Seat Post Length

My son is wanting to use the same seat post for trials (on the lower end) and muni/regular riding around town (higher end). Would like to know the minimum length of post he needs in the frame when the seat is raised as there are no indicators. It seems 2-3" would be sufficient…

Also, it is a double-bolt seat clamp.

Use 4 seat post diameters as the minimum insertion length. That’s the height at which he should do his street riding. He’ll set the seat lower for more abusive riding so it will be a stronger joint then anyway.