How accurate are the speed cslculators?

[lovemylegacy]

I am using the speed calculators from various dources and Im having a hard time believing them. How accurate are they on calculating speed?

[ultrastealth]

Are you talking about chronographs?

[Saltyag15]

They will get you fairly close if your inputs are 100% correct. But then again, every bow company is different. A lot depends on how inflated their IBO ratings are.

[lovemylegacy]

Are you talking about chronographs?

No

[lovemylegacy]

They will get you fairly close if your inputs are 100% correct. But then again, every bow company is different. A lot depends on how inflated their IBO ratings are.

338IBO according to company specs, that puts my bow around 290fps….which I dont believe.

[BrianL]

Unless you are shooting 80#s and max bow draw length, and 400 gr arrow... Run it thru a chrono.

[BrianL]

That being said, I did run mine thru a chrono, and this calculator was within 2fps.

https://www.omnicalculator.com/physics/arrow-speed First one that came up on google.

[ultrastealth]

They test them with absolutely nothing on the string, and even then they add 2-5 fps

[lovemylegacy]

That being said, I did run mine thru a chrono, and this calculator was within 2fps.

https://www.omnicalculator.com/physics/arrow-speed First one that came up on google.

It said 289fps….

[lovemylegacy]

They test them with absolutely nothing on the string, and even then they add 2-5 fps

So you are saying the IBO is incorrect?

[lovemylegacy]

Can others weigh in on this please?

[100%TtId]

Just ran the numbers on my setup and the online calculator linked above was dead-on with what my chrono says.

[ctom87]

I was about 10 fps faster per that calc than what I shot thru a chrono. Disclaimer, I don't know how much additional weight I have on my bowstring. When I bumped it from 20 gr to 50, it was within 2-3 fps.

[muddyfuzzy]

Look all these speed calculators are completely accurate if they are set up correctly. The force of gravity as well as the arrow weight are constant. The devil is in the details in this case the variables entered into the program such as the IBO speed of the bow. The IBO parameters that are used have a tolerance so it can be spun however you like. I think the standard 30” draw length used in the calculation is like +\- 1/2”. I also believe the 70# draw weight requirement is +\- 1-2 pounds. So that means that the 350 IBO isn’t really a 350 fps bow if you run it to the high side of both variables. On the average a bow with an increase in draw length of 1/2” will net a speed increase of 2-5 fps depending on the rig. Now 1-2 pounds of draw weight over 70 is going to an additional 3-6 fps over the standard 350 grain arrow @ 70#s @ a measured 30” of draw length. And the weight on the string…….most don’t really know so they just guess.

Soooo, we take a factory inflated number and some bad weight in the string data and enter them into a program that gives a squat on how fast or slow your bow is, that output creates an expectation of performance. Now we take the same rig and shoot it through a reputable chronograph and now we have a negative delta in fps back the calculator used previously. Garbage in garbage out they say. None of its malicious, at least not on the consumer end. Want to know how fast the bow really is run it to the published nominal requirements and you’ll get good, reliable and most importantly repeatable data.


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[lovemylegacy]

Well, thats what I did. Used the manufacture numbers cor a Creed and an XS. Im pretty close on the added weight on string. It just seemed fast for a 60# draw weight. I was surprised. All the calcs were in 5 fps range.