I run my 39.5 super swamper between 8 and 10 pounds with no problem. If the snow gets real deep I go down to four and take it easy. At four pounds, if I hit a good bump my tires will leak are for a second and then seal back up. I went lower once to somewhere around two to three pounds and blow all four off trying to power around a corner. Thank God I have onboard air. I dont think I would go much below 7 pounds but if you have a source of air, experiment.