OT2 software has too high arrow speed?

[paulsnapp]

I recently purchased the software so I am new to it. I have input very carefully all parameters for my bow and setup. The program seems to give me much higher than real arrow speeds. The IBO speed of 340 used by the program is for a Reezen 6.5, 70 pound draw weight and 30 inch draw length. I did not change that. My bow is a Reezen 6.5, 60 pound draw weight, 29.5 inch draw length. My assumption is that you leave the default IBO speeds alone and the software will do its calculations and adjust for actual draw weight, draw length, etc. My chrony measures this setup as 272 speed but the program predicts 298. From the Mathews forum, all the feedback is that there is no way I can get a speed of 298 with a Reezen 6.5, 60 lb, 29.5 inch draw shooting a 422 grain arrow. Is there something wrong with the software I have done something wrong?

[PSI]

The most likely answer is that you need to calibrate the program to your setup. Either calibrate to Arrow Weight (VPG) or Draw Weight(VPP).

Since you have a digital DW scale and a chrono, this is relatively easy. In the User Guide, look in the Calibration section for Efficiency From Arrow Weight or Efficiency From Draw Weight.

An easy way to validate the program output for your setup is to set DW, DL and arrow weight to IBO specs. The calculated velocity should be very close to the stated IBO velocity. Don't forget to 0 out everything but nock point weight in the Weight On String frame. I also set the %letoff to 65, but that should only make a minimal difference

I'll look into the code to verify that there isn't a problem.

It's possible I need to update the program "default" efficiency values. If people want to send data on their setups, just use the support link in OT2 or the contact e-mails on the webpage.

[gjarcher]

I believe that 272 fps was too low for a 60/29.5 Reezen 6.5 shooting a 422 grain arrow, and 298 was slightly optimistic.

IBO 340 fps at 70/30, 350 grain arrow
Subtract 20 fps for -10lb DW = 320 fps
Subtract 5 fps for DL -5" = 315 fps
Subtract 24 fps for Arrow wt > 350 = 291 fps
Subtract 4 fps for string weight = 287 fps

There may be some additional subtractions for weight on string, and as Larry said, the program is more accurate once it is calibrated to your setup.

If all you get out of 60/29.5 Reezen 6.5 w/ 422 gr arrow is 272 fps, there is either a lot of unaccounted for weight on the string (peep tubing, brass nocks, etc.), or the bow is out of spec, or there are other issues, such as bow scale way off, arrow grain scale way off, or a problem with the bow that deserves dealer inspection/warranty work.

Just my :2cents.