Mad, you should have at least 8 full turns of thread engagement between the lug nuts and the wheel stud, at which point the threads should be stronger than the tensile strength of the stud. Anything more than that is just gravy.
Since I assume the studs are 1/2-20, that means you have .05" axial travel per revolution, so you really only need .40" minimum thread engagement. The thickness of your wheel center and depth of the countersinks for the lug nuts will then determine your actual thread engagement. You can get extended snout lug nuts for additional thread engagement if needed assuming your wheels use 60 degree conical seat lug nuts, not something else.
Tobin