The IBO Speed Calculator provides a method to estimate the speed of an arrow launched from a bow, considering several variables that affect its flight. This includes the bow’s IBO speed rating, the weight of the arrow, and the draw length of the bow. Understanding these variables and their impact on arrow speed can significantly enhance an archer’s ability to select the right equipment and make adjustments for optimal performance.
Formula of IBO Speed Calculator
To estimate the speed of your arrow, the IBO Speed Calculator uses a straightforward formula:
Speed = IBO Speed - (5 grains difference in arrow weight / 3) - ((30 inches - actual draw length) * 10)
Where:
- Speed is the estimated speed of your arrow in feet per second (fps).
- IBO Speed is the manufacturer’s rated speed of the bow under International Bowhunting Organization conditions, usually measured in fps.
- 5 grains difference in arrow weight is the deviation in the arrow’s weight from the 350-grain standard set by the IBO, divided by 3 to account for the speed loss per 5 grains.
- 30 inches – actual draw length calculates the change in speed based on how the draw length differs from the IBO standard of 30 inches.
This formula encapsulates the critical factors influencing arrow speed, offering a simplified yet accurate way to predict changes based on modifications to arrow weight and draw length.
General Terms and Calculator
To aid in the practical application of this formula, here’s a table that provides quick references for common scenarios:
| Arrow Weight Difference (grains) | Draw Length Change (inches) | Speed Loss/Gain (fps) |
|---|---|---|
| +5 | 0 | -1 to -2 |
| -5 | 0 | +1 to +2 |
| 0 | +1 | +10 |
| 0 | -1 | -10 |
This table helps archers quickly estimate how changes in arrow weight and draw length can affect the speed of their arrows, without the need for detailed calculations every time.
Example of IBO Speed Calculator
For an illustrative example, consider a bow with an IBO Speed of 320 fps. Using an arrow that is 360 grains (10 grains heavier than the standard), and a draw length of 28 inches. Using the formula:
Speed = 320 - (10 / 3) - ((30 - 28) * 10) = 320 - 3.33 - 20 = 296.67 fps
This example demonstrates how to apply the formula to predict the arrow speed based on specific adjustments.
Most Common FAQs
A1: Increasing the weight of the arrow decreases its speed because the bow has to impart more energy to a heavier object. Conversely, a lighter arrow will travel faster, given the same amount of energy.
A2: While a longer draw length can increase speed due to the greater energy transfer. It’s essential to use a draw length that matches your physical capabilities for safety and accuracy.
A3: The IBO Speed Calculator provides a good estimation of arrow speed based on the given variables. However, real-world factors like air resistance and bow efficiency can lead to slight variations.