How To Determine The Real Speed Of Your Bow

Every fall when new compound bows are released, it's easy to get caught up in the marketing hype. Every company is pushing their specifications and claims around why their newly released compound bow should be your choice. Most bow specifications are fairly straight forward and you get what is advertised. Speed ratings are not.

When it comes to speed specifications, what is advertised and what you get in a hunting scenario is drastically different! Here is how to calculate your hunting rigs speed without any special tools. 

IBO/ATA

To start we need to show the two industry standards for speed testing because these are the standards producing the speed numbers we are getting fed. There are two standardize procedures for testing arrow velocity from compound bows. 

IBO ( International Bowhunting Organziation) endorses the following:

Draw weight = Max of 80 lb  (+/- 2 lbs)

Arrow weight = 400 grains or 5 GPP of draw weight

Draw Length = N/A

It's easy to see with IBO standards there is no uniformity apples to apples comparisons. Any manufacturer can run IBO speed tests at 82 lbs with a 400 grain arrow at a 33" draw length while other manufacturers may run a different set of parameters. Do you see the problem? The issue here is that IF a bow manufacturer wanted to push the limits of procedure protocol, ultimately they can, all for the claim of being the fastest! This further creates a rat race within the bowhunting community and puts pressure on other manufacturers to do the same.

ATA ( Archery Trade Association) endorses the following:

Draw weight = 70 lb (+/- .2lbs)

Arrow weight = 5 GPP

Draw length = 30" (+/- 1/4")

With ATA guidelines the room for testing variance or manipulation drastically closes. This shows the ATA guidelines being much more transparent for apples to apples comparisons. No test can be validated outside of these exact parameters. 

Also, keep in mind, neither entity enforces their test procedures. The transparency and honesty of testing results lies within the hands of the bow manufacturers. This is another thing to keep in mind as you direct your hard earned dollars towards supporting companies. 

Variables That Impact Arrow Speed

Unfortunately in the bowhunting world, there are no absolutes only a matrix of variables. I specifically used the word matrix to show that each variable is intertwined with one another, an action and reaction, with any change of one thing creates the possibility of changing something else.  Changing your draw weight could have impact on your static spine selection, changing your broadhead could result in having the incorrect vane configuration or center of pressure, etc etc. This never ending matrix is why most accomplished bowhunters will tell you, tinkering is a key to finding success with your archery setup.

Draw Length

For every 1″ of change in draw length, you can expect a change around 10 FPS of arrow speed. IBO speed tests are conducted using 30″ draw length, however the average whitetail bowhunter has a draw length of around 28″. This is already a 20 FPS reduction compared to the IBO speed rating. While draw length has a big impact on arrow speeds, it's not something a bowhunter should tinker with too drastically. Outside of possibly picking up or losing a 1/4", your draw length is your draw length. Having a compound setup with a draw length too long or too short is only going to hurt your form and ability to consistently replicate your shot process. Accept those T-rex arms and dial in your draw length.

Draw Weight

For every 10 lbs change in draw weight, expect to see an associated change of 15-20 FPS. It's important to note that your draw weight will likely be different than the limb specifications. For example, a 70 lb bow, with it's limb bolts buried, will often draw a few pounds heavier. As strings and cables start to wear that same draw weight will likely decrease. In short, when you are attempting to figure you real hunting arrow speeds it's imperative you get an accurate draw weight reading via a scale if you're calculating from IBO/ATA speed numbers.

Accessories On The String

The more you add, the more speed you lose.  In the real world, adding accessories like a d-loop and peep sight to your string are basically requirements. The results of adding just those to items will result in a loss of 5 FPS.

Arrow Weight

The truth is arrows get complicated when you go beyond the surface level. Every little thing matters to some extent but for the sake of this article we're looking at arrow weight from the surface. A general rule of thumb around arrow weight implications on arrow speed is this: For every extra 5 grain of arrow weight, expect the speed of your bow to be reduced by around 1.5 FPS. IBO/ATA speed tests are conducted using 400 grain arrows or 5 GPP of draw weight, however most bowhunters will be hunting utilizing a heavier total arrow weight. For a simple example with all specifications the same, just changing to a 500 grain arrow during a typical IBO/ATA test would result in a 30 FPS loss in arrow speed. 

Release Type

This is often the biggest overlooked variable when considering the different impacts on arrow speeds. IBO/ATA tests are done with shooting machines, that result in a torque free perfect release every shot. 99% of bowhunters are not capable of this type of perfection. A clean release minimizes any arrow speed lose.

Real World Calculations

With the guidelines above, let's take a look at a few real life hunting arrow speeds vs IBO/ATA specifications. 

Impact On Your Arrow's Lethality Metrics

At the end of the day, your hunting arrows lethality is the most important key to the puzzle. Arrow speed greatly impacts the lethality metrics and the trajectory of your hunting arrow. 

When calculating the KE or P of your hunting arrow, the higher the arrow velocity the more lethal potential the arrow has. While KE certainly favors velocity and P favors mass, arrow velocity matters to both. In the same breath, an increase in arrow velocity also allows for a bigger margin of error when judging yardages on the fly. 

However, higher arrow velocities can also present some challenges. The faster your arrow is traveling the less room for error you have in your shot process, arrow build, and bow tuning. In short, speed will expose your flaws! When you get to a point where accuracy starts to suffer due to arrow speeds you need to make the decision to either fix the issue at hand or limit yourself to a slower arrow. 

Still, even computing these real life arrow speed numbers, this is at point blank range. Your hunting arrow's velocity downrange at distance will be lower, keep this in mind as you continue to research and understand lethality metrics when it matter mosts...THE MOMENT OF IMPACT ON YOUR TARGET.

Author: Chad Sylvester, Exodus Co-Founder/Owner