Section 2 The Basics of the Compound Bow
The Basics of the Compound Bow
The compound bow is not entirely mechanical witchcraft! They are actually easier to understand than you think. The compound bow is simply an energy storing device. This is why the advent of the cam and wheel systems make such a huge shift in archery today.
This guide will breakdown everything you need to know in an easy to understand way!
Table of Contents
1. The Basic Parts of the Compound Bow
2. What Bow Specifications Mean & How They Relate To You
3. Bow Components and Accessories
1. The Basic Parts of the Compound Bow
Before we dive into the numbers and how they relate to your needs in a bow package, let's start with the basic parts of the compound bow.
Grip - Where you place your bow hand on the bow to hold it to draw.
Riser - The "chassis" of the bow where all accessories attach and all limbs and cams attach.
Limbs - Where the bow stores the energy to transfer into the arrow.
Cams - The engine of the bow, where the draw cycle, speed and letoff comes from.
2. The Numbers and How They Relate to You
Before we can get into the more technical aspects of the compound bow, we have to start at the numbers associated in the Specification chart and what they mean. Typically most all bow manufacturers will list the Axle to Axle Length, Brace Height, IBO Speed, Letoff, Draw Length Range and Draw Weight Range in their specification charts.
Axle to Axle Length or ATA:
This is the length from the center of the axle on the top to the center of the axle on the bottom. This measurement dictates how long a bow will be but not it's overall length. Typically, the longer the ATA, the more "forgiving" and easier to shoot a bow will be. Likewise, a shorter ATA bow will be less "forgiving" and a bit tougher to shoot very well. This is why you see most target archers with very long, almost cumbersome looking bows. Most novices as well as hunters start out with a shorter length bow.
How ATA Relates To You:
For every archer, their draw length will dictate the axle to axle that will be the easiest to shoot though there are certainly exceptions to this! In general, a shorter draw person will shoot a shorter ATA length bow whereas a longer draw length person will shoot a longer ATA length bow.
Many novice bows on the market will be in the 30-33" ATA range. This is typically due to cost saving measures as a longer bow is more expensive to produce as well as market trends that typically favor a shorter bow. Bowhunters also are in the market for a shorter ATA length bow. You will usually see a strict bowhunter shooting in that same length range as well. On the other side of the coin, for most hobby archers and target archers, they will favor the 36" to 40" ATA bows. There is a grey area in the 33" to 35" length category. This is where the two worlds meet for many archers. These bows are just short enough to be easy to hunt with but just long enough to be comfortable to shoot as well as consistent to shoot. These bows are a great blend if you wish to hunt, shoot competitively or simply want a faster bow to shoot that isn't too long ATA for your draw length.
There are a few things at work in regards to ATA length. The more obtuse the angle the string is when fully drawn, the easier the bow will be to anchor your face to the string, the closer the peep will be to your eye and the easier the arrow will leave the string without excess pressure on the nock of the arrow. Typically this is referred to as String Angle.
Brace Height is the distance from the deepest point of the grip to the center of the string. This measurement is as old as time itself with long bows of old having a short brace height where a recurve style bow has a longer brace height.
Now how this relates to modern bows has not changed much since the dawn of the bow. Typically a shorter brace height is found on faster bows or more hunting focused bows. Longer brace heights are typically found on novice level bows and target bows. The idea behind the brace height measurement is that a longer brace height is more "forgiving" to your mistakes in form as well as increasing the distance from your forearm to the bow string resulting in less string slap if you have incorrect form or grip.
How Brace Height Relates to You:
For the novice archer, the longer the brace height the better. For the bowhunter, a shorter brace height helps as you generate more speed. For the target shooter, they too are better suited with a longer brace height bow. A long draw archer (Over 30" of draw length) will want to look at bows in the 7" brace height or longer range.
How Brace Height Effects Speed:
Brace height also has an effect on speed as a faster IBO rated bow will have between a 5.5" to 6.25" brace height due to increasing the power stroke by an added inch. This typically adds 10-12fps going from a 7" brace height bow to a 6" brace height bow if all things are equal. You will find however many bows on the market are between a 6.5" and 7.5" brace height. These bows are typically the novice and target bows on the market which are slower IBO rated but easier to draw, easier to be accurate with and "forgiving".
For slow motion video to better understand what brace height does, we recommend watching this video by PSE Archery. (Hotlink)
IBO Speed is a manufacturer agreed way to test the speed on each bow. It is measured at a 30in draw length, 70lb draw weight with a 5 grain per pound of draw weight arrow which is 350 grains at 70lbs of draw weight. It is measured in Feet Per Second (FPS).
Just like the muscle car era, the bow industry are always pushing each other to create a faster bow than the competition. This is great for the consumer as you can shoot less draw weight than ever before and still be faster than bows have ever been in the past without having to sacrifice comfort or overall shootability which all effects accuracy and consistency.
Most novice bows will be in the 300 to 315 IBOfps range, most mainstream hunting bows will be in the 320-340fps IBO range where the more extreme hunting bows and all out speed bows will be from 350fps up to an unreal 370fps! (PSE holds the record for the fastest production bow with the Full Throttle) Many target oriented models will fall in the 315-330fps range.
So My New Bow Will Shoot 340fps!? Wow!
Technically yes, but in reality more than likely not. If you remember the draw length we measured as well as draw weight we determined in the last section of the guide, you more than likely are under a 30" draw length and under 70lbs of draw weight and that is okay! The real test is to take a bow that is 340fps, adjust it down to your specs and it still be fast. This is a measure on how efficient the system is.
How IBO Speed Relates to You
As you can see, if you are shooting a 28in draw at 60lbs from a 340fps IBO bow, you automatically take 40fps off of the 340fps rating. This is before we get into the arrow weight aspect. Typically, a complete arrow will weight between 350-375grs for standard arrows however that is dictated by a few things we will address in our Arrow Information Guide.
Letoff on the compound bow is measured by a percentage of the total draw weight of the bow. Thus the amount the bow "lets off" at full draw. This percentage comes out to your holding weight of the string at full draw.
A Quick History Lesson
In the beginning, the traditional bows of history were 0% letoff, you held the full 60,70,80lbs from start to finish of the shot. When the compound bow came onto the scene in the late 1960s, the term letoff was coined. The original compound bows were 20-30% which was a huge improvement. As time went on, they went to 50% then 65% to the modern age where most are 75% to 80% with some models reaching 90%!
How Letoff Relates to You:
For all novice archers as well as bowhunters, we recommend 80% letoff. This will allow you to be comfortable at full draw without having the bow trying to let itself down from full draw if you get weak holding it drawn. For those with shoulder injury, we recommend the 85% and 90% letoff options. For more target oriented use, 65% to 75% is where these bows typically stay.
Draw Length Range
The Draw Length Range is the amount of draw length the bow can be adjusted. Most all models from PSE Archery and Bear Archery can be adjusted in the cam. We will cover how to adjust this in our After The Sale guide.
How Draw Length Range Relates to You:
When looking the many models on the market, be sure to narrow your search down first by the bows within your draw length range. If you are a 31 in draw or a 26 in draw, you will want to look at models that can extend or shorten to these draw lengths.
Draw Weight Range
The Draw Weight Range is the amount that a bow will adjust for draw weight
How Draw Weight Range Relates to You:
After you determine a draw length range, be sure to narrow your search down to bows that fit your draw weight range. Typically if you want to shoot 60lbs max, order a 60lb bow as it will perform better in speed, draw cycle and sound level. In the past, many archers would buy a 70lb max weight bow and only shoot it on 60lbs. This was only holding them back from experiencing the full potential of their new bow! The closer you can get your draw weight to the max weight of that bow, the better it will shoot.
With an understanding of the basic components are and where they are located, we now can move onto something more exciting, the Accessories.
It can get a bit confusing when you look at various "packages" trying to understand what each part is and does. Thankfully, as always, we are here to help!
Arrow Rest - This is where the arrow rides when you draw back and when you fire the bow. To learn more about the components of arrow rests and types, visit our arrow rest guide here (hotlink)
Sight - Your sight contains the pin which is your aiming reference. There are two main types of sights. Fixed pin and single pin moveable. To learn more about the components of the sights and types of sights, visit out sight guide here (hotlink)
Stabilizer - The stabilizer assists you in steadying the sight picture. Some package bows include a basic one that helps vibration where others have an advanced one that will aid in significantly in holding the bow steady at full draw. To learn more about the components and types of stabilizers, visit our stabilizer guide here (hotlink)
Wrist Sling - You put your hand through these which allows you to hold the bow loosely with no fear of it coming out of your hand and hitting the ground. Highly recommend to use a wrist sling on any bow.
Peep Sight - This is the rear aiming point. You will line the peep up with the ring of the front sight. To learn more about peep sights and peep sizes, visit our peep guide here (hotlink)
D Loop - This is the loop in which you attach your release rather than drawing with the release on the string directly. This allows the bow to be drawn from the very center of the string which aids in accuracy.
Quiver - The quiver holds your arrows while you are shooting or hunting. It is convenient as the arrows are carried on the bow. Some opt to take these off and shoot without them on. Typically found on hunting bows.