How to determine thrust to weight ratios of motors not listed. Probably the best way is to get a rocket simulator program and put your rocket data into the calculator. It will also give you more data about the complete flight. There are some great programs out there and some are free. One of the best is RockSim by Apogee Components
Thrust curves of model and high power rocket motors can be found at: http://www.thrustcurve.org/
There are several different methods you can use to determine maximum lift off weight for a motor.
The simplest (and oldest) is a method that divides the maximum thrust of the motor by 4.
Use the average thrust produced during the first part of the burn, while the rocket is still accelerating on the launch rod. Once you know this, the max lift-off weight is at least ten times less than the average initial thrust.
You can find a simple online calculator at:
REMINDER: Data presented here is a guideline only. Common sense, experience and a little effort on the part of the flyer is required. Use this guide at your own risk. There are several ways to determine the maximum thrust to weight ratio and many factors can impact that ratio, including the rocket design. Always follow your RSO’s decision.