The max pressure on the sidewall is the maximum recommend for the tire. Usually given for mounting purposes. Your quad ( 4 wheeler ) should have it stamped on a plate or somewhere on the fenders. Probably some where around 3.2 to 7 psi .
You shouldn't put anything on your tires. When you are off driving on the area with loose stones, check the pressure for the tires and ensure that all of them are at per. If not, check in to the nearest auto shop and adjust the air pressure.