Types of Tyre
Radial ply tyres are now the most common tyres in use on
British roads representing more than 90%.
Some radial ply tyres now have a run flat capability known as Self Supporting Run Flat (SST) tyres which are becoming more common
particularly when fitted as an original equipment.
Older diagonal (cross-) ply tyres are now very rarely seen and
have effectively been replaced by radial ply tyres.
Radial ply tyres may be either steel or textile braced and
are identified in the size marking by the letter “R” and often
the word “Radial”.
Self Supporting Run Flat (SST) tyres are designed to
provide a limited run on period following a puncture. These
are identified by the letters “RF” in the size marking. To be
categorised as a run flat tyre, the minimum distance they
must achieve in a run flat condition is 50 miles (80 km)
at a maximum speed of 50 mph (80 km/h) and at a minimum
of 80% of their maximum load capacity.
It is essential the vehicle is equipped with a tyre pressure
monitoring system to enable use of run flat tyres
DO NOT MIX TYRE TYPES
Except in the case of temporary use spare tyres supplied as
original equipment, it is illegal in the United Kingdom and
dangerous to mix tyres of different types on the same axle. It
is also advised that the same tyre type is fitted to all wheel