On low pro tires, look at the max pressure rating and start at 5-6 lbs less that the max rating. You have to consider tire temp as pressure will rise when hot and decrease when cold. Ride quality will also be effected by pressure. Some have even gone to nitrogen gas to keep pressure even at all temps. Nitrogen also works on air shocks and air ride suspension.
When you do the wet tire test, do it cold and hot and check for any difference.
This will show you the best over all pressure to run or if you got it right.