ORIGINAL: davepjr71
ORIGINAL: gzg38b
When I used On Target, I found that my "predicted speed" versus my chrono'd speed was identical with my 365 grain "speed" arrows, and I didn't need to change the performance meter at all to get these results.
However, with my 515 grain hunting arrows, On Target predicted a speed that was 18 fps faster than the actual chrono. This was from the same bow, same setup, same tune, same wt on the string, same day, same chrono. Granted the KE was higher, but that's just due to the weight of the arrow. The gap between predicted speed and actual speed was huge with the heavy arrows and non-existent with the light arrows. This is where the performance slider comes into play, I believe.
With the heavy arrows, I had to slide the performance meter way down the scale just to get the predicted speed down to match the chrono. When I did that, those heavy hunting arrows went from being perfectly spined to overspined (according to OnTarget). I believe the results. It makes perfectly good sense that a launch speed of 18 fps slower would change the spine requirement of my arrows.
I think I would have got the same results with On Target if I'd just changed the IBO speed to get the predicted speed to match my chrono'd speed. Instead of using my bows advertised IBO of 316, I would have put in 298 for the IBO speed. The arrows that spined perfectly at a 316 IBO would have been overspined if I changed the IBO to 298, correct?
My trial version has expired, or else I'd try it to verify.
You are correct in what you have said and asked about in regards to adjusting the IBO in your last paragraph. However, it suprises me that the program was that far off. After I set up the program with known info and adjusted the IBO for that one setup I've been able to adjust my DW and use arrows from 370 gr to 460 gr and get accurate results from OT2. I believe the program takes into account the efficiency changes that happen with heavier arrows and DW adjustments. You are telling the program that your bow only shoots a certain speed with a certain arrow.
If you'd like I can run your setup with my OT2 to verify what you think? Just supply me with all the info and I'll run and post.
I just ran it a coupld days ago. Here's my info:
06 Pearson Stealth 316 IBO
70 lbs verified with scale ; 75% letoff
29.5" draw (AMO measured)
33.75" ATA (measured)
7.5" BH (measured)
Overdraw: 0
2 Cam Hard (not sure about what to call my hybrid cams)
CX Terminator Hunter 6075 cut at 28.5"
125 grain point
11 grain insert
FOB 24grains (be sure to type "1" for number of vanes)
5 grain wrap
Carbon Express TCX nock 8.7 grains
No bushing/pin (0 grains)
Total Arrow weight: 515.7
Peep 10 grains
D Loop 8 grains
Nock Point 2 grains
Silencers 20
Silencer DFC 0.0000
Release Box Checked
My actual chrono speed with this setup was 257 fps.
Actual Arrow weight (measured) was 515 grains.
The software predicted271.5 fps,much faster than 257 fps actually chrono'd.In order for me to "calibrate" to 257 fps, I had to slide the performance meter almost all the way to the left. After doing this, my arrows were showing overspined.
Are you able to duplicate my results?
The strange thing is that for a lighter arrow (just over 350 grains), my predicted matched my actual. Figure that one out LOL.