Originally Posted by shrink
Traction is the main concern here, the car and road don't care whether its a run flat or not, as long as traction characteristics are similar.
It's not traction that is the potential concern, it's grip. If you change the grip at one end of the car but not the other there is potential for it to behave differently in extreme circumstances (e.g. a high speed swerve).
Now how much this is a problem is a matter for endless "reckoning" but if you believe that there is little or no difference between an RFT and a non-RFT
a) Why ditch the RFT?
b) There is no problem running a mix on the same axle.