Hey Rick. It’s not foot-pounds. It’s just plain pounds, which is short hand for pounds-force. Standard conversion between newtons to pounds force. You can find on line.
https://www.unitconverters.net/force/newtons-to-lbs.htm
In this case, 1050 newtons is 236 pounds-force. But remember, the BRP spec is based on lifting up the Spyder by the frame, and allowing the swing arm to drop until it stops and the rear wheel is off the floor. That relaxes the tension on the belt compared to when the Spyder is on the floor. Don’t ask me what the change in the two values is. I haven’t done that “on the floor” - “off the floor” comparison. Because I don’t care about it.
Most folks check their belt tension with a Cricket, with the wheel on the the floor. 160 - 180 pounds with the Cricket, with the wheel on the floor provides plenty of tension, is way below the maximum allowable tension, and helps minimize vibration. Mike has been running around at 160 for years. No issues. I had to adjust my alignment and ended up at 180. Runs great….and no whining.