Run Flat Tyres: Keep Them or Switch?
Run flats let you keep driving after a puncture by carrying the car on a reinforced sidewall, and that same stiff sidewall is why owners often replace them.
A run flat supports the car with reinforced sidewalls rather than air, typically for a limited distance at a reduced speed. Switching to conventional tyres is usually possible, but you then need a way to deal with a puncture.
Run flats arrived as a way to delete the spare wheel, saving weight and boot space. They work, but they change the ride and they change what happens after a puncture.
How they work
The common design is self supporting. Thick rubber inserts in the sidewall are stiff enough to carry the vehicle’s weight with no air in the tyre, so the wheel rim never contacts the road. Manufacturers quote a limited get home distance at a reduced speed, and those limits are specific to the tyre, so the figure in the handbook is the one to trust. Because a deflated run flat looks and steers almost like a healthy one, a tyre pressure monitoring system is not optional equipment on these cars. It is the only thing telling you the tyre is flat.
The trade offs
A sidewall stiff enough to hold up a car does not deflect much over bumps, so ride quality suffers, especially on sharp edges and expansion joints. The tyres are heavier, which adds unsprung mass. They cost more to buy, the choice of patterns is narrower, and most manufacturers advise against repairing one that has been run flat, because the sidewall may be damaged internally in ways you cannot see. That turns a nail in the tread, which on a normal tyre is often a cheap repair, into a new tyre.
Switching to conventional tyres
Standard tyres fit the same wheels on most modern cars, so the swap is usually straightforward and normally improves ride and reduces cost. Two things follow from it. You lose the get home capability, so carry a sealant and compressor kit or a space saver spare, and check there is somewhere in the car to put one. You should also keep the pressure monitoring system working and pay attention to it. Change all four together rather than mixing run flats and conventional tyres across an axle, since their behaviour under load is not the same.
The conditions that matter
- ✓Most cars fitted with run flats accept conventional tyres on the same wheels.
- !Dropping run flats means carrying a sealant kit or a spare.
- !Most makers advise replacing rather than repairing a run flat that has been driven on flat.
General guidance only. Details vary by exact vehicle and change over time; confirm with a reputable specialist before modifying.