What Car? Q&A - What's the best tyre sealant?

Q: I am considering changing the run-flat tyres on my BMW 535d M Sport Touring to normal ones to improve the ride quality. Also, what's the best tyre sealant, because the car currently has no spare wheel?
Barrie Myers

A: The new BMW 5-series was developed and tested solely on run-flat tyres. It is questionable whether your dealer would honour the warranty on your car should you replace them with normal tyres.

We would advise that you obtain written authorisation from your dealer before going ahead with the tyre swap, because it is possible that it could dispute any subsequent warranty claims you may wish to make.

With regard to the best tyre sealant, BMW has no preference for tyre sealant, and says run-flats don't need it. However, it does suggest that when your tyres are due for replacement to see your BMW dealer, as tyre manufacturers are working on improvements to smooth the ride quality, and these may well be in place by the time your tyres have worn.

We would also add that it is highly inadvisable to fit run-flats to a car without a tyre-pressure monitoring system, because although the tyre sidewall remains rigid in the event of a puncture, its overall efficiency is reduced.