Many modern cars come with run-flat tyres from the factory. Unsurprisingly, these do exactly as their name suggests, and allow the tyre to be driven for a limited amount of time with no air pressure to inflate them. This is great news if you get a puncture, as it means you can drive the car directly to the garage to have the tyre replaced without being left stricken at the roadside. However, run-flats are not very popular among enthusiasts, because they feature extremely stiff and rigid sidewalls. The sidewalls need to be strong enough to support the weight of the car if the tyre is deflated, and as a result they can prove quite uncomfortable, giving a crashy and bumpy ride. The reduced flex in the sidewall also hampers performance ( remember, it’s the movement of the rubber and the way it interacts with the road surface that gives us grip) so are often best used on cars covering lots of motorway miles, where the convenience of not having to replace the tyre at the roadside outweighs the performance differential.