I have been using run flats for 5 yrs now - never had a need for a spare. I did run on 0 psi for 70 km at one point though, the tire was a wreck but no damage to the rim (which is a $2500 OEM item).

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2011 X5 35d
Silver with black interior
Tech, Sound, Sport and Premium packages

2007 Jeep GC SRT8
*returning to stock condition (more or less)*