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I was asked today why people choose different thicknesses of Thera-band and how to adjust band dimensions.

Why?

Thinner bands shoot slightly faster, especially when they shoot light projectiles, but they don't last as long as thicker bands. I generally don't like anything thinner than Silver and only sometimes Black, but the speed freaks among us like thinner bands, even if their bands only last a few shots.

Adjusting Dimensions

Theoretically, all you do is scale width of the band proportionally as the thickness decreases.

  • Gold; .025" thickness
  • Silver; .022" thickness
  • Black; .015" thickness
  • Blue; .012" thickness
  • Green; .010" thickness
  • Red; .008" thickness
  • Yellow; .006" thickness
  • Tan; .004" thickness
Gold 21.5cm x 3 x 2 is roughly equivalent to:

Green 21.5cm x (3 x .025/.010) x (2 x .025/.010) ...

i.e. Green 21.5cm x 7.5 x 5

However, note that draw weight is not quite directly proportional to thickness; you also can use that as a guideline if the data exists.

  • Gold; .025" thickness; 11.8 lbs at 100% elongation
  • Silver; .022" thickness; 8.6 lbs at 100% elongation
  • Black; .015" thickness; 4.9 lbs at 100% elongation
  • Blue; .012" thickness; 4.5 lbs at 100% elongation
  • Green; .010" thickness; 3.1 lbs at 100% elongation
  • Red; .008" thickness; 2.7 lbs at 100% elongation
  • Yellow; .006" thickness; 1.8 lbs at 100% elongation
  • Tan; .004" thickness; 1.1 lbs at 100% elongation
If you are normalising for speed (until I get the testing done) you may need to chrony.



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lucifer93
Jan 04 2011 10:38 AM

This was really handy ZDP-189
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GreyOwl
Jan 04 2011 11:19 AM

Thanks so much Dan.These data and formula will help me.GreyOwl


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Northerner
Jan 04 2011 07:49 PM

I've got some black, silver and gold. My black is .015", silver .022" and gold is .030". The previous batch of gold that I had was .029". I guess it has a wide variation.Cheers,Northerner


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Itamar J
Jan 04 2011 09:00 PM

does this mean that your green cut will deliver the same power as the gold but at a lower draw weight?


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ZDP-189
Jan 05 2011 12:25 AM

I need to do some detailed testing to answer this. For example, (1) Chrony several bands with the same dimensions and (2) Chrony several bands with width dimension proportionally adjusted for thickness. I am waiting for a member to whom I sent several band samples for scientific testing to come back with his results before I do my testing.


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ZDP-189
Nov 16 2011 12:24 AM

If you fancy slightly more detailed look at this, see this other blog entry:

http://slingshotforu...ds-be-too-thin/
 
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