Piper don't do it by airspeed.
Fill you aircraft up to the MLW.
Put a bit of string on the airframe/window.
Then go up to 1000 feet and desend in landing config at the POH speed.
Take note of angle of said bit of string.
This is then you angle of approach. Then go to your min weight you can manage again at the same alt. Then configure and pitch to the same angle. See what the speed is. The POH is the max speed and the last one is the min speed. Then make up a table for the weights between the two.
The stall is the critical angle of attack. The approach is something which is an angle of attack less than this by a safe margin. The speed is just the thing we can see in the cockpit all you are doing by changing the speed with weight is getting the angle off attack correct