# String effect on drag (air resistance)

#### hobl4

##### Rookie
I made a (possibly useless) comparison between different string setups and their effects on drag. I did the calculations in Excel and I set it up so that it could be easily used by anyone to compare any setup, but this forum doesn't allow me to post an image of it, let alone the Excel file.

Some points:

- I calculated the difference in drag in % because I don't think it's useful to calculate the actual value for drag in this case. We can assume every variable in the drag equation to be similar between the setups, except the share of stringbed covered in string (which is what this calculation is based on). We could maybe factor in string skin friction but I couldn't find any values for that.

- Nadal's setup creates a relatively high drag. This coupled with the relatively thick beam (not taken into account in calculations) of the Pure Aero means that Nadal had to cope with about 8% more drag compared to Federer back when Fed was using a small frame. Compared to Nadal, Federer seemed to have a flatter racquet path on the forehand side as well which would eliminate even more drag caused by strings. Please tell me if you have a different opinion or if you think this matters in any way.

 Racquet # / name Head size (area of stringbed) String pattern String pattern String material String material String diameter (gauge) String tension String tension String tension String diameter (gauge) after tensioning String area String area String area String area Comparison of string setup's effect on drag (air resistance) Comparison of string setup's effect on drag (air resistance) Mains Crosses Mains Crosses Mains Crosses Mains Crosses Mains Crosses Mains Crosses Mains & crosses Against average drag Against setup with worst drag (inch²) (mm) (mm) (kg) (kg) (mm) (mm) (mm²) (mm²) (mm²) % % Federer PS90 90 16 19 NatGut Poly 1,30 1,25 22,5 22,5 1,23 1,10 7171 6424 13595 -3,8% -7,7% Federer RF97 97 16 19 NatGut Poly 1,30 1,25 27,0 25,5 1,21 1,08 7357 6548 13905 -1,6% -5,5% Wawrinka Yonex 95 16 20 Poly Poly 1,30 1,30 27,0 25,0 1,13 1,14 6958 7037 13996 -0,9% -4,9% Djokovic 95 18 19 NatGut Poly 1,26 1,26 26,8 28,0 1,17 1,07 7513 6894 14408 +2,0 % -2,1% Nadal 100 16 19 Poly Poly 1,35 1,35 25,0 25,0 1,20 1,20 7361 7361 14722 +4,2 % 0,0%

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#### happyandbob

##### Legend
Poly string's diameter decreases twice as much as a natural gut string's when the strings are of equal thickness and under the same tension.
What do you base this assumption on?

#### hobl4

##### Rookie
What do you base this assumption on?
It was hard to find info but one source said poly string's modulus of elasticity is 2x natural gut's, basically meaning it's twice as elastic. This means it streches twice as much under the same tension, hence the decrease in diameter is twice as big. I can post the equation I used to calculate the change in diameter later.

#### happyandbob

##### Legend
It was hard to find info but one source said poly string's modulus of elasticity is 2x natural gut's, basically meaning it's twice as elastic. This means it streches twice as much under the same tension, hence the decrease in diameter is twice as big. I can post the equation I used to calculate the change in diameter later.
I suspect that may be true over their respective useful lives, but if you string natural gut vs equivalent diameter poly, the natural gut stretches at least 2x more under tension during stringing than the poly does.

#### MisterP

##### Hall of Fame
I suspect that may be true over their respective useful lives, but if you string natural gut vs equivalent diameter poly, the natural gut stretches at least 2x more under tension during stringing than the poly does.
I’d say more than 2x. I have “bottomed out” the ratchet mechanism on my dropweight stringing thin gut.

#### hobl4

##### Rookie
I’d say more than 2x. I have “bottomed out” the ratchet mechanism on my dropweight stringing thin gut.
Okay so I think I have the wrong value in the calculation for poly's elasticity. I'll try to find a more accurate value.