anywhere from 90-150 psi. you don't need anywhere near that much air in them unless you're planning to pull a 40 foot camper. I've run air shocks for years without anything bad happening. I've seen tore up mounts like the others have said, but if you're just after some rake, then put 50 psi in the shocks and be done. but the better idea is to replace your springs, or add an extra leaf or two.