I have been towing all my life and most of the trailers and trucks were less then perfect equipment. That said I start with the recommended tire pressure and then check the tire temperature at a rest park or by pulling off the road at a wide burm and FEEL the tires, be careful as even at recommended pressure a load can heat up a tire. I will go as much as 30 lbs over max to keep the tires cool! If they need more air than that I go to the next tire rating. This has worked for many years on all kinds of tires, even worked on the old Hemi charger when I raced it street stock with the polyglass tires. Duals are especially susceptible to this because one low tire will overload the other and they will both fail. Same way with dual axle trailers except it is fron to back. Hope this saves you from a blown tire or pair.

Fred, Kenna and Buster the whippet