Which string and which tension for your game: gauge, tension and the limits of the advice
Fine string for touch at the net, tension by level, and why websites contradict each other.
Gauge: what the makers say
The gauge is the string's diameter, in millimetres. Makers place fine strings on repulsion and precision, and thicker ones on durability. Yonex lists Exbolt 63 at 0.63 mm for precision, BG66 Ultimax at 0.65 mm, BG80 at 0.68 mm and BG65 at 0.70 mm for durability. Victor groups its strings the same way: 0.63 and 0.66 for repulsion, 0.68 for control, 0.69 and 0.70 for durability (VICTOR LAB article). The price of a fine string is a shorter life.
Tension: the sources disagree
For a beginner you will find 16 to 18 lb with plastic shuttles and 17 to 19 lb with feathers from a British stringer (badminton-coach.co.uk), and 22 to 24 lb from shops, with an old manufacturer page going as low as 12 to 18 lb. The gap comes from the era, the country, the shuttle (plastic needs 2 to 3 lb less) and the racket frame. Two hard limits are not up for debate: your frame's maximum, for example 20 to 28 lb for a Yonex 4U Astrox 88D Pro, and the stringer's capacity. Victor even gives separate maximums for the vertical and horizontal strings (marking explained), which is why many stringers put the crosses a little higher.
What the studies show, and what they do not
In a 2013 laboratory test on five rackets, the shuttle left faster at lower tensions (22 lb beat 30 lb). The sample is small: one racket per tension and ten hits each. A 2013 study by Zhu tested whether players can perceive the benefit of a tension for power shots: qualified players can, but only experts try to save energy (PubMed 23414453, abstract only). Our reading: the right tension depends on the player's swing speed and technique more than on a magic number.
Our physical reasoning (not a sourced fact)
A higher tension makes the string bed stiffer: it deflects less and the shuttle stays on the strings for a shorter time. That gives a cleaner, more predictable direction, which is what a net player wants, while power at the back comes from the swing. A lower tension acts like a trampoline: more help at a moderate swing, less feel for direction. A thinner string stretches more and loses tension and strength faster. That fits the makers' positioning, and it explains why a precise net player may like a fine string and a durable one a thicker string.
A starting point for your profile
- Light, handle-heavy racket, fine string (0.63 to 0.66), touch and net play: start in the middle of your frame's range and move by 1 lb steps, because the sources do not give a precise figure for this profile. Some shops advise a little less tension for net-focused doubles, others more: only your hands can settle it.
- Power player from the back: the sources contradict each other (lower tension for more help, or higher tension for control at high swing speed). Test both with the same string.
- Tension drops by roughly 5 to 10% in the first day according to several sources, with no independent measurement. Restring rather than chase the number.