Guest TerryH Posted February 27, 2006 Report Share Posted February 27, 2006 Is there a formula for figuring rough arrow speed without shooting through a chronograph. Also, when people talk about your arrow needing to weigh at least 5 grains per inch, is that including point. Or, is it just the arrow? Quote Link to comment Share on other sites More sharing options...
VtBowhunter Posted February 27, 2006 Report Share Posted February 27, 2006 Re: Formula for arrow speed. Weight includes tip. Quote Link to comment Share on other sites More sharing options...
Gator Posted February 27, 2006 Report Share Posted February 27, 2006 Re: Formula for arrow speed. The 5 grains per inch is for TOTAL arrow weight, from point to nock. As far as the formula, if you go to Mathews's web site, and to their forums, then into the Archery Tech forum, there is a calculator theer. I would post a link, but my dial-up and Mathews web site mix like oil and water. Quote Link to comment Share on other sites More sharing options...
tedicast Posted February 27, 2006 Report Share Posted February 27, 2006 Re: Formula for arrow speed. Here is a formula that works pretty close on Mathews bows. not 100% sure if it is the same for all brands. You need to find the IBO rated speed of your bow first. You can use the following to work backwards off listed IBO specs, this will put you pretty darn close to chrono: IBO Specs - 30" draw/70lb draw weight and a 350gr arrow. For every inch of draw length you go down you will lose 10 FPS For every 5# draw weight you go down you will lose 10 FPS For every 3 grains of weight your arrow is over IBO ( 5 grains per pound) you will lose 1 FPS For every 3 grains of weight you add to your string you will lose 1 FPS The 5 grains per inch is for a complete arrow. Quote Link to comment Share on other sites More sharing options...
tedicast Posted February 28, 2006 Report Share Posted February 28, 2006 Re: Formula for arrow speed. [ QUOTE ] keep in mind when they test for the IBO speed there is absolutely nothing on the string not even serving [/ QUOTE ] In the formula, there is a 1 fps deduction for ever 3 grains of weight on the string, to make up for this. Quote Link to comment Share on other sites More sharing options...
Leo Posted February 28, 2006 Report Share Posted February 28, 2006 Re: Formula for arrow speed. [ QUOTE ] Here is a formula that works pretty close on Mathews bows. not 100% sure if it is the same for all brands. You need to find the IBO rated speed of your bow first. You can use the following to work backwards off listed IBO specs, this will put you pretty darn close to chrono: IBO Specs - 30" draw/70lb draw weight and a 350gr arrow. For every inch of draw length you go down you will lose 10 FPS For every 5# draw weight you go down you will lose 10 FPS For every 3 grains of weight your arrow is over IBO ( 5 grains per pound) you will lose 1 FPS For every 3 grains of weight you add to your string you will lose 1 FPS The 5 grains per inch is for a complete arrow. [/ QUOTE ] These are just rules of thumb. Good for a rough guess only even if you know all the weights accurately. The further your setup is from IBO the more approximate the values will be and larger the error from actual. To get a more accurate projected speed you really need two known speeds for two different known weight arrows. From that you can calculate the bows virtual mass. You also need the SE/PDF ratio. You might find it published for your bow. With that info you can predict a certain arrows speed pretty accurately as long as the arrow weight is accurate. You still won't get an absolutely perfect result because different spine arrows absorb potential energy from the bowstring differently. (IE. a real flexible arrow might be slower than predicted because it absorbs more forward momentum by flexing) try this site Bow Jackson Ballistic Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.