Understanding Bow Speeds
About understanding Bow Speeds
Archery manufacturers use the IBO (International Bowhunter’s Organization) speed rating when advertising the speed of their bows. The bow has to be set to the following specs and then shot through a chronograph.
- IBO Speed Rating = 70#s – 30 inch draw – 350 grain arrow
Most archers will never actually get this performance out of their bow, but it serves as a reference point that can be used to compare bows. This means an archer shooting a bow with an IBO rating of 330fps set at 60#s – 28 inch draw – 400gr arrow may get an actual speed of approximately 275fps.
Remember: This is initial velocity within a foot or two of the chronograph. Your arrow will lose additional speed and Kinetic Energy as it travels down range.
Kinetic Energy = arrow velocity squared X mass weight of the arrow
Items that affect arrow velocity (these are approximate):
- Poundage – 1# = 2.3-2.4 fps
- Draw Length – 1 inch = 10-12 fps
- Brace Height – 1 inch = 10-12 fps
- Arrow Weight – 3-5 grs = 1 fps
- Let-off percentage – varies on efficiency of the bow or draw stop location
- Brass nok – loss of 2-4 fps
- Peep sight – loss of 3-6 fps
- Silencers – loss of 2-6 fps
- String Loop – loss of 1-3 fps