What influences your Arrow Speed
What influences your arrow speed? Well… just about everything!
The question, however, is by How Much?
Small gains may give you a great result, or eat away at your total arrow speed. That said, there are some things that are inevitable… you must have fletches on your arrow, for instance… but you can control size and helical, and ultimately drag.
Keep in mind, though… There exists a “no-man’s land” when you chase speed as a bowhunter. It’s a point where you already have an excess of Kinetic Energy (in other words, your arrow has the energy and ability to pass through the animal every time the conditions are good, and in your favour*), but you cannot speed it up enough to eliminate a string jump.
All you are doing is potentially creating a scenario where you will pass through the animal… but faster, and actually increasing the chances of causing damage to a second animal as the arrow can go in any direction as it exits the first one. Whether you really need more speed, only you will know. But take a minute to decide, how much is enough.
*Murphy's Law of Bowhunting states that the possibility of a complete passthru exponentially increases if another animal is directly behind the one you are aiming at. The odds increase by a Factor of 4 if the animal behind is of Trophy size...
IBO Rating (Manufacturers Claimed Speed)
The IBO Rating is supposed to be the actual, measurable speed of a 350gr arrow, measured at 1yd, shot from a bow without any extras, set to 70lbs Draw Weight and 30″ Draw Length. It is an indicator of how well the bow transfers stored energy from the strings and limbs into the arrow on release.
This should, in theory, give you an apples vs apples measure between bows… but unfortunately, those advertised and claimed speeds are rarely attainable. Various archery voices have suggested that a much more practical figure would be actual average hunting setups: 450gr arrow, @29″ and 65lbs.
Typically, a bow with an IBO rating of 330-335fps would then give you a “Real World” result of 278-280fps.
In other words:
Drop approx 50fps from the stated IBO rating to get a more realistic hunting setup figure. If that figure is enough for your needs, then this is the bow for you. If your bow performs above that figure, you are already winning!
Draw Weight
Draw weight is probably one of the main influences in arrow speed.
5lbs = 10-12fps
If you have a bow with a performance module, this can creep up a bit more, but 10fps is a good guestimate per 5lbs change,
Draw Length
Draw length is a definitely a factor, especially in adjustable bows, that influences arrow speed. That is why you will often find a Short or Long Draw + the Standard bow to maintain performance for shorter draw archers.
Typically, you can bargain on losing approx 8-12fps per inch.
The various brands get around this in different ways, for instance, Mathews has modules that can be switched out which would leave the bow closer to its peak performance state, but the module changes the Draw Length and or Draw Weight and or Let-off.
Arrow weight
The Arrow Weight is a double edged sword.
A light arrow gains a lot of speed, but loses it quicker over distance than a heavier arrow, While a heavier arrow starts out slow, but carries more momentum, and thus more penetrating efficiency.
50gr = 10-12fps
(Depending on your Draw Weight, Draw Length and Bow’s IBO Rating)
"Speed" Mods and Let-off
Holding more weight on the backwall is generally believed to give you a bit more speed, but most modern bows only have a few fps gain on a 75% let-off vs an 85% let-off… only about 2-3fps.
Many modern bows also has an option for a speed mod. A second module (like the Darton and Mathews) or a flipdisk (like the Bowtechs) that will give you a performance boost between 5-12fps (depending on the bow and the existing setup)
The benefit is the bit more performance from the bow, with a better transfer of energy to the arrow. This comes at the cost of a more agressive valley on the back wall (at Full Draw) and often more holding weight.
Drag (Points and Fletches)
Fletches is not something we frequently think about for arrow speed, but it hits you double… a bigger fletch than you need can steal a few fps in drag over distance, but also, the extra arrow weight will drop a few feet per second. So if you you add an extra 15gr in fletch weight (2-3fps) plus bigger fletches (3-4fps) you can drop your arrow speed by 6 or 7fps…
4 vanes, arrow wrap, nock collars, etc… all add a bit, and combined has a measurable effect. It doesn’t mean it is bad, the extra weight improves your momentum and penetration, but if you are not getting the speeds you expect, this could be why.
String Weights
Weight in the right place on your string (aka Speed Nocks) will give you an extra few feet per second (in the region of 4-6fps if placed correctly) but conversely, any extra weight or drag on your string will also slow it down. So you might find that a Peep sight will have an effect on your string speed, and influence your overall result. A heavier Peep Sight with extras (like clarifiers and verifiers) might slow down your arrow speed between 1-4fps.
