Impact of stringing on swing weight

I have 2x of the same racquets
#1 - unstrung; 312.5g/292sw/312bal & strung; 327.4g/325sw/322bal
#2 - unstrung; 314.1g/295sw/314bal & strung; 328.8g/325.5sw/323bal

When I strung #1, it added 14.9g and 33sw. Then strung #2 with the same string setup/tension and it added 14.7g, but only 30.5sw

Not a big issue as they've ended up very close in spec, however why is it that the same string added 2.5 less 'SW' on #2??

New to customizing and interested in the explanation, thanks in advance
 

Return_Ace

Hall of Fame
SW will depend on how the mass is distributed in the head.

Could just be string QC, that in the heavier racket it was either slightly thicker towards the end of the racket, or maybe the cross strings at the top weren't pulled as tight (i.e. stretched as much) so it retained more weight at the top.

Could also just be variation in measurements, not sure how you did your measuring.
 
Thanks

String was the same combo (alu power/nxt hybrid) in both and added 14.9g and 14.7g respectively - so seems the weight of the string v close

SW was done on a yonex precision scan. Not sure if the reading is slightly different depending on how much of a flick you give the racquet to start?
 

Wheelz

Professional
Doesn’t seem to make sense on paper. Seems like a measurement error. Unless strings can vary in wet but 0.2g is not 3SW
 
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Arak

Hall of Fame
It’s difficult to guess what exactly happened in your case. It could be all within the measuring latitude. However, I know that adding string weight to a lighter racket affects swing weight more than adding the same weight to a heavier racket. Now I’m not sure if the 3 gram difference could affect the SW in this way. I’m not familiar with the maths involved.
 

Irvin

Talk Tennis Guru
The length of your 2 rackets is not the same, or the patterns are different. A difference of 0.2 g only makes a difference of about 0.4 kgcm^2 in SW so there must be a difference in the center of mass in the stringbed or you make a pattern that has more mass higher. Simple math I = mr^2 m (0.2 g) only accounts for 0.4 kgcm so r (radius from 10 cm to COM of string bed) must be greater. I know it can’t be in your spec measurements. LOL
 

Dragy

Legend
Error could creep in when measuring unstrung and then when measuring strung, which unluckily combined with some minor frame difference, as @Irvin pointed, like slight difference in length. Not big deal if they ended up close enough in specs.
 

LOBALOT

Hall of Fame
I do not think string would cause this variance and would chalk up to variability in measurement.
 
Thanks all. The racquets are same model, same length, same string pattern etc. I'm leaning towards this being some type of variability in measuring. They were measured on different days, different staff member etc. I might be best to get them both remeasured at the same time
 

HitMoreBHs

Semi-Pro
Thanks all. The racquets are same model, same length, same string pattern etc. I'm leaning towards this being some type of variability in measuring. They were measured on different days, different staff member etc. I might be best to get them both remeasured at the same time
There is no real need. They are close enough to be a matched pair as is. Unless of course your game is super sensitive to such small degrees of variation!
 

alexg

New User
3SW is about 1 gram at 12 o'clock.

If measurements are accurate, then my best bet is that tour 14.9g racquet has larger knots and / or extra string dangling from the knots at the tip of the racquet, whereas the 14.7g racquet has larger knots / extra string at the knot on the throat side of the hoop.

Seriously, it's probably the SW measurement before or after stringing that's slightly off. How many times did you swing the racquet?
 

LOBALOT

Hall of Fame
That is slick machine by the way.

I may know why. Racquet 2 was already at a higher swing weight than racquet 1. As the change to Swingweight by adding string is so slight it's impact into changing the swingweight for racquet 2 with it's higher unstrung swingweight will be less than for racquet 1. We are talking about slight differences but I suspect this is the reason.
 
Thanks again for the responses

My game is definitely not sensitive enough to feel the difference! I'm of course very happy to have a matched pair of Ultra Pro 16/19's. I'm only asking to get a better understanding of racquet customization/measurement etc. I put in quite a bit of research time and then work to take off the bumpers, add lead, replace bumpers, add leather grip, take measurements throughout etc. So this was more out of curiosity and also that my estimates told me the SW of stick #2 might be slightly higher (when it wasnt)

I checked the knots on both sticks. Stick #2 14.7g (lower added SW once strung) has 4x tie offs (hybrid), 3x of those are on throat side and YES @alexg they have longer tag ends on the knots! Whilst the tip knot tag on the 14.9g stick is shorter, its only 1x knot. So I think I'm down to 2x reasons;

1. The 3x longer throat tag ends on stick #2 are slightly reducing SW vs stick #1 (in my mind a small counterbalance?)
2. The measurements were slightly off (at some stage ill remeasure same day to check)

Great to get everyone's feedback and hopefully this thread helps someone else one day! Cheers
 
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