It really depends on how bumpy you can take it. Put as much as you can in at the cold rate without going over the max pressure that is stamped on the tire and without making it too bumpy of a ride for your taste. What is on the sticker inside the door jamb will give the most comfort. Obviously, the max pressure will make it very bumpy. I started with mine at 40 lbs. It was too bumpy. So I backed it back down to 35. It's a lot better, but I haven't checked the gas mileage yet. I won't go below 33 which is what the door jamb has.