The more sand, the more wear and tear. Twice a season if you ride a four times a month. Adjust if you ride more or less. You can re-ring if you want instead, then new piston once a year. Rings will go out sooner, but you can check by pulling off the head and check the cylinder wall or take off the jug and look for blow by. I've been there when the rings were left in one too many rides, not a nice sight and can get costly. It's a simple job, worth the hour to do it right a couple of times a season.