Measured values

Stiffness

154lb/in

lower = softer, kinder on the arm

Tension loss

64%

lower = stays where you strung it

Energy return

80%

higher = livelier, more free power

Spin potential

3.6

higher = more spin off the string bed

Ball bite

0.385COF

higher = grabs the ball harder

String friction

0.107COF

lower = strings slide and snap back

How it ranks against all 791 strings

Stiffness 154 lb/in · 17th pct

Stiffer than 17% of strings tested.

Tension loss 64 % · 99th pct

Sheds more tension than 99% of strings tested — goes dead fast, expect frequent restringing.

Energy return 80 % · 3rd pct

Livelier than 3% of strings tested — very muted and low-powered.

Spin potential 3.6 · 21st pct

More spin potential than 21% of strings tested.

Ball bite 0.385 COF · 15th pct

Grips the ball harder than 15% of strings tested.

String friction 0.107 COF · 72nd pct

More string-on-string friction than 72% of strings tested.

Like Cobra 17/1.20, but…

Almost nobody looks a string up out of curiosity. You are here because something about your current setup is wrong. Each list below keeps the rest of this string's profile as close as it can while moving decisively on the one thing you picked, so these are swaps rather than merely different strings.

SofterKinder on the arm

FirmerMore control, less launch

More spinBites and snaps back harder

More powerHands more back to the ball

Holds tensionStays where you strung it

What Cobra 17/1.20 is actually good for

Its standing on each of the site's rankings, out of every measured string in the database. Same arithmetic as the finder, not a separate opinion.

How long it lasts, and how far it stretches

Playable life

~10hours

Estimated from tension loss, on a scale running from 40 hours for the best-holding strings in the database down to 10 for the worst. At four hours a week that is about 3 weeks.

Estimated, not measured. This estimates when the bed goes dead, not when the string snaps. If you break strings before you notice them going dull, you are a breaker, and thickness and material matter far more to you than tension hold does.

Track this in a setup

Elongation under load

This stringDatabase median

How far the string stretches when tensioned to a given load. A string that elongates more absorbs more of the impact itself and feels softer; one that barely moves passes more of it on to the frame and the arm.

Measured at every tension and swing speed

The figures at the top of this page come from one test condition: 51 lb at fast swing speed. There are nine in total, and all of them are below. Tension moves the bed more than the choice between two similar strings does, so this is the table that actually answers "what will it feel like for me".

Bed stiffness against tension · Fast swing

Measured at 3 tensionsFitted response

Measured at three tensions, with the fitted response drawn across the whole stringable range. The line does not pass through the origin: this bed carries about -14 lb/in that does not come from tension at all, and gains roughly 3.4 lb/in for every extra pound you string it at.

Convert a tension with this

What that means

Stringing Cobra 17/1.20 at 30 lb gives a bed of about 88 lb/in; at 70 lb it is about 224 lb/in. That range is wider than the gap between most pairs of strings on this site, which is the single most useful thing this page can tell you.

Stiffness lb/in lower = softer, kinder on the arm

Strung at	Slow swing	Medium swing	Fast swing
40 lb 18.1 kg	177	145	125
51 lb 23.1 kg	192	172	154
62 lb 28.1 kg	242	222	200

Tension loss % lower = stays where you strung it

Strung at	Slow swing	Medium swing	Fast swing
40 lb 18.1 kg	65	65	65
51 lb 23.1 kg	63	63	64
62 lb 28.1 kg	49	49	50

Energy return % higher = livelier, more free power

Strung at	Slow swing	Medium swing	Fast swing
40 lb 18.1 kg	87	79	74
51 lb 23.1 kg	92	85	80
62 lb 28.1 kg	95	90	86

The highlighted cell is the condition every other figure on this site is quoted at.

What else the machine recorded

Further measurements from the same test, given at the reference condition of 51 lb, fast swing.

Dwell time

39.9ms

How long the ball stays on the string bed. Longer dwell is the physical basis of what players call hold or pocketing.

Bed deflection

35.4mm

How far the string bed moves at impact. More deflection means the bed is doing more of the work of stopping the ball.

Peak force

30lb

The highest force perpendicular to the string bed during impact. The spike the frame and the arm actually receive.

Tension at impact

19.1lb

What the bed is actually pulled to by the time the ball arrives, after it has settled. Always lower than the tension it was strung at.

Loss: settling

10.5lb

Tension lost simply from being strung and left alone, before a ball is hit.

Loss: bedding in

21.2lb

Tension lost while the bed settles over its first impacts.

Loss: impact

0.7lb

Tension lost to the impact itself. Frequently negative, because a bed often gains tension across an impact rather than losing it.

Loss: total

32.2lb

The three losses above added together, in pounds.

Strings that play like this

Closest matches across stiffness, tension loss, energy return and spin potential.

Polyfibre Hightec Premium 17 96% match Polyfibre Poly Hightec 18 96% match Polyfibre Viper 17/1.20 96% match Polyfibre Poly Hightec 17 95% match Polyfibre TCS 17 92% match Head Sonic Pro 16 91% match

Head to head: Cobra 17/1.20 vs Hightec Premium 17 · Cobra 17/1.20 vs Poly Hightec 18 · Cobra 17/1.20 vs Viper 17/1.20

More from Polyfibre

What these numbers mean

Stiffness · lb/in

How much the string bed resists deflection. Higher plays firmer and more controlled; lower plays softer and easier on the arm.

Tension loss · %

Share of the reference tension the string sheds under a fixed test protocol. Lower means the bed stays where you strung it for longer.

Energy return · %

Share of impact energy handed back to the ball. Higher plays livelier and more powerful.

Spin potential

Ball friction divided by string-on-string friction. Higher means better bite with a cleaner snapback, so more spin.

Ball bite · COF

String-on-ball friction. Higher grabs the ball harder through the brush.

String friction · COF

String-on-string friction. Lower lets the mains slide and snap back into place after impact.

Compare Cobra 17/1.20 against 791 strings Switching from this? Convert your tension Use it in a hybrid Find it on the map Find the right string for me