What is a run flat tyre? Why are they more expensive? run flat tryes have been designed with strengthened sidewalls allowing the tyre to be driven with a puncture. You are able to drive on the run flat for a maximum distcance of 50 miles at 50mph. The biggest advantage of run flat tyres is that it allows you to continue your journey to change the tyre in a safe location. It is becoming more common now for car manufacturers such as BMW and Mercedes to fit the run flats as standard (oe original equipment).