Run-Flat Tyres: All You Need To Know
Run Flats are most widely used by BMW, standard on all their cars besides the M cars. The have many benefits over normal tubeless tyres, but also are worse off in a way or two. Other manufacturers also use run flats on some models.
Run flat tyres can be repaired For a normal puncture, run flats can be repaired just like a normal tubeless tyre. They will work just fine after that. Even the way of fixing a puncture is the same. BMW owners note that if you go to a dealership they will ask you to replace, since that is their policy. We don't do autobahn speeds all the time so even fixing the puncture may suffice.
When Can run flats NOT be repaired Run flats can not be repaired if they are driven on zero air for some distance. They are designed to be driven only a certain distance on zero air, and since the sidewall is supporting the car weight, it weakens. In this case the tyre will have to be replaced.
Also if the sidewall is torn, or there is a huge puncture, or the tyre is shredded, and in other situations where a normal tubeless tyre would have to be changed. These are the situations where a run flat will have to be replaced.
Run flats can also puncture slowly Again like normal tubeless tyres, you may just get a small puncture, in which case the air will leak slowly, maybe reduce just a few psi over a couple of days. A common misconception is that run flats have to be changed as soon as they are punctured since they get damaged. Like I mentioned above, the puncture is fixable, and you can continue using the tyre as long as it doesn't run on ZERO air for any distance.
What if you are driving long distance? Run flats are always at the back of any car owners mind on a long distance trip, since there is no spare to change to. Since run flats can only run a maximum of 150-200km (would probably be less with Indian roads) at 80kph people wonder what they would do if they are in between Mumbai and Goa, since there are no dealers in between.
Every car with run flats would have a tyre pressure loss indicator, which would tell you some tyre has lost pressure if it senses a pressure loss of more than approx 5psi in any of the tyres. So this is like an early warning.
Now as soon as the tyre pressure loss light/sound comes on, you pull into the nearest petrol pump (there would be enough on any major highway) and check the air pressure, note which tyre has lost air, fill in more air and continue. Depending on the loss in air you can stop accordingly along the way again to top up air/fix the puncture.
BUT if the tyre gets torn, bursts, or any other such thing you will be running it on no air, and that will be a problem.
Run flats can be good for you too If at a high speed, for any reason which would cause a tubeless tyre to burst or lose air totally, the runflat would still have its sidewall and help to a certain extent to keep the car in control. This is also shown in the video above.
What are disadvantages of run flats Run flat tyres give a car a much stiffer ride becau
se of the strengthened sidewall, which absorbs less shocks. They also weigh upto 40% more than tubeless tyres in some cases and lower the fuel economy because of more rolling resistance. Some also say the grip on these tyres is not as good because of the stiff sidewall.
Hope I managed to clear a few things up.