Is string tension the same for similar gauges of flats/rounds?

Discussion in 'Strings [BG]' started by Thom Fioriglio, Jul 29, 2020.

  1. I have a question about string tension. Would strings with similar gauges have the same tension regardless if they are flatwounds or roundwounds? For example, a set of 45-65-86-105 strings both flatwound and roundwound, would the tension be the same? I am not talking about "stiffness" I know flatwounds are more stiff, just curious about tension.


  2. It all depends on the specific set and how they're constructed; gauges are only part of the whole equation. But it's quite possible for flats and rounds of the same gauges to have similar tension figures. But not all the time.

    For example...

    GHS Boomer M3045 (45-65-85-105) = 186.5 lbs. in total tension.
    Precision Flats M3050 (45-65-85-105) = 184.6 lbs. in total tension.
  3. Here's another example...

    D'Addario Chromes Flats 45-65-85-105 = 206.76 lbs. in total tension.
    D'Addario XL Nickel roundwound 45-65-85-105 = 174.29 lbs. in total tension.

    The same gauges of rounds and flats by the same company = over 30 lbs. of difference.
  4. Wow, great info. Thanks. How did you calculate this?

    Would you know the tension of Fender 7250 45-65-85-105 and LaBella 760FS 45-65-85-105?
  5. The tension figures for GHS are right out of the GHS Tension Guide.

    The D'Addario figures are off of their website.

    No tension info available for either Fender or La Bella.

    Are you trying to make a change from Fender rounds to La Bella flats? If so, go ahead and make the change, then tweak the truss rod according to how the neck reacts to the difference in tension. No big deal.
  6. Thanks again for the info. Yeah, was thinking of trying a set of LaBellas. Also tried a set of Fender 9050 flats on there which were 45-60-80-100. Just curious how the tensions differed.
  7. Based on my experience, my educated guess would be Fender 9050L flats (45-100) are fairly close to, or only slightly more than, Fender 7250M (45-105) rounds in tension, while the La Bella 760FS (45-105) would be heavier than either. If you want to try a set of La Bella flats, the 760FL (43-60-82-104) might be a better choice to keep the tension in the same ballpark as the other two.
    Thom Fioriglio likes this.
  8. Thanks. The LaBella 760FL's get a lot of love around here. From what I read, even though they are a slightly lighter gauge than the 760FS's quite a difference in tension and stiffness.
  9. I once had Fender 9050CL (45-60-80-105) on my J-bass and La Bella 760FL (43-60-82-104) on my P-bass at the same time and found them to be very similar in overall playing feel, and was able to switch back and forth between the two basses with no big adjustment in my playing technique.
    Thom Fioriglio likes this.
  10. Bassamatic

    Bassamatic keepin' the beat since the 60's

    The tension depends on the material and gauge of the core material. There may be several layers of windings on top of that to make the final size that add little if any to the tension.
    Thom Fioriglio likes this.
  11. iiipopes

    iiipopes Supporting Member

    May 4, 2009
    It depends. Tension is a function of the mass of the string, not its diameter. The entire string. The core size determines the compensation needed, and can affect the flexibility and feel, but it is the entire mass of the string over the scale length is what determines overall tension, pitch and scale length being constant.

    For example, flats tend to have more tension than rounds of the same diameter, because the ribbon wrap of the flats essentially has no space between the windings, as do roundwound strings. (look at all manufacturers cross-section pictures). This means more mass. The old D'Addario tension guide actually gave the unit mass in grams of every particular string, so a person can compare. More mass means more tension to bring a string up to a given pitch on a given scale length.

    And it is not just bass strings. The tension formula applies to everything, from bass strings to tennis racquets to bridge cables. Again, mass over the scale length at pitch, not diameter, and not core by itself.

    "Understanding what determines string tension. In order to determine the tension at which a string will vibrate, you need three pieces of information: the Unit Weight, the Scale Length, and the Frequency of the string. You can use the charts in this brochure to get a pre-calculated tension for the D’Addario strings listed or you can use the formulas below to calculate the exact tension for any string using the scale length of your particular instrument. All of the charts illustrate string tensions for each string at a variety of pitches, in case you use alternative tunings. UW- Unit Weight. In all the charts and formulas in the brochure, unit weight is expressed in pounds per linear inch (lb/in). L- Scale Length. This is the vibrating length of the string. This is determined by measuring the distance from the nut to the bridge of the instrument in inches (in). F- Frequency or pitch. This is the pitch at which you will be tuning the string expressed in cycles per second (Hertz). On the following page are two fingerboard graphics detailing the various frequencies for the standard guitar and electric bass guitar. To calculate the tension of a string in pounds use the formula below, inserting the three variables described above: T (Tension) = (UW x (2 x L x F)^2 ) / 386.4 To convert the result into Newtons, simply multiply by 4.45. If you know what tension you want the string to have, you can calculate the string unit weight. You can then use the charts in this guide to locate a string with approximately the same desired unit weight. UW (unit weight) = (T x 386.4) / (2 x L x F)^2."
    Last edited: Jul 30, 2020
    hasbeen and michael_t like this.
  12. Bassamatic

    Bassamatic keepin' the beat since the 60's

    That is really fascinating! However, I believe it applies to the string in motion as it takes the mass of the string and the frequency into consideration. I always think of tension as being the at-rest condition. You learn something every day!!
  13. Just to illustrate the point made by @iiipopes, here's an example of how two sets of strings with similar construction and size can have two different tensions due to different materials used for the outer cover wire.

    GHS Round Core Boomers (NPS roundwound on a round core):

    G 040 - 36.2 lbs.
    D 055 - 33.2
    A 075 - 36.4
    E 100 - 38.2 (Total 144.0)

    GHS Balanced Nickels (Pure Nickel roundwound on a round core):

    G 040 - 43.2 lbs.
    D 056 - 42.9
    A 076 - 43.5
    E 101 - 42.7 (Total 172.3)

    The difference in tension between these two sets can largely be attributed to the difference in the material for the cover wire, not just for the core. Pure nickel, being a heavier metal (= more mass) than nickel-plated steel, takes more tension to be tuned up to pitch.
    iiipopes and Thom Fioriglio like this.
  14. iiipopes

    iiipopes Supporting Member

    May 4, 2009
    Tension applies to statics, or as an engineering friend of mine defined statics: why bridges don't fall down. You are talking about kinetics, the behavior of the string, which is independent of tension, of which my same engineering friend described kinetics, why doors swing on hinges. The bridge doesn't fall down because the cabling retains the tension, even if the wind wants to make it vibrate (unless, like the old video, the force of the bridge vibrations exceed the load rating of the cabling, just like the string will break if we hit it too hard or tune it up too high); and the tension provides the foundation for the string to be able to vibrate, just like the door frame and hinges provide the stable structure on which the door will actually open and shut without wobbling.
    Last edited: Jul 30, 2020
  15. IMHO String stiffness is even more important than string tension, unless the tension is radically different.

    I feel differences in stiffness AS though it feels like a tension thing, much more than I feel differences in actual tension or gauge.

    Maybe it's just me.

    So like, hex strings are much stiffer than round core strings, and I can really feel that.
    Last edited: Jul 30, 2020
    hasbeen likes this.
  16. It's not just you. I'm the same way. I normally choose the gauges of any specific set based more on their overall playing feel than just tension figures. The difference in tension can be dealt with easily by way of a truss rod tweak, while the difference in stiffness/flexibility is something you're stuck with for the duration of the strings being on the bass.
    dkelley likes this.
  17. groovaholic

    groovaholic The louder the better. Supporting Member

    Sep 19, 2004
    Mount Prospect, IL
    Assuming the same scale length and tuned pitch, the metric that would determine tension is the unit weight (UW) of the string.

    That depends on string construction - gauge would be related to UW, but it wouldn’t be an apples-to-apples comparison.
  18. ixlramp

    ixlramp Guest

    Jan 25, 2005
    iiipopes is correct.
    As discussed, see the D'Addario pdf, it is scientifically correct (i have a physics degree). Tension is determined by scale, frequency and 'unit weight' (mass of 1" of string) only. Not by core gauge.
    The confusion may come from the fact that only the core is 'under tension'. The wrap wire is not 'under tension' but it adds mass.
    String mass is the important property, the way to thnk about it is this:
    More string mass requires more tension to be applied to the core wire to achieve the desired frequency.
    The 'tension of a string' is best thought of as 'the stretching force you need to apply to the mass of a string to achieve the desired frequency'.
    No, the D'Addario/scientific equations apply whether the string is vibrating or not.
    dkelley likes this.
  19. Doug4321


    May 29, 2017
    Yes. I found I like to go down a gauge, rounds to flats, to keep a similar preferred tension. 45-105 rounds, 40-100 flats. Very roughly!
  20. I ordered a set of LaBella Deep Talkin 760FL 43-60-82-104. The reviews around here say the tension is similar to a set of standard roundwounds and noticeably not as stiff as the 760FS 45-65-85-105. Currently have Fender 9050 on my p bass 45-60-80-100 so I will be able to compare them. LaBellas come Monday.
    michael_t likes this.

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