pretty sure 28psi cold will probably trigger low pressure warnings. are you getting those and just ignoring them? they go away after a while when the pressure increases about 4psi, but in winter i had to bump up my cold pressures to not have it nag me.I always have ran with 1,9 bar (27,5 psi ) cold on oem pirelli pz4 and has been perfect
perfect wear over the whole tire width