Allowable differential in tire diameter front to rear?

Does anyone know what the allowable differential in tire diameter front to rear is before the computer would think there is a problem? I have seen people mention a 3% allowable differential based on the 27" 255/40R19 front and 27.7" rear 275/40R19 PP combo. I also see retailers selling packaged drag tire sets approaching a 10% differential with a 26" front and a 28" or more rear.

I have run a about 2.2" difference on my car before; it never threw any codes or abs faults. Sorry but I really don't know the limit.