40psi all the way around for me. 45 rear when Im loaded for a trip, 50 if Im also pulling a trailer.
Your best bet would be to A) use the manufacturers specs or B)to do your own tests and see whats best for your vehicle.
Ive found that with my truck, 40lbs gives me the best compromise between tire wear and mileage. The more air in the tire, the more it bulges andthe less contact patch you have on the ground. Less contact patch equals less friction which equals better mileage. BUT, it also equals less traction for braking and control. Hence, the happy medium Ive found with mine.