thanks for your help, you can get 19" bmw performance 313 factory wheels on the E90 , which i have.
i also rang BMW and for 2 people they state
front - 35 psi, rear - 39 psi
not sure what is the best to go for, but i have changed to the above pressures (mine were FAR too low) and handling is greatly improved.
Before they were 30 front/ 32 rear and the back end liked to come round much more easily in the wet