35's and they show no wear, the trailers weigh less than half of the recommended weight. I do sometimes raise it to 40 if nothing but freeway driving for like a trip to Colorado but it really is not necessary I have found other than may help the mileage a scosch. I have been towing and building trailers for over 40 years and that is what I have found to work best for me. Others have different ideas. But ask oneleglance about my trailer and how easy it is to lift, he saw it. Said I should do a video on it, no one would believe it. Some trailers are exceptions, due to the placement of certain items in the trailer, but I always try to center the water over the axle and just above it. My batteries set right on top of the axle, keeping the center of gravity very low. You can watch a video of it on Carvacer Trail on my website, and notice that it does not leave the ground on any of the twists.
I run a torsion axle and that allows for less tire preasure or requires it, however you want to look at it. lol