I have had a 20" street uni for a while now and im still not really sure how much psi to put in my tire. i’ve been into drops and hopping a lot if that helps but i still like it to be sort of squishy so i can hop well.
Only you can tell. It depends on all sorts of variables such as your weight, your technique, and the “section” and quality of the tyre. By “section” I mean that you will need more pressure in a skinny tyre (e.g. 20 x 1.75") than in a fatter tyre (e.g. 20 x 2.5").
I have always relied on the finger and thumb pinch test for bike and unicycle tyres. Too hard to squeeze at all is good for road; be able to squeeze it a bit for general riding off road; and a bit softer for tougher riding.
If you’re going to be dropping, then tyre’s main job is to keep the rim off the ground, and it needs to be as soft as you can get away with without it being too soft. But still a huge percentage of the impact absorption should be accounted for by your technique.
i weigh about 75-80 pounds and my tire is i think 2.5. my tire is good by this i mean not really worn at all. do you think a 35-40 psi would be good?
it’s all about feel, I used to ride my tire at the minimum PSI (35 on the Maxxis Creepy Crawler) until I started hopping higher and going a little bigger. Now I ride at the maximum PSI for that tire.
Start high and try lower and lower your PSI until you start getting rim hits or the tire starts to feel unstable. Add a few PSI and you should be good.
All about feel… I’ve seen people ride 20 inch tires that are practically flat.