329 sw, 32,3 balance, 21,00 MGR/I
Backing up my numbers with screens from the app when you add 4 grams in the handle instead of 2 grams

EDIT
One last important info: when you add weight in the bottom of the hoop, follow these two rules:
1. Skip the space between middle strings, as stringing machines often hold a racket there and damage lead tape
2. Don't add lead in the hoop wider than 5 cm from racket axis (hoop middle). Adding weight wider than 5 cm from the axis will affect twistweight and racket will be noticeably "clunkier".
 

Pp3355

Rookie
Backing up my numbers with screens from the app when you add 4 grams in the handle instead of 2 grams

EDIT
One last important info: when you add weight in the bottom of the hoop, follow these two rules:
1. Skip the space between middle strings, as stringing machines often hold a racket there and damage lead tape
2. Don't add lead in the hoop wider than 5 cm from racket axis (hoop middle). Adding weight wider than 5 cm from the axis will affect twistweight and racket will be noticeably "clunkier".


Thanks, I don't have an iOS devicewhat happens if you had all the weight on top of the handle, just out of curiosity?

Could you post the resulting image :)
 

tomkowy

Rookie
10 grams at the top of the handle, (19,5 cm from the bottom):
342 grams
326 sw
32 balance
21,01 MGR/I
I can share the screen later ;)

I didn't know that the app is only for IOS, shame
 

Pp3355

Rookie
10 grams at the top of the handle, (19,5 cm from the bottom):
342 grams
326 sw
32 balance
21,01 MGR/I
I can share the screen later ;)

I didn't know that the app is only for IOS, shame

no worries -- indeed it is similar with what I get with the online calculator I linked at the top of my opening post

To me putting all in the spot at 19.5/20cm achieves two things: keeps swing weight very close to original, moves balance slightly lower which makes for a more HL racket -- so for me its win win
 

Pp3355

Rookie
@tomkowy @Irvin

I realised that replacing the standard grip with a 18g Fairway leather grip may achieve the same results.. lowering balance and adding static mass... no lead needed!

Thoughts?

Screenshot-20220105-194145-Opera-2.jpg
 

tomkowy

Rookie
@tomkowy @Irvin

I realised that replacing the standard grip with a 18g Fairway leather grip may achieve the same results.. lowering balance and adding static mass... no lead needed!

Thoughts?

Screenshot-20220105-194145-Opera-2.jpg
1. Did you subtract the weight of Head standard grip before adding Fairway? Head Hydrosorb Pro weights 18 grams so if you take one and put another, you end up with zero weight added.
2. Adding a grip is adding weight in the bottom of the racket. It's not good for getting MGR/I higher. This way you are making the racquet more polarized, not less. It's only good if you want to get balance lower. Earlier you mentioned that you want to keep the balance.
3. 18 grams more is a lot. I wouldn't start from such a big change. I would add 5 grams of weight per iteration. This way you will feel if you like the changes. Adding 18 grams is like playing with a different racquet.
 

Pp3355

Rookie
1. Did you subtract the weight of Head standard grip before adding Fairway? Head Hydrosorb Pro weights 18 grams so if you take one and put another, you end up with zero weight added.
2. Adding a grip is adding weight in the bottom of the racket. It's not good for getting MGR/I higher. This way you are making the racquet more polarized, not less. It's only good if you want to get balance lower. Earlier you mentioned that you want to keep the balance.
3. 18 grams more is a lot. I wouldn't start from such a big change. I would add 5 grams of weight per iteration. This way you will feel if you like the changes. Adding 18 grams is like playing with a different racquet.


No I did not, silly me!

I am ok with lowering the balance 1-2 PTS headlight

Sure about iteration
 

tomkowy

Rookie
No I did not, silly me!

I am ok with lowering the balance 1-2 PTS headlight

Sure about iteration
If you don't want to play with lead tape, start with adding an overgrip like Head Xtreme Soft - weights 8,5 grams, so you will get:
340 grams weight
31,9 cm balance
325 SW
20,93 MGR/I

an easy starting point to see, what you like and what not. An overgrip like Yonex Super Grap (6 grams) will work out too.
 

t_pac

Semi-Pro
Is there an issue with the way your frame plays that you are hoping to solve by increasing the mgr/I by 0.2?
 
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