Losing air between rides is pretty normal, I check mine "before" every ride but going down in 3 hrs. that's gota be a slow leak in the tube. I'd take off the tube pump it up put it in tub of water and look for leak, then patch it. If the tube has been in there a long time you might just need a new tube and I'd recommend some sort of tire/tube sealer (Flat Attack, Blu Goo, Slime, etc. ) or the "tire liners" which ever you prefer! Jmho, Ymmv! Have a most excellent day!