APRIL 9 55TECH TALK
APRIL 2019 55RUN-FLAT TYRES
These deserve a mention because BMW has been championing
them for a very long time, for better or worse. While there are a
number of diff erent systems, including self-sealing, which utilise
a layer inside the tyre that can fi ll the sort of small holes made
by nails and screws, and those that have a tough ring that can
support the vehicle in the event of a puncture.
The most common system is the self-supporting run-fl at and,
while it goes by many names, the principle involved is always
the same. Basically, these tyres have a thicker sidewall that can
support the weight of the car in the event of a puncture, allowing
you to drive safely without damaging the wheel itself, and
without the tyre coming apart. Typically, run-fl ats are designed
to allow you to travel 50 miles at 50mph and, while that might
not sound very far, it’s far enough and is far better than being
completely stranded.
The main downsides are that run-fl ats are heavier than
regular tyres and the thicker, stiff er sidewalls mean they are less
compliant, making for a less comfortable ride. What’s more, the
combination of larger wheels, low-profi le run-fl ats and rough roads
has been known to damage alloys.