Understanding Ibo Speed: The Compound Bow's Secret Power

If you're new to archery, you've likely come across the term IBO speed when looking at compound bows. IBO stands for the International Bowhunters Organization, which has created a standard for measuring bow speed. The IBO speed test involves shooting a bow with a maximum pull weight of 80 pounds (give or take 2 pounds) and an arrow weighing 400 grains or 5 grains per pound of draw weight. The draw length is typically around 30 inches, but can vary. The higher the IBO number, the more powerful the bow. However, it's important to note that IBO tests can be lenient, with manufacturers using different weights and draw lengths, so comparing IBO numbers between bows may not always be accurate. Other standards, such as the Archery Trade Association (ATA) speed, are also used and offer more precise comparisons. When choosing a bow, it's important to consider not just the speed but also factors like quietness, pull, construction, and draw smoothness.

IBO vs. ATA standards

IBO and ATA are two different standards used to measure the speed of a compound bow. IBO stands for the International Bowhunters Organization, and their standard is obtained by shooting a bow with a maximum pull weight of 80 pounds, with a 30-inch draw length and an arrow weighing 400 grains or 5 grains per pound of draw weight. The IBO standard is considered more lenient, as manufacturers can use bow weights of up to 82 pounds and draw lengths of almost 33 inches.

On the other hand, the ATA standard, set by the Archery Trade Association, is considered stricter and more precise. The maximum pull weight for ATA is 70 pounds, with a draw length of 30 inches and an arrow weight of 350 grains or 5 grains per pound.

The main differences between the two standards lie in the draw weight and arrow weight requirements. IBO allows for a higher draw weight and does not specify a maximum draw length, whereas ATA has a lower draw weight requirement and a more precise draw length requirement.

Some bow manufacturers list both IBO and ATA standards, while others may not list any standards at all. It is important to note that these standards are not federally regulated, and companies can choose to declare whatever they want. Therefore, it is essential to consider other factors when purchasing a bow, such as quietness, pull, construction, quality, and draw smoothness, in addition to testing out the bow by shooting it.

Draw weight

The draw weight of a compound bow is the amount of force required to pull the bowstring back to its maximum draw length. It is measured in pounds and is one of the most important factors that determine the power and speed of an arrow when released from the bow. The higher the draw weight, the more energy is stored in the bow, and the faster the arrow will travel. Draw weights of adult compound bows typically range from 40 to 80 pounds, which can create arrow speeds of 250 to 370 feet per second.

The draw weight is determined by the combination of the bow's limbs and the bowstring. As the bowstring is drawn back, it stores energy in the bow's limbs, which is then transferred to the arrow when it is released. The right draw weight for an individual will depend on their personal strength and experience level. For example, a draw weight of 40-50 pounds is a good starting point for experienced archers, while a lower draw weight of 20-30 pounds is more suitable for beginners.

It is important to choose a draw weight that is comfortable and suitable for your needs. A good rule of thumb is to select a draw weight that requires about 75% of your maximum strength. If the bow is too heavy to draw back, you will quickly become fatigued, making it difficult to practice and improve your accuracy. On the other hand, a bow with too low of a draw weight may not provide enough power to the arrow, leading to reduced accuracy and decreased distance.

The draw weight of a compound bow is not static or linear. It is controlled by the geometry of the cam system, so the required effort rises and falls during the draw cycle. The draw cycle of a compound bow is mechanically manipulated to maximize energy storage and provide ergonomic advantages over traditional bows. This is why compound bows store more energy and shoot faster than an equivalent peak weight recurve bow or longbow.

Arrow weight

When choosing arrow weight, it's important to consider your objectives. For target practice, an arrow should weigh around 5 to 6 grains per pound of draw weight. For hunting, you'll need an arrow with a total weight of between 6 and 8 grains per pound of draw weight.

It's worth noting that using an arrow that weighs less than 5 grains per pound of draw weight can severely damage your bow and void its warranty. Therefore, it's crucial to select the appropriate arrow weight for your compound bow.

The International Bowhunters Organization (IBO) and Archery Trade Association (ATA) standards provide guidelines for arrow weight in relation to bow speed testing. According to IBO standards, the arrow weight should be 400 grains or 5 grains per pound of draw weight, with a maximum draw weight of 80 pounds (+/- 2 pounds). On the other hand, ATA standards specify a draw weight of 70 pounds (+/- 0.2 pounds) and an arrow weight of 350 grains or 5 grains per pound.

When selecting arrows, it's recommended to consult with professionals at an archery pro shop. They can guide you in choosing arrows that are suitable for your compound bow's draw weight and length, ensuring a safe and enjoyable archery experience.

Draw length

The draw length of a bow is the distance, in inches, that a bow is drawn. On a compound bow, each bow is set at a particular length and should always be fired from that set length. The correct draw length is important for maximising accuracy.

There are several methods for determining the correct draw length. One involves measuring the wingspan of the shooter, dividing that number by 2.5, and using the resulting number as the draw length. Another method involves measuring the distance from the nock point to the throat of the grip, adding 1 3/4", and using that as the draw length.

The IBO speed advertised for bows is measured at a 30" draw length. If the draw length is shortened, the bow will lose speed. Therefore, it is important for shooters to use the correct draw length for their bow and not try to shoot a longer draw length to gain more speed.

The IBO standard for bow speed is obtained by shooting a bow with a maximum pull weight of 80 pounds, with an arrow weighing 400 grains or 5 grains per pound of draw weight. However, manufacturers sometimes use bow weights of up to 82 pounds and draw lengths of almost 33 inches to maximise the rating. This makes it difficult to compare bows based solely on their IBO speed.

Bow speed calculation

The speed of a compound bow is a key metric for bowhunters. The speed of an arrow is determined by a range of factors, including the bow's draw weight, the draw length, and the arrow weight.

IBO and ATA Standards

The International Bowhunters Organization (IBO) has created a standard for measuring bow speed. The IBO speed is obtained by shooting a bow with a maximum pull weight of 80 pounds, +/- 2 pounds, and an arrow weight of 400 grains or 5 grains per pound of draw weight. The IBO test is conducted at a draw length of 30 inches, though manufacturers may use a longer draw length of up to 33 inches.

The Archery Trade Association (ATA) also has a standard for measuring bow speed. The ATA speed is obtained using a maximum pull weight of 70 pounds +/- 0.2 lbs, an arrow weight of 350 grains, and a draw length of 30 inches +/- 1/4 inch.

Variables Impacting Arrow Speed

When it comes to arrow speed, there are several variables that can impact its velocity. For every 1" change in draw length, there is an approximate change of 10 ft/s in arrow speed. The average whitetail bowhunter has a draw length of 28", which is 2" shorter than the standard IBO and ATA tests, resulting in a significant reduction in arrow speed.

Draw weight also has a notable impact on arrow speed. For every 10 lbs change in draw weight, there is an associated change of 15-20 ft/s in arrow speed. It's important to note that the actual draw weight may differ from the limb specifications, and string wear can also affect draw weight over time.

Adding accessories to the bowstring, such as a D-loop and peep sight, can further reduce arrow speed by approximately 5 ft/s.

Arrow weight also plays a crucial role in arrow speed. For every extra 5 grains of arrow weight, the speed of the bow is reduced by around 1.5 ft/s. IBO and ATA speed tests typically use arrows weighing 400-500 grains, while most bowhunters use heavier arrows.

Real-World Calculations

When calculating real-world hunting arrow speeds, it's important to consider the specific setup of the bow and the arrow weight being used. Here's an example calculation:

Let's say you have a bow with a draw length of 32", a draw weight of 70 lbs, and you're using arrows weighing 400 grains with 5 extra grains of weight on the bowstring.

Using the IBO specification formula:

> v = IBO + (L - 30) x 10 - W/3 + min(0, -(A - 5D)/3)

Where:

• V = actual arrow speed in ft/s
• IBO = arrow speed according to the IBO specification in ft/s
• L = draw length in inches
• W = additional weight on the bowstring in grains
• A = arrow weight in grains
• D = draw weight in pounds

Plugging in the values:

> v = 300 + (32 - 30) x 10 - 5/3 + min(0, -(400 - 5 x 70)/3)

> v = 300 + 2 x 10 - 1.67 + min(0, -(400 - 350)/3)

> v = 300 + 20 - 1.67 + min(0, -50/3)

> v = 318.33 - 16.67

> v = 301.67 ft/s

So, with these parameters, the expected arrow speed would be approximately 301.67 ft/s.

Measuring Arrow Speed

To measure arrow speed, you can use optical chronographs, Doppler chronographs, or laptop-based audio applications. These tools can help you understand the actual performance of your bow and arrows, which may differ from the IBO or ATA specifications due to variations in setup and individual technique.

While bow speed is an important consideration for bowhunters, it's just one factor in the overall performance of your equipment. Other factors, such as accuracy, arrow lethality, and trajectory, also come into play. Understanding how different variables impact arrow speed can help you make informed decisions about your equipment setup and technique to optimize your hunting experience.

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