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How does a run-flat tyre work?
A run-flat tyre works thanks to reinforced sidewalls, stiffer than those of a conventional tyre. When the pressure drops, the sidewall doesn't collapse completely and continues to support the vehicle's weight.
This way the rim doesn't rest on the road and the vehicle stays controllable, within certain limits. Other systems exist too, such as support rings fitted to the rim, but on production cars the most common solution is the self-supporting sidewall.
How do you recognise a run-flat tyre?
You can recognise a run-flat tyre by the marking printed on the sidewall, near the size. The marking isn't standard: it varies by manufacturer and product line.
| Sidewall marking | Notes |
|---|---|
| RFT, Runflat, Run Flat | Generic wording used by several manufacturers |
| RSC | Marking found on run-flat tyres supplied to certain vehicle manufacturers |
| ZP | Marking used by one manufacturer for its own run-flat technology |
| SSR | Marking used by one manufacturer for its own run-flat technology |
| ROF | Marking used for "Run On Flat" technology |
| DSST | Marking used by one manufacturer for its own run-flat technology |
If you can't find any marking, check the owner's handbook or the vehicle documentation: cars fitted with run-flats as standard often have neither a spare wheel nor a kit.
How far can you drive on a punctured run-flat?
On a punctured run-flat you can drive a limited distance, at reduced speed. Many manufacturers give, as a rough guide, up to about 80 km at a maximum of 80 km/h.
These figures aren't universal, though: the real distance depends on the tyre, the vehicle's load, the temperature and your driving style. The instructions in the vehicle handbook and from the tyre manufacturer are what count. Avoid sudden manoeuvres and heavy loads while you drive.
Why do run-flats need TPMS?
Run-flats need a tyre pressure monitoring system (TPMS) because, precisely thanks to their reinforced sidewalls, a deflated tyre may not be noticeable either by looking at it or from the way the car drives.
Without a warning, you'd risk driving a long way without pressure beyond the intended limits, destroying the tyre. TPMS warns you of the pressure drop: from that moment you must respect the speed and distance limits. Find out more in the guide to the tyre pressure warning light.
Can a punctured run-flat be repaired?
It depends on the manufacturer's instructions and the damage. Some manufacturers advise against or rule out repair, particularly after the tyre has been driven without pressure, because internal damage to the sidewall isn't always visible.
Where repair is permitted, the general criteria apply: small hole in the tread, no shoulder damage, structure intact on internal inspection. See when can a tyre be repaired.
Can you fit run-flats together with normal tyres?
It's generally not advisable to mix run-flats and conventional tyres on the same vehicle, because they behave differently when cornering and braking. The precise instructions depend on the vehicle manufacturer and the tyre manufacturer.
If you need to replace just one run-flat, ask for a tyre of the same type and size. To read the size correctly, see how to read a tyre size.
Punctured run-flat in Milan?
If you have a punctured run-flat in Milan or the surrounding province and aren't sure you can reach a tyre specialist within the manufacturer's limits, SOS Tyre comes out to you 24/7, with an average arrival time of 30 minutes. On the phone we work out together what's feasible based on the size and the damage. Read the page on a punctured run-flat or call +39 377 326 0999.
Frequently asked questions
How can I tell whether my car has run-flats?
Look at the tyre sidewall: next to the size you'll usually find a marking such as RFT, Runflat, RSC, ZP, SSR, ROF or DSST, depending on the manufacturer. Alternatively, check the vehicle handbook. One clue is the absence of a spare wheel and kit in the boot.
Can you feel a punctured run-flat while driving?
Often very little or not at all, because the reinforced sidewall keeps the wheel's shape. That's why the warning from the tyre pressure monitoring system is essential. If the light comes on, treat the tyre as punctured and respect the manufacturer's limits straight away.
Do run-flats give a firmer ride?
The reinforced sidewalls generally make run-flats stiffer than conventional tyres, and some drivers notice less comfort over bumps. The feel depends a great deal on the tyre model and the vehicle's suspension set-up, which is usually tuned for the run-flats fitted as standard.
What happens if I exceed a run-flat's distance limits?
If you exceed the manufacturer's limits, the sidewall overheats and gets damaged, potentially to the point of destroying the tyre. In that case you also lose the run-flat advantage and the vehicle can become difficult to control. Stop safely before you reach the limit.