Originally Posted by rayusaFL
Hope it's not a stupid question... But why more psi on the rear tires??
Not in the least bit stupid.
BMW is balancing the feel and handling of the car partially trough the choice of tire pressures. Every tire has a pressure at which it provides maximum grip. As the pressure is lowered or raised from this point,the grip decreases. Intererstingly, grip falls off more quickly with lowered pressure than with raised pressure.
The F30 is a street car which has a good amunt of understeer designed into it. This is much safer and most comfortable for street drivers. BMW has determined that the handling balance it wants is best accomplished through a significantly higher rear tire pressure. The rear tires exhibit more grip than the front with this setup, contributing to the understeer BMW wants.
Raising the front tire pressures will increase grip and will balance the handling more toward neutral by decreasing understeer. It will not eliminate understeer as a lot of understeer is built into the suspension geometry, alignment, etc.
Try the stock tire pressures and compare the handling to what you have been experiencing. My guess is that 32-35 PSI all around provides the best overall grip and handling for the car.