I have one of those portable cigarette lighter air compressors.The name on it is truck air, I think Interdynamics makes them. They work pretty well. I air down to 20 psi, tire size 235/75/15. Airing back up takes around 15-20 minutes for all (4) tires. Though not the greatest, it beats the alternative of not airing down and getting stuck. (which is why I bought mine in the first place).Good Luck.