Run-Flat Tyres and Tyre Pressure Sensors: What to Know

What a run-flat tyre actually is

A run-flat tyre has strengthened sidewalls, and sometimes an internal support ring, so it keeps its shape when pressure is lost. Instead of collapsing onto the rim, it lets you keep moving for a limited distance to reach a safe place or a garage, rather than changing a wheel at the roadside.

They are usually fitted as original equipment on cars that have no spare wheel, and are often marked on the sidewall with letters such as RFT or similar. Check the markings and your handbook, because not every tyre that looks the same is a run-flat.

• Stiffer sidewalls mean the ride can feel firmer
• Often fitted where there is no spare wheel
• Usually marked on the sidewall
• Normally intended to be used with a pressure monitoring system

Driving limits after a puncture

Manufacturers usually give a maximum speed and distance for driving on a deflated run-flat tyre. Those limits vary by tyre and by car, so look at your handbook rather than relying on a number someone remembers. In general terms, you should slow down, avoid hard cornering and braking, and go straight to somewhere safe.

The tyre is not designed to be driven on flat indefinitely. Driving beyond the limit, or at higher speed, can destroy the internal structure of the tyre. That matters for repair, as we explain next.

Can a run-flat be repaired?

This is where run-flats differ most. Many tyre makers advise against repairing a run-flat tyre that has been driven while flat or under-inflated, because the damage to the sidewall cannot always be seen from outside. Some makers have their own rules about repair even when it has not been driven on flat.

For any tyre, a repair depends on where the damage is, how big it is and the tyre's condition. Damage to the sidewall or shoulder generally rules out a repair. We assess each tyre on its own merits, and if we cannot repair it safely we will tell you why and talk through replacement. Our article on puncture repair or new tyre covers the general rules.

Tyre pressure monitoring and its warning light

Tyre pressure monitoring systems warn you when a tyre is losing air. Some measure pressure with a sensor inside each wheel, called direct systems. Others estimate it through the ABS wheel speed sensors, called indirect systems. Direct sensors run on a small internal battery that eventually runs down.

If the warning light comes on, check your tyre pressures when the tyres are cold. A drop in temperature, as in a Tyneside winter, can reduce pressure enough to trigger the light. If a tyre looks low, do not ignore it, as run-flats can look nearly normal even when flat. If the light flashes and then stays on, the system itself may be faulty, perhaps due to a failed sensor.

• Check pressures cold and set them to the figure in the handbook
• Some systems need resetting after inflating or rotating
• A light that returns may point to a slow leak
• A flashing light often suggests a system fault

Fitting care and wheel balancing

Run-flat tyres are stiff and can be harder to fit than ordinary tyres. The right equipment and technique protect the tyre bead, the wheel rim and, importantly, the pressure sensors. Sensors can be damaged by careless fitting, and they may need to be reused, checked or reprogrammed. When we fit new tyres we take care with sensor valves and can talk you through anything that needs attention.

Every new tyre should be balanced on the wheel. Out-of-balance wheels can cause vibration through the steering wheel or seat at certain speeds, and uneven wear. Because run-flat tyres are heavier and stiffer, any vibration is often more noticeable. Tracking and alignment are worth checking too if the tyres have worn unevenly.

Replacing run-flats

If your car came with run-flat tyres, it is usually sensible to replace them with the type specified for the car, particularly if there is no spare wheel and the monitoring system is calibrated for them. Mixing types can change handling. Ask us at Banks of the Tyne in Hebburn about the right fit for your car, and we will explain the options clearly.

Frequently asked questions