Which brand and size tires and what size width rim? We use to run 15 to 17 lbs on a nine inch bias ply tire on a ten inch rim years ago before the radials came out for use in NHRA stock class I'm pretty sure there was a change in the tire construction or compuond before those tires(Firestones) where being bought, we use to use (before that) 9 to 12 lbs on the same size tires and rims The M/T liked less air than the Firestones tires did in the same size on the same rims and car