I have about an average of 25 ft/sec loss with my bows actual chrono speed and its calculated speed. IBO 332 Draw length 29 Draw weight 65# Arrow 451 grains String weight 20 grains (peed and dloop) So by info I have found, I subtract 10 for my draw length(10 ft/sec for every inch), 10 for my draw weight(2 ft/sec for every pound), 16 for my arrow (1 ft/sec for every 6 grains over 325 grains (65#dw = 325 grain arrow)), and 7 for my string weight (1ft/sec for every 3 grains). That gives me a total deduct of 48 ft/sec so 284 ft/sec. My actual chrono is 262 ft/sec average. I have shot a 512 grain arrow at both 65# and 71#. Those calculate 274 and 291. There actuals are 246 and 255. I have new cables and string and the bow is tuned. What am I missing? If any one else has actuals for their set up, I'd like to compare them as well. I want to either modify my calculator to be more representative or see if my bow is just under performing. Thanks.
I have done the calculations on my Monster and my son's Vector Turbo and both come out to about 1fps per 2.5-3 grains of arrow weight above the 350IBO standard. I recalculated your setup and came out with a loss of 1fps per just over 2 grains. my Monster rated 354fps -20 (28" draw) -14 (63#) -9 (peep/loop/kisser) -265 (actual arrow speed) =46fps (due to 132 grains above IBO arrow weight) then calculated my 482 grain arrow minus the 350 grain IBO standard= 132 grain additional weight divided by the 46 fps difference in actual and rated comes to 2.87 grains per 1fps of arrow speed. The Hoyt comes out almost identical. At least that makes sense to me.
I ran your specs through my calculator and some online ones. It does appear that 6 grain is 1ft/sec loss is a little generous. I'm coming out around 3.75. Then when I run mine specs through, I have to adjust it to 3 grains = 1 ft/sec loss. I would think that the effect of the arrow weight would be a constant.
I just ran your numbers on this site http://www.stickemarchery.com/stickemcart/archery-calculators.aspx and came up with 271.67 fps.
I'm an idiot. I just thought of my variable. The arrow rest and the resistance it places on the arrow. Duh! I shoot a Whisker Biscuit which will add drag. Where as a drop away would be far less drag. So it looks like a range of 3-4 grains is probably correct. 6 grains would probably be a combination of drop away rest and no vanes.
Thanks, I had used that website as well as backcountrycalculator and was getting around 9-15 ft/sec more.
What type of vanes are you shooting? That can make a difference also. This is a good article that illustrates the difference in speed that your fletching choice can make. http://archeryreport.com/2009/10/fletching-review-speed-drop/
just had my invasion cpx chronographed the other day, at 70# and 29" draw shooting a 425 grain arrow it shot 287 fps and the guy calculated it at 77 lbs of kinetic energy, bowtech advertises that bow at 30" draw at 70# with a 350 grain arrow at 343 fps and 91 lbs of kinetic energy
